Infrared Thermography Guide (Revision 3)

Infrared Thermography Guide (Revision 3)

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Infrared Thermography Guide (Revision 3) 1006534

Final Report, May 2002

EPRI Project Manager P. Zayicek

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA 800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR (B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT. ORGANIZATION(S) THAT PREPARED THIS DOCUMENT EPRI

ORDERING INFORMATION Requests for copies of this report should be directed to EPRI Orders and Conferences, 1355 Willow Way, Suite 278, Concord, CA 94520, (800) 313-3774, press 2 or internally x5379, (925) 609-9169, (925) 609-1310 (fax). Electric Power Research Institute and EPRI are registered service marks of the Electric Power Research Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric Power Research Institute, Inc. Copyright © 2002 Electric Power Research Institute, Inc. All rights reserved.

CITATIONS This report was prepared by Nuclear Maintenance Applications Center (NMAC) 1300 W.T. Harris Boulevard Charlotte, NC 28262 This report describes research sponsored by EPRI. The report is a corporate document that should be cited in the literature in the following manner: Infrared Thermography Guide (Revision 3), EPRI, Palo Alto, CA: 2002. 1006534. The enclosed CD contains a PDF file of this report featuring full-color images.

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REPORT SUMMARY

Costly equipment outages can be reduced by implementing a comprehensive predictive maintenance program. Infrared thermography (IR), a fundamental component of such programs, uses nonintrusive techniques to monitor the operating condition of equipment and components. This revised report provides updated information to assist utilities in implementing an effective IR program. Background IR has proven to be an effective predictive maintenance and diagnostic tool. For example, it can be used to identify areas of condenser air in-leakage, bad terminal lugs/connections, leaking valves, and nozzle blockages in the containment spray ring header. To broaden the range of IR applications, EPRI sponsored the development of a guide to address IR diagnostic capabilities. This guide was originally published in 1990 and is being revised to incorporate user input and to update information on IR equipment and vendors. Objective • To develop and maintain a guide that provides a consistent approach for using IR as a predictive maintenance tool Approach The EPRI Nuclear Maintenance Applications Center (NMAC) originally worked with Alabama Power personnel to assess the viability of IR as a predictive maintenance tool in a nuclear plant application. An initial IR survey and a subsequent follow-up survey identified the effectiveness of IR for identifying abnormal operating conditions for the surveyed components. Revisions to the guide include updated information on IR equipment, applications, training, and certification. Results This guide, which provides a compendium of information rather than definitive standards, describes IR theory, summarizes existing and potential IR applications, and offers technical information necessary for developing an effective in-house IR program. Key topics that are included in this guide are: • • • • • •

The science of thermography Selection of infrared instruments Inspection techniques IR applications Basic elements of an in-house program Training and certification v

This revision provides updated information on commercial infrared sensing and imaging instruments, IR applications, and training and certification criteria. EPRI Perspective Infrared thermography is a valuable tool in a predictive maintenance program, as has been demonstrated by those applying the principles described in the Infrared Thermography Guide. Periodic updates of the guide keep the utility thermographer aware of recent developments in IR equipment technology, criteria for training and certification, and proven IR applications that add value to the utility IR program. The guide also serves as benchmark reference for those who contract their IR inspection services. Keywords Nuclear power Infrared thermography Fossil fuel power plants Predictive maintenance

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ABSTRACT This guide is a valuable reference for the development of infrared thermography (IR) capabilities as part of a plant predictive maintenance program. The guide includes IR theory, a summary of IR inspection applications, and the technical information necessary to develop an effective in-house program. The body of the guide is structured for the general user of IR, and the appendices provide a more in-depth look at this technology for the advanced user. This third revision of Infrared Thermography Guide contains updated information on IR equipment technology, IR inspection applications, and training and certification criteria.

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ACKNOWLEDGMENTS The Infrared Thermography Guide was produced by the Nuclear Maintenance Applications Center (NMAC). Extensive information for the original guide was provided by Alabama Power Company (the primary demonstration plant) and other electric power generating utilities, and is gratefully acknowledged. A. E. Hammett from SONOPCO is acknowledged for his efforts, enthusiasm, and support of this project. The following utilities are acknowledged for their review of the original guide and their comments: Alabama Power Co. Arkansas Power & Light Co. Duquesne Light Co. Florida Power & Light Co.

Florida Power Corp. Maine Yankee Atomic Power Co. Pacific Gas & Electric Co. Toledo Edison Company

The following utility personnel are acknowledged for their review of Revision 1 of the Guide and their comments: Larry Shay – Entergy Operations Scot Stewart – Florida Power Corp. Joe Connolley – Omaha Public Power District Russ Cabrel – Washington Public Power Supply System Tom George – Wisconsin Public Service Corp. Gary Thomas of Florida Power & Light Co. is acknowledged for his contribution of IR inspection application images for Revision 2 of the Guide. FLIR Systems Inc. and the Infrared Training Center are acknowledged for their contributions of IR inspection application images for Revision 3 of the Guide. In addition, NMAC and EPRI NDE Center staff reviewed Revisions 1, 2, and 3 and offered comments. NMAC was supported in its efforts to develop this guide by Herb Kaplan of Honeyhill Technical. Honeyhill Technical 65 Fawn Ridge Lane Norwalk, CT 06851

Honeyhill Technical 11550 Ballylee Terrace Boynton Beach, FL 33437

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INTRODUCTION Many electric generating stations and utilities have integrated the non-contact, nondestructive capabilities of infrared thermography (IR) for condition monitoring and diagnostics in their predictive maintenance program. The purpose of this guide is to assist the nuclear industry in its efforts to factor IR into its predictive maintenance program. This guide provides the theory of IR, a summary of existing and potential applications, and the technical information necessary to develop an effective in-house program. Also included is a matrix that lists all of the known manufacturers of IR instruments for a broad range of applications. IR has been used in commercial applications since the early 1970s. In the early 1990s, at the time this guide was first completed, the most frequent applications centered on building energy losses, roof moisture detection, and inspections of major electric equipment. Applications have since expanded to almost all areas of plant predictive maintenance (PdM), product and process control, and nondestructive testing of materials. The wide and growing selection of thermal imagers and viewers available for these applications provides both qualitative and quantitative displays of temperature distribution patterns. The manufacturers of modern thermal imagers and viewers have kept pace as detector and microprocessor technologies have advanced. The capabilities of today’s IR thermal imagers and viewers have yet to be fully explored and developed for commercial applications. In addition, computer software programs are now available to store, retrieve, analyze and compare infrared images. Much of the information presented in the original guide was developed as a result of a demonstration project at a U.S. nuclear utility. In addition to information gathered through this demonstration project, all Nuclear Maintenance Applications Center (NMAC) members were surveyed to provide data on the implementation status of IR technology at their facilities. This latest revision of the guide (Revision 3) was undertaken to correct text errors, to update the information on IR products vendors, certification, training, and techniques, and to restructure the guide so that it can become a living document, able to be readily updated to reflect technology changes. The body of the guide is structured for the general user of IR, and the appendices provide an in-depth look at this technology designed for the more advanced user. Basic IR Concepts A target at any temperature above absolute zero will emit infrared radiation in proportion to its temperature. Thermal imagers develop an electronic image by converting the invisible heat radiation emitted by that target into electrical signals that can be displayed on a monitor and/or xi

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recorded on a variety of electronic storage media. By monitoring these targets with thermal imaging equipment, a visual image of their temperature differentials can be displayed. The variations in intensities of the blacks, grays, and whites (or color variations) provide an indication of the temperature differences. Areas of higher temperatures will appear brighter and the areas at lower temperatures will appear darker (or appear as different colors). The quantity and wavelength distribution of the energy that is radiated depends upon the temperature and spectral characteristics of the material, and on that material’s radiation efficiency (emissivity). Thermal imagers convert the invisible heat radiation into visible images while spot radiometers convert the heat radiation from a single spot into a number indication on a meter. The thermographer views the target through an IR instrument, while looking for unexpected or unusual temperature patterns. A qualitative examination compares the apparent temperature pattern of one component to that of an identical or similar component under the same or similar operating conditions. Temperature differences can be measured quantitatively as well. The achievement of accurate temperature indications, however, is dependent upon many factors and extreme care must be taken in the selection of variables used in temperature calculations. The thermal images obtained can be stored on memory sticks, PCMCIA cards, computer hard drives, floppy disks, CDs, ZIP disks, or video tape. An advantage of infrared monitoring or testing is that it can be performed with the equipment in service at normal operating conditions (that is, it will not interfere with normal plant operations).

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CONTENTS

1 THERMOGRAPHY OVERVIEW.............................................................................................1-1 1.1

Advantages of Non-Contact Thermal Measurement....................................................1-1

1.2

Heat Transfer and Infrared Radiation Basics...............................................................1-2

1.2.1

Heat and Temperature ........................................................................................1-2

1.2.2

Instruments for Temperature Measurement (Contact and Non-Contact)............1-2

1.2.3

Converting Temperature Units ............................................................................1-3

1.2.4

The Three Modes of Heat Transfer.....................................................................1-3

1.3

Measuring and Mapping Temperature Without Contact ..............................................1-7

1.3.1 1.4

The Three Elements of a Non-Contact Temperature Measurement...................1-7

Performance Parameters of Thermal Sensing Instruments.........................................1-9

1.4.1

Point-Sensing Instruments ..................................................................................1-9

1.4.2

Line Scanners and Imagers—Qualitative and Quantitative ..............................1-10

1.4.3

Thermal Imaging Software ................................................................................1-11

2 A COMPENDIUM OF COMMERCIAL INFRARED SENSING AND IMAGING INSTRUMENTS .........................................................................................................................2-1 2.1

Classification of Instruments ........................................................................................2-1

2.2

Instrument Manufacturers ............................................................................................2-2

2.3

Discussion of Instruments............................................................................................2-2

2.3.1

Point Sensors (Radiation Thermometers)...........................................................2-2

2.3.1.1

Probes...........................................................................................................2-2

2.3.1.2

Portable Hand-Held ......................................................................................2-3

2.3.1.3

On-Line Monitoring and Control....................................................................2-3

2.3.1.4

Specials ........................................................................................................2-4

2.3.2

Line Scanners .....................................................................................................2-5

2.3.2.1

Opto-Mechanically Scanned Line Scanners .................................................2-5

2.3.2.2

Electronically Scanned Focal Plane Array Line Scanners ............................2-6

2.3.3

Thermographic Instruments ................................................................................2-6

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2.4

2.3.3.1

Thermal Viewers, Opto-Mechanically Scanned ............................................2-7

2.3.3.2

Opto-Mechanically Scanned Imaging Radiometers......................................2-8

2.3.3.3

Thermal Viewers, Electronically Scanned (Pyrovidicon Imagers).................2-9

2.3.3.4

Focal Plane Array (FPA) Imagers—Qualitative and Quantitative ...............2-10

2.3.3.5

FPA Imager Performance Comparisons .....................................................2-11

Thermal Imaging Diagnostic Software .......................................................................2-13

2.4.1

Quantitative Thermal Measurements of Targets...............................................2-13

2.4.2

Detailed Processing and Image Diagnostics.....................................................2-13

2.4.3

Image Recording, Storage, and Recovery ........................................................2-14

2.4.4

Image Comparison............................................................................................2-15

2.5

Recording, Hard Copy, and Storage of Images and Data .........................................2-15

2.6

Report Preparation ....................................................................................................2-15

3 THE MEASUREMENT MISSION ...........................................................................................3-1 3.1

Thermal Behavior of the Target ...................................................................................3-1

3.1.1

Emissivity Difference...........................................................................................3-2

3.1.2

Reflectance Difference........................................................................................3-2

3.1.3

Transmittance Difference ....................................................................................3-2

3.1.4

Geometric Difference ..........................................................................................3-2

3.1.5

Mass Transport Difference..................................................................................3-2

3.1.6

Phase Change Difference ...................................................................................3-3

3.1.7

Thermal Capacitance Difference.........................................................................3-3

3.1.8

Induced Heating Difference.................................................................................3-3

3.1.9

Energy Conversion Difference ............................................................................3-3

3.1.10 3.2

Equipment Preparation ................................................................................................3-3

3.2.1

The Mission Checklist .........................................................................................3-3

3.2.2

Equipment Checkout and Calibration..................................................................3-4

3.2.3

Batteries ..............................................................................................................3-4

3.2.4

Facility Personnel Participation ...........................................................................3-4

3.3

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Direct Heat Transfer Difference .......................................................................3-3

Some Cautions for Correct Instrument Operation........................................................3-4

3.3.1

Start-Up Procedure .............................................................................................3-5

3.3.2

Memorizing the Default Values ...........................................................................3-5

3.3.3

Setting the Correct Emissivity .............................................................................3-5

3.3.4

Filling the IFOVmeas for Accurate Temperature Measurements......................3-12

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3.3.5

Aiming Normal to the Target Surface................................................................3-12

3.3.6

Recognizing and Avoiding Reflections From External Sources ........................3-12

3.3.7

Avoiding Radiant Heat Damage to the Instrument............................................3-12

4 INSPECTION TECHNIQUES .................................................................................................4-1 4.1

Mitigating Inherent Effects ...........................................................................................4-1

4.1.1

Emissivity and Reflectivity...................................................................................4-1

4.1.2

Foot Powder........................................................................................................4-3

4.1.3

Dye Check Developer .........................................................................................4-3

4.1.4

Electricians' Tape................................................................................................4-5

4.2

Proven Inspection Techniques.....................................................................................4-5

4.2.1

Mirrored Surfaces................................................................................................4-5

4.2.2

Thermal Transfer Imaging...................................................................................4-6

4.2.3

Thermal Transients .............................................................................................4-6

4.2.4

Differential Thermography...................................................................................4-7

4.2.5

Using Infrared Transmitting Windows .................................................................4-7

5 EXAMPLES OF INFRARED APPLICATIONS .......................................................................5-1 5.1

Current Applications.....................................................................................................5-1

5.2

Electrical Applications ..................................................................................................5-1

5.2.1

High Electrical Resistance ..................................................................................5-1

5.2.2

Induced Currents.................................................................................................5-2

5.2.3

Open Circuits ......................................................................................................5-2

5.3

Mechanical Applications ..............................................................................................5-2

5.3.1

Friction ................................................................................................................5-2

5.3.2

Valve Leakage/Blockage.....................................................................................5-2

5.3.3

Insulation.............................................................................................................5-3

5.3.4

Building Envelopes..............................................................................................5-3

5.4

Miscellaneous Applications..........................................................................................5-3

5.4.1

Containment Spray Ring Header ........................................................................5-3

5.4.2

Hydrogen Igniters................................................................................................5-4

5.4.3

Condensers.........................................................................................................5-4

5.4.4

Thermal Plume Detection....................................................................................5-4

5.5

Applications Summary .................................................................................................5-5

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6 BASIC ELEMENTS OF AN IN-HOUSE PROGRAM..............................................................6-1 6.1

Basic Elements ............................................................................................................6-1

6.1.1

Introduction .........................................................................................................6-2

6.1.2

Definitions ...........................................................................................................6-2

6.1.3

Scope ..................................................................................................................6-2

6.1.4

Responsibilities ...................................................................................................6-2

6.1.5

Precautions .........................................................................................................6-2

6.1.6

Prerequisites .......................................................................................................6-2

6.1.7

Conduct of the Survey.........................................................................................6-2

6.1.8

Acceptance Criteria.............................................................................................6-3

6.1.9

Reporting Criteria ................................................................................................6-3

6.1.10

Qualification of Personnel ................................................................................6-4

6.1.11

Scheduling .......................................................................................................6-4

6.1.12

Equipment Matrix .............................................................................................6-4

6.1.13

References ......................................................................................................6-4

6.2

Sample Program ..........................................................................................................6-5

7 TRAINING AND CERTIFICATION .........................................................................................7-1 7.1

Background..................................................................................................................7-1

7.2

Levels of Qualification..................................................................................................7-2

7.3

Training Requirements ................................................................................................7-2

7.4

Predictive Maintenance (PdM) Level III Certification Program ....................................7-4

APPENDICES: A THE SCIENCE OF THERMOGRAPHY (PRACTICAL APPLICATION OF THERMOGRAPHIC AND THERMAL SENSING EQUIPMENT).............................................. A-1 A.1

Introduction ................................................................................................................. A-1

A.2

Heat Transfer and Radiation Exchange Basics for Thermography............................. A-1

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A.2.1

Heat and Temperature ....................................................................................... A-2

A.2.2

Converting Temperature Units ........................................................................... A-2

A.2.3

The Three Modes of Heat Transfer.................................................................... A-7

A.2.4

Conduction ......................................................................................................... A-7

A.2.5

Convection ......................................................................................................... A-8

A.2.6

Radiation ............................................................................................................ A-9

A.2.7

Radiation Exchange at the Target Surface ...................................................... A-10

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A.2.8

Specular and Diffuse Surfaces......................................................................... A-12

A.2.9

Transient Heat Exchange................................................................................. A-12

A.3

The Basic Physics of Infrared Radiation and Sensing .............................................. A-13

A.3.1

Some Historical Background............................................................................ A-14

A.3.2

Non-Contact Thermal Measurements .............................................................. A-14

A.3.3

The Target Surface .......................................................................................... A-14

A.3.4

The Transmitting Medium ................................................................................ A-20

A.3.5

The Measuring Instrument ............................................................................... A-23

A.3.6

Introduction to Thermal Scanning and Imaging Instruments............................ A-25

A.4

A.3.6.1

Line Scanning............................................................................................ A-25

A.3.6.2

Two-Dimensional Scanning....................................................................... A-26

Performance Parameters of Thermal-Sensing Instruments...................................... A-29

A.4.1

Point-Sensing Instruments ............................................................................... A-29

A.4.2

Scanners and Imagers—Qualitative and Quantitative ..................................... A-35

A.4.3

Performance Parameters of Imaging Radiometers.......................................... A-35

A.4.3.1 Temperature Sensitivity, Minimum Resolvable Temperature Difference (MRTD) or Minimum Resolvable Temperature (MRT) ............................ A-36 A.4.3.2 Spot Size, Instantaneous Field of View (IFOV), Imaging Spatial Resolution, Measurement Spatial Resolution (IFOVmeas) ...................................... A-37 A.4.3.3 A.4.4

Speed of Response and Frame Repetition Rate....................................... A-41

Thermal Imaging Software ............................................................................... A-42

B MEASURING EMISSIVITY, REFLECTANCE, AND TRANSMITTANCE............................. B-1 B.1

Introduction ................................................................................................................. B-1

B.2

Measuring Emissivity .................................................................................................. B-2

B.2.1

Reference Emitter Technique ............................................................................ B-2

B.2.2

Reflective Emissivity Technique......................................................................... B-3

B.2.3

Transmittance Measurement ............................................................................. B-5

B.2.4

Generic Emissivity Values.................................................................................. B-6

C QUICK REFERENCE CHARTS AND PLATES.................................................................... C-1 D REFERENCES...................................................................................................................... D-1 E BIBLIOGRAPHY ................................................................................................................... E-1

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LIST OF FIGURES Figure 1-1 Categories of Conditions for Infrared Thermal Measurements.................................1-8 Figure 1-2 Components of an Infrared Sensing Instrument.......................................................1-9 Figure 4-1 Emissivity Improvement by Coating—Setup ............................................................4-4 Figure 4-2 Thermogram of an Uncoated Shiny Metal Container ...............................................4-4 Figure 4-3 Container Has Been Coated to Improve Emissivity—Thermogram Now Reveals Fluid Level............................................................................................................4-5 Figure 5-1 Step-Up Transformer High-Resistance Connection .................................................5-8 Figure 5-2 250 kV Transformer................................................................................................5-10 Figure 5-3 Steam Line Leaks...................................................................................................5-12 Figure 5-4 Isophase Bus Bellows ............................................................................................5-14 Figure 5-5 Electric Generator...................................................................................................5-16 Figure 5-6 Regulating Transformer Cooling Oil Migration .......................................................5-18 Figure 5-7 Generator Casing ...................................................................................................5-20 Figure 5-8 Energized Ground Cable ........................................................................................5-22 Figure 5-9 480 V Breaker Connection .....................................................................................5-24 Figure 5-10 Current Transformer .............................................................................................5-26 Figure 5-11 Fuse Holder ..........................................................................................................5-28 Figure 5-12 Connection to Fuse Holder...................................................................................5-30 Figure 5-13 Knife Switch..........................................................................................................5-32 Figure 5-14 Motor Control Center Breaker ..............................................................................5-34 Figure 5-15 Motor Control Center Terminal Block ...................................................................5-36 Figure 5-16 Motor Control Center Control Wire .......................................................................5-38 Figure 5-17 Padmount Transformers.......................................................................................5-40 Figure 5-18 Vacuum Leak on Turbine Condenser...................................................................5-42 Figure 5-19 Small Transformer ................................................................................................5-44 Figure 5-20 Motor ....................................................................................................................5-46 Figure 5-21 Shell Relief Valve .................................................................................................5-48 Figure 5-22 Shell Relief Valve (Weeping)................................................................................5-50 Figure 5-23 Shell Relief Valve (Leaking) .................................................................................5-52 Figure 5-24 Vacuum Leak on Turbine .....................................................................................5-54 Figure 5-25 Steam Trap...........................................................................................................5-56 Figure 5-26 Pump Bearing.......................................................................................................5-58

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Figure 5-27 Office Building ......................................................................................................5-60 Figure 5-28 Building Roof with Water Saturation.....................................................................5-62 Figure 5-29 Induction Motor Air Intake Plenum .......................................................................5-64 Figure 5-30 Generator Step-Up Transformer...........................................................................5-66 Figure 5-31 Printed Circuit Module ..........................................................................................5-68 Figure 6-1 Infrared Survey Results ..........................................................................................6-14 Figure A-1 Conductive Heat Flow ............................................................................................. A-7 Figure A-2 Convective Heat Flow ............................................................................................. A-9 Figure A-3 Infrared in the Electromagnetic Spectrum ............................................................. A-10 Figure A-4 Radiative Heat Flow .............................................................................................. A-11 Figure A-5 Radiation Exchange at the Target Surface ........................................................... A-12 Figure A-6 Blackbody Curves at Various Temperatures......................................................... A-16 Figure A-7 Spectral Distribution of a Blackbody, a Gray Body, and a Non-Gray Body........... A-18 Figure A-8 Components of Energy Reaching the Measuring Instrument ............................... A-19 Figure A-9 Aiming the Instrument to Avoid Point Source Reflections ..................................... A-19 Figure A-10 Infrared Transmission of 0.3 km of Sea Level Atmosphere ................................ A-20 Figure A-11 Infrared Spectral Transmission of Glass ............................................................. A-21 Figure A-12 Characteristics of IR Transmitting Materials ....................................................... A-22 Figure A-13 Components of an Infrared Radiation Thermometer........................................... A-23 Figure A-14 Typical Infrared Radiation Thermometer Schematic ........................................... A-24 Figure A-15 Spectral Sensitivity of Various Infrared Detectors ............................................... A-25 Figure A-16 Scanning Configuration of an Infrared Line Scanner .......................................... A-26 Figure A-17 Schematic of a Typical Opto-Mechanically Scanned Imager .............................. A-28 Figure A-18 Schematic of a Typical FPA-Based Thermal Imager .......................................... A-29 Figure A-19 Instrument Speed of Response and Time Constant ........................................... A-31 Figure A-20 Fields of View of Infrared Radiation Thermometers ............................................ A-32 Figure A-21 Spectral Filtering for Polyethylene Temperature Measurement .......................... A-34 Figure A-22 Spectral Filtering for Polyester Temperature Measurement................................ A-34 Figure A-23 Test Setup for MRTD Measurement, MRTD Curve ............................................ A-37 Figure A-24 Modulation Transfer Function, Imager Spatial Resolution .................................. A-39 Figure A-25 MRTD and MTF for a System Rated at 1.0 Milliradian ....................................... A-40 Figure A-26 Setup and Curves for Slit Response Function Test ............................................ A-41 Figure B-1 Target Radiosity ...................................................................................................... B-1 Figure B-2 Using the Reference Emitter Technique ................................................................. B-3 Figure B-3 Using the Reflective Emissivity Technique ............................................................. B-4 Figure B-4 Using the Transmittance Technique (Measuring Transmittance)............................ B-5

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LIST OF TABLES Table 1-1 Temperature Conversion Chart .................................................................................1-4 Table 2-1 Instrument Characteristics .......................................................................................2-16 Table 2-2 Equipment Manufacturers........................................................................................2-29 Table 2-3 Compilation of Typical Industrial Applications of Thermal Imaging Instruments......2-33 Table 3-1 Table of Normal Spectral Emissivities .......................................................................3-6 Table 3-2 Emissivity for Wavelengths of 8–14 µm at 0°C........................................................3-10 Table 4-1 Normal Emissivity Values of Common Materials .......................................................4-2 Table 5-1 Composite List of Infrared Applications .....................................................................5-5 Table 5-2 List of IR Application Examples .................................................................................5-6 Table A-1 Temperature Conversion Chart ................................................................................ A-4 Table B-1 Normal Emissivity Values of Common Materials...................................................... B-6

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1

THERMOGRAPHY OVERVIEW

Temperature and thermal behavior of plant machinery, power generation and distribution equipment, control systems, and related materials are the most critical factors in the maintenance of operations. For this reason, temperature is frequently considered the key to successful plant maintenance and is, by far, the most measured quantity. Although conventional methods of temperature measurement using thermometers and thermocouples are still commonly used for many applications, infrared thermography (IR) sensors have become less expensive, more reliable, and electrically interchangeable with conventional thermistors and thermocouples. Noncontact measurement using infrared sensors has become an increasingly desirable alternative over conventional methods. Now, with the proliferation of innovative computer hardware and software, computer-aided predictive maintenance is feasible and efficient.

1.1

Advantages of Non-Contact Thermal Measurement

The four most commonly stated advantages of non-contact thermal infrared measurement over contact measurement are that it is non-intrusive, remote, much faster than conventional methods, and that it measures the temperature at the surface of the target (test subject) not the surrounding air. Any one, or a combination of the following conditions, warrants the consideration of a noncontact sensor: •

Target in motion – When the target to be measured is moving, it is usually impractical to have a temperature sensor in contact with its surface. Bouncing, rolling, or friction can cause measurement errors and the sensor might interfere with the process.

•

Target electrically hot – Current-conducting equipment and components present a hazard to personnel and instruments alike. Infrared sensors place both out of harm's way.

•

Target fragile – When thin webs or delicate materials are measured, a contacting sensor can often damage the product.

•

Target very small – The mass of a contacting sensor that is large with respect to the target being measured will usually conduct thermal energy away from the target surface, thus reducing the temperature and producing erroneous results.

•

Target remote – If a target is very far away from, or inaccessible to, contacting sensors, infrared measurement is the only option.

•

Target temperature changing – Infrared sensors are much faster than thermocouples. Infrared radiant energy travels from the target to the sensor at the speed of light. A rapidly changing temperature can be monitored by infrared sensors, with a millisecond response or faster. 1-1

EPRI Licensed Material Thermography Overview

•

Target destructive to thermocouples – When the high mortality rate of thermocouples due to jarring, burning, or erosion becomes a serious factor, an infrared sensor is a far more costeffective alternative.

•

Multiple measurements required – When many points on a target need to be measured, it is usually more practical to re-aim an infrared sensor than it is to reposition a thermocouple or to deploy a great number of thermocouples. The fast response of the infrared sensor is important.

There are, of course, limitations to the non-contact approach—conditions that might make it impractical or ineffective. These will be covered as the discussion progresses.

1.2

Heat Transfer and Infrared Radiation Basics

Infrared thermography is based on measuring the distribution of radiant thermal energy (heat) emitted from a target surface and converting this to a surface temperature map or thermogram. The thermographer requires an understanding of heat, temperature, and the various types of heat transfer as an essential prerequisite in preparing to undertake a program of IR thermography. This section is an overview discussion to provide the reader with a basic understanding of how heat transfer phenomena affect non-contact infrared thermal sensing and thermographic measurements. For a more detailed discussion of temperature and heat transfer basics, see Appendix A. 1.2.1 Heat and Temperature Heat is defined as thermal energy in transition, flowing from one place or object to another as a result of temperature difference, with the flow of heat changing the energy levels in the objects. All of the energy must be taken into account because energy can neither be created nor destroyed. What we often refer to as a heat source (like an oil furnace or an electric heater) is really one form or another of energy conversion; the energy stored in one object is converted to heat and flows to another object. Temperature is a property of matter and not a complete measurement of internal energy. It defines the direction of heat flow when another temperature is known. Heat always flows from the object that is at the higher temperature to the object that is at the lower temperature. As a result of heat transfer, hotter objects tend to become cooler and cooler objects become hotter, approaching thermal equilibrium. To maintain a steadystate condition, energy needs to be continuously supplied to the hotter object by some means of energy conversion so that the temperatures and, hence, the heat flow, remain constant. 1.2.2 Instruments for Temperature Measurement (Contact and Non-Contact) Conventional temperature measuring instruments use various contact sensors. A mercury thermometer works on the principle of expansion with heat: the mercury expansion is calibrated based on its known characteristics and the reading is an indication of the temperature at the site of the mercury reservoir. Thermometers using thermocouples, thermopiles, and thermistors are based on the electrical-thermal characteristics of these sensors and produce a reading based on 1-2

EPRI Licensed Material Thermography Overview

the temperature of the object with which the sensor is in contact. Infrared thermal instruments are non-contact devices and produce readings based on the surface temperature of objects at which the instrument is pointed. 1.2.3 Converting Temperature Units Temperature is expressed in either absolute or relative terms. There are two absolute scales called Rankine (English system) and Kelvin (metric system). There are two corresponding relative scales called Fahrenheit (English system) and Celsius or Centigrade (metric system). For a detailed discussion of temperature units and formulas for converting from one scale to another, see Appendix A. Table 1-1 is a conversion table to facilitate the rapid conversion of temperature between Fahrenheit and Celsius values. Instructions for the use of the table are shown at the top. For convenience, Table 1-1 is repeated in Appendix A (Table A-1). For quick reference, the conversion factors are summarized in Appendix C, Plate 1. 1.2.4 The Three Modes of Heat Transfer There are three modes of heat transfer: conduction, convection, and radiation. All heat transfer processes occur by one or more of these three modes. Infrared thermography is based on the measurement of radiative heat flow and is, therefore, most closely related to the radiation mode of heat transfer. For a detailed discussion of heat transfer modes and the relationship between infrared measurements and radiative heat flow, see Appendix A.

1-3

EPRI Licensed Material Thermography Overview Table 1-1 Temperature Conversion Chart Instructions for Use: 1. Start in the Temp. column and find the temperature that you wish to convert. 2. If the temperature to be converted is in °C, scan to the right column for the °F equivalent. 3. If the temperature to be converted is in °F, scan to the left column for the °C equivalent. °C

1-4

Temp.

°F

°C

Temp.

°F

°C

°F

Temp.

-101

-150

-238

-36.7

-34

-29.2

-26.7

-16

3.2

-95.6

-140

-220

-36.1

-33

-27.4

-26.1

-15

5

-90

-130

-202

-35.6

-32

-25.6

-25.6

-14

6.8

-84.4

-120

-184

-35

-31

-23.8

-25

-13

8.6

-78.9

-110

-166

-34.4

-30

-22

-24.4

-12

10.4

-73.3

-100

-148

-33.9

-29

-20.2

-23.9

-11

12.2

-67.8

-90

-130

-33.3

-28

-18.4

-23.3

-10

14

-62.2

-80

-112

-32.2

-26

-14.8

-22.8

-9

15.8

-56.7

-70

-94

-31.7

-25

-13

-22.2

-8

17.6

-51.1

-60

-76

-31.1

-24

-11.2

-21.7

-7

19.4

-45.6

-50

-58

-30.6

-23

-9.4

21.1

-6

21.2

-40

-40

-40

-30

-22

-7.6

-20.6

-5

23

-39.4

-39

-38.2

-29.4

-21

-5.8

-20

-4

24.8

-38.9

-38

-36.4

-28.9

-20

-4

-19.4

-3

26.6

-38.3

-37

-34.6

-28.3

-19

-2.2

-18.9

-2

28.4

-37.8

-36

-32.8

-27.8

-18

0.4

-18.3

-1

30.2

-37.2

-35

-31

-27.2

-17

1.4

-17.8

0

32

EPRI Licensed Material Thermography Overview Table 1-1 (cont.) Temperature Conversion Chart °C

°F

Temp.

°C

°F

Temp.

°C

Temp.

°F

-17.2

1

33.8

-2.8

27

80.6

11.7

53

127.4

-16.7

2

35.6

-2.2

28

82.4

12.2

54

129.2

-16.1

3

37.4

-1.7

29

84.2

12.8

55

131

-15.6

4

39.2

-1.1

30

86

13.3

56

132.8

-15

5

41

-0.6

31

87.8

13.9

57

134.6

-14.4

6

42.8

0

32

89.6

14.4

58

136.4

-13.9

7

44.6

0.6

33

91.4

15

59

138.2

-13.3

8

46.4

1.1

34

93.2

15.6

60

140

-12.8

9

48.2

1.7

35

95

16.1

61

141.8

-12.2

10

50

2.2

36

96.8

16.7

62

143.6

-11.1

12

53.6

2.8

37

98.6

17.2

63

145.4

-10.6

13

55.4

3.3

38

100.4

17.8

64

147.2

-10

14

57.2

3.9

39

102.2

18.3

65

149

-9.4

15

59

4.4

40

104

18.9

66

150.8

-8.9

16

60.8

5

41

105.8

19.4

67

152.6

-8.3

17

62.6

5.6

42

107.6

20

68

154.4

-7.8

18

64.4

6.1

43

109.4

20.6

69

156.2

-7.5

19

66.2

6.7

44

111.2

21.1

70

158

-6.7

20

68

7.2

45

113

21.7

71

159.8

-6.1

21

69.8

7.8

46

114.8

22.2

72

161.6

-5.6

22

71.6

8.3

47

116.6

22.8

73

163.4

-5.0

23

73.4

8.9

48

118.4

23.3

74

165.2

-4.4

24

75.2

10

50

122

23.9

75

167

-3.9

25

77

10.6

51

123.8

24.4

76

168.8

-3.3

26

78.8

11.1

52

125.6

25

77

170.6

1-5

EPRI Licensed Material Thermography Overview Table 1-1 (cont.) Temperature Conversion Chart °C

Temp.

°C

Temp.

°F

°C

Temp.

°F

25.6

78

172.4

54.4

130

266

193

380

716

26.1

79

174.2

60

140

284

199

390

734

26.7

80

176

65.6

150

302

204

400

752

27.2

81

177.8

71.1

160

320

210

410

770

27.8

82

179.6

76.7

170

338

216

420

788

28.3

83

181.4

82.2

180

356

221

430

806

28.9

84

183.2

87.8

190

374

227

440

824

29.4

85

185

93.3

200

392

232

450

842

30

86

186.8

98.9

210

410

238

460

860

30.6

87

188.6

104

220

428

243

470

878

31.1

88

190.4

110

230

446

249

480

896

31.7

89

192.2

116

240

464

254

490

914

32.2

90

194

121

250

482

260

500

932

32.8

91

195.8

127

260

500

288

550

1022

33.3

92

197.6

132

270

518

316

600

1112

33.9

93

199.4

138

280

536

343

650

1202

34.4

94

201.2

143

290

554

370

700

1292

35

95

203

149

300

572

399

750

1382

35.6

96

204.8

154

310

590

427

800

1472

36.1

97

206.6

160

320

608

454

850

1562

36.7

98

208.4

166

330

626

482

900

1652

37.2

99

210.2

171

340

644

510

950

1742

37.8

100

212

177

350

662

538

1000

1832

43.3

110

230

182

360

680

566

1050

1922

48.9

120

248

188

370

698

593

1110

2012

621

1150

2102

843

1550

2822

1066

1950

3542

649

1200

2192

871

1600

2912

1093

2000

3632

677

1250

2282

899

1650

3002

1149

2100

3812

704

1300

2372

927

1700

3092

1204

2200

3992

732

1350

2462

954

1750

3182

1260

2300

4172

760

1400

2552

982

1800

3272

1316

2400

4352

788

1450

2642

1010

1850

3362

1371

2500

4532

816

1500

2732

1038

1900

3452

Conversion Factors °C = (°F - 32) x 5/9 °F = (°C x 9/5) + 32

1-6

°F

0 Kelvin = -273.16°C 0 Rankine = -459.69°F

EPRI Licensed Material Thermography Overview

1.3

Measuring and Mapping Temperature Without Contact

All targets radiate energy in the infrared spectrum. The hotter the target, the more energy that is radiated. Very hot targets radiate in the visible spectrum as well as in the infrared. As targets cool, they no longer glow but they continue to radiate. The radiation can be felt on a hand placed near the target's surface, but the glow can't be seen because the energy has shifted from red to infrared. Infrared detectors can sense infrared radiant energy and produce useful electrical signals proportional to the temperature of target surfaces. Instruments using infrared detectors allow a fast and highly sensitive target surface temperature measurement without contact. Instruments that combine this measurement capability with the capability of scanning a target surface area are called infrared thermal imagers. They produce thermal maps, or thermograms, where the brightness intensity or color of any spot on the map is representative of the surface temperature of that spot. In other words, they extend non-contact point temperature measurements to non-contact thermography. 1.3.1 The Three Elements of a Non-Contact Temperature Measurement In using infrared instruments for making non-contact temperature measurements, three sets of characteristics need to be considered:

•

Target surface

•

Transmitting medium between the target and the instrument

•

Measuring instrument

Figure 1-1 shows how the instrument is aimed at the target and makes the measurement through the medium.

1-7

EPRI Licensed Material Thermography Overview

Figure 1-1 Categories of Conditions for Infrared Thermal Measurements

Every target surface above absolute zero radiates energy in the infrared. The hotter the target, the more radiant infrared energy is emitted. The physical laws that define this behavior are discussed in detail in Appendix A, along with a detailed discussion of medium and instrument characteristics. Emissivity is a very important characteristic of a target surface and must be known in order to make accurate non-contact temperature measurements. Methods for estimating and measuring emissivity are discussed throughout this guide, and the emissivity setting that is needed to dial into the instrument can usually be estimated from available tables and charts. The proper setting needed to make the instrument produce the correct temperature reading can be learned experimentally by using samples of the actual target material. This more practical setting value is called effective emissivity. Although the transmitting medium is usually air, non-contact temperature measurements can be made through a vacuum, gas, or certain solid materials. The characteristics of the medium need consideration and a detailed explanation of this is included in Appendix A. Figure 1-2 shows the necessary components of an infrared radiation thermometer that makes a single point non-contact temperature measurement on the target surface. Collecting optics (that is, infrared lenses, etc.) is necessary in order to focus the energy radiated from the target onto the sensitive surface of an infrared detector. The detector converts this energy into an electrical signal that is representative of the temperature of a spot on the target. Adding scanning elements between the target and the detector (also shown in Figure 1-2) allows the instrument to scan the target surface and to produce a thermogram. Most currently available infrared thermal imagers incorporate 1-8

EPRI Licensed Material Thermography Overview

multi-detector focal plane array (FPA) sensors that are electronically scanned and that eliminate the requirement for an opto-mechanical scanning mechanism. When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, it collects energy within a collecting beam, the shape of which is determined by the configuration of the optics and the detector. The cross-section of this collecting beam is called the field of view (FOV) of the instrument and it determines the size of the area (spot size) on the target surface that is measured by the instrument. On scanning and imaging instruments this is called the instantaneous field of view (IFOV) and becomes one picture element on the thermogram.

Figure 1-2 Components of an Infrared Sensing Instrument

1.4

Performance Parameters of Thermal Sensing Instruments

This section previews the performance parameters of point-sensing instruments and scanning and imaging instruments. For a detailed discussion of these parameters and how to specify and test the performance of instruments, please refer to Appendix A. 1.4.1 Point-Sensing Instruments Point-sensing instruments are defined by the following performance parameters: •

Temperature range – The high and low limits over which the target temperature might vary

•

Absolute accuracy – As related to the NIST (National Institute of Standards and Technology) standard

•

Repeatability – How faithfully a reading is repeated for the same target

1-9

EPRI Licensed Material Thermography Overview

•

Temperature sensitivity – The smallest target temperature change that the instrument needs to detect

•

Speed of response – How fast the instrument responds to a temperature change at the target surface

•

Target spot size and working distance – The size of the spot on the target to be measured and its distance from the instrument

•

Output requirements – How the output signal is to be utilized

•

Spectral range – The portion of the infrared spectrum over which the instrument will operate

•

Sensor environment – The ambient conditions under which the instrument will operate

1.4.2 Line Scanners and Imagers—Qualitative and Quantitative The parameters used for assessing the performance of infrared thermal line scanners and imagers are more complex because a thermal line-scan or image is made up of a great number of discrete point measurements. Many of the performance parameters of infrared thermal line-scanners and imagers, such as accuracy, repeatability, and spectral range, however, are the same as those of radiation thermometers. Others are derived from, or are extensions of, radiation thermometer performance parameters. Some types of thermal imagers show comparative temperatures and not actual temperature measurements. For users of these thermal viewers (see section 3), parameters dealing with accuracy and repeatability do not apply. Parameters exclusive to thermal line-scanners and imagers are as follows: •

Total field of view (TFOV) – The thermogram image size, in terms of scanning angle. (example: TFOV=20° Vertical x 30° Horizontal) The TFOV of a line scanner is considered to be the TFOV of one scan line.

•

Instantaneous field of view (IFOV) – The spot size represented by one detector element at the target plane: Imaging spatial resolution. (example: IFOV= 2 milliradians) (1° = 35 milliradians)

•

Measurement spatial resolution: (IFOVmeas) – The spatial resolution that describes the minimum target spot size on which an accurate temperature measurement can be made. (example: IFOVmeas = 5 milliradians)

•

Frame (or line) repetition rate – The number of times every point on the target is scanned in one second. (example: Frame rate = 30/second or 30 Hz; Scan rate = 60 lines/second)

•

Minimum resolvable temperature (MRT) – The smallest blackbody equivalent target temperature difference that can be observed: Temperature sensitivity. (example: MRT=0.1°C @ 30°C target temperature)

1-10

EPRI Licensed Material Thermography Overview

•

Other parameters such as spectral ranges, target temperature ranges, accuracy and repeatability, and focusing distances are essentially the same as those for point-measuring instruments.

1.4.3 Thermal Imaging Software In order to optimize the effectiveness of thermographic measurement programs, the thermographer needs a basic understanding of the thermal image processing techniques. The following is a list of broad categories of thermal image processing and diagnostics currently available. A discussion of each of these categories is included in Appendix A. A detailed description of currently available thermal imaging and diagnostic software is provided in section 2. Thermal imaging software can be categorized into the following groups: •

Quantitative thermal measurements of targets

•

Detailed processing and image diagnostics

•

Image recording, storage, and recovery

•

Image comparison

•

Archiving and database* *Although data and image database development is not an exclusive characteristic of thermal imaging software, it should be considered an important part of the thermographer’s tool kit.

1-11

EPRI Licensed Material

2

A COMPENDIUM OF COMMERCIAL INFRARED SENSING AND IMAGING INSTRUMENTS

This chapter begins with a classification of infrared sensing and imaging instruments by type and application. The list includes commercially available instruments, from single-point thermal probes to on-line control sensors, to high-speed, high-resolution thermal imaging (thermography) systems [1]. A detailed overview of performance characteristics and features follows, along with a discussion of the typical thermographic display approaches that are used by various imager manufacturers. This is followed by a discussion of currently available thermographic image processing software and image hard-copy recording accessories. Finally, a tabulation of currently available instruments by category and manufacturer is appended, including a digest of performance characteristics and features. A current index of manufacturers' addresses, phone numbers, Web sites (where available), and/or e-mail addresses is also included.

2.1

Classification of Instruments

Infrared sensing instruments are traditionally classified into three groups: point-sensing, linescanning, and thermographic (two-dimensional scanning). Point-sensing devices (commonly called Infrared Radiation Thermometers) collect radiant energy from a spot or area on the surface of an object to be measured (the target) and provide an output indication, usually in terms of target temperature. Line-scanning instruments provide an output, generally an analog trace, of the radiant energy (or, in ideal cases, temperature) distribution along a single straightline projection from the target surface. Thermographic instruments (imagers) provide an image of the energy distribution over a scanned area on the target surface. This is presented in the form of an intensity-modulated black and white picture or a synthesized color display called a thermogram. Point sensors, line scanners, and imagers can be further divided into sub-groups. This section will review commercially available instruments along the lines of this breakdown: Point-Sensing •

Probes and IR thermocouples

•

Portable (hand-held)

•

On-line monitoring and control

•

Specials 2-1

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

Line-Scanning •

Opto-mechanically scanned

•

Focal plane array (FPA), electronically scanned

Thermographic •

Opto-mechanically scanned imagers

•

Electronically scanned pyrovidicon imagers

•

Electronically scanned focal plane array imagers

2.2

Instrument Manufacturers

Particularly in the point-sensing category, there are many companies offering the same instrument under different private label arrangements. In order to avoid duplication, the original manufacturer or prime (U.S.) distributor will be listed in the material that follows. At the end of Section 2, a comprehensive list of instruments is included (Table 2-1), for which descriptive literature was available at the time of the preparation of this text. The performance characteristics are summarized rather than presented in detail. The listed manufacturer should be contacted for detailed performance information. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, for the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. In addition, a third table is included, which summarizes proven industrial applications for thermal imaging instruments (Table 2-3). The information that follows will highlight the applications for which each instrument category and group is particularly suited, based on configuration or performance characteristics.

2.3

Discussion of Instruments

2.3.1 Point Sensors (Radiation Thermometers) 2.3.1.1

Probes

Temperature probes are characterized by low price (from less than $100 to about $1,000), pocket-portability, and wide-collecting angle. They are battery-powered and are generally optically pre-adjusted for minimum spot size at a short working distance (a 1/4" (6.35 mm) spot at a 3/4" (19.05 mm) working distance is typical). Some models are designed to operate into a conventional multi-meter and some incorporate their own readout box with a liquid crystal diode (LCD) display. They usually feature disposable batteries and some models have ac adapters. Temperature ranges are from about 0°F, or slightly below, to 600°F, and a sensitivity of +/- 1°F is easily achieved. Emissivity adjustments are available on some models. Probes are ideal for

2-2

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

close-up measurements and are used in circuit board analysis, troubleshooting of electrical connections, the inspection of plumbing systems, and in application to biological and medical studies. 2.3.1.2

Portable Hand-Held

With few exceptions, these instruments are pistol-shaped and designed for middle-distance measurements. They are usually optically pre-adjusted for infinity focus. A typical 2° field of view resolves a 7.5-cm (3-inch) spot at a 150-cm (60-inch) working distance, and a 30-cm (1foot) spot at a 9-m (30-foot) working distance. Prices range from about $100 to more than $3,500. Sighting and aiming methods vary from simple aiming notches to enclosed illuminated reticles. There are instruments with extremely narrow fields of view (0.5°) that include a rifle stock and telescopic sight. Most instruments in this group incorporate emissivity adjustments and some include microcomputers with limited memory and data-logging capabilities. Most are available with a recorder output, although this feature is seldom used. A meter is always provided and, with one exception that reads in BTU/ft²-h, the readout is always in temperature units. Analog displays are still available, although they are decreasing in popularity. Digital readouts featuring light emitting diodes (LEDs) were introduced first but the LCD display, introduced more recently, is now used almost universally because its tiny power drain extends battery life. For this reason, the more recent instruments offer replaceable rather than rechargeable batteries and battery life approaches one year. Some instruments in this group have zeroing adjustments, but all of the newer instruments include auto-zeroing features. Temperature ranges are, typically, from 0°C to 1500°C. Temperature sensitivity and readability are usually 1°C (or °F) or 1% of scale, although sensitivities on the order of 0.1°C (or °F) are achievable. This instrument group is particularly suited to applications where spot-checking of target temperatures is sufficient and continuous monitoring is not required. A typical use would be for periodic maintenance checks of rotating machinery to detect whether or not bearings are beginning to overheat. These instruments, over the past few years, have become an important part of many plant energy conservation programs. Although many of these instruments provide extremely accurate readings, accuracy, like the recorder output, is less important to most users than repeatability, ruggedness, portability, reliability, and ease of use. Some newer models incorporate microcomputers with special features such as a data-logger, which has the capability to store as many as 60 readings for future retrieval and printout. 2.3.1.3

On-Line Monitoring and Control

These instruments are primarily used for monitoring and control of manufacturing processes. The one feature that distinguishes this instrument group from the others is dedicated use. The instrument is generally mounted where it can measure the temperature of one specific target, and it remains there for the life of the instrument or the process. With few exceptions, these instruments operate on line power. The output signal of the instrument can be observed on a meter, used to operate a switch or relay, feed a simple or sophisticated process control loop, or it can be used in any combination of these functions. 2-3

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

Early on-line instruments consisted of an optical sensing head and an electronics/control readout unit at the other end of an interconnecting cable. This configuration still exists to some extent, but most of the newer units feature sensing heads that are more stable electronically and, hence, more independent of the remote control units. The trend is for these new sensors to mate with universal indicator/control units that accept input from various types of industrial sensors. This instrument group is selected to perform a specific task, so the manufacturer provides a shopping list ordering format to the customer, enabling them to purchase all required features. Manufacturers offer sensing head features such as variable or fixed focus, sighting tubes, light pipes, water-coolable housings, air purge fittings, air curtain devices, and see-through aiming with target-defining reticles. The shopping list for the indicator/controller unit might include digital readout, binary coded decimal (BCD) output, analog output, single, double, or proportional set point, rate signals, sample and hold, peak or valley sensor, and data-logger interface. Emissivity controls, located in a prominent place on a general-purpose instrument, are more likely to be located behind a bezel on the sensor on these dedicated units, where they are set one time and locked. Spectral characteristics are worth mentioning separately, although, technically, they are part of the sensing head shopping list. The spectral interval over which the sensing head operates is selected to optimize the signal from the target, to reduce or eliminate the effect of an interfering energy source, or to enable the instrument to measure the surface temperature of thin films of material that are largely transparent to infrared energy. This last application has made these instruments important factors in the manufacture of thin film plastics and also of glass. 2.3.1.4

Specials

There are several special categories of spot-measuring instruments that are worth mentioning, although they might, by strict definition, fit into one or more of the above categories. Two-color or ratio pyrometers are one special case of an on-line instrument. These are particularly useful in high-temperature applications and in measuring small targets. The effective emissivity of the target need not be known, providing that it is constant and that reflections are controlled. The target need not fill the field of view, provided that the background is cool, constant, and uniform. Impurities in the optical path that result in broadband absorption, do not affect the measurement because the measurement is based on the ratio of energy in two spectral bands. Ratio pyrometers are, generally, not applicable to measurements below 500°F. Another special case is the fiber optic-coupled thermometer. With this instrument, inaccessible targets can be measured by replacing the optic with a flexible or rigid fiber optic bundle. This, of course, limits the spectral performance and, hence the temperature range, to the higher values, but it has allowed temperature measurements to be made when none were possible. The infrared microscope is a third special case. This instrument is configured like a conventional microscope. Through the use of reflective microscope objectives and beam splitters, it enables 2-4

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

the operator to simultaneously view and measure targets down to 0.0003" (.00762 mm) in diameter with an accuracy and resolution of about 0.5°F. Another special case, known as the laser pyrometer, has also become available. This instrument uses the reflected energy of an active laser to measure target reflectance. A built-in microcomputer calculates target effective emissivity and uses this to provide a corrected true temperature reading. The laser pyrometer is useful for high-temperature diffuse target surfaces. Prices of instruments in the on-line control instrument group vary from less than $1,000 for an infrared switch, to more than $15,000 for infrared microscopes and on-line instruments equipped with many control features. Generally speaking, the price goes up when sensitivity, small spot size, and speed of response are all required and, of course, when many shopping list items, or additional features, are added. 2.3.2 Line Scanners The purpose of spatial scanning is to derive information concerning the distribution of radiant energy over a target scene. Quite often, a single straight line scanned on the target is all that is necessary to locate a critical thermal anomaly. In the newer line scanners, the single-element detector is replaced by a multi-element single-line focal plane array (FPA) and the optomechanical scanning element is eliminated. Probably the first approach to line scanning that was adopted commercially was in an aerial-type thermal mapper in which the line scanner was mounted on a moving aircraft and scanned lines normal to the direction of motion. The outputs representing these individual scan lines were intensity-modulated and serially displayed in shades of gray on a strip map. This display represented the thermal map of the surface being overflown by the vehicle. 2.3.2.1

Opto-Mechanically Scanned Line Scanners

The earliest process-monitoring line scanners (many of which are still in use) employed a singleelement detector and a single scanning element, usually a mirror. The instantaneous position of the scanning element is usually controlled or sensed by an encoder or potentiometer so that the radiometric output signal can be accompanied by a position signal output and be displayed on a chart recorder, an oscilloscope, or some other recording device. One portable, battery-powered line scanner, still used commercially, scans a single line on target, develops a visible temperature trace using light emitting diodes and, by means of optical beamsplitting techniques, superimposes this trace over the visible scene viewed by the operator. The operator selects the line to be scanned by aiming the instrument's horizontal centerline. Photorecording of the composite scene is accomplished by aiming a conventional instant color camera through the eyepiece of the scanner. This instrument has no recorder output and is, therefore, not suited for process control applications. Unlike most thermal viewers, however, absolute temperatures are obtainable with this device. Good applications for this line scanner include electrical switchgear and transmission lines, the troubleshooting of plumbing systems, and webprocess profiling. 2-5

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2.3.2.2

Electronically Scanned Focal Plane Array Line Scanners

The newest high-speed on-line commercial line scanners employ linear focal plane detector arrays that are electronically scanned. They develop high-resolution thermal maps by orienting the linear array along an axis normal to the motion of a moving target such as a paper web, a rotating kiln, or a strip steel process. The output signal information is in real-time computercompatible format and can be used to monitor, control, or predict the behavior of the target. The best applications for this scanner are in on-line real-time process monitoring and control. In significant recent developments, families of line cameras have been made available with a wide selection of linear focal plane array detectors based on the speed, resolution, and spectral sensitivity requirements of the process being monitored. 2.3.3 Thermographic Instruments An important advantage of radiation thermometers over contact thermometers is their speed of response. The measured energy travels from the target to the sensor at the speed of light. The response of the instrument can then be in milliseconds or even microseconds. This important feature has allowed the field of infrared radiation thermometry to expand into real-time thermal scanning and thermal mapping. When problems in temperature monitoring and control cannot be solved by the measurement of one or several discrete points on a target surface, it becomes necessary to spatially scan (that is, to move the collecting beam (instantaneous field of view) of the instrument relative to the target). The detector output is intensity-modulated in proportion to the total exitant radiant energy at each point scanned on the target surface. The image produced is presented in monochrome or color, where the gray shades or color hue are intended to represent a thermal level at the target surface. These thermal images are called thermograms. The purpose of spatial scanning is to derive information concerning the distribution of infrared radiant energy over a target scene. Scanning can be accomplished either opto-mechanically or electronically. Opto-mechanical scanning can be done by moving the target with the instrument fixed, or by moving (translating or panning) the instrument, but is most practically accomplished by inserting movable optical elements into the collected beam. Although an almost infinite variety of scanning patterns can be generated using two moving elements, the most common pattern is rectilinear. This is most often accomplished by two elements that each scan a line normal to the other. A typical rectilinear scanner employs two rotating prisms behind the primary lens system (refractive scanning). An alternate configuration uses two oscillating mirrors behind the primary lens (reflective scanning). This is also commonly used in commercially available scanners, as are combinations of reflective and refractive scanning elements. Electronic scanning involves no mechanical scanning elements—the thermal pattern of the surface is scanned electronically. The earliest method of electronically scanned thermal imaging is the pyrovidicon (pyroelectric vidicon) or thermal video system. With this method, charge proportional to target temperature is collected on a single pyroelectric detector surface, within an electronic picture tube. Scanning is accomplished by an electronic scanning beam. Although 2-6

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

many of these devices are currently in use in the field, manufacturers have all but discontinued offering them in favor of instruments based on solid-state focal plane array technology. Most recently, electronically scanned thermal imaging is accomplished by means of an infrared focal plane array (IRFPA), whereby a two-dimensional staring array of detectors collects radiant energy from the target and is digitally scanned to produce the thermogram. All of the above approaches to producing an infrared thermogram will be discussed. Commercial thermal imaging systems fall into the following categories and sub-categories: •

Thermal viewers, opto-mechanically scanned

•

Imaging radiometers, opto-mechanically scanned

•

Thermal viewers, electronically scanned (pyrovidicon imagers)

•

Focal plane array (FPA) imagers, qualitative (thermal viewers), and quantitative (imaging radiometers)

A comprehensive list (Table 2-1) of all known, commercially available thermal-imaging instruments, on which descriptive literature was available at the time of the preparation of this document, is included at the end of Section 2. Performance characteristics are also briefly summarized. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, of the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. In addition, a third table is included, which summarizes proven industrial applications for thermal imaging instruments (Table 2-3). The information that follows will highlight the applications for which each instrument category and group is particularly suited, based on configuration or performance characteristics. 2.3.3.1

Thermal Viewers, Opto-Mechanically Scanned

Note: Although they are being replaced gradually by focal plane array imagers (see section 2.3.3.4), at the time of this writing, opto-mechanically scanned thermal viewers are still in wide use commercially. For this reason, the following operational description is provided. Opto-mechanically scanned thermal viewers are inexpensive battery-powered scanning instruments producing a qualitative image of the (thermally associated) radiant exitance distribution over the surface of a target. The battery packs are rechargeable and usually provide 2–3 hours of continuous operation. These are one-piece, lightweight instruments, designed to be simple to operate. The first viewers required cryogenic cooling of the detector elements, which was accomplished by means of a small tank of compressed argon. These early units, while still in use, are no longer manufactured. Newer units feature thermoelectric detector cooling provided by a battery-powered cooler. Thermal viewers are not designed for absolute temperature measurements, but they can demonstrably sense temperature differences in tenths of degrees. Some manufacturers have modified these viewers and introduced absolute temperature references so that absolute 2-7

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

measurements are possible in certain applications. This generally requires an additional box, however, and diminishes the portability that defines the instrument group. (It also increases the price.) Thermal viewers operate most effectively with cooler targets (0°C–150°C) but, through the use of optical attenuators, they can be used for targets of up to 1500°C. Typically, the area scanned (field of view) with thermal imagers is from 6° to 8° high and from 12° to 18° wide, with spatial resolution (instantaneous spot size) of 2 mRad (1 cm at 2 m). Although a hard copy of the thermal image can be acquired by through-the-eyepiece recording using either conventional or instant film, currently available units offer direct video recording by means of a conventional VCR output jack and camcorder accessories. Applications for thermal viewers are found throughout the industrial environment but are generally limited to those in which the temperature measurements are not critical and the recording quality does not need to be optimum. The combination of a thermal viewer (to locate thermal anomalies) and a hand-held thermometer (to quantify them) is powerful and costeffective. Thermal viewers are particularly useful industrially in tight spaces or, conversely, when a sizable area must be traversed and user fatigue becomes a factor. 2.3.3.2

Opto-Mechanically Scanned Imaging Radiometers

Note: Although they are being replaced gradually by focal plane array imagers (see Section 2.3.3.4), at the time of this writing, opto-mechanically scanned imagers are still in wide use commercially. For this reason, the following operational description is provided. Opto-mechanically scanned imaging radiometers provide potentially quantitative temperature measuring capability and high-resolution image quality. Detector cooling is almost always required and this is done using any of several means including thermoelectric (Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers, and, most recently, electricpowered Stirling cycle nitrogen coolers. Most commercial imaging radiometers use a single detector, but some manufacturers offer dual-detector or multi-detector (linear array) instruments. All provide a means of measuring target surface temperature. These imagers use refractive, reflective, or hybrid scanning systems and operate in either the 3–5 µm or the 8–14 µm atmospheric window. In addition to quantitative temperature measuring capability in idealized circumstances, these instruments feature excellent capabilities for both spatial resolution (about 1 mRad) and minimum resolvable temperature (0.05°C to 0.1°C). Most manufacturers offer isotherm graphics features, spectral filtering, interchangeable optics for different total fields of view, color or monochrome (black and white) displays, flexible video recording capabilities, and computer compatibility. Most general-purpose systems in use today feature compact, field-portable, battery-operable sensing heads and control/display units, some of which are integrated into camcorder configurations. A complete system, including battery and video recorder, can usually be handled by one person, by either mounting the components on a cart or assembling them on a harness. Detector cooling for all newer models that are intended for field operation is accomplished by means of thermoelectric or Stirling-cycle cooler, thus eliminating the inconvenience of liquid nitrogen refills in the field.

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EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

2.3.3.3

Thermal Viewers, Electronically Scanned (Pyrovidicon Imagers)

Note: Although they are being replaced gradually by focal plane array imagers (see section 2.3.3.4), at the time of this writing, pyrovidicon imagers are still in wide use commercially. For this reason, the following operational description is provided. Pyrovidicon imaging systems are not unlike home video-recording systems except that the camera tube is a pyroelectric vidicon (pyrovidicon) rather than a conventional vidicon. It records target radiation in the infrared rather than the visible spectrum. The significant difference is that the pyrovidicon has no dc response; that is, if the camera is not continuously panned over the target or the collecting beam is optically chopped, the image fades from the screen. This behavior is caused by the fundamental photoelectric response characteristics of the detector material. Aside from the tube, which is costly, and the lens, which is generally made of germanium and also costly, these systems use commercially available television equipment and recording accessories. By comparison with other infrared imaging systems, the picture quality and resolution are good, approaching conventional television format. The thermal image can be viewed or videotaped with equal convenience and no cooling is required. The requirement for continuous target panning can be made less objectionable by the ability to play back an image and freeze the frame for detailed image inspection. Compact synchronous choppers that provide flicker-free performance and enhance image quality are incorporated in most instruments. Pyrovidicon systems do not intrinsically offer absolute measurement capability, but a thermal profile feature, available on some units, provides an analog of the center scan line displayed to the side of the image. Some models incorporate a spot-measuring sensor boresighted with the scanner and its measurement superimposed on the video display, along with a defining reticle in the center of the display. Software packages are offered that are specified to provide quantitative measurements by compensating for field variations and introducing temperature references. Thermal resolution of pyrovidicon instruments is between 0.1°C and 0.2°C in panned mode and between 0.2°C and 0.4°C (half as good) in chopped mode. Another useful feature available on some models integrates a video camera into the viewing channel so that simultaneous visual and thermal images can be seen on a split-screen or in a fade in, fade out format. Although pyrovidicon displays are monochrome (black and white), some models incorporate colorizer accessories and image-processing software packages. Pyrovidicon systems are particularly suited to moving targets, airborne scanning, and distant measurements. They operate well in the 8–4 µm atmospheric transmission window. They are susceptible to a momentary loss of sensitivity from saturation phenomena, known as depoling, when suddenly aimed at very hot targets with the aperture improperly open. The automatic repoling circuits require about a 30-second restoration time, resulting in some operator inconvenience. Operating costs are very low because no coolant is required, and common erasable videocassettes are used for recording purposes. Videotapes can be monitored on conventional television receivers.

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EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

2.3.3.4

Focal Plane Array (FPA) Imagers—Qualitative and Quantitative

In the mid 1980s, detector mosaics, or staring infrared focal plane arrays, were used successfully for military night vision Forward Looking InfraRed (FLIR) viewers and have since been made widely available for use in commercial thermal-imaging instruments. In an IRFPA imager, each detector element is assigned one display picture element and mechanical scanning is eliminated altogether. IR focal plane array (IRFPA) radiometers are adaptations of military and aerospace FLIRs but, unlike FLIRs, they are designed to allow measurement of the apparent temperature at the target surface and to produce quantitative as well as qualitative thermograms. They represent the most recent developments in FPA imagers. Although measurement-capable IRFPA imagers were promised as early as 1987, these capabilities were slow in arriving because of the complexity of the task. It was well into the 1990s before good quality measurement capabilities became available. At the present time, most commercial manufacturers offer a wide choice of high-resolution IRFPA imagers and radiometers. Today’s IRFPA imagers offer thermal resolution that is comparable to opto-mechanically scanned imagers (0.05°C to 0.2°C) and spatial resolution that is considerably better (1 mRad or better with standard optics). With inherently faster response, no moving parts, and superior spatial resolution, IRFPA imagers and radiometers have all but completely replaced opto-mechanically scanned imagers throughout the user community. Currently, most commercially available measuring and non-measuring IRFPA cameras use uncooled focal plane arrays of bolometric or pyroelectric/ferroelectric thermal detectors. Although detector cooling is not required, the detector arrays are temperature-stabilized by means of low-power thermoelectric devices to ensure instrument stability. Although there are no scanning elements, pyroelectric FPAs require a mechanical chopper because they have no dc response. For special applications where high speed, improved sensitivity, or spectral selectivity is required, cooled photo-detector arrays are used. These include platinum silicide (PtSi), indium antimonide (InSb), mercury-cadmium-telluride (HgCdTe) and, most recently, gallium arsenide (GaAs) quantum well infrared photo-detectors (QWIP), all of which require cooling. Detector cooling can be accomplished by any of several means, including TE (thermoelectric Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers and, most recently, electric-powered Stirling-cycle nitrogen or helium coolers. Most of today’s commercially available cooled imagers are equipped with either a TE cooler or a compact, high-efficiency Stirling-cycle cooler. The Stirling-cycle cooler operates like a micro-miniaturized electric refrigerator.

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EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

2.3.3.5

FPA Imager Performance Comparisons

Most application needs can be fulfilled by means of selecting from among five categories of instruments available in today’s commercial thermal imager market. These include: Un-Cooled FPAs (the general purpose choice) Un-cooled IRFPA imagers, operating within the 7–14 µm region, are suitable for most applications in: •

Predictive maintenance, condition monitoring

•

Buildings, roofs, and infrastructure

•

Process monitoring and control (except where there are high-speed or spectral considerations)

•

Medical and biological studies

•

Materials evaluation and nondestructive testing (except for high-speed or high-resolution applications)

•

Security, surveillance, night vision, search and rescue, firefighting

Typical performance characteristics of imagers in this category are: Temperature sensitivity (noise-equivalent temperature difference [NETD]): 0.08°C (80 milliKelvins) @ 30°C Spectral range: 7.5–13 µm Spatial resolution: 1.3 milliradian (320x240 element micro-bolometric FPA) Frame repetition rate: 50/60 Hz Mid-Range Infrared (MWIR) Indium Antimonide (InSb) or Platinum Silicide (PtSi) FPAs Cooled platinum silicide (PtSi) or indium antimonide (InSb) imagers are preferable where spectral selectivity at shorter wavelengths is important (such as in some manufacturing processes) or for high-temperature applications (such as furnace measurements). A typical imager in this category could have the following performance characteristics: Temperature sensitivity (NETD): 0.07°C (70 milliKelvins) @ 30°C Spectral range: 3.4–5 µm Spatial resolution: 1.2 milliradian (256x256 element PtSi FPA)

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EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

Frame repetition rate: 50/60 Hz InSb-based imagers have somewhat better thermal sensitivity than PtSi-based imagers and are somewhat more expensive. High-speed, high-sensitivity photo-detector FPAs (for special applications) For special applications involving high-speed phenomena, high thermal sensitivity, and processing flexibility at longer wavelengths, the detector of choice has become the gallium arsenide (GaAs) QWIP FPA. A typical imager in this category could have the following performance characteristics: Temperature sensitivity (NETD): 0.02°C (2 milliKelvins) @ 30°C Spectral range: 8–9 µm Spatial resolution: 1.1 milliradian (320x240 element GaAs QWIP FPA) Frame repetition rate: selectable from 50/60 Hz to 750/900 Hz NIR (near-infrared) FPAs (for telecommunications, fiber optic, and laser-profiling applications) A typical imager in this category could have the following performance characteristics: Radiant sensitivity Noise Equivalent Irradiance (NEI): 1x1010 ph/cm2/sec (Because the applications for this type of instrument are concerned with measuring radiant power rather than temperature, sensitivity is expressed in NEI rather than NETD.) Spectral range: 900–1700 nm (0.9–1.7 µm) Spatial resolution: 1.2–1.6 milliradian (320x256 element InGaAs FPA) Frame repetition rate: 30 Hz Special High-Temperature FPA Imaging Pyrometers (for special high-temperature applications, such as furnace temperature monitoring) A typical imager in this category could have the following performance characteristics: Temperature sensitivity (NETD): Spectral range: 700–1100 nm (0.7–1.1 µm) selected filters for ranges from 600°C to 2400°C Spatial resolution: 1.2–1.6 milliradian (776x484 near-infrared FPA detector) Frame repetition rate: 30 Hz 2-12

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments

2.4

Thermal Imaging Diagnostic Software

The new generation of thermal imagers features image processing capabilities that can be generally categorized into four groups. Applications for thermal imaging often require the use of more than one of these four groups: •

Quantitative thermal measurements of targets

•

Detailed processing and image diagnostics

•

Image recording, storage, and recovery

•

Image comparison

2.4.1 Quantitative Thermal Measurements of Targets This is the temperature value of any point (or all points) on the target surface. For true radiance measurements, the system throughput attenuation must be taken into consideration as well as losses through the measurement medium (atmosphere, in most cases). For true temperature measurement, the target effective emissivity must also be considered. In order to provide true radiance values, the system calibration constants are fed into the computer on initial setup and a system of prompts assures the operator that changes in aperture settings, target distance, interchangeable lenses, etc. are fed into the keyboard each time a change in operating condition occurs. For true temperature values, it is necessary for an effective emissivity value to be inserted by the operator. The temperature readings that are then displayed assume that the entire target surface effective emissivity is equal to this inserted value. In operation, a color scale (or monochrome gray scale) is provided along one edge of the display with a temperature shown corresponding to each color or gray level. The operator can also place one or more spots or cross hairs on the image and the temperature value of that pixel will appear in an appropriate location on the display. Some systems allow the assignment of several different effective emissivities to different areas of the target, as selected by the operator, with the resulting temperature correction. One system, developed for the thermal imaging of semi-conductor devices and other microtargets, offers a spatial effective emissivity correction based on the actual measurement of the surface effective emissivity of the target. By means of a precision-controlled heated sub-stage, the operator heats the unpowered device to two known temperatures in sequence. At each temperature, a radiance image is recorded. Using the known temperature and the known radiance for two temperatures, the effective emissivity matrix is computed, pixel by pixel, and stored. This matrix is subsequently used to correct the powered radiance image of that specific device and to provide a true temperature thermogram. 2.4.2 Detailed Processing and Image Diagnostics Detailed processing and image diagnostics is a phrase that describes the capability of the computer to analyze each pixel of the thermal image and to present information in a wide variety

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of qualitative and quantitative forms for the convenience of the user. Some (by no means all) of these forms are discussed below. In addition to the spot meter capability discussed previously, the operator might call for profile displays. The analog trace (in x, y, or both) of the lines on the image that intersects at the selected spot will then appear at the edge of the display. Some systems allow the operator to display as many as seven sets of profiles simultaneously. Profiles of skew lines can also be displayed on some systems. The operator can draw areas on the display in the form of circles, rectangles, or point-to-point free forms. These areas can be shifted, expanded, shrunken, or rotated. They can be used to blank out or analyze portions of the image. On command, the computer will provide a detailed analysis of the entire image or the pixels within the area including maximum, minimum, and average values, number of pixels, or even a frequency histogram of the values within the area. Although a standard (default) color scale is usually provided by the manufacturer, color scales can be created by the operator in almost infinite variety from as many as 256 colors stored within the computer. Zoom features allow the operator to expand a small area on the display for closer examination, or to expand the colors for a small measurement range. Auto-scale features provide the optimum display settings for any image that is selected. 3-D features provide an isometric thermal contour map of the target for enhanced recognition of thermal anomalies. 2.4.3 Image Recording, Storage, and Recovery This is the capability to index, record, and retrieve images and data. Most commercial thermal imaging systems offer limited image storage by means of on-board removable floppy disks, PCMCIA cards, or other reusable storage devices. Limited image analysis software can also be incorporated into the field-portable instrument. Images can be stored from a frozen-frame thermogram of a live target on operator command, or the operator can set up an automatic sequence and a pre-set number of images will be stored at pre-set time intervals. Most systems also offer VCR options so that an entire measurement program can be recorded on videotape. These videotapes can then be played back into the system and images can be stored on playback from videotapes. Stored images can be retrieved from storage and displayed at the operator’s command. Diagnostic software is generally offered separately from the basic imaging instrument, although some limited diagnostic software is usually included in the basic package for on-site analysis. The current trend by manufacturers is to offer more and more on-board image analysis capabilities but, for extensive image storage and analysis, the images are more often downloaded from the cards to computers with large storage capacities and memory. The extensive image and data analysis software is resident on the computer hard drive.

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2.4.4 Image Comparison Image comparison is a very significant capability in that it allows the automatic comparison of images taken at different times. The computer allows the operator to display two images, sideby-side or in sequence, and to subtract one image from another, or one area from another, and to display a pixel-by-pixel difference thermogram. This provides the capability for archiving thermal images of acceptable components, assemblies, and mechanisms, and for using them as models for comparison to items produced subsequently. Subtractive routines produce differential images illustrating the deviation of each pixel (picture element) from its corresponding model. Image averaging allows the computer to accumulate several scan frames and to display the average of these frames. Comparison (subtraction) of images can be derived from two real-time images, two stored images, or a real-time and a stored image.

2.5

Recording, Hard Copy, and Storage of Images and Data

Thermal image recording and storage has evolved dramatically from Polaroid® instant photos of the display screen, to magnetic storage and archiving of images and data (such as labels, dates, conditions of measurement, and instrument settings), to the instant digital image storage capabilities incorporated into most of today’s thermal imagers. Hundreds of images can be recorded in the field and stored on removable, reusable memory cards. The problem of making a hard copy of the displayed image has also been solved with the advent of miniaturized digital cameras and photo-quality color printers that can print high-resolution images directly from camera outputs or from downloaded images and process them on the computer. Thermal images are saved in any one of several digital image formats such as .bmp, .tif, and .jpeg for archiving and future analysis. Corresponding visible reference images of the same targets can be recorded in the same format by digital cameras. Some manufacturers have integrated digital visible photo-recording capabilities into their new models of thermal imagers. Both thermal and visible images can be printed independently or as part of a detailed report, as described in Section 2.6.

2.6

Report Preparation

Stimulated by the demand of the predictive maintenance community for timely and comprehensive reporting of the findings of IR surveys, most manufacturers of thermal imagers have developed comprehensive report preparation software. These packages provide templates that allow the thermographer to prepare reports in standard word processor formats (such as Word for Windows®), into which digital thermal images and visible images imported from various imaging radiometers and digital cameras, can be directly incorporated. Additional diagnostic software is customarily provided in these packages so that post-analysis and trending can be added to the report.

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EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing Probes and IR Thermocouples

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Dickson

D161

Various models -40°C to +500°C, hold button LCD display, laser pointer, emissivity control (e set).

Exergen

SnakeEye and Smart IRt/c series

Wide range of infrared thermocouples with standard and custom configurations.

Horiba

IT580

32°F to 572°F, 0–300°C, LCD display, e set, hold button.

Ircon

Ultimax Jr

-40°C to +500°C, e set, LCD display, laser aiming spectral range: 8–14 µm.

Linear

QuickTEMP, C500, C1600, and C1700 series

-18°C to +315°C, QuickTEMP has LCD display and optional laser pointer, C500 connects to a multi-meter, C1600 has multiple models with various ranges, some models have e set. C1700 reads heat flow in BTU/sq ft/hr.

Mikron

Model M50, M500 IR thermocouples

Various temperature ranges from 0°C –500°C.

Omega

OS36, OS37, and OS38 series IR thermocouples

Modular and hand-held infrared thermocouples, various ranges.

OS200, 500, 600, 88000 and OS20 series

Close-focus probes with LCD readouts.

Raytek

Raynger IP series

A family of plug-in accessory probes that convert a digital multi-meter (DMM) or thermocouple meter into a close focus, non-contact IR thermometer. -18°C to 250°C, 8–14 µm.

Telatemp

TH1-440S and TemptestR

Ranges from -50°C to +500°C, LCD display, LED aiming available e set.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing, Hand-Held Dickson

D160 series

Various models -40°F to +950°F, -45°C to +538°C, hold button LCD display, laser pointer, emissivity control (e set).

Everest

Model 100.3ZL and ZH

Two models from -30°C to +1100°C, LCD display, analog output, aiming light, peak sampler, differential available. Rechargeable battery.

Exergen

E series Microscanner

-50°F to +550°F or -5°C to +285°C, one piece with LED bar graph and numerical scale, high- and low- hold feature, audio alarm.

DX series

Close-up sensor with reflective cone for target emissivity correction; ranges from -4.5°C to +871°C, digital read-out.

Ircon

ULTIMAX series

Various models from -30°C to +3000°C, thru-the-lens sighting, spectral ranges 0.65, 0.96–1.06, and 8–13 µm (some models are ratio-pyrometers), LCD display, analog and RS-232 outputs, replaceable batteries.

Irtronics

Sniper series

Laser or visual sights, 8 wavelengths, 0–3000°F/C.

Land

Cyclops series (Minolta), 33, 41, 52, Compac 3

High- and low-temperature (to 5500°C), small targets, variable focus, reticle display, Compac 3 has low-temperature, fixed-focus, thru-lens sight.

Linear

LT, LTL, and LTS series

-29°C to 1093°C, 30:1 or 60:1 optics, laser pointer or non-parallax sight available, 1% accuracy. F-C switch, LCD display.

Mikron

M90, M100, M101, M102, and M103 series

Various models, including ratio pyrometers, from -40°C to +3000°C, LCD displays, options: laser aiming light, telescope, e set, various FOVs.

Omega

HHM, OS520, OS631, OS900 series, others.

Wide range of models with ranges from -18°C to 2482°C, options include laser aiming, through-the-lens viewing, BTU read-out.

Palmer-Wahl

Heat Spy DHS-100 series, DHS-200 series, DHS-20 series, DHS-34 series, DHS53 series, HAS-201 series

Various models from -40°C to +1760°C, analog, LCD, and LED displays. Series DHS has e set, peak-hold, and various FOVs, including telescopic. Through-the-lens sighting and laser aiming features are available.

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EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing, Hand-Held (cont.) Pyrometer

Pyrolaser laser pyrometer

Ranges from 600°C–3000°C, uses laser to measure reflectance and correct for emissivity, thru-lens sight, rechargeable battery.

Pyrofiber series

Fiber-optic-coupled, ranges from 600°C–3000°C, uses laser to measure reflectance and correct for emissivity, thru-lens sights, rechargeable battery.

Raytek

Raynger MiniTemp, MX, 3I, IP, ST series

Various models from -30°C to 900°C, dual LCD display, hi-lo alarms, RS232/analog output, datalogger, max-min-mean, differential, laser aiming available.

Teletemp

INFRAPRO 3 and 4

Various models from -32°C to +760°C, rechargeable battery, e set, LED display. Laser aiming and scope available.

Williamson

600, Viewtemp, Truetemp

Viewtemp is 25°C to 1650°C, LED inside reticle, e set, and rechargeable battery. Truetemp is 2-color, 550°C to 2200°C. 600 has analog display, various ranges from 75°F to 3000°F.

E2 Technology (now part of Mikron)

Heat switch (Solar TD100 and Meteor 300), Pulsar and Quasar Series Photon, Nova, Comet, other models

Various heat pulse switches and ruggedized models from 260°C–1650°C, including ratio pyrometers.

Everest

3000 series, 4000 series

Ranges from -40°C to +1100°C, spot size available down to 0.01". Multiplexes up to 8 heads through electronics.

Horiba

IT-230

0°C–300°C, multiple ranges, digital output with e set, multiple control features.

Ircon

Modline 3 and 4 series, SA, SR, and 1100 Series, Javelin, Mirage and MiniIRT series, others.

Various models and accessories, -18°C to +1375°C, integrated, fixed-focus, two-wire transmitters, spectral selection. Various models of two-piece, -18°C to 3600°C with thru-lens sights, LCD display, spectral selection (including ratio pyrometers), and control and output options. IR pulse switches and fiber opticcoupled heads.

Irtronics

Argosy, Spartan, others

Various ranges from 30°C to 3000°C, spectral selection, telephoto, multizones, fiber-optic-coupled heads available.

Point-Sensing On-line

2-18

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing On-line (cont.) Land

System 4, SOLO, UNO, CF series

Wide selection of instruments, 120°C to 2600°C, two-color, spectral selection, fiber optic, telephoto lens option, modular, many accessories. SOLO is a line of two-wire thermometers.

Linear

TM1000 series, M series, MX series

TM 1000 series are modular sensors, ranges from 0°C–2000°C, spectral selection, thru-lens sights, linearized outputs, many control options. M series are lower cost, fewer options. MX series are customized units with hightemperature and high-resolution options.

Mikron

M67 series

Modular, ranges from 0°C–1650°C, spectral selection, fixed- and variablefocus, thru-lens sights, many accessories.

M68, M668, M600, M680 series

Fiber optic, one color and ratio pyrometers, ranges from 250°C–3500°C.

M190 series

Two-piece, 0°C–3000°C, spectral selection, fixed- and variable-focus, thrulens sights, many accessories.

M77/78

M77 is two-color, M78 is two-color, fiber-optic-coupled.

Omega

OS36, 39, 42, 65, 101, 1592 series, many others

Wide range of sensors including fiber-optic-coupled, ranges from -45°C to +3700°C.

Raytek

Thermalert IT series Thermalert ET series

Various models, -15°C to +538°C, two-piece, small sensing head. Various models, -15°C to +1650°C, integrated sensing head, e set, spectral selections, processing options.

Thermalert III series

Various models, -15°C to +3000°C, two-piece, LED display, e set, spectral selections, processing options.

Thermalert IV series

Various models, -15°C to +3000°C, two-piece, dual LED display, set points, e set, processing options, spectral selections.

Compact Series

Intended for low-cost, multiple-sensor applications.

2-19

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing On-line (cont.) Raytek (cont.)

Marathon Series

For high-temperature applications, up to 3000°C, 1 µm spectral region, include ratio pyrometer and fiber-optic-coupled models.

Quantum Focus

RM2

Infrared microscope. Spot size down to 0.0003".

Williamson

PRO 80, PRO 90, PRO 100, PRO 200

Various models including two-color, fiber-optic-coupled, 30°C–2500°C, spectral selections, many accessories.

TempMatic 4000, FiberView 5000, 500, 700, and 1000 series

Various models, ranges from 30°C–2500°C, two-wire, fixed-focus transmitters and two-wire, fixed-focus single wavelength and ratio pyrometers, some fiberoptic-coupled models.

HGH (France)

ATL-100 narrow angle (6 deg) ATL-020 wide angle (90 deg)

Modular thermoelectrically cooled, high-resolution analog and digital outputs, operates with control system host computer.

Ircon

ScanIR II series

Modular thermoelectrically cooled and un-cooled detectors for various spectral bands from 1 to 5.1 µm, high-resolution analog and digital outputs, visible laser alignment feature, operates with host computer.

Infrared Solutions

IR ScanPro 1000

Scanner based on no moving parts, un-cooled 120-element thermoelectric linear array. Extensive computer interface.

Land

Landscan LS Series optomechanically scanned

Modular, adjustable scan rate, six models with wavelengths from 1 to 5 µm, temperature ranges from 70°C–1400°C, high-resolution analog and digital outputs, operates with control system host computer.

ScanTemp ST Series optomechanically scanned

Low cost, adjustable scan rate, eight models with wavelengths from 1 to 14 µm, temperature ranges from 0°C–1400°C, analog and digital outputs, operates with control system host computer.

Line Scanners

2-20

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Mikron

MikroLine series, 250, 2128, 2256

128-, 160-, or 256-element arrays of PbSe, pyroelectric or GaAs and other detectors, temperature ranges of 0°C–1300°C, spectral ranges of 1.4–1.8 µm, 3-5 µm, 4.8–5.2 µm, and 8–14 µm, frame rates up to 18 kHz, full-processanalysis software.

Pyrometer

ThermATrace

Un-cooled, provides composite visual image and IR scan line superimposed, portable, rechargeable battery, photo-recording only.

Raytek

CS-100, GS-100, TF-100, TIP-450 (all using the MP-50 Thermalert line scanner)

Each system for a different process application, modular thermoelectrically cooled, high-resolution analog and digital outputs, various wavelengths, operate with integral control system or host computer.

Line Scanners (cont.)

Thermographic Opto-Mechanically Scanned Imaging Radiometers Bales

BSI TIP

Very high-resolution desk-top imager with liquid nitrogen cooling, 2–12 µm, TFOV 20x30 deg, extensive on-board, real-time diagnostic software, advanced capability for variable frame rate, multiple simultaneous images. Part of pulsed multi-mode inspection system.

Compix

PC2000 and 2000/e

TE-cooled single-element PbSe (3–5 µm) with PC card module to convert IBM-based desktop and notebook computers to thermal imagers, slow scan (10 seconds and 15 seconds per frame) 244x193 pixel image. 2100 series has magnifier lens for microscope resolution down to 0.002 inch.

PC2100 and 2100/e CMC-Cincinnati Electronics (also markets AVIO)

AVIO TVS Series

TE-cooled and Stirling-cycle cooled models featuring 10-element InSb, 3–5 µm, 10degVx15degH TFOV, lightweight and portable with on-board LCD color monitor, accessories.

Infrared Solutions

IR SnapShot (also sold by Ircon as DIGICAM-IR)

120-element, un-cooled thermoelectric array for 8–12 µm operation, mounted on slide-mechanism for single image one-second frame. Extensive diagnostic software, remote operation capability.

2-21

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Opto-Mechanically Scanned Imaging Radiometers (cont.) Jenoptik

Varioscan series

Stirling-cycle cooled, liquid nitrogen cooled, and TE-cooled HgCdTe detector models for 8–12 µm and 3–5 µm performance, 30°x20° FOV slow-scan, highsensitivity, extensive diagnostic software.

Land

Cyclops T135

Camcorder-configured reflective scanner using TE-cooled, 12-element HgCdTe, 3–5 µm, 25 f/s, 16x16deg TFOV, monochrome viewer, separate image processor available.

FPA Thermal Viewers (Non-Measuring) AIM

µ Cam, FS, and FL FLIR families

Modular, building block cameras using cooled HgCdTe, GaAs QWIP and PtSi FPAs from 128x128 element to 640x486 element.

BAE

MicroIR

Un-cooled 320x240 element micro-bolometric FPA imager module in a weatherproof, ruggedized housing.

CMC-Cincinnati Electronics

Nightmaster, Night Conqueror, others

Many models of Stirling-cycle cooled 160x120, 256x256, and 640x512 element InSb FPA imagers (3–5 µm) for a wide variety of military, search, and surveillance applications.

Electrophysics

PV-320

Un-cooled barium-strontium-titanate (BST) IRFPA imager, 2–14 µm or 0.6–20 µm 320x240 element array, 60 Hz frame rate, quantifiable option.

FLIR

ThermaCAM E series

Un-cooled miniaturized (less than 1.5 lbs) 160(H)x120(V) element microbolometer FPA, portable, battery-powered, 7.5–13 µm, laser aimer, nonmeasuring version.

ThermoVision 1000, Sentry and Ranger; MilCAM SAFIRE, UltraFORCE, SeaFLIR, others

High-resolution, Stirling-cycle cooled InSb and PtSi, (3–5 µm) QWIP (8–9 µm) selectable TFOV-thermal viewers for military, law enforcement, air and sea, and other security and surveillance applications.

SAT – HY600

Un-cooled amorphous silicon micro-bolometer 320(H)x240(V) element FPA, 8–14 µm.

Guangzhou SAT

2-22

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Thermal Viewers (Non-Measuring) (cont.) Indigo

Alpha NIR

Miniaturized, 320x256 element InGaAs FPA, 900–1700 nm, for telecommunication, fiber optic, and laser-profiling applications.

Alpha

Miniaturized, 160x128 element micro-bolometer FPA, 7.7–13.5 µm.

Merlin

Family of imagers offering 320x256 element FPAs in four spectral bands: InGaAs (0.9–1.68 µm un-cooled), InSb (1.0–5.4 µm Stirling-cycle cooled), GaAs QWIP (8–9 µm Stirling-cycle cooled), and micro-bolometer (7.5–13.5 µm un-cooled).

Phoenix

Family of imagers offering 320x256 and 640x512 element FPAs in three spectral bands: InGaAs (0.9–1.7 µm un-cooled), InSb (2–5 µm and GaAs QWIP (8–9.2 µm Stirling-cycle cooled).

Omega

Miniaturized, 160x128 element micro-bolometer FPA, 7.7–13.5 µm.

Infrared Solutions

Modular 160

120x160 pixel un-cooled micro-bolometer FPA in miniaturized (three-inch cube) module for 8–14 µm operation.

IRISYS

IXS 9004

Very low-cost portable, battery-powered viewer using un-cooled 16x16 element pyroelectric FPA, 8–14 µm spectral region, connects to IBM PC and includes image and color display software.

Marconi

Argus Series

Firefighter thermal imagers.

Mine Safety Appliance Corp.

VideoTherm 2000

Un-cooled 320x240 element pyroelectric FPA hand-held viewer with added measurement capability by means of boresighted radiation thermometer, monochrome or color display (8–14 µm).

Raytheon

PalmIR-250

Un-cooled ferroelectric 320x240 FPA, 7–14 µm, battery-powered portable viewer, monochrome display.

2-23

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Thermal Viewers (Non-Measuring) (cont.) Raytheon (cont.)

Sentinal

Un-cooled micro-bolometer 320x240 element FPA 8–14 µm, battery-powered portable viewer, monochrome display.

Santa Barbara Focal Plane

Various Models

High-resolution front-end detector and optics for integration into user's system, based on liquid nitrogen-cooled, 128x128 element 256x256, 320x240, 320x256, 640x480, and 512x512 element InSb FPA (focal plane array) detectors, 1–5 µm.

US Infrared

THERMOviewer

Portable, battery-powered, un-cooled barium-strontium-titanate (BST) 320x240 element IRFPA imager, 2–14 µm spectral range, 60 Hz frame rate, boresighted IR thermometer provides spot measurement reference, color display, aimed at low-cost PdM applications.

Wuhan

IR920, 922, and 923

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 920 has image radio transmitter and receiver. 922 is helmet-mount, 923 is long-range monitoring/surveillance camera.

FPA Imaging Radiometers (Measuring) Cedip

Jade MW Jade LW Jade UC

Stirling-cycle cooled 320x256 element FPA MCT or InSb, 3–5 µm, extensive diagnostic software. Stirling-cycle cooled 320x256 element FPA MCT, 7.5–9.6 µm, extensive diagnostic software. Un-cooled 320x240 micro-bolometer FPA, 8–14 µm, extensive diagnostic software.

CMC-Cincinnati Electronics

2-24

TVS8500

Stirling-cycle cooled 256x256 element InSb FPA, 3–5 µ, 13.7degVx14.6degH TFOV, multiple-temperature measurement on multiple-selected pixels, emissivity compensation, lightweight and portable with on-board LCD color monitor, accessories.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) FLIR

ThermaCAM PM390

Stirling-cycle cooled PtSi 256x256 element FPA, portable battery-powered, 3.4–5 µm, integral display, extensive diagnostic software.

ThermaCAM E2

Un-cooled miniaturized (less than 1.5 lbs) 160(H)x120(V) element microbolometer FPA, portable, battery-powered, 7.5–13 µm, LCD display, laser aimer, extensive diagnostic software.

ThermaCAM P40 ThermaCAM P60

Un-cooled high-sensitivity micro-bolometer 320(H)x240(V) element FPA, portable, battery-powered, 7.5–13 µm, integral or LCD display, extensive diagnostic software. P60 has improved sensitivity, laser aimer, added LCD color display.

ThermaCAM PM545

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, batterypowered, 7.5–13 µm, integral or LCD display, extensive diagnostic software.

ThermaCAM PM675 ThermaCAM PM695 ThermaCAM SC300

Un-cooled micro-bolometer 160(H)x120(V) element FPA, 7.5–13 µm, extensive diagnostic software, low-cost research camera.

ThermaCAM SC500

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 7.5–13 µm, extensive diagnostic software, for high-performance scientific applications.

ThermaCAM SC1000

Stirling-cycle cooled PtSi 256x256 element FPA, portable battery-powered, 3.4–5 µm, integral display, extensive diagnostic software, for high-performance scientific applications.

ThermaCAM SC2000

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, batterypowered, 7.5–13 µm, integral display, extensive diagnostic software, for highperformance scientific applications.

ThermaCAM SC3000

Stirling-cycle cooled GaAs QWIP 320(H)x240(V) element FPA, 8–9 µm spectral response, high-speed, up to 900 Hz, high-sensitivity, broad dynamic range, extensive diagnostic software, for high-performance scientific applications.

2-25

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) FLIR (cont.)

2-26

ThermoVision 160M

Un-cooled micro-bolometer 160(H)x120(V) element FPA, 7.5–13 µm, extensive diagnostic software, many lenses available, including microscope, low-cost industrial automation camera.

Thermovision 320 series

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 7.5–13 µm, extensive diagnostic software, for multiple-process monitoring and machine vision applications, high-performance industrial automation cameras.

Guangzhou SAT

SAT – HY6000 and 6800

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 8–14 µm, extensive diagnostic software, and wide selection of field-interchangeable lenses.

Indigo

Alpha

Miniaturized, 160x128 element micro-bolometer FPA, 7.7–13.5 µm. Measuring capability by means of added diagnostic software.

Merlin

Family of imagers offering 320x256 element FPAs in four spectral bands: InGaAs (0.9–1.68 µm un-cooled), InSb (1.0–5.4 µm Stirling-cycle cooled), GaAs QWIP (8–9 µm Stirling-cycle cooled), and micro-bolometer (7.5–13.5 µm un-cooled). Measuring capability by means of added diagnostic software.

Phoenix

Family of imagers offering 320x256 and 640x512 element FPAs in three spectral bands: InGaAs (0.9–1.7 µm un-cooled), InSb (2–5 µm Stirling-cycle cooled) and GaAs QWIP (8–9.2 µm Stirling-cycle cooled). Measuring capability by means of added diagnostic software.

TVS-620

Un-cooled, 320x240 element micro-bolometer FPA, 8–14 µm, portable handheld unit with integrated display, software, removable PC card image storage.

IRISYS

IRI 1001

Very low-cost portable, battery-powered using un-cooled 16x16 element pyroelectric FPA, 8–14 µm spectral region, connects to IBM PC and includes measurement and color display software.

Infrared Solutions

Modular 160

120x160 pixel un-cooled micro-bolometer FPA in miniaturized (three-inch cube) module for 8–14 µm operation.

Ircon

Stinger

Un-cooled pyroelectric 320(H)x240(V) element FPA, spectral range: 8–14 µm, extensive diagnostic software, for multiple-process monitoring and machine vision applications.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) HGH

Source of AVIO and CMC Cincinnati Cameras.

Jenoptik

VarioTHERM series

Stirling-cycle cooled, 256x256 PtSi FPA. 3.4–7 µm, portable, battery-powered, extensive diagnostic software.

Land

Cyclops PPM

Radiometric version of the Raytheon PalmIR 250 (same as Raytheon PalmIR 500D) modified by Electrophysics and sold by Land); 320(H)x 240(V) uncooled BST FPA, 0°C–300°C, PC memory card.

FTI-6

FPA imager with on-board diagnostic software.

MikroScan 5102

Stirling-cycle cooled 255x223 element HgCdTe FPA, 8–12 µm, line- or batterypowered portable viewer, on-board display, and flip-up LCD option.

MikroScan 5104

TE-cooled 255x223 element HgCdTe FPA, 3–5.2 µm, line- or battery-powered portable viewer, on-board display, and flip-up LCD option, spectrally selective models available for working with glass or flame.

MikroScan 5104i

TE-cooled 255x223 element HgCdTe FPA, 3–5.2 µm, line-powered fixedmount camera for on-line process monitoring and control.

MikroScan 7102i

Un-cooled micro-bolometer 320x240 element FPA 8–14 µm, fixed-mount camera for on-line process monitoring and control.

MikroScan 7200

Lightweight, un-cooled micro-bolometer 320x240 element FPA 8–14 µm, battery-powered portable viewer, on-board display, and flip-up LCD option.

MikroScan 7515

Lightweight, un-cooled micro-bolometer 320x240 element FPA 8–14 µm, battery-powered portable viewer, on-board display, and flip-up LCD option, upgrade version of the 7200 with remote control option and analysis and report-writing software.

M9000 series

Imaging Pyrometer, un-cooled 776x484 near infrared FPA detector for hightemperature targets, multi-range with selected filters from 600°C to 2400°C, extensive diagnostic software integrates PC with color monitor.

Mikron

2-27

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) Nikon (see HGH)

Laird S270 and 3A series

537x505 and 768x494 element Stirling-cycle cooled PtSi FPAs, (3–5 µm) battery- and line-powered, ac adapter, interchangeable color display available. Multiple temperature measurement on multiple selected pixels, emissivity compensation.

Quantum Focus Instruments

InfraScope, InfraScope II

Lab-operated imager for microelectronics applications, features liquid nitrogen-cooled InSb FPA, automatic emissivity compensation, full field temperature measurement, spatial resolution down to 2.5 µm, 60 Hz frame rate.

Raytheon

Radiance HSX

Stirling-cycle cooled 256x256 element InSb FPA, 3–5 µm, 60 Hz frame rate (Radiance HS has selectable frame rates up to 1400 Hz, optional displays, extensive thermal analysis software).

PalmIR 500D

Radiometric version of the Raytheon PalmIR modified by Electrophysics and sold by Land); 320(H)x240(V) un-cooled BST FPA, 0°C–300°C, PC memory card.

Thermoteknix

VisIR

Un-cooled micro-bolometer 160(H)x120(V) element FPA, portable, batterypowered, 7.5–13 µm, integral LCD display, image storage, radio link, extensive diagnostic software.

Thermal Wave Imaging

EchoTherm

EchoTherm is an NDE system, built around a selection of high-speed FPA imagers. Includes flashlamp sources, power supplies, synchronizing electronics, and analytical software for TRIR. ThermoScope is a field-portable version.

ThermoScope Wuhan

2-28

IR912 and 913

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, batterypowered, 8–14 µm, 912 and 913 have fold-out LCD display, extensive diagnostic software.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

AIM Infrarot-Module GmbH

Theresienstrasse 2 D-74072 Heilbron, Germany

+49-7131-6212-460

www.aim-ir.com

BAE, Information and Electronic Warfare Systems

2 Forbes Rd., LEX01-112 Lexington, MA 02421-7306

(781) 863-3684

www.iews.baesystems.com/iris

Bales Scientific Inc., div. CTI

1620 Tice Blvd. Walnut Creek, CA 94595

(510) 945-0144

www.balesscientific.com

CEDIP, SA

19 Blvd. G. Bidault F-77183 Croissy Beaubourg, France

(+33) 01 60 37 01 00

[email protected]

CMC-Cincinnati Electronics Corp. Div BAE Systems

7500 Innovation Way Mason, OH 45040-9699

(513) 573-6744

www.cmccinci.com [email protected]

Compix

15824 SW Upper Boone’s Ferry Road Lake Oswego, OR 97035

(503) 639-8496

www.compix.com [email protected]

The Dickson Company

930 S. Westwood Ave. Addison, IL 60101

(800) 323-2448

http://www.dicksonweb.com/

Electrophysics Corp.

373 Rte 46 West, Building E Fairfield, NJ 07004

(973) 882-0211 (800) 759-9577

www.electrophysicscorp.com

E2Technology Corporation (part of Mikron)

4475 Dupont Court, Unit 9 Ventura, CA 93003

(805) 644-9544

www.e2t.com [email protected]

Everest Interscience Corp.

1891 N. Oracle Rd. Tucson, AZ 85705

(520) 792-4545 (800) 422-4342

http://www.everestinterscience.com/ [email protected]

Exergen Corporation

51 Water St. Watertown, MA 02472

(617) 923-9900 (800) 422-3006

www.exergen.com [email protected]

2-29

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 (cont.) Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

FLIR Systems, Inc. World Headquarters

16505 SW 72 Ave. Portland, OR 97444

(503) 684-3771 (800) 322-3731

www.flir.com

FLIR Systems, Boston Formerly Inframetrics

16 Esquire Road N. Billerica, MA 01862

(978) 670-5555

www.flir.com

FLIR Systems AB, Sweden Formerly AGEMA

Rinkebevägen 19, PO Box 3 SE182-11 Danderyd, Sweden

+(46) 8 753 2500

www.flir.com

Guangzhou SAT Infrared Technology Co., Ltd.

10 Diongjiang Ave., Guangzhou Econ. & Tech. Dev. District, China 51073

+86-20-82229925 +86-20-82227947

www.sat.com.cn [email protected]

HGH Systemes Infrarouges

3, rue du Saule-Trapu, F91300 Massy, France

(33-1) 60110141

http://www.hgh-infrarouge.fr/ [email protected]

Horiba

17671 Armstrong Ave. Irvine, CA 92614

(800) 446-7422 (949) 250-4811

www.horiba.com [email protected]

Indigo Systems Corp.

5385 Hollister Ave. #103 Santa Barbara, CA 93111

(805) 964-9797

www.indigosystems.com

Infrared Solutions, Inc.

3550 Annapolis Lane North, Suite 70 Plymouth, MN 55447

(763) 551-0038

[email protected]

IRCON Instruments

7300 N. Natches Ave. Niles, IL 60714

(847) 967-5151 (800) 323-7660

www.ircon.com

IRISYS

Towcester Mill, TowcesterNorthants NN12 6AD, UK

+44(0)1327 357824

www.irisys.co.uk [email protected]

Irtronics

132 Forest Blvd. Ardsley, NY 10502

(914) 693-6291

No e-mail address

JENOPTIK, GmbH

Goschwitzer Strabe 25, D-07745 Jena, Germany

+49(3641) 65 33 11

www.jenoptik.de [email protected]

2-30

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 (cont.) Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

Land Infrared

10 Friends Lane Newtown, PA 18940-1804

(215) 504-8000

www.landinst.com [email protected]

Linear Laboratories

42025 Osgood Rd. Fremont, CA 94538

(800) 536-0262

www.linearlabs.com

Marconi Electronic Systems

4 Westchester Plaza Elmsford, NY 10523

(914) 592-6050 (800) 342-5338

www.marconitech.com [email protected]

Mikron Instrument Co., Inc.

16 Thornton Road Oakland, NJ 07436

(201) 405-0900 (800) 631-0176

www.mikroninst.com

Mine Safety Appliances

1000 Cranbury Woods Road Cranbury, PA 16066

(800) 821-3642 (724) 776-7700

www.msanet.com

Minolta (see Land)

101 Williams Dr. Ramsey, NJ 07446

(201) 529-6049 (888) 473-2656

www.minoltausa.com

NEC

(see Mikron)

Nikon (see Pyrometer Instruments and HGH) Omega Engineering, Inc.

One Omega Drive P.O. Box 2349 Stamford, CT 06906

(203) 359-1660 (800) 826-6342

[email protected] www.omega.com

Palmer Wahl Instrumentation Group

234 Old Weaverville Road Asheville, NC 28804

(828) 658-3121 (800) 421-2853

www.instrumentationgroup.com

Pyrometer Instrument Co.

209 Industrial Pkwy. Northvale, NJ 07647

(201) 768-2000 (800) HOT-PYRO

www.pyrometer.com [email protected]

2-31

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 (cont.) Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

Quantum Focus Instruments Corp.

990 Park Center Drive, Suite D Vista, CA 92083

(760) 599-1122

www.quantumfocus.com

Raytek, Inc.

1201 Shaffer Rd. Santa Cruz, CA 95060

(831) 458-1110

www.raytek.com [email protected]

Raytheon Corporation

5756 Thornwood Dr. Goleta, CA 93117

(805) 683-6621 (800) 990-3275

www.raytheoninfrared.com

Raytheon Corporation, Ind. Auto. Div.

P.O. Box 655012 Dallas, TX 75265

(800) 990-3275

www.raytheoninfrared.com

Santa Barbara Focal Plane Division of Lockheed Martin

69 Santa Felicia Dr. Goleta, CA 93117

(805) 562-8777

www.sbfp.com

Teletemp Corp.

P.O. Box 5160, 351 S. Raymond Fullerton, CA 92635

(800) 321-5160 (714) 879-2901

www.telatemp.com [email protected]

Thermal Wave Imaging, Inc.

845 Livernois Street Ferndale, MI 48220-2308

(248) 414-3730

www.thermalwave.com

US Infrared

1535 S. Memorial Dr. Suite 117 Tulsa, OK 74112

(918) 663-7833

www.bpcintl.com

Williamson Corp.

70 Domino Dr. Box 1270 Concord, MA 01742

(978) 369-9607

www.williamsonir.com [email protected]

Wuhan Guide Electronic Industrial Co. Ltd.

Hongshan Chuangye Ctr. Bldg. Luoyu Rd. No. 424 Wuhan, China

+86-27-87659277 +86-27-87659069

www.wuhanguide.com [email protected]

Thermoteknix Systems, Ltd.

2-32

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-3 Compilation of Typical Industrial Applications of Thermal Imaging Instruments Typical Applications by Industry Industry

Applications

Metals

Continuous casting, strip annealing, extrusion presses, rolling mills, induction heating, resistance heating, heat treating, electrolytic refining

Glass

Tank refractories, glass body temperatures, mold temperatures, bottle machines, float glass, tempering and annealing, fiberglass manufacturing

Cement

Kiln shell, refractory insulation, bridge delamination inspection

Textiles

Permanent press heat setting, dye setting, foam lamination, carpet backing

Plastics

Vacuum forming, extrusion, film process monitoring and control

Paper

Dryer drums, coating ink drying

Chemical and Petroleum

Furnace tube temperatures, pipe and vessel corrosion, mixing process monitoring and control

Food and Confectionary

Rotary cooker temperatures, continuous infrared ovens, mixers, continuous baking ovens, freeze-dry processes

Asphalt Paving

Road stone dryer, mixing temperature, rolling temperature

Rubber

Hot rubber sheets—cooling and rolling, tire testing

Utilities

Electrical systems, steam valves, motors, pumps, boilers, circuit boards, switchyards, transmission and distribution lines

2-33

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-3 (cont.) Compilation of Typical Industrial Applications of Thermal Imaging Instruments Typical Applications by Discipline Discipline Design

Workmanship

Component Failure

2-34

Applications •

Exhaust stacks, flue pipes

•

Heating units (ovens, boilers, furnaces)

•

Buildings (offices, schools, hospitals, plants)

•

Process pipes, vessels, lines—steam and water lines

•

Kilns

•

Cryogenic storage vessels

•

Electrical and electronic circuits and micro-circuits

•

Operational procedures

•

Installation of refractory materials

•

Installation of foam insulation materials

•

Installation of fiberglass materials (roof insulation and so on)

•

Replacement of parts and other repairs

•

Roof inspection for moisture saturation

•

Steam traps, underground steam lines, plumbing lines and systems

•

Electrical lines and substations

•

Electrical and electronic components and modules

•

Insulation—foam, fiberglass, and refractory

•

Seals—low- and high-temperature

•

Doors, ports, windows

•

Cooling towers, heat exchangers

•

Motors, pumps, ventilators, bearings

EPRI Licensed Material

3

THE MEASUREMENT MISSION

The successful completion of a field measurement mission requires planning, caution, and the ability to interpret the thermographic results. The thermographer also needs a clear understanding of the thermal behavior of the targets involved in the measurement mission. The mission tasks can be subdivided as follows: •

Understanding the thermal behavior of the target

•

Preparing the equipment for the mission

•

Using correct instrument operating procedures

3.1

Thermal Behavior of the Target

There are 10 sources of energy transfer at the target surface that can cause IR thermal imaging equipment to register apparent temperature changes. Some of these represent real temperature changes at the target surface and some do not. It is important for the thermographer to understand these phenomena and to be able to distinguish between apparent and real target temperature changes. Examples of the 10 sources of apparent target temperature differences will be described. They are tabulated as follows: Apparent •

Emissivity difference

•

Reflectance difference

•

Transmittance difference

•

Geometric difference

Real •

Mass transport difference

•

Phase change difference

•

Thermal capacitance difference

•

Induced heating difference

•

Energy conversion difference

•

Direct heat transfer difference 3-1

EPRI Licensed Material The Measurement Mission

3.1.1 Emissivity Difference As discussed in Appendix A, Section A.3.3, the radiant energy emitted by a target surface is proportional to emissivity as well as to a power of the target temperature. If the emissivity of the target surface changes, or if the wrong effective emissivity value is assumed for the target, the apparent temperature reading will be in error. The resultant inaccuracy will not be the result of a real temperature change at the target surface. 3.1.2 Reflectance Difference An apparent temperature change will occur when thermal radiant energy from an external heat source is reflected off the target surface. The apparent change will be proportional to a power of the temperature difference between the actual target and that of the external heat source. It will also be proportional to the reflectance (1.0 minus the emissivity value) of the target and to the emissivity of the external heat source. This apparent change will not be the result of a real temperature change at the target surface. 3.1.3 Transmittance Difference An apparent temperature change will occur when thermal radiant energy from an external heat source behind the target surface is transmitted through the target surface. The apparent change will be proportional to a power of the temperature difference between the actual target and that of the external heat source. It will also be proportional to the transmittance of the target and to the emissivity of the external heat source. This apparent change will not be the result of a real temperature change at the target surface. 3.1.4 Geometric Difference An apparent temperature change might occur as a result of the geometric shape of the target. If the target surface is shaped so as to form a cavity, for example, multiple reflections of radiant energy between the cavity walls will result in an apparent increase in emissivity. The corner of an enclosure with three mutually perpendicular surfaces in close proximity is a good example of this. The apparent change will be similar to that caused by an emissivity variation and will not be the result of a real temperature change at the target surface. 3.1.5 Mass Transport Difference An example of a mass transport difference is air leakage from the inside of a building through the building surface that happens to be the target. The air in transit might heat or cool the target surface. This results in a real temperature change at the target surface.

3-2

EPRI Licensed Material The Measurement Mission

3.1.6 Phase Change Difference An example of a phase change difference is water that condenses (changes from gas to liquid) on or behind a target surface and temporarily cools the surface. This results in a real temperature change at the target surface. 3.1.7 Thermal Capacitance Difference An example of a thermal capacitance difference is when solar heat stored in water-saturated sections of a roof warms the surface of the roof at night, in contrast to the non-saturated sections. This is because the water-saturated sections have higher thermal capacitance than the dry sections and it results in a real temperature change at the target surface. 3.1.8 Induced Heating Difference An example of an induced heating difference is the inductive heating of ferrous bolts that are improperly installed in an aluminum buss bar. The magnetic field will cause inductive heating in ferrous materials, which results in a real temperature change at the target surface. 3.1.9 Energy Conversion Difference Most temperature rises observed in a plant environment are the result of energy conversion (friction to heat, chemical reaction to heat, and so on). A common example of an energy conversion difference is when the resistance of a poor connection converts electric current to heat. This results in a real temperature change at the target surface. 3.1.10 Direct Heat Transfer Difference A direct heat transfer difference occurs by conduction, convection, or radiation as described in Appendix A, Section A.2. Examples of direct heat transfer are found in the nondestructive testing of materials where a uniform heat flow is generated and observed thermal anomalies indicate flaws. These are real temperature changes at the target surface.

3.2

Equipment Preparation

3.2.1 The Mission Checklist In preparation for the measurement mission, the thermographer should use checklists to ensure that there are no surprises on site. A standard checklist should be prepared to include all items in the thermographic equipment inventory. The list should include: instruments, spare lenses, tripods, harnesses, transport cases, carts, batteries, chargers, liquid or gaseous cryogenic coolant, if applicable, safety gear, special accessories, film, diskettes, spare fuses, tool kits, data sheets, operator manuals, calibration data, radiation reference sources, inter-connecting cables, 3-3

EPRI Licensed Material The Measurement Mission

accessory cables, and special fixtures. Well in advance of the mission, the thermographer can highlight all of the items that will be required for a particular job. The highlighted standard list will then become the checklist for the job. 3.2.2 Equipment Checkout and Calibration All quantitative thermography equipment should be calibrated periodically in accordance with the manufacturer's recommendations found in the operator's handbook. In addition, a quick operation and calibration check should be performed by the thermographer to make certain that the equipment is in working order and in calibration. This can be performed by using an infrared radiation reference blackbody source or by a more quick and simple means such as a two-point check. This approximate test can be performed by using two known targets such as ice water (0°C) and the palm of the thermographer's hand (approximately 35°C). 3.2.3 Batteries Too many thermographic measurement missions have had to be postponed or prematurely terminated because the thermographer ran out of charged batteries. This can be very costly in terms of lost inspection time and customer confidence. The batteries item on the mission checklist should be understood to mean fully-charged batteries and it is the thermographer's responsibility to ensure that there is a comfortable surplus of battery power available for each mission. The fact that batteries become discharged more rapidly in cold weather also needs to be considered in preparing for the mission. 3.2.4 Facility Personnel Participation A knowledgeable facility representative should accompany the thermographer on the measurement mission or be available during measurements. By providing expert information concerning the processes taking place and the likely sources of temperature differences, this assistance will enable the thermographer to anticipate thermal behavior and to better understand and interpret the thermographic results.

3.3

Some Cautions for Correct Instrument Operation

Assuming that the instrument selected is appropriate to the measurement application, there are a few things that the thermographer should remember to avoid common mistakes in use. These include the following: •

Learn and memorize the start-up procedure.

•

Learn and memorize the default values.

•

Set or use the correct effective emissivity.

•

Make sure that the target to be measured is larger than the instantaneous field of view for measurement (IFOVmeas) of the instrument.

3-4

EPRI Licensed Material The Measurement Mission

•

Aim the instrument as close to normal (perpendicular) with the target surface as possible.

•

Check for reflections off the target surface.

•

Keep portable inspection instruments as far away as possible from very hot targets.

3.3.1 Start-Up Procedure Thermographers that operate several different models of thermographic and thermal-sensing equipment need to be certain that they re-familiarize themselves with the start-up procedure of the equipment selected for each measurement mission. This allows the data-gathering process to begin with no unnecessary delays. It saves valuable on-site time and inspires confidence on the part of facility personnel. A quick review of the operator's manual and a short dry run prior to leaving home base is usually all that is required. 3.3.2 Memorizing the Default Values The operator's manual also provides default values for several important variables in the measurement such as emissivity, ambient (background) temperature, distance from sensor to target, temperature scale (°F or °C), lens selection, and relative humidity. These are the values that the instrument processor automatically uses to compute target temperature unless the thermographer changes these values to match the actual measurement conditions. Typical default values are: 1.0-meter distance to target, emissivity of 1.0, and ambient temperature of 25°C. Failure to correct for these (for example, if the target is known to be 10 meters away, is known to have an effective emissivity of approximately 0.7, and is in an ambient of 10°C) can result in substantially erroneous results. By memorizing the default values, the thermographer will know when it is necessary to change them, and when time can be saved by using them unchanged, without having to refer to a look-up menu. 3.3.3 Setting the Correct Emissivity Table 3-1 and Table 3-2 list various targets and their approximate generic emissivities. There are emissivities shown for various temperatures and in several spectral bands. Where it is not otherwise indicated, temperatures should be assumed to be 30°C. If possible, it is always better to directly determine the actual effective emissivity of the surface to be measured by using the actual instrument to be used in the measurement. Effective emissivity (e*) is defined as: “…the measured emissivity value of a particular target surface under existing measurement conditions, that can be used to correct a specific measuring instrument to provide a correct temperature measurement.”

3-5

EPRI Licensed Material The Measurement Mission Table 3-1 Table of Normal Spectral Emissivities Short Wave (SW) = 2–5.6 µm Long Wave (LW) = 6.5–20 µm Material

3-6

Wavelength (micrometers)

Temperature (°C)

Emissivity

Alumina brick

SW

17

0.68

Aluminum, heavily weathered

SW

17

0.83–0.94

Aluminum foil

3

0.09

Aluminum foil (bright)

3

0.04

Aluminum disk, roughened

3

0.28

Asbestos slate (wallboard)

3

0.96

Brick, common

SW

Brick, facing, red

SW

0.92

Brick, facing, yellow

SW

0.92

Brick, masonry

SW

0.72

Brick, red

5

0

0.94

Brick, waterproof

SW

17

0.9

Chipboard, untreated

SW

Concrete, dry

5

36

0.95

Concrete, rough

SW

17

0.92–0.97

Copper, polished, annealed

10

0.01

Fibre board (hard), untreated

SW

0.85

Fibre board (porous), untreated

SW

0.85

Filler, white

SW

0.88

Firebrick

SW

17

0.68

Formica

LW

27

0.937

Frozen soil

LW

Glass, chemical ware (partly transparent)

5

35

0.97

Granite, natural surface

5

36

0.96

Gravel

LW

Hardwood, across grain

SW

17

0.82

Hardwood, along grain

SW

17

0.68–0.73

Hessian Fabric, green

SW

0.88

Hessian Fabric, uncolored

SW

0.87

17

0.81–0.86

0.9

0.93

0.28

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Iron, heavily rusted

SW

17

0.91–0.96

Limestone, natural surface

5

36

0.96

Mortar

SW

17

0.87

Mortar, dry

5

36

0.94

P.V.C.

SW

17

0.91–0.93

Broma Alkyd enamel 102 gold leaf

3

40

0.98

Broma Alkyd enamel 113 light blue

3

Chromatone® stabilized silver finish— Alumatone Corp.

3 10

25

0.26 0.31

Krylon® flat black 1502

3

50

0.95

Krylon flat white

3

40

0.99

Krylon ultra-flat black

5

36

0.97

3M® black velvet coating 9560 series optical black

3

40

>0.99

Oil

SW

17

0.87

Paint (by manufacturer)

0.95

black flat

SW

0.94

black gloss

SW

0.92

gray flat

SW

0.97

gray gloss

SW

0.96

Plastic, black

SW

0.95

Plastic, white

SW

0.84

Paper, cardboard box

5

0.81

Paper, white

SW

17

0.68

Perspex , plexiglass

SW

17

0.86

Plaster Pipes, glazed

SW

17

0.83

Plaster

SW

17

0.86–0.9

®

3-7

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Plasterboard, untreated

SW

0.9

Plastic, acrylic, clear

5

Plastic paper, red

SW

Plywood

SW

17

0.83–0.98

Plywood, commercial, smooth finish, dry

5

36

0.82

Plywood, untreated

SW

Polypropylene

SW

36

0.94 0.94

0.83 17

0.97

Redwood (wrought), untreated

SW

0.83

Redwood (unwrought), untreated

SW

0.84

Rendering, gray

SW

0.92

Roofing Metal Azure blue, smooth

SW

0

0.54

Azure blue, textured

SW

0

0.51

Burnished copper, smooth

SW

0

0.54

Burnished copper, textured

SW

0

0.56

Dark bronze, textured

SW

0

0.7

Mansard brown, smooth

SW

0

0.58

Matte black, smooth

SW

0

0.73

Roman bronze, smooth

SW

0

0.69

Slate gray, smooth

SW

0

0.64

Stone white, smooth

SW

0

0.57

Terra Cotta, smooth

SW

0

0.61

Adobe

SW

0

0.77

Black

SW

0

0.83

Bright red

SW

0

0.96

Chestnut brown

SW

0

0.67

Colonial green

SW

0

0.83

Dawn mist

SW

0

0.76

Desert tan

SW

0

0.74

Frost blende

SW

0

0.76

Meadow green

SW

0

0.78

Noire black

SW

0

0.90

Shingles—asphalt (sm. Ceramic-coated rock granules)

3-8

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Shingles—asphalt (sm. Ceramic-coated rock granules) cont. Sea green

SW

0

0.83

Shadow gray

SW

0

0.81

Slate blende

SW

0

0.65

Snow white

SW

0

0.81

Wedgewood blue

SW

0

0.75

Wood blende

SW

0

0.75

Average

SW

0

0.89

Frost blende

SW

0

0.83

Mahogany

SW

0

0.84

Meadow mist

SW

0

0.98

Noire black

SW

0

0.93

Snow white

SW

0

0.74

Wood blende

SW

0

0.81

Average

SW

0

0.86

SW

0

0.79

Fiberglass—asphalt (sm. Ceramic-coated rock granules)

Solid vinyl Autumn gold, textured Butternut beige, textured

SW

0

0.80

Lexington green, textured

SW

0

0.86

Oyster white, textured

SW

0

0.88

Quaker gray, textured

SW

0

0.89

Sunshine yellow, textured

SW

0

0.75

White, smooth

SW

0

0.93

Average

SW

0

0.94

Styrofoam, insulation

5

37

0.60

Tape, electrical, insulating, black

5

35

0.97

Tape, masking

5

36

0.92

Tile, floor, asbestos

5

35

0.94

Tile, glazed

SW

17

0.94

3-9

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Varnish, flat

SW

0.93

Wallpaper (slight pattern) lt. gray

SW

0.85

Wallpaper (slight pattern) red

SW

0.90

Wood, paneling, light finish

5

36

0.87

Wood, polished spruce, gray

5

36

0.86

Table 3-2 Emissivity for Wavelengths of 8–14 µm at 0°C Material

3-10

Emissivity (%)

Material

Emissivity (%)

Asbestos Board Paper Slate

96 94 96

Aluminum, polished Rough surface Strongly oxidized

5 7 25

Brick Glazed, rough Fireclay Red, rough Carbon, purified Cement Charcoal, powder Clay, fired Enamel Fabric, asbestos

85 85 94 90 80 54 96 91 90 78

Brass, dull, tarnished Polished

22 3

Bronze, polished Porous, rough

10 55

Cast iron, casting Polished

81 21

Glass Frosted

92 96

Chromium, polished

10

Ice

97

Copper, commercial burnished Electrolytic, polished Oxidized Oxidized to black

7 2 65 88

Lacquer, bakelite Black, dull Black, shiny (on metal) White

93 87 87 87

Gold, polished

2

Lampblack

96

Iron, hot-rolled Oxidized Sheet, galvanized, burnished Sheet, galvanized, oxidized Shiny, etched Wrought, polished

77 74 23 28 16 28

Pure and Oxidized Metals

EPRI Licensed Material The Measurement Mission Table 3-2 (cont.) Emissivity for Wavelengths of 8–14 µm at 0°C Material

Emissivity (%)

Material

Emissivity (%)

Oil paint, various colors

94

Paper, black, shiny Black, dull White

90 94 90

Lead, gray Oxidized Red, powder Shiny

28 63 93 8

Porcelain, glazed

92

Mercury, pure

10

Nickel on cast iron Pure, polished

5 5

Pure and Oxidized Metals

Quartz

93

Platinum, pure

8

Rubber

95

Steel, galvanized Oxidized strongly Rolled freshly Rough surface Rusty, red Sheet, nickel-plated Sheet, rolled

28 88 24 96 69 11 56

Shellac, black, dull Black, shiny on tin plate

91 82

Tin, burnished

5

Snow

80

Tungsten

5

Tar paper

92

Zinc, sheet

20

Water

98

There are several methods described in Section 4 that can be used to estimate target effective emissivity quickly. Using the instrument chosen for measurement, one method of determining the setting needed for a particular target material is to: 1. Prepare a sample of the material large enough to contain several spot sizes or IFOVs of the instrument. A 10 cm x 10 cm (4" x 4") sample is a good choice. 2. Spray one half of the target sample with flat black (light absorbing) paint; cover it with black masking tape or use some other substance of known high emissivity. 3. Heat the sample to a uniform temperature as close as possible to the temperature at which you estimate your actual measurement will be made. 4. Set your instrument emissivity control to the known emissivity of the coating and measure the temperature of the coated area with your instrument. Note the reading. 5. Immediately point to the uncoated area and adjust the emissivity set until you repeat the reading you obtained in 4. above. This is the effective emissivity, the value you should use in measuring the temperature of this material with this instrument. For quick reference, this procedure is illustrated and summarized in Appendix C, Plate 5. 3-11

EPRI Licensed Material The Measurement Mission

3.3.4 Filling the IFOVmeas for Accurate Temperature Measurements If you need to measure the temperature of a spot on a target, be certain that this spot completely fills the Instantaneous Measurement Field of View (IFOVmeas) of the instrument. If it doesn't, you can still learn some useful things about the target with the instrument, but you can't get an accurate reading of target temperature. Use the quick calculation that is provided in Appendix C, Plate 2 to determine spot size based on IFOVmeas and actual working distance. If your target spot size is 5 cm or larger, for example, and the calculated spot size is 5 cm, move the instrument closer to the target or use a higher magnification lens, if either is possible. If not, expect to see some background effect in your reading. Also, be sure to allow for aiming errors and instrument imperfections; to be sure, allow an extra 30%. 3.3.5 Aiming Normal to the Target Surface The effective emissivity of a target surface is due partially to the surface texture. It stands to reason, then, that if you look at a surface at a skimming angle, you won't see the texture; the effective emissivity will change greatly and you will see misleading reflections. These can result in cold errors as well as hot errors. A safe rule is to view the target at an angle within 30° of normal (perpendicular). If the target effective emissivity is very high, you can go as high as a 60° angle if necessary. 3.3.6 Recognizing and Avoiding Reflections From External Sources If there is a source of radiant energy in a position to reflect off your target surface and into your instrument, you should take steps to avoid the misleading results of this effect. The greatest likelihood of errors due to reflections from external sources occurs when: •

The target emissivity is low.

•

The target is cooler than its surroundings.

•

The target surface is curved or irregularly shaped.

You can find out if a thermal anomaly is due to a point source by moving the instrument and pointing it at the target from several different directions. If the anomaly moves on the thermogram, it is a reflection. You can eliminate the effect of an interfering source, once you identify it, by changing your viewing angle, by blocking the line of sight to the source, or by doing both (refer to Appendix A, Figure A-9). For reflections from hot backgrounds, refer to Appendix A, Section A.3.3. 3.3.7 Avoiding Radiant Heat Damage to the Instrument Unless specifically selected for continuous operation in close proximity to a very hot target, your instrument might be damaged by extensive thermal radiation from a target. Don't leave the instrument in areas that are too warm to place your hand comfortably.

3-12

EPRI Licensed Material

4

INSPECTION TECHNIQUES

This section is divided into two sub-sections that deal with the common problems and solutions that are encountered when using infrared thermography in a plant or industrial environment. The first section deals with the inherent or indigenous problems, such as emissivity or reflectance. The second section explains the tricks of the trade that are used to get the best possible information out of the imaging systems. The references (Appendix D) and the bibliography (Appendix E) provide many sources of additional information on a wide variety of problems, both theoretical and practical.

4.1

Mitigating Inherent Effects

There are several factors that affect the production and subsequent proper interpretation of a thermal image. These factors include the target's emissivity, reflectance, distance from the imager, temperature, background temperature, ambient temperature, orientation, target size, and the transmittance of the intervening atmosphere. In addition, the image, as presented on the imager, is not temperature but radiosity. Imagers measure the radiant energy emitted by the target plus the radiant energy reflected from and transmitted through the target. The sum of these radiant energies is the commonly accepted definition of radiosity. There are practical considerations that will simplify the following discussions of the inherent effects. In general, the transmittance (energy transmitted through the targets) can be ignored in most, if not all, cases for targets in a power plant. Transmittance is an important factor in industries where the temperature of a thin film of plastic or other infrared opaque targets are being observed. Also, with the exception of absolute temperature measurements being required, the transmittance through the atmosphere can be ignored as well. The major exception would be in cases where long distances were involved in a humid atmosphere (that is, hydrogen igniters or spray nozzles in containment). 4.1.1 Emissivity and Reflectivity A review of the references in the bibliography (Appendix E) will show that no one subject is discussed more than emissivity. The effective emissivity of a target clearly must be known in order to measure its absolute temperature. This is discussed in detail in Appendix A. Table 4-1 provides some values of emissivity for common objects. Aluminum, the most commonly used electrical conductor, can range from 0.55 for a rough highly oxidized plate, to 0.039 for a highly polished plate. In practical terms, this means that 45% of the anodized plate and 96% of the polished plate's incident energy are reflected and that any hot or cold objects in the optical 4-1

EPRI Licensed Material Inspection Techniques

background will reflect their energy off these surfaces. These mirrors do have surface thermal patterns. It is difficult to measure them, however, because of the low emitted energy and the natural ability to reflect thermal energy as well as light. In general, if a target is acting as a visible mirror, it is acting as an infrared mirror as well. An exception to this rule is the germanium lenses used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum. Table 4-1 Normal Emissivity Values of Common Materials Material

Emissivity

Aluminum Highly polished plate 98.3% pure

0.039

Polished plate

0.040

Rough plate

0.55

Chromium

0.080

Copper Commercial, emeried, polished, with no pits remaining

0.030

Commercial, scraped, shiny but not mirror-like

0.072

Polished

0.023

Iron and steel Cast iron, polished

0.21

Wrought iron, highly polished

0.28

Cast iron, newly turned

0.435

Oxidized surfaces

4-2

Iron plate, pickled then rusted red

0.612

Completely rusted

0.685

Rolled sheet steel

0.657

Steel oxidized at 110°

0.79

Cast plate, smooth

0.80

Cast plate, rough

0.82

EPRI Licensed Material Inspection Techniques

Given that shiny objects have surface thermal patterns that are hard to image, there are several techniques that improve the ability to establish a satisfactory image. The most common way to obtain a useful thermal image from a shiny or low-emissivity surface is to add a coating to it that has a higher emissivity. (This is not practical and is not recommended for an energized electrical surface.) There are three common non-permanent materials that have been used to improve emissivity. These are: •

Foot powder

•

Dye check developer

•

Electricians’ tape

4.1.2 Foot Powder Foot powder is sprayed on a target to create a uniform layer that reduces the reflections. After the powder has reached thermal equilibrium with the surface, the temperature measurements can be made. The emissivity of foot powder has been estimated to be 0.96. Before any coating is applied, however, the chemical composition of the coating should be determined to avoid any negative effects from its application. 4.1.3 Dye Check Developer (Caution: Ensure that all manufacturer precautions are followed prior to use of any developer. For example, Magnaflux Zyglo® developers, such as ZP-9E and ZP-9F, might produce chlorine gas or become flammable when they come in contact with moderately heated surfaces.) An alternative to foot powder is liquid dye penetrant developer. It has an estimated emissivity of 0.97 and might already have been formulated to conform to QA requirements for sulfur and halogen purity. Application of it is identical to the foot powder. Given the temperature of the target, it might take several minutes for the developer to reach thermal equilibrium as its propellant cools the target's surface. The best way to use this in an actual survey would be to apply it to all targets to be surveyed before commencing the actual survey. This will ensure that all target surfaces will have reached thermal equilibrium. The target in Figures 4-1 and 4-2 is a shiny metal can of dye check developer with the label removed. There are no hot objects in or near the can. With the imager's emissivity set at 1.0, an analysis of the temperature distribution over the can yielded a temperature range of 74.6°F to 67.9°F (6.7°F ∆T). The reason for the variation is reflection of the cold window plus geometric considerations in measuring a curved surface. Setting the emissivity at 0.10, a more realistic figure for a shiny surface, yielded a maximum temperature of 66.2°F and a minimum temperature of 23.9°F (42.3°F ∆T). The room ambient temperature was 68°F. Without changing anything, the can surface was coated with developer and allowed to achieve thermal equilibrium. The first effect noted was the observation of the level of the developer in the can (Figure 4-3). This was due to the difference in the heat capacity of the liquid and vapor present inside the can. The cooling action of the propellant developed a thermal transient that resulted in the liquid level 4-3

EPRI Licensed Material Inspection Techniques

visible on the thermogram. The emissivity was reset to 0.97 and the can was allowed to achieve thermal equilibrium with the room. After 10 minutes, the maximum temperature observed was 70.4°F and the minimum temperature was 69.5°F (0.9°F ∆T), close to room ambient of 68°F. (The 0.9°F temperature spread is normal because the dye check developer might not have uniformly coated the surface.) Clearly, the developer served its intended function of improving the surface emissivity and, therefore, the results.

Figure 4-1 Emissivity Improvement by Coating—Setup

Figure 4-2 Thermogram of an Uncoated Shiny Metal Container

4-4

EPRI Licensed Material Inspection Techniques

Figure 4-3 Container Has Been Coated to Improve Emissivity—Thermogram Now Reveals Fluid Level

4.1.4 Electricians' Tape Another alternative that improves the surface emissivity is the use of electricians' tape (it has an estimated emissivity of 0.95). This method is easy to use and apply but can present problems if the glue on the tape contains chlorine or other chemicals that can attack the target surface.

4.2

Proven Inspection Techniques

4.2.1 Mirrored Surfaces A commonly encountered situation is one where there is little or no room to place the imager and the area of interest is behind another object. This is commonly found in electrical switchgear. One method that works well is to use a material with a high reflectivity (low emissivity) as an infrared mirror. The mirror is placed in such a manner that the reflected image is viewed from a more convenient position. This is a common technique for visual inspection. The determination of temperature, though, requires that the emissivity of the reflecting surface be taken into account. Also, as in the visual technique, the mirrored image will appear reversed, thus requiring care in interpreting the data. There are excellent front surface mirrors available for this technique. These mirrors have the reflecting material on the front surface so that the incoming energy is not refracted by the glass. Sources for these mirrors include most optics manufacturers.

4-5

EPRI Licensed Material Inspection Techniques

4.2.2 Thermal Transfer Imaging As reported in “Subsurface Flaw Detection in Reflective Materials by Thermal-Transfer Imaging” [2], there are a number of inspection techniques that can easily be applied in the field to handle targets with low emissivity. One of these techniques is called Thermal Transfer Imaging (TTI). This technique was developed primarily for the steel industry where low emissivity and high temperatures exist as major problems in infrared imaging. In a case included in “Subsurface Flaw Detection in Reflective Materials by Thermal-Transfer Imaging” [2], the surface thermal patterns of a piece of hot steel needed to be determined. The resultant thermal image provided too much reflection and too little emission to observe meaningful surface thermal patterns. The patterns were observed after they had been transferred to a material that had a higher emissivity. In other words, the surface patterns of the target were observed on the surface of another object after the two had been in contact with each other. If the emissivities of both materials are known and accounted for, temperature measurements can be made this way. 4.2.3 Thermal Transients Another useful inspection technique for handling targets with low emissivity is to add or subtract heat from a target. Most uses of IR are in the steady state condition. When there are two materials with different heat capacities involved, however, a thermal transient is most useful. A graphic example of this is shown in Figure 4-3, dealing with the can of dye check developer. A thermal transient was induced on the can just by spraying it. The endothermic reaction of the propellant as it evaporated caused heat to transfer from the inside of the can (warmer) to the outside. In the case of the propellant inside, the liquid had a higher heat capacity (Cp) than the vapor space above it. During the transient, the liquid, therefore, caused a larger transfer and resultant temperature difference due to conduction on the can surface. The higher emissivity of the developer on the can’s surface allowed it to be seen more readily. This is an extremely useful technique. Where large masses are concerned, however, a large amount of heat transfer might be needed for observation. This technique can be used to determine relative thicknesses of material and locations of voids, delaminations, and internal structures. The heat transfer can be induced by several methods. In the case of locating reinforcing bars (rebar) in concrete, a large induction coil placed on the concrete causes the bars to heat. The locations of the bars and their relative depth can, subsequently, be observed on the surface. When looking for voids in composite materials [3], a flash lamp can be used for a short pulse of energy. Hot air from a compressor can be used for containment spray ring header nozzle inspections and for locating materials near the surface of concrete [4]. It should be noted, however, that heating is not always the most effective approach. Cooling is sometimes more effective, especially in hot areas.

4-6

EPRI Licensed Material Inspection Techniques

4.2.4 Differential Thermography Another state of the art inspection technique is differential thermography. This method was originally developed for the U.S. Army for the identification of defective components on the surface of a printed circuit board. The reports, “Infrared Automatic Mass Screening (IRAMS) System for Printed Circuit-Board Fault Detection” [5] and “Infrared Automatic Screening (IRAMS) Progress Report” [6], provide details on this successful technique and results. As applied in a power plant, a good example would be to observe the resultant surface thermal patterns of reflective insulation to learn about its efficiency. Given that the reflective insulation on a pipe or heat exchanger is not only reflective but large in size, coating with dye check developer or tape is impractical; an infrared imager shows the surface and all reflections from it. The technique here involves a computer, image enhancement, and commercial software. A baseline image is taken at one temperature, for example, during start-up. This image is digitized and stored on a computer. A second image, or subsequent images, are taken from the same location but at a different temperature, at full power for example. This image is also digitized and stored on the computer. The two images are then subtracted. The high reflectance due to the low emissivity exactly cancels out, leaving an image of true surface thermal patterns. One important assumption here is that the background remains the same. These patterns can then be correlated with a visual image for location of internal insulation damage. Also, knowing the emissivity of the insulation and the resultant temperature patterns provides an opportunity to measure the Rvalue of the insulation. This should help in determining the cost-effectiveness of insulation repair or replacement. The differential thermography technique requires that the images be taken from the same place. There are several ways to do this. The first is called pin registration and involves drilling small pilot holes into the floor so that the pins of a tripod's feet would fit in to them. The only variable then becomes the orientation of the thermal imager head on the tripod. A better application of this differential thermography technique is to have the computer at the imager. The original is placed on the screen as a mask. When the mask and the live image cancel each other out, there is exact registration (within the accuracy of the optics). In some cases, such as measuring the Rvalue for the entire heat exchanger, the temperatures above and below certain targets are canceled out (chopped). The analysis is then done on the resultant images. The criteria for chopping can be due to background sources and/or hot reflective sources. 4.2.5 Using Infrared Transmitting Windows For the purpose of safety, it might be inadvisable or in violation of safety regulations, to remove bolts from operating high voltage equipment or to open panels. However, it might be possible to install viewing windows of infrared transmitting materials for infrared inspection. There are numerous materials available for this purpose. In Appendix A, Figure A-12 shows the spectral transmission characteristics of several of these materials, many of which transmit energy past 10 µm. These materials are often used as lenses and optical elements in low-temperature infrared sensors. Installing IR transmitting windows in critical locations is a growing trend, enabling periodic inspection of these locations without the hazard or inconvenience of opening panels or removing bolts. 4-7

EPRI Licensed Material

5

EXAMPLES OF INFRARED APPLICATIONS

5.1

Current Applications

The applications described below are broken down into three categories: electrical, mechanical, and miscellaneous. The primary use of infrared thermography has been in the electrical area. The mechanical area involves rotating equipment, heat exchangers, valves, and buildings. The miscellaneous section describes research in progress and unique applications. The Bibliography section of this Guide (Appendix E) provides references to many other publications where examples of other applications are presented.

5.2

Electrical Applications

The primary use for infrared thermography, and usually the most straightforward application for it, is in the area of electrical predictive maintenance. Within this area, there are three main categories of problems: high electrical resistance, inductive currents, and open circuits. 5.2.1 High Electrical Resistance High electrical resistance is the most common problem that can be identified by using an infrared imager. Based on Ohm's law, power (watts) is calculated as the square of the current multiplied by the resistance (P = I2R). When the resistance is high, the power that is dissipated will be high. A higher power translates into a higher temperature at the same location. This creates the hot spots that are detected by the infrared thermal imager. Typical problems in this category include loose and/or corroded connections (see Figure 5-9), under-sized electrical conductors, and open individual strands of a multiple-stranded conductor. A special case in this category is phase imbalance. The situations that cause a phase imbalance are numerous, but all involve the situation where the current in one phase of a three-phase circuit is significantly different than in the other phase(s). The difference in the higher current phase will be seen as a heating difference. The individual phase currents should be measured to verify this. Another special case within the category is high resistance within a battery cell. Normally, batteries under trickle charge will be near ambient temperatures. High resistance, internal to the battery, can be observed on the battery exterior as areas of higher temperature when compared to similar batteries. These observed temperature differences on an unloaded battery cell will be very 5-1

EPRI Licensed Material Examples of Infrared Applications

small (that is, 0.25°F to 1.0°F). Any temperature differences along the inner cell connections with the battery on float indicate a potentially serious connection problem. There have been several cases where high internal battery resistance has gone unnoticed and has subsequently led to battery failure. 5.2.2 Induced Currents In situations involving high currents, hot spots might appear, not from the primary current but from currents induced in nearby ferrous elements or structures. This is often the case near the main electrical generator. These hot spots can appear in unlikely places such as the supporting steel structure of the generator. Other inductive hot spots have been observed on the generator stator casing and on the frames of motors. Not all of the hot spots are problems, however. In the case of the steel structure, the hot spots might be at the location where the electrical fields from the generator coincide. Hot spots are also common on motors. In both cases, this type of problem should be well documented and, where necessary, trended for future evaluation. 5.2.3 Open Circuits One frequently overlooked application of infrared thermography is in identifying open circuits. For example, a common problem with inverters happens when one or more capacitors fail open. In this case, the failed capacitors will appear to be cooler than other similar capacitors within the inverter.

5.3

Mechanical Applications

IR applications that do not fall into the electrical category are usually described as mechanical. Within this category, there are four major subsets: heating due to friction, valve leakage/blockage, insulation, and building applications. 5.3.1 Friction In the case of rotating or moving equipment, the result of friction is readily observable as an increase in temperature. Typical situations evolve in the area of bearings on pumps (see Figure 5-26) and motors. If a bearing or coupling is inadequately lubricated, internal friction can cause heating, which can usually be observed during operation. A misaligned shaft can result in unequal loading, which causes heat generation at the point of highest mechanical resistance. This situation can be detected from the resultant elevated temperatures seen at the shaft bearing or coupling. 5.3.2 Valve Leakage/Blockage The leakage of fluid past a normally closed valve might be easy to observe with an infrared imager, provided that the insulation on the pipe is accounted for or removed, and that there is a 5-2

EPRI Licensed Material Examples of Infrared Applications

sufficient temperature difference between the pipe surface and ambient. Typical situations are leaking safety valves (see Figures 5-21, 5-22, 5-23, and 5-25), drain valves, and steam traps. Blockage in a pipe or a valve is a special case. In this situation, it might be necessary to add or remove heat from the area in question in order to locate the blockage. As an example, if a blockage were suspected in a boric acid transfer line, adding or removing heat in the area of the blockage would result in a thermal discontinuity at the location of the blockage. The discontinuity exists because boric acid, in the solid form, has a different heat capacity (Cp) than boric acid in the liquid form. Therefore, if a uniform amount of heat is added or removed from both areas, the areas will cool or heat at different rates. The rate difference will, for some period of time, show up as a temperature difference. The interface will be at the location of the blockage. This same mechanism, transient heating or cooling, is the mechanism that allows the remote detection of fluid levels in a tank by means of thermal imaging. 5.3.3 Insulation Insulation on piping and equipment can be tested for integrity using an infrared imager. IR applications include the assurance of complete coverage of the area, thinning/degradation of the insulation, and wet insulation. A most challenging application is when the insulation is a reflective type of insulation or has a reflective covering. The very low emissivity of the surface can result in reflected hot spots from the background, thus, making temperature measurements difficult. One process that can be used is to observe the insulation over a period of time when the system is heating up or cooling down. Using differential thermography, and subtracting two images, cancels out the effects of emissivity and might result in an interpretable thermal difference image. 5.3.4 Building Envelopes Buildings can be inspected for energy conservation with an infrared imager. Typical problems that can be found include air infiltration or exfiltration, poor insulation, and wet roofs. These are traditional applications for infrared thermography. The bibliography (Appendix E) provides sources of further information on these types of applications.

5.4

Miscellaneous Applications

There are numerous applications for infrared thermography that are unique to the nuclear industry or that require special mention. These applications include, inspecting the containment spray ring header, the hydrogen igniters, and the condensers for air in-leakage, and observing thermal plumes. 5.4.1 Containment Spray Ring Header Due to the inaccessibility of the containment spray ring header for physical inspection, infrared imagers have proven to be quite useful in detecting nozzle blockage. In the past, verification of 5-3

EPRI Licensed Material Examples of Infrared Applications

unblocked nozzles on the header has involved several methods including smoke tests and balloons. The infrared method involves pumping heated air into the header and observing the thermal patterns at the nozzles. A blocked nozzle will not pass any hot air and an unblocked nozzle will. Due to the small size of the nozzle and the distance involved, a telescopic lens must be used with the imager for this inspection. 5.4.2 Hydrogen Igniters Infrared thermography has been used for inspecting the containment hydrogen igniters. Through the use of telescopic attachments, the temperature of the igniters can be measured from a remote distance. This technique eliminates the need for staging for close-up inspection. 5.4.3 Condensers Infrared thermal imagers have been used for inspecting condensers for both tube leaks and vacuum leaks (air in-leakage). As the air is drawn into the condenser, the leaks are observable as cooler areas. This inspection technique, however, is very labor-intensive and requires close and careful inspection of valve stems, bonnets, flanges, penetrations, and tubes. 5.4.4 Thermal Plume Detection The use of an infrared imager in a helicopter or airplane can assist the plant in verifying thermal discharge patterns in cooling ponds or other bodies of water. The thermal plume, or outfall, is easily observed from the air. The hottest spots on the surface of the water are easily located. This facilitates routine environmental monitoring for thermal discharge.

5-4

EPRI Licensed Material Examples of Infrared Applications

5.5

Applications Summary

Table 5-1 is a composite list of potential applications for infrared thermal imaging in the areas discussed. Table 5-1 Composite List of Infrared Applications Electrical •

Electrical connections (loose/corroded)

•

Switchyard disconnects

•

Transformers (connections, arrestors, cooling)

•

Transformers (internals)

•

Misaligned contacts, brushes, fuses, fuse clips, holders

•

Splices, crimps

•

Motor Control Center (MCC) heaters

•

Conductors (stranded, undersized, damaged)

•

Inductive heating (structure, bus ducts)

•

Batteries (connections, cells)

•

Open circuits (capacitors)

•

Load imbalance

•

Printed circuit boards

•

Motors (frames, bearings, connections)

•

Motors (failed coil in stator)

Mechanical •

Valves (leakage, blockage)

•

Bearings

•

Couplings

•

Insulation (wet, damaged, coverage)

•

Pipes (thin areas, blockage, missing lining)

•

Refractory buildings (insulation, air leakage, roofs)

•

Reinforcing bar location

•

Underground leaks

•

Steam traps

•

Boiler tubes

Miscellaneous •

Containment spray ring header nozzles

•

Containment hydrogen igniter temperatures

•

Condensers (air in-leakage, tube leaks)

•

Thermal plumes

•

Heat transfer evaluation of heat exchangers

5-5

EPRI Licensed Material Examples of Infrared Applications

To assist utility personnel in thermal image interpretation and recognition, this section also contains a number of examples of applications. These are thermal and visual images of components that appear to be in a degraded condition, along with a number of thermal and visual images of other components that appear to be in good working order. Table 5-2 is a listing of the example images that follow. Full-color images are available on the enclosed CD. Table 5-2 List of IR Application Examples

5-6

Figure Number

Application Description

5-1

Step-Up Transformer High-Resistance Connection

5-2

250 kV Transformer

5-3

Steam Line Leaks

5-4

Isophase Bus Bellows

5-5

Electric Generator

5-6

Regulating Transformer Cooling Oil Migration

5-7

Generator Casing

5-8

Energized Ground Cable

5-9

480 V Breaker Connection

5-10

Current Transformer

5-11

Fuse Holder

5-12

Connection to Fuse Holder

5-13

Knife Switch

5-14

Motor Control Center Breaker

5-15

Motor Control Center Terminal Block

5-16

Motor Control Center Control Wire

5-17

Padmount Transformers

5-18

Vacuum Leak on Turbine Condenser

5-19

Small Transformer

5-20

Motor

5-21

Shell Relief Valve

5-22

Shell Relief Valve (Weeping)

5-23

Shell Relief Valve (Leaking)

5-24

Vacuum Leak on Turbine

5-25

Steam Trap

5-26

Pump Bearing

5-27

Office Building

5-28

Building Roof with Water Saturation

5-29

Induction Motor Air Intake Plenum

5-30

Generator Step-Up Transformer

5-31

Printed Circuit Module

EPRI Licensed Material Examples of Infrared Applications

Full-color images of the following figures are provided on the enclosed CD.

5-7

EPRI Licensed Material Examples of Infrared Applications

Figure 5-1 Step-Up Transformer High-Resistance Connection Figures and text provided by Richard Bjornson, Seabrook Nuclear Power Station, Seabrook, NH, FLIR/InfraMation 2000 Proceedings

5-8

EPRI Licensed Material Examples of Infrared Applications

Figure 5-1 (cont.) Step-Up Transformer High-Resistance Connection

5-9

EPRI Licensed Material Examples of Infrared Applications

Figure 5-2 250 kV Transformer

5-10

EPRI Licensed Material Examples of Infrared Applications

Figure 5-2 (cont.) 250 kV Transformer

5-11

EPRI Licensed Material Examples of Infrared Applications

Figure 5-3 Steam Line Leaks Figures and text provided by Mark Lanius, PECO, Peach Bottom Nuclear Station, Delta, PA, FLIR/InfraMation 2000 Proceedings

5-12

EPRI Licensed Material Examples of Infrared Applications

Figure 5-3 (cont.) Steam Line Leaks

5-13

EPRI Licensed Material Examples of Infrared Applications

Figure 5-4 Isophase Bus Bellows

5-14

EPRI Licensed Material Examples of Infrared Applications

Figure 5-4 (cont.) Isophase Bus Bellows

5-15

EPRI Licensed Material Examples of Infrared Applications

Figure 5-5 Electric Generator

5-16

EPRI Licensed Material Examples of Infrared Applications

Figure 5-5 (cont.) Electric Generator

5-17

EPRI Licensed Material Examples of Infrared Applications

Figure 5-6 Regulating Transformer Cooling Oil Migration Figures and text provided by James Dan Roark, Knoxville Utilities Board, Knoxville, TN, FLIR/InfraMation 2001 Proceedings

5-18

EPRI Licensed Material Examples of Infrared Applications

Figure 5-6 (cont.) Regulating Transformer Cooling Oil Migration

5-19

EPRI Licensed Material Examples of Infrared Applications

Figure 5-7 Generator Casing Figures and text provided by Greg Stockton, Stockton IR Thermography Service, Randleman, NC, FLIR/InfraMation 2000 Proceedings

5-20

EPRI Licensed Material Examples of Infrared Applications

Figure 5-7 (cont.) Generator Casing

5-21

EPRI Licensed Material Examples of Infrared Applications

Figure 5-8 Energized Ground Cable

5-22

EPRI Licensed Material Examples of Infrared Applications

Figure 5-8 (cont.) Energized Ground Cable

5-23

EPRI Licensed Material Examples of Infrared Applications

Figure 5-9 480 V Breaker Connection

5-24

EPRI Licensed Material Examples of Infrared Applications

Figure 5-9 (cont.) 480 V Breaker Connection

5-25

EPRI Licensed Material Examples of Infrared Applications

Figure 5-10 Current Transformer

5-26

EPRI Licensed Material Examples of Infrared Applications

Figure 5-10 (cont.) Current Transformer

5-27

EPRI Licensed Material Examples of Infrared Applications

Figure 5-11 Fuse Holder

5-28

EPRI Licensed Material Examples of Infrared Applications

Figure 5-11 (cont.) Fuse Holder

5-29

EPRI Licensed Material Examples of Infrared Applications

Figure 5-12 Connection to Fuse Holder

5-30

EPRI Licensed Material Examples of Infrared Applications

Figure 5-12 (cont.) Connection to Fuse Holder

5-31

EPRI Licensed Material Examples of Infrared Applications

Figure 5-13 Knife Switch

5-32

EPRI Licensed Material Examples of Infrared Applications

Figure 5-13 (cont.) Knife Switch

5-33

EPRI Licensed Material Examples of Infrared Applications

Figure 5-14 Motor Control Center Breaker

5-34

EPRI Licensed Material Examples of Infrared Applications

Figure 5-14 (cont.) Motor Control Center Breaker

5-35

EPRI Licensed Material Examples of Infrared Applications

Figure 5-15 Motor Control Center Terminal Block

5-36

EPRI Licensed Material Examples of Infrared Applications

Figure 5-15 (cont.) Motor Control Center Terminal Block

5-37

EPRI Licensed Material Examples of Infrared Applications

Figure 5-16 Motor Control Center Control Wire

5-38

EPRI Licensed Material Examples of Infrared Applications

Figure 5-16 (cont.) Motor Control Center Control Wire

5-39

EPRI Licensed Material Examples of Infrared Applications

Figure 5-17 Padmount Transformers Figures and text provided by Jeff Sullivan, Mississippi Power Co., Hattiesburg, MS, FLIR/InfraMation 2000 Proceedings

5-40

EPRI Licensed Material Examples of Infrared Applications

Figure 5-17 (cont.) Padmount Transformers

5-41

EPRI Licensed Material Examples of Infrared Applications

Figure 5-18 Vacuum Leak on Turbine Condenser Figures and text provided by Mark Lanius, PECO, Peach Bottom Nuclear Station, Delta, PA, FLIR/InfraMation 2000 Proceedings

5-42

EPRI Licensed Material Examples of Infrared Applications

Figure 5-18 (cont.) Vacuum Leak on Turbine Condenser

5-43

EPRI Licensed Material Examples of Infrared Applications

Figure 5-19 Small Transformer

5-44

EPRI Licensed Material Examples of Infrared Applications

Figure 5-19 (cont.) Small Transformer

5-45

EPRI Licensed Material Examples of Infrared Applications

Figure 5-20 Motor

5-46

EPRI Licensed Material Examples of Infrared Applications

Figure 5-20 (cont.) Motor

5-47

EPRI Licensed Material Examples of Infrared Applications

Figure 5-21 Shell Relief Valve

5-48

EPRI Licensed Material Examples of Infrared Applications

Figure 5-21 (cont.) Shell Relief Valve

5-49

EPRI Licensed Material Examples of Infrared Applications

Figure 5-22 Shell Relief Valve (Weeping)

5-50

EPRI Licensed Material Examples of Infrared Applications

Figure 5-22 (cont.) Shell Relief Valve (Weeping)

5-51

EPRI Licensed Material Examples of Infrared Applications

Figure 5-23 Shell Relief Valve (Leaking)

5-52

EPRI Licensed Material Examples of Infrared Applications

Figure 5-23 (cont.) Shell Relief Valve (Leaking)

5-53

EPRI Licensed Material Examples of Infrared Applications

Figure 5-24 Vacuum Leak on Turbine

5-54

EPRI Licensed Material Examples of Infrared Applications

Figure 5-24 (cont.) Vacuum Leak on Turbine

5-55

EPRI Licensed Material Examples of Infrared Applications

Figure 5-25 Steam Trap

5-56

EPRI Licensed Material Examples of Infrared Applications

Figure 5-25 (cont.) Steam Trap

5-57

EPRI Licensed Material Examples of Infrared Applications

Figure 5-26 Pump Bearing

5-58

EPRI Licensed Material Examples of Infrared Applications

Figure 5-26 (cont.) Pump Bearing

5-59

EPRI Licensed Material Examples of Infrared Applications

Figure 5-27 Office Building

5-60

EPRI Licensed Material Examples of Infrared Applications

Figure 5-27 (cont.) Office Building

5-61

EPRI Licensed Material Examples of Infrared Applications

Figure 5-28 Building Roof with Water Saturation Figures and text provided by Kathryn Barker, American Infrared Testing and Consulting, FLIR/InfraMation 2000 Proceedings

5-62

EPRI Licensed Material Examples of Infrared Applications

Figure 5-28 (cont.) Building Roof with Water Saturation

5-63

EPRI Licensed Material Examples of Infrared Applications

Figure 5-29 Induction Motor Air Intake Plenum

5-64

EPRI Licensed Material Examples of Infrared Applications

Figure 5-29 (cont.) Induction Motor Air Intake Plenum

5-65

EPRI Licensed Material Examples of Infrared Applications

Figure 5-30 Generator Step-Up Transformer Figures and text provided by Mark Goff, Tennessee Valley Authority, Chattanooga, TN, InfraMation 2001 Proceedings

5-66

EPRI Licensed Material Examples of Infrared Applications

Figure 5-30 (cont.) Generator Step-Up Transformer

5-67

EPRI Licensed Material Examples of Infrared Applications

Figure 5-31 Printed Circuit Module Figures and text provided by Richard Fishbune, IBM, Rochester, MN, FLIR/InfraMation 2000 Proceedings

5-68

EPRI Licensed Material Examples of Infrared Applications

Figure 5-31 (cont.) Printed Circuit Module

5-69

EPRI Licensed Material

6

BASIC ELEMENTS OF AN IN-HOUSE PROGRAM

The creation of an in-house program to utilize infrared thermography would be customized to each facility's methods of conducting operations. The basic elements of each program, however, would probably be much the same. This section outlines a generic approach to developing and implementing a comprehensive infrared thermography program. A discussion of the basic elements is followed by a sample program.

6.1

Basic Elements

An in-house program can be developed by many different approaches. A program that is limited to the use of only qualitative thermal imaging instruments (as compared to radiometric/quantitative) is likely to be less comprehensive. Assuming that a program was created to make full use of a radiometric/quantitative imager and image processing software, the following topics would need to be addressed: •

Introduction

•

Definitions

•

Scope

•

Responsibilities

•

Precautions

•

Prerequisites

•

Conduct of the Survey

•

Acceptance criteria

•

Reporting requirements

•

Qualification of personnel

•

Scheduling

•

Equipment matrix

•

References

6-1

EPRI Licensed Material Basic Elements of an In-House Program

6.1.1 Introduction This section provides a discussion of the purpose and goal of the IR survey. 6.1.2 Definitions In order to put the program in the proper context, the definitions should be at the front. This will allow the reader or reviewer to have an easy reference for the terminology that follows. 6.1.3 Scope The scope of the program should be very specific as to what is covered and what is not. The applications for infrared thermography are very broad. Inspections of roofs and buildings should not be addressed in a document that has inspections of safety-related equipment as its main purpose. An addendum to the main procedure should be used to avoid confusion. 6.1.4 Responsibilities This section should clearly delineate who is responsible for the various aspects of the program from administration through corrective action. The main areas of responsibility are administration, inspection (Infrared Thermographer), and corrective action. Most of the difficulty in applying this technology is in image interpretation and diagnosis. It might be necessary to use others in this effort and, if so, their role should be specifically identified. 6.1.5 Precautions Many of the infrared inspections necessitate that panels be removed from energized electrical equipment. Precautions as to electrical and personnel safety should be included. 6.1.6 Prerequisites All of the prerequisites for conducting the survey should be identified here. This should include the qualification of personnel, calibration of equipment, approvals needed from Operations and/or Management, and the required resources (equipment and personnel). 6.1.7 Conduct of the Survey This section could reference or include specific procedures for inspections. Specific techniques and a suggested sequence of inspections could also be included.

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EPRI Licensed Material Basic Elements of an In-House Program

6.1.8 Acceptance Criteria All survey results should be compared to either a baseline thermogram or other industry accepted standards. Problems or anomalies should then be reviewed for determination of which corrective action, if any, should be undertaken. The following acceptance criteria provide a generic example but would need adaptation for component-specific use. Advisory

1°F to 15°F rise above a reference (0.5°C–8°C)

Intermediate

16°F to 50°F rise above a reference (9°C–28°C)

Serious

51°F to 100°F rise above a reference (29°C–56°C)

Critical

in excess of 100°F rise above a reference (56°C)

An alternative to the above classification is that used in Military Standard MIL-STD-2194 (1988). The MIL Standard uses four categories as follows: Desirable

Component is 10°C (18°F) to 24°C (44°F) above ambient

Important

Component is 25°C (45°F) to 39°C (71°F) above ambient

Mandatory

Component is 40°C (72°F) to 69°C (125°F) above ambient

Immediate

Component is 70°C (126°F) or more above ambient

The main difference between the two methods of problem classification is that the MIL Standard references temperature rise above ambient and the guide classification relates to a temperature rise above a reference value. That reference value could be ambient or, in the case of three-phase electrical circuits, a temperature rise above an adjacent phase. Each facility should adopt criteria that provide a balance between maintenance requirements and operational considerations. 6.1.9 Reporting Criteria A rigid process should be established when reporting the results of infrared inspections. This rigidity is necessary due to the ease of misinterpretation of the thermograms by untrained personnel. A typical quarterly survey of electrical equipment might result in 25 to 50 problems in 200 pieces of inspected equipment. The vast majority of these problems might be minor in nature and require corrective action on a low priority. The process that works best, based on industry responses, is one that keeps the report distribution and decision-making in the hands of the right people (operations, maintenance, and/or program managers). The format for the report should also be consistent. At a minimum, it should include the following: •

Time/date

•

Equipment identification

•

Location 6-3

EPRI Licensed Material Basic Elements of an In-House Program

•

Specific problem

•

Corrective action recommended

•

Problem action criteria

•

Visible photograph

•

Infrared photograph

•

Inspector’s name and signature

6.1.10 Qualification of Personnel Personnel responsible for conducting the surveys and interpreting the results should be trained in the use of the equipment and certified by their employer. The training and certification criteria, established by the American Society for Nondestructive Testing (ASNT), should be adapted and incorporated into the program. These criteria are outlined in their document SNT-TC-1A and will be discussed in more detail in Section 7. 6.1.11 Scheduling The documentation requirements and listing of equipment to be evaluated during the survey should be established in advance so that trends in equipment operation can be translated easily into predictions of future results. This is the key to predictive maintenance. The program must also be flexible enough to accommodate emergency inspections and inspections during unplanned outages. Typically, the administrator of the IR program provides this interface. 6.1.12 Equipment Matrix The equipment to be surveyed, the selection criteria, and the locations and frequency of inspection should be compiled in a matrix. Typically, the electrical equipment is grouped together, as are the other major component groups. An alternate approach would be to list the equipment in a route of survey-format, which might save time for the infrared thermographer. 6.1.13 References References to any helpful information should be provided. These typically include training materials, textbooks on the subject, and equipment operation manuals.

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EPRI Licensed Material Basic Elements of an In-House Program

6.2

Sample Program

This section incorporates the above recommendations and could serve as the basis for a program using infrared thermography as part of a predictive maintenance program. 1.0

INTRODUCTION

1.1

This program is for the administration and conduct of an infrared inspection program of electrical and mechanical equipment. The purpose of this program is to identify equipment that requires maintenance and to improve its reliability through the use of infrared thermography (IR).

1.2

This document contains the recommended scope, frequency, and corrective action criteria for routine and unscheduled infrared surveys.

1.3

Requests for changes to this program and questions relative to it shall be directed to the administrator of the IR program.

2.0

DEFINITIONS

2.1

Infrared – Electromagnetic radiation having wavelengths that are greater than those of visible light, but shorter than microwaves. As it applies to IR thermography, the wavelengths are between 3 to 15 micrometers.

2.2

Infrared Survey – A comprehensive examination of components and equipment with an infrared imaging system.

2.3

Emissivity – The ratio of radiance from a surface to the radiance at the same wavelength from a perfect blackbody at the same temperature. Functionally, this is the radiation efficiency of a surface in the infrared spectrum.

2.4

Radiosity – Thermal energy of a surface as seen by the infrared detector.

2.5

Thermogram – A recorded, displayed, or hard-copy image of the output of an infrared imaging system.

2.6

Isotherm – A thermal contour on a thermogram where all of the spots along it are at the same apparent temperature.

2.7

Infrared thermographer – An individual who is trained and qualified to operate infrared imaging equipment and to interpret the images.

3.0

SCOPE

3.1

The requirements of this procedure shall apply to all safety-related components. It shall also be applicable to non-safety-related equipment where financial benefit might be achieved by monitoring (that is, increased plant availability, decreased maintenance costs, and so on).

3.2

This procedure includes guidelines for the following: •

Component selection

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EPRI Licensed Material Basic Elements of an In-House Program

• •

6-6

Interval selection Determining component acceptability

4.0

RESPONSIBILITIES

4.1

Administrator of IR – It is the administrator’s responsibility to oversee the program. This includes making changes to the procedure. All surveys, whether they are scheduled or conducted on an emergency basis, shall be approved by the administrator or his/her designee. The administrator shall be responsible for budgeting, planning, and interfacing with outside organizations.

4.2

Infrared Thermographer – The infrared thermographer is the only person trained and qualified to operate the infrared imaging equipment. He/she is responsible for conducting the surveys, interpreting the images, writing the reports, and acting as a technical resource to other plant departments. The infrared thermographer is responsible for the maintenance and calibration of the infrared imaging equipment.

4.3

Cognizant Engineer – At the request of the infrared thermographer, a discipline-cognizant engineer will provide assistance in diagnosing a problem. The cognizant engineer will also suggest corrective action and provide coordination with other plant disciplines.

4.4

Root Cause – Determination of root cause and the subsequent applicable action level shall be the responsibility of plant management. When necessary, the infrared thermographer shall request assistance from a cognizant systems or maintenance engineer in determining the root cause or the recommended corrective action.

5.0

PRECAUTIONS

5.1

Many of the components that are being inspected represent potential plant trip hazards; exercise extreme care.

5.2

All safe work practices as outlined in the plant safety manual, shall be followed. These practices include exhibiting caution near energized electrical equipment, rotating equipment, and hot pipes. All surveys shall be conducted from a safe stable location.

5.3

Infrared surveys within the Radiological Controls Area shall be conducted within the guidelines of the Health Physics Department. In areas of potential contamination, the infrared thermographer shall be responsible for covering the equipment with plastic as directed by Health Physics.

5.4

When practical, surveys in areas of airborne contamination should be avoided. When this is not possible, a thin piece of polyethylene or plastic can be placed over the lens. If this is done, the transmittance of the covering must be taken into account.

6.0

PREREQUISITES

6.1

Personnel – The infrared thermographer and one craft person constitute the minimum personnel necessary to conduct a survey when the operating or opening of equipment is necessary.

EPRI Licensed Material Basic Elements of an In-House Program

6.2

Approvals – The required approvals to conduct a survey shall be coordinated with the IR administrator. The control room should be notified both prior to the start of the survey and at its end. If requested, the infrared thermographer will inform the control room prior to opening equipment that presents a possible plant trip hazard.

6.3

Emergencies – In cases where requests for surveys are done on an emergency basis, the infrared thermographer shall fulfill the duties of the IR administrator and provide the necessary coordination.

7.0

CONDUCT OF THE SURVEY

7.1

The equipment survey matrix shall identify the equipment to be surveyed and the frequency of the survey.

7.2

The sequence of the survey is not important unless specifically stated in the procedure or requested by either Maintenance or Operations. All equipment on the matrix must be surveyed unless it is not in operation or conditions dictate otherwise. The infrared thermographer shall note any exceptions in the inspection report.

7.3

Standard practice is to videotape all surveys and to include an audio track for verbal identification and discussion.

7.4

The thermal images must be of sufficient resolution to identify the components and any problem areas.

7.5

When problems are identified, the thermographer shall reposition the imager and obtain more than one view. This is done to eliminate the possibility of apparent problems being caused by reflections from hot objects. The hard-copy images should be obtained from the position that provides the best image.

7.6

All problems are to be photographed in the visible as well as in the infrared. This is to allow proper and easy identification of the problem areas, which will facilitate maintenance activities.

7.7

The problems shall be customarily reported as a temperature rise. This rise can be calculated from ambient, thermal baseline data, or made by comparison in the cases where similar equipment exists.

7.8

When absolute temperatures are requested or required, the infrared thermographer shall determine and use the target's effective emissivity to assure accuracy. A standard table of effective emissivities will be developed by measurement and will be maintained by the infrared thermographer.

7.9

Important information relating to test conditions, such as load, flow, and pressure shall be noted by the thermographer if it is available. This information will be used in component trend analysis.

7.10

The components shall be inspected with the imager aimed along a line normal (perpendicular) to the target surface whenever possible, to minimize the potential for errors due to reflections.

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EPRI Licensed Material Basic Elements of an In-House Program

6-8

7.11

During the infrared inspection, the components must also be inspected visually and any discolorations, questionable noise, or smell should be reported.

7.12

In cases where precise measurements must be obtained, the instrument background radiation effects must be taken into account. Instrument background temperature can be determined by placing a good diffuse reflector (such as a piece of aluminum foil that has been crumpled and re-flattened) in ambient air and measuring its apparent temperature with the imager’s emissivity set to 1.0.

7.13

Where external optics, such as telescopic and wide-angle lenses are used, the transmittance of the optics must be taken into account. The information that corrects the effects of these devices is supplied by the manufacturer and is entered directly into the imager software.

7.14

When measurements are being made on targets, the size of the target and the distance must be known. The IFOVmeas (Instantaneous Field of View for measurement) of the instrument must fit comfortably within the required target spot at the measurement distance. If these criteria are not satisfied, the instrument must be moved closer to the target and/or a higher magnification lens must be used. (See section 3.3.4 for a more detailed discussion of this subject).

7.15

The survey should be done with the imager scanned at a speed that does not cause blurring of the image so that acceptable thermograms can be obtained from the videotape on playback.

7.16

If requested or desired, a second (backup) measure of temperature can be obtained through the use of contact thermocouples or spot radiometers. (Care should be used in evaluating the results of measurements that are not calibrated.)

7.17

In general, equipment shall be surveyed when in a normal operational state. In cases where equipment is not energized or running normally, the thermographer shall note it in the IR inspection report.

7.18

Equipment such as batteries shall be surveyed during both normal operation and during discharge tests.

7.19

Requests for equipment operation for the sole purpose of an infrared inspection shall be coordinated with operations by the IR administrator. In most cases, this should be avoided.

7.20

All infrared inspections, whether done by on-site personnel or outside contractors, will be performed under the guidance and procedures listed in this program. Special tests outside of the normal inspection shall be reviewed and approved in advance by the IR administrator.

8.0

ACCEPTANCE CRITERIA

8.1

Subsequent to an initial thermal baseline, the following action levels are to be used to classify each problem:

EPRI Licensed Material Basic Elements of an In-House Program

Advisory (Level 1)

1°F to 15°F rise

Intermediate (Level 2)

16°F to 50°F rise

Serious (Level 3)

51°F to 100°F rise

Critical (Level 4)

in excess of 100°F rise

8.2

When indications on components fall into levels 2, 3, 4, section 9 of the program shall be followed for reporting.

8.3

To determine acceptability of the inspection, the results and final report shall be compared against the criteria set forth in this program.

9.0

REPORTING REQUIREMENTS

9.1

Every scheduled and unscheduled infrared inspection shall be documented and reported in accordance with the requirements of this section (see Figure 6-1).

9.2

At a minimum, the report shall contain the following:

9.3

•

Summary of inspection and findings

•

Equipment list

•

Data sheets with IR and visible photographs of anomalies

•

Root cause analysis and corrective action

• Comments The report shall be issued to the IR administrator within five working days of the completion of the survey.

9.4

A verbal report shall always be given to the on-site IR administrator upon completion of the survey.

9.5

The reporting of problems that fall within the four acceptance action levels are as follows: Advisory (Level 1)

Normal cycle of corrective maintenance.

Intermediate (Level 2) High priority during an unscheduled shutdown. Serious (Level 3)

Alert Operations—potential failure. Correct ASAP.

Critical (Level 4)

Alert Operations, Management. Remove from service ASAP.

9.6

Items classified as serious are to be immediately reported to the IR administrator who will advise Maintenance and Operations.

9.7

Items classified as critical are to be immediately reported to Operations, Maintenance, and the IR administrator.

6-9

EPRI Licensed Material Basic Elements of an In-House Program

10.0

QUALIFICATION OF PERSONNEL

10.1

The infrared thermographer shall be qualified by examination and certified by the plant to conduct the survey.

10.2

The qualifying examination and training shall meet the guidelines of ASNT SNT-TC-1A (current edition).

10.3

In addition to the ASNT qualifications, the thermographer shall be knowledgeable in the following areas: • • • •

Equipment-specific operation Infrared theory Heat transfer modes Safety practices

10.4

Certification of the thermographer shall be made through a written and a practical examination.

10.5

The plant Training Department shall administer the initial and re-qualification training.

11.0

SCHEDULING

11.1

The IR administrator is responsible for scheduling all routine infrared inspections.

11.2

The Equipment Matrix (Program, section 12.0) lists the frequency of inspection for each component.

11.3

Inspections on an emergency basis or for a special test shall be scheduled and coordinated by the IR administrator.

12.0

EQUIPMENT MATRIX

12.1

Component Selection Criteria

12.1.1 The components that are to be included in the thermographic analysis program should be selected based on the perceived or documented benefit of thermography on the type of equipment and the following criteria categories: A. Critical: Critical equipment shall be defined as: •

Equipment whose function is necessary and must be available at all times.

•

Equipment upon which thermography has been used to deviate from a specific vendor-recommended preventive maintenance activity.

•

Equipment necessary to maintain full-power generating capabilities (that is, nonredundant).

B. Vital: Vital equipment shall be defined as those components whose function is necessary but that, through redundant design, do not have to be available at all times.

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EPRI Licensed Material Basic Elements of an In-House Program

C. Vendor Recommended: Vendor-recommended equipment whose manufacturer or vendor recommends the periodic monitoring of the equipment with infrared thermography. D. Non-Vital: Non-Vital equipment shall be defined as: •

Equipment whose replacement cost versus periodic monitoring cost does not differ greatly and does not fall into category A or B above.

•

Components that are used very infrequently and do not fall into category A or B.

12.1.2 The IR administrator shall maintain a listing of all of the components in the thermographic analysis program, the category to which they belong, and their monitoring interval. 12.1.3 Equipment in category D that has a failure history relating to thermography might be included in the program in order to determine root cause, or to prevent failure recurrences or significant inconveniences. Otherwise, equipment in category D should be omitted from the program. 12.1.4 The above recommended component selection criteria should be applied predominantly to electrical equipment such as: • • • • • • •

Motor control centers Load centers Transformers Switchgear Battery chargers Switchyard equipment Large motor termination

12.1.5 The above criteria can also be applied to: • • • 12.2

Pumps/motors Steam traps Valves

Performance Intervals

12.2.1 The selection of performance intervals should be based upon several factors, such as: •

The impact of the component on plant operation and personnel safety if an unexpected failure were to occur.

•

The speed at which a component fault manifests itself into a stage of degradation, which affects the component’s operability.

•

Vendor/manufacturers’ recommendations.

•

The category of the component as stated in section 12.1.1 of the program.

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EPRI Licensed Material Basic Elements of an In-House Program

12.2.2 When considering the vendor’s recommended frequency for thermography, the application of the equipment should be taken into consideration (that is, the run time experienced by the equipment in this installation versus what the vendor expects for typical run times). Also, if the component falls into categories A or B of 12.1.1, then the most limiting interval (between the vendor-recommended interval and the recommended interval in section 12.2.3 of the program) shall be used for the monitoring of the equipment. 12.2.3 The following recommended intervals for the given categories should be used: A. Critical Equipment •

Monitor quarterly for those components that are operated continuously or are optested at least quarterly.

•

Monitor semi-annually for those components that are operated continuously or are run-tested at least semi-annually.

•

At start-up, monitor when the component is placed on-line, is at a stabilized temperature, and has not been monitored for at least one monitoring interval.

•

Equipment less than 240 V does not require periodic monitoring.

B. Vital Equipment • • •

Monitor equipment greater than 480 V quarterly. Monitor equipment greater than 240 V but less than 480 V semi-annually. Equipment less than 240 V does not require periodic monitoring.

12.2.4 Changes to monitoring intervals should be reviewed carefully prior to making changes in order to ensure that maximum component availability and program efficiency is provided. 12.2.5 At a minimum, documentation for interval changes shall be maintained, by the IR administrator. 12.2.6 Components need not be operated for the sole purpose of collecting thermography data.

6-12

13.0

SUGGESTED PROGRAM REFERENCES

13.1

Infrared Thermography Guide (Revision 3), (formerly NP-6973)

13.2

Plant Administrative Procedures Manual

13.3

Plant Safety Manual

13.4

Plant Training Manual

13.5

Plant Quality Assurance Procedures Manual

13.6

Plant Systems Training Manual

EPRI Licensed Material Basic Elements of an In-House Program

13.7

Infrared Imager Instruction Manual

13.8

Plant Predictive Maintenance, INPO Good Practice 89-009.

13.9

Wolfe, W. L. and Zissis, G.J., The Infrared Handbook. Environmental Research Institute of Michigan (1996).

13.10

Mil-Std-2194, Infrared Thermal Imaging Survey Procedure Electrical Equipment.

13.11

American Society for Nondestructive Testing Standard Practice SNT-TC-1A, Qualifications Guidelines.

13.12

American Society for Nondestructive Testing Infrared and Thermal Testing Handbook, 2001.

13.13

American Society for Nondestructive Testing Level III Study Guide: Infrared and Thermal Testing Method, 2001.

6-13

EPRI Licensed Material Basic Elements of an In-House Program

Figure 6-1 Infrared Survey Results

6-14

EPRI Licensed Material

7

TRAINING AND CERTIFICATION

This section deals solely with the efforts of the American Society of Nondestructive Testing (ASNT) in the training and certification of infrared thermographers. The purpose is to provide guidelines for training individuals who will be able to deliver the best level of service possible. It is important to understand that certification via the ASNT Certification Program, does not imply authorization or licensing of the certificate holder to perform infrared thermography tasks. It is solely the employer's responsibility to review the individual's qualification records for completeness and to authorize individuals to perform infrared thermography tasks.

7.1

Background

Commercially available infrared imagers are quite easy to both use and misuse [7, 8, 9, 10, 11]. Many small, independent contractors, from electricians to engineers, provide a wide range of services to many different industries. In the absence of formal training, most of these people have learned on the job while working with more experienced individuals. At the request of many ASNT members, a committee was formed in the fall of 1989 to propose modifying ASNT Recommended Practice No. SNT-TC-1A, the qualification guideline for nondestructive testing, to accept and recognize infrared thermography as a valid nondestructive examination method. At this writing, all of the training, qualification, and certification guidelines are in place and SNT-TC-1A has been updated (1996) to include the T/IR (Thermal Infrared) method. Two additional ASNT publications were released in 2001 to support training and certification: •

ASNT Infrared and Thermal Testing Handbook, 2001

•

ASNT Level III Study Guide: Infrared and Thermal Testing Method, 2001

Recommended training and certification guidelines for infrared thermographers are summarized in the ASNT Infrared and Thermal Testing Handbook on pages 15–18, and are explained in detail in SNT-TC-1A. The ASNT training program is intended to supplement equipment-specific training that might be offered by the manufacturers. Certification is the responsibility of the individual employer. SNT-TC-1A states the following in this regard:

7-1

EPRI Licensed Material Training and Certification

“Written Practice. The employer shall establish a written practice for the control and administration of nondestructive personnel training, examination and certification. The employer’s written practice should describe the responsibility of each level of certification for determining the acceptability of materials and components in accordance with applicable codes, standards, specifications and procedures.”

7.2

Levels of Qualification

The recommended Levels of Qualification for infrared thermographers follow those of traditional NDE methods. These levels are as follows: Level I

A Level I infrared thermographer shall be qualified to perform specific IR inspections in accordance with detailed written instructions and to record the results; the Level 1 infrared thermographer shall perform inspections under the cognizance of a Level II or Level III. The Level I shall not independently perform nor evaluate inspection results for acceptance or rejection when such inspection results are for the purpose of verifying compliance to code or regulatory requirements.

Level II

A Level II infrared thermographer shall be qualified to set up and calibrate equipment, conduct inspections, and to interpret inspection results in accordance with procedure requirements. The individual shall be familiar with the limitations and scope of the method employed and shall have the ability to apply techniques over a broad range of applications within the limits of their certification. The Level II shall be able to organize and report inspection results. A Level II must have the ability to correctly identify components and parts of components within the scope of the IR inspection.

Level III

A Level III infrared thermographer is capable of designating a particular inspection technique, establishing techniques and procedures, and interpreting results. The individual shall have sufficient practical background in his/her area of expertise to develop innovative techniques and to assist in establishing acceptance criteria where none are otherwise available. The individual shall have general familiarity with other nondestructive evaluation (NDE) methods and inspection technologies. The Level III individual shall be qualified to train and examine Level I and Level II personnel for qualification and certification as an infrared thermographer.

7.3

Training Requirements

The training requirements for each level of the infrared thermographer qualification parallel those for the other traditional NDE methods in that on-the-job training, educational background, and classroom work all count toward qualification. There are qualification examinations and annual re-qualification requirements at all levels. It is up to the utilities’ training organization and individual employers to implement the appropriate recommendations of the training program set forth in SNT-TC-1A. 7-2

EPRI Licensed Material Training and Certification

The experience and education recommendations for the three levels are: Level I

A high school diploma (or equivalent) or 6 months of experience

Level II

A two-year college or technical degree or 18 months of experience

Level III

A four-year technical degree from a college or university or 5 years of experience

The required classroom training is as follows: Level I

40 hours of instruction, 50-question written examination, classroom experiment

Level II

40 hours of instruction, 75-question written examination, classroom experiment

Level III

40 hours of instruction, 75-question written examination, procedure preparation for classroom experiment

The classroom training is based on the body of knowledge reviewed, adopted, and updated by ASNT, summarized in ASNT Recommended Practice No. SNT-TC-1A, and reviewed in ASNT Level III Study Guide: Infrared and Thermal Testing Method, 2001. The depth that is covered by these areas corresponds to the level of the training. This translates into more extensive training at Level III than Level I, even though the classroom hours are the same. The four areas for training and associated practical aspects are listed below. At the conclusion of training, the trainee will: A. Radiosity or Target Exitance •

Understand the concepts of radiosity and associated parameters.

•

Be able to measure emissivity, reflectance, transmittance, background temperature, foreground temperature, and target temperature.

•

Be cognizant of potential errors in the measurement of the above parameters, caused by variation across the target surface.

B. Spatial Resolution •

Understand the concept of spatial resolution.

•

Understand the difference between image resolution and measurement resolution.

•

Understand the effect on measurement of the distance between the instrument and the target.

•

Be able to calculate measurement spot size.

•

Be able to exploit equipment-specific aids to determine measurement adequacy.

7-3

EPRI Licensed Material Training and Certification

C. Heat Transfer •

Understand the fundamental concepts of heat transfer including conduction, convection, and radiation.

•

Understand the difference between steady state and transient heat flow and application dependence.

•

Understand the effect of the environmental conditions of sky temperature, view factor, wind velocity, and surface orientation.

•

Understand the potential problems if evaporation or condensation occur at the target surface.

D. Equipment Operation •

Be able to set up and operate the necessary equipment.

•

Understand dynamic range and its implication in image acquisition.

•

Demonstrate good data acquisition practices.

•

Demonstrate the use of accessories.

•

Understand how to compensate for external optics.

•

Understand the implications of system spectral response.

The written examination is derived from a pool of 200-300 questions that are reviewed and approved by the ASNT T/IR committee members. During training, practical exams are conducted through classroom experiments and are focused on one particular concept, such as transient thermal heat transfer. The actual practical exam is determined by the trainer and is conducted within the guidelines for each particular level. Infrared thermography was adopted as a nondestructive inspection method in the fall of 1991.

7.4

Predictive Maintenance (PdM) Level III Certification Program

Recognizing that there are areas of specialization within the infrared thermography discipline, the ASNT T/IR committee has promoted the development of specialty certification. The Predictive Maintenance Level III Certification Program has been developed by ASNT in response to this effort. Developed to meet the needs of the predictive maintenance sector of the industry, this program incorporates the vibration analysis (VA) and infrared/thermal (IR) test methods. A PdM-specific body of knowledge, including knowledge of the Recommended Practice No. SNT-TC-1A and the ANSI/ASNT CP-189 standard, is used for the two-hour PdM basic examination. The VA and IR method tests are the same as those used in the ASNT NDT Level III program. A separate and distinct PdM Level III certificate is issued for this certification. The PdM basic examination is more specific than the ASNT NDT Level III basic examination, and thus, PdM certificate holders wishing to gain traditional NDT Level III certification will still 7-4

EPRI Licensed Material Training and Certification

be required to sit for the ASNT NDT Level III basic examination, as well as taking an ASNT NDT Level III method test. Certification via the ASNT PdM Level III Certification Program, as with the ASNT NDT Level III program, does not imply authorization or licensing of the PdM certificate holder to perform PdM tasks. It is solely the employer's responsibility to review the individual's qualification records for completeness and to authorize individuals to perform PdM.

7-5

EPRI Licensed Material

A

THE SCIENCE OF THERMOGRAPHY (PRACTICAL APPLICATION OF THERMOGRAPHIC AND THERMAL SENSING EQUIPMENT)

A.1

Introduction

This appendix is presented as a reference guide to provide the practical thermographer with an understanding of the science behind the measurements. It is intended as an aid in performing and understanding non-contact thermal and thermographic measurements using infrared sensing equipment. The deployment and operation of infrared sensing instruments was, at one time, cumbersome and difficult. Thermographers were often required to perform on-the-spot calculations in order to reduce their measurement data and determine actual temperature values; this is no longer so. Modern instruments are light in weight, portable, and rugged. Menu-driven on-board software now makes it relatively simple to operate equipment and to gather data directly in terms of target temperature. Because of this very ease of operation, it is also relatively simple to misinterpret the results so easily and quickly obtained. Erroneous conclusions can have an extremely negative effect on the measurements program and on the credibility of the thermographer. A solid understanding of the basis on which thermographic measurements are made will go a long way toward minimizing operator error and ensuring the success of the thermographic program. The subject matter in this appendix begins with a discussion of heat transfer and how radiative heat transfer is the basis for infrared thermography. The basic physics of infrared radiation and how it applies to instrument performance is explained. Finally, the performance parameters of infrared point-sensing and imaging instruments are discussed, including how to select, calibrate, and evaluate the performance of the instrument that is best suited to your application.

A.2

Heat Transfer and Radiation Exchange Basics for Thermography

This section is to provide the reader with an understanding of how heat transfer phenomena affect non-contact infrared thermal sensing and thermographic measurements. Infrared thermography depends on measuring the distribution of radiant thermal energy (heat) emitted from a target surface, thus, the thermographer requires an understanding of heat, temperature,

A-1

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

and the various types of heat transfer as an essential prerequisite in preparing to undertake a program of IR thermography. A.2.1 Heat and Temperature What is often referred to as a heat source (like an oil furnace or an electric heater) is really one form or another of energy conversion; the energy stored in one object is converted to heat and flows to another object. Heat can be defined as thermal energy in transition. It flows from one place or object to another as a result of temperature difference, and the flow of heat changes the energy levels in the objects. Temperature is a property of matter and not a complete measurement of internal energy. It defines the direction of heat when another temperature is known. Heat always flows from the object that is at the higher temperature to the object that is at the lower temperature. As a result of heat transfer, hotter objects tend to become cooler and cooler objects become hotter, approaching thermal equilibrium. To maintain a steady-state condition, energy needs to be continuously supplied to the hotter object by some means of energy conversion so that the temperature and, hence, the heat flow remains constant. A.2.2 Converting Temperature Units Temperature is expressed in either absolute or relative terms. There are two absolute scales called Rankine (English system) and Kelvin (metric system). There are two corresponding relative scales called Fahrenheit (English system) and Celsius or Centigrade (metric system). Absolute zero is the temperature at which no molecular action takes place. This is expressed as zero Kelvins or zero Rankines (0 K or 0 R). Relative temperature is expressed as degrees Celsius or degrees Fahrenheit (°C or °F). The numerical relations among the four scales are as follows: T Celsius = 5/9 (T Fahrenheit - 32 ) T Fahrenheit = 9/5 T Celsius + 32 T Rankine = T Fahrenheit + 459.7 T Kelvin = T Celsius + 273.16 Absolute zero is equal to -273.1°C and is also equal to -459.7°F. To convert changes in temperature or delta T between the English and Metric systems, the simple 9/5 (1.8 to 1) relationship is used: DELTA T Fahrenheit (or Rankine) = 1.8 DELTA T Celsius (or Kelvin)

A-2

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Table A-1 is a conversion table to allow for the rapid conversion of temperature between Fahrenheit and Celsius values. Instructions for the use of the table are shown at the top. For quick reference, the above conversion factors are also summarized in Appendix C, Plate 1.

A-3

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment) Table A-1 Temperature Conversion Chart Instructions for Use: 1. Start in the Temp. column and find the temperature that you wish to convert. 2. If the temperature to be converted is in °C, scan to the right column for the °F equivalent. 3. If the temperature to be converted is in °F, scan to the left column for the °C equivalent. °C

A-4

Temp.

°F

°C

Temp.

°F

°C

°F

Temp.

-101

-150

-238

-36.7

-34

-29.2

-26.7

-16

3.2

-95.6

-140

-220

-36.1

-33

-27.4

-26.1

-15

5

-90

-130

-202

-35.6

-32

-25.6

-25.6

-14

6.8

-84.4

-120

-184

-35

-31

-23.8

-25

-13

8.6

-78.9

-110

-166

-34.4

-30

-22

-24.4

-12

10.4

-73.3

-100

-148

-33.9

-29

-20.2

-23.9

-11

12.2

-67.8

-90

-130

-33.3

-28

-18.4

-23.3

-10

14

-62.2

-80

-112

-32.2

-26

-14.8

-22.8

-9

15.8

-56.7

-70

-94

-31.7

-25

-13

-22.2

-8

17.6

-51.1

-60

-76

-31.1

-24

-11.2

-21.7

-7

19.4

-45.6

-50

-58

-30.6

-23

-9.4

21.1

-6

21.2

-40

-40

-40

-30

-22

-7.6

-20.6

-5

23

-39.4

-39

-38.2

-29.4

-21

-5.8

-20

-4

24.8

-38.9

-38

-36.4

-28.9

-20

-4

-19.4

-3

26.6

-38.3

-37

-34.6

-28.3

-19

-2.2

-18.9

-2

28.4

-37.8

-36

-32.8

-27.8

-18

0.4

-18.3

-1

30.2

-37.2

-35

-31

-27.2

-17

1.4

-17.8

0

32

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment) Table A-1 (cont.) Temperature Conversion Chart °C

°F

Temp.

°C

°F

Temp.

°C

Temp.

°F

-17.2

1

33.8

-2.8

27

80.6

11.7

53

127.4

-16.7

2

35.6

-2.2

28

82.4

12.2

54

129.2

-16.1

3

37.4

-1.7

29

84.2

12.8

55

131

-15.6

4

39.2

-1.1

30

86

13.3

56

132.8

-15

5

41

-0.6

31

87.8

13.9

57

134.6

-14.4

6

42.8

0

32

89.6

14.4

58

136.4

-13.9

7

44.6

0.6

33

91.4

15

59

138.2

-13.3

8

46.4

1.1

34

93.2

15.6

60

140

-12.8

9

48.2

1.7

35

95

16.1

61

141.8

-12.2

10

50

2.2

36

96.8

16.7

62

143.6

-11.1

12

53.6

2.8

37

98.6

17.2

63

145.4

-10.6

13

55.4

3.3

38

100.4

17.8

64

147.2

-10

14

57.2

3.9

39

102.2

18.3

65

149

-9.4

15

59

4.4

40

104

18.9

66

150.8

-8.9

16

60.8

5

41

105.8

19.4

67

152.6

-8.3

17

62.6

5.6

42

107.6

20

68

154.4

-7.8

18

64.4

6.1

43

109.4

20.6

69

156.2

-7.5

19

66.2

6.7

44

111.2

21.1

70

158

-6.7

20

68

7.2

45

113

21.7

71

159.8

-6.1

21

69.8

7.8

46

114.8

22.2

72

161.6

-5.6

22

71.6

8.3

47

116.6

22.8

73

163.4

-5.0

23

73.4

8.9

48

118.4

23.3

74

165.2

-4.4

24

75.2

10

50

122

23.9

75

167

-3.9

25

77

10.6

51

123.8

24.4

76

168.8

-3.3

26

78.8

11.1

52

125.6

25

77

170.6

A-5

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment) Table A-1 (cont.) Temperature Conversion Chart °C

Temp.

°C

Temp.

°F

°C

Temp.

°F

25.6

78

172.4

54.4

130

266

193

380

716

26.1

79

174.2

60

140

284

199

390

734

26.7

80

176

65.6

150

302

204

400

752

27.2

81

177.8

71.1

160

320

210

410

770

27.8

82

179.6

76.7

170

338

216

420

788

28.3

83

181.4

82.2

180

356

221

430

806

28.9

84

183.2

87.8

190

374

227

440

824

29.4

85

185

93.3

200

392

232

450

842

30

86

186.8

98.9

210

410

238

460

860

30.6

87

188.6

104

220

428

243

470

878

31.1

88

190.4

110

230

446

249

480

896

31.7

89

192.2

116

240

464

254

490

914

32.2

90

194

121

250

482

260

500

932

32.8

91

195.8

127

260

500

288

550

1022

33.3

92

197.6

132

270

518

316

600

1112

33.9

93

199.4

138

280

536

343

650

1202

34.4

94

201.2

143

290

554

370

700

1292

35

95

203

149

300

572

399

750

1382

35.6

96

204.8

154

310

590

427

800

1472

36.1

97

206.6

160

320

608

454

850

1562

36.7

98

208.4

166

330

626

482

900

1652

37.2

99

210.2

171

340

644

510

950

1742

37.8

100

212

177

350

662

538

1000

1832

43.3

110

230

182

360

680

566

1050

1922

48.9

120

248

188

370

698

593

1110

2012

621

1150

2102

843

1550

2822

1066

1950

3542

649

1200

2192

871

1600

2912

1093

2000

3632

677

1250

2282

899

1650

3002

1149

2100

3812

704

1300

2372

927

1700

3092

1204

2200

3992

732

1350

2462

954

1750

3182

1260

2300

4172

760

1400

2552

982

1800

3272

1316

2400

4352

788

1450

2642

1010

1850

3362

1371

2500

4532

816

1500

2732

1038

1900

3452

Conversion Factors °C = (°F - 32) x 5/9 °F = (°C x 9/5) + 32

A-6

°F

0 Kelvin = -273.16°C 0 Rankine = -459.69°F

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

A.2.3 The Three Modes of Heat Transfer There are three modes of heat transfer: conduction, convection, and radiation. All heat transfer processes occur by one or more of these three modes. Infrared thermography is based on the measurement of radiative heat flow and is, therefore, most closely related to the radiation mode of heat transfer. A.2.4 Conduction Conduction is the transfer of heat in stationary media. It is the only mode of heat flow in solids, but can also take place in liquids and gases. It occurs as the result of molecular collisions (in liquids) and atomic vibrations (in solids), whereby energy is moved one molecule at a time, from higher temperature sites to lower temperature sites. Figure A-1 is an illustration of conductive heat flow. The Fourier conduction law expresses the conductive heat flow through the slab shown in Figure A-1.

Figure A-1 Conductive Heat Flow

The Fourier Conduction Law: Q = K (T1 - T2) A L

where: Q/A = the rate of heat transfer through the slab per unit area perpendicular to the flow A-7

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

L

= the thickness of the slab

T1

= the higher temperature (at the left)

T2

= the lower temperature (at the right)

K

= the thermal conductivity of the slab material

Thermal conductivity is analogous to electrical conductivity and is inversely proportional to thermal resistance, as shown in the lower portion of Figure A-1. The temperatures, T1 and T2, are analogous to voltages V1 and V2, and the heat flow, Q/A, is analogous to electrical current, I, so that: if:

R electrical = V1 - V2 I

then:

R thermal = T1 - T2 = L Q /A K

Heat flow is usually expressed in English units. K is expressed in BTU/hr-ft²-°F and thermal resistance would then be expressed in °F-hr-ft²/BTU. A.2.5 Convection Convective heat transfer takes place in a moving medium and is almost always associated with transfer between a solid and a moving fluid (such as air). Forced convection takes place when an external driving force, such as wind or an air pump, moves the fluid. Free convection takes place when the temperature difference necessary for heat transfer produces density changes in the fluid and the warmer fluid rises as a result of increased buoyancy. In convective heat flow, heat transfer takes effect by means of two mechanisms, the direct conduction through the fluid and the motion of the fluid itself. Figure A-2 illustrates convective heat transfer between a flat plate and a moving fluid. The presence of the plate causes the velocity of the fluid to decrease to zero at the surface and influences its velocity throughout the thickness of a boundary layer. The thickness of the boundary layer depends on the free velocity, V∞, of the fluid. It is greater for free convection and smaller for forced convection. The rate of heat flow depends on the thickness of the convection layer, as well as the temperature difference between Ts and T∞ (Ts is the surface temperature, T∞ is the free field fluid temperature outside of the boundary layer.) Newton’s cooling law defines the convective heat transfer coefficient: h = Q /A (Ts- T∞)

A-8

(h is expressed in BTU/hr-ft²-°F)

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

rearranged: Q /A = (Ts- T∞)

Rc where: Rc = 1/h and is the resistance to convective heat flow

Rc is also analogous to electrical resistance and is easier to use when determining combined conductive and convective heat transfer.

Figure A-2 Convective Heat Flow

A.2.6 Radiation Radiative heat transfer is unlike the other two modes in several respects: •

It can take place in a vacuum.

•

It occurs by electromagnetic emission and absorption.

•

It occurs at the speed of light.

•

The energy transferred is proportional to the fourth power of the temperature difference between the objects.

The electromagnetic spectrum is illustrated in Figure A-3. Radiative heat transfer takes place in the infrared portion of the spectrum, between 0.75 µm and about 100 µm, although most A-9

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

practical measurements can be made out to 20 µm. (µ or µm stands for micrometers or microns. A micron is one-millionth of a meter and is the measurement unit for radiant energy wavelength.)

Figure A-3 Infrared in the Electromagnetic Spectrum

A.2.7 Radiation Exchange at the Target Surface The measurement of thermal infrared radiation is the basis for non-contact temperature measurement and thermal imaging (or thermography). The process of thermal infrared radiation leaving a surface is called exitance or radiosity. It can be emitted from the surface, reflected off of the surface, or transmitted through the surface. This is illustrated in Figure A-4. The total radiosity is equal to the sum of the emitted component (E), the reflected component (R), and the transmitted component (T). The surface temperature is related to E, the emitted component only.

A-10

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Figure A-4 Radiative Heat Flow

Thermal infrared radiation impinging on a surface can be absorbed, reflected, or transmitted as illustrated in Figure A-5. Kirchhoff's law states that the sum of the three components is always equal to the received radiation (the percentage sum of the three components equals unity): A (absorptivity) + R (reflectivity) + T (transmissivity) = 1 When making practical measurements, the specularity or diffusivity of a target surface is taken into effect by accounting for the emissivity of the surface. Emissivity is discussed as part of the detailed discussion of the characteristics of infrared thermal radiation in section A.3.

A-11

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Figure A-5 Radiation Exchange at the Target Surface

A.2.8 Specular and Diffuse Surfaces It should be noted that the roughness or structure of a surface will determine the type and direction of reflection of incident radiation. A smooth surface will reflect incident energy at an angle complementary to the angle of incidence. This is called a specular reflector. A rough or structured surface will scatter or disperse some of the incident radiation. This is a diffuse reflector. No perfectly specular or perfectly diffuse surface can exist in nature. All real surfaces have some diffusivity and some specularity. A.2.9 Transient Heat Exchange The discussions of the three types of heat exchange in sections A.2.4, A.2.5, and A.2.6 deal with steady-state heat exchange for reasons of simplicity and easier understanding. Two fixed temperatures are assumed to exist at the two points between which the heat flows. In many applications, however, temperatures are in transition, so that the values shown for energy radiated from a target surface are the instantaneous values from the moment that measurements are made. There are numerous instances where existing transient thermal conditions are exploited in order to use thermography to reveal material or structural characteristics in test articles. The thermogram of the outside surface of an insulated vessel carrying heated liquid, for example, should be relatively isothermal and somewhat warmer than the ambient air. Insulation voids or defects will cause warm anomalies to appear on the thermogram, allowing the A-12

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

thermographer to pinpoint areas of defective or damaged insulation. Here a passive approach can be taken because the transient heat flow from the liquid through the insulation to the outside air produces the desired characteristic thermal pattern on the product surface. Similarly, watersaturated areas on flat roofs will retain solar heat well into the night; long after the dry sections have radiated their stored heat to the cold night sky, the saturated sections will continue to radiate and exhibit distinct anomalies to the thermographer. When there is no heat flow through the material or the test article to be evaluated, an active, or thermal injection, approach is used to generate a transient heat flow. This approach requires the generation of a controlled flow of thermal energy across the laminar structure of the sample material under test, thermography monitoring of one of the surfaces (or sometimes both) of the sample, and a search for anomalies in the thermal patterns that will indicate a defect in accordance with established accept-reject criteria. This approach has been used extensively and successfully by the aerospace community in the evaluation of composite structures for impurities, flaws, voids, disbonds, delaminations, and variations in structural integrity. Most recently, time-based heat injection methods have been applied successfully to measure the depth of voids, as well as their location. This is effective because thinner sections of a given material will heat more rapidly than thicker sections.

A.3

The Basic Physics of Infrared Radiation and Sensing

All targets radiate energy in the infrared spectrum. The hotter the target, the more energy is radiated. Very hot targets radiate in the visible as well, and our eyes can see this because they are sensitive to light. The sun for example, at about 6000 K, appears to glow white-hot; a tungsten filament, at about 3000 K, has a yellowish glow, and an electric stove element, at 800 K, glows red. As the stove element cools, it loses its visible glow but it continues to radiate. We can feel it with a hand placed near the surface but we can't see the glow because the energy has shifted from red to infrared. Infrared detectors can sense infrared radiant energy and produce useful electrical signals proportional to the temperature of target surfaces. Instruments that use infrared detectors and optics to gather and focus energy from the targets onto these detectors are capable of measuring target surface temperatures with sensitivities better than 0.1°C, and with response times as fast as microseconds. Instruments that combine this measurement capability with capabilities for scanning the target surface are called infrared thermal imagers. They can produce thermal maps or thermograms where the brightness intensity or color hue of any spot on the map is representative of the temperature of the surface at that point. In most cases, thermal imagers can be considered as extensions of radiation thermometers or as a radiation thermometer with scanning capability. The performance parameters of thermal imagers are extensions of the performance parameters of radiation thermometers.

A-13

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A.3.1 Some Historical Background The color of a glowing metal is a fair indication of its temperature (the higher the temperature, the whiter the color). The ancient sword-maker and blacksmith knew from the color of a heated part when it was time to quench and temper. This technique is still in use today; precision optical matching pyrometers are used to match the brightness in color of a product with that of a glowing filament. The brightness of the filament is controlled by adjusting a knob that is calibrated in temperature. The next logical step is to substitute a photomultiplier for the operator's eye and, thus, calibrate the measurement. Finally, a differential measurement is made between what the brightness of the product is and what it should be (the set point), and the differential signal is injected into the process and used to drive the product temperature to the set point. With the advent of modern infrared detectors, the precision measurement of thermal energy radiating from surfaces that do not glow became possible. Measurements of cool surfaces, well below 0°C, are accomplished routinely with even the least expensive of infrared sensors. A.3.2 Non-Contact Thermal Measurements Infrared non-contact thermal sensing instruments are classified as infrared radiation thermometers by the American Society of Testing and Materials (ASTM), even though they don't always read out in temperatures [12]. The laws of physics allow for the conversion of infrared radiation measurements to temperature measurements. This is done by first measuring the self-emitted radiation in the infrared portion of the electromagnetic spectrum of target surfaces, and then converting these measurements to electrical signals. In making these measurements, three sets of characteristics need to be considered: •

The target surface

•

The transmitting medium between the target and the instrument

•

The measuring instrument

A.3.3 The Target Surface The chart of the electromagnetic spectrum (Figure A-3) indicates that the infrared portion of the spectrum lies adjacent to the visible. Every target surface above absolute zero (0 Kelvins or -273° Centigrade) radiates energy in the infrared. The hotter the target, the more radiant energy is emitted. When targets are hot enough, they radiate or glow in the visible part of the spectrum as well. As they cool, the eye becomes no longer able to see the emitted radiation and the targets appear to not glow at all. Infrared sensors are employed here to measure the radiation in the infrared, which can be related to target surface temperature. The visible spectrum extends from energy wavelengths of 0.4 µm for violet light to about 0.75 µm for red light. (µ or µm stands for micrometers or microns. A micron is one-millionth of a meter and is the measurement unit for radiant energy wavelength.) For practical purposes of temperature measurement, the infrared spectrum extends from 0.75 µm to about 20 µm. A-14

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Figure A-6 shows the distribution of emitted energy over the electromagnetic spectrum of targets at various temperatures. The sun, at 6000 K, appears white hot because its emitted energy is centered over the visible spectrum with a peak at 0.5 µm. Other targets, such as a tungsten filament at 3000 K, a red-hot surface at 800 K, and the ambient earth at 300 K (about 30°C), are also shown in this illustration. It becomes apparent that, as surfaces cool, not only do they emit less energy, but the wavelength distribution shifts to longer infrared wavelengths. Even though the eye becomes no longer capable of sensing this energy, infrared sensors can detect these invisible longer wavelengths. They enable us to measure the self-emitted radiant energy from even very cold targets and, thereby, determine the temperatures of target surfaces remotely and without contact.

A-15

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Figure A-6 Blackbody Curves at Various Temperatures

A-16

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Two physical laws define the radiant behavior illustrated in Figure A-6: The Stephan-Boltzmann Law (1): W = ξδT4 and Wien's Displacement Law (2): λm = b/T where: W = Radiant flux emitted per unit are a (watts/cm²) ξ = Emissivity (unity for a blackbody target) δ = Stephan-Boltzmann constant = 5.673 x10-12 watts cm-2 T = Absolute temperature of target (K) λm = Wavelength of maximum radiation (µm) b = Wien's displacement constant = 2897 (µm - K) According to (1), the radiant energy emitted from the target surface (W) equals two constants multiplied by the fourth power of the absolute temperature (T) of the target. The instrument measures W and calculates T. One of the two constants, δ, is a fixed number. Emissivity (ξ) is the other constant and is a surface characteristic that is only constant for a given material over a given range of temperatures. For point measurements, one can usually estimate the emissivity setting needed to dial into the instrument from available tables and charts. One can also learn, experimentally, the proper setting needed to make the instrument produce the correct temperature reading by using samples of the actual target material. This more practical setting value is called effective emissivity (e*). According to (2), the wavelength at which a target radiates its peak energy is defined as simply a constant (b = 2897 ≅ 3000) divided by the target temperature (T) in Kelvins. For the 300 K ambient earth, for example, the peak wavelength would be ≅ 300/3000 or ≅ 10 µm. This quick calculation is important in selecting the proper instrument for a measurement task, as will be discussed in section A.4. Target surfaces can be classified in three categories: black bodies, gray bodies, and non-gray bodies. The targets shown in Figure A-6 are all blackbody radiators (or black bodies). A blackbody radiator is a theoretical surface having unity emissivity at all wavelengths and absorbing all of the energy available at its surface. This would be an ideal target to measure because the temperature calculation within the instrument would be simply mechanized and always constant. Fortunately, although blackbody radiators do not exist in practice, the surfaces of most solids are gray bodies, that is, surfaces whose emissivities are high and fairly constant with wavelength. A-17

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Figure A-7 shows the comparative spectral distribution of energy emitted by a blackbody, a gray body, and a non-gray body (also called a spectral body), all at the same temperature. For gray body measurements, a simple emissivity correction can usually be dialed in when absolute measurements are required. For non-gray bodies, the solutions are more difficult. To understand the reason for this, it is necessary to see what an instrument sees when it is aimed at a non-gray target surface.

Figure A-7 Spectral Distribution of a Blackbody, a Gray Body, and a Non-Gray Body

Figure A-8 shows that the instrument sees three components of energy: first, emitted energy (e); second, reflected energy from the environment (R); and third, energy transmitted through the target from sources behind the target (T). The percentage sum of these components is always unity. The instrument sees only e, the emitted energy, when aimed at a blackbody target because a blackbody reflects and transmits nothing. For a gray body, the instrument sees e and R, the emitted and reflected energy. The instrument sees all three components when aimed at a nongray body because a non-gray body is partially transparent.

A-18

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

Figure A-8 Components of Energy Reaching the Measuring Instrument

If the emissivity of a gray body is very low, as in the case of polished metal surfaces, the reflectance becomes high (reflectance = 1 minus emissivity) and can generate erroneous readings if not properly handled. Reflected energy from a specific source can generally be redirected by proper orientation of the instrument with respect to the target surface, as shown in Figure A-9. This illustrates the proper and improper orientation that is necessary to avoid reflected energy from a specific source.

Figure A-9 Aiming the Instrument to Avoid Point Source Reflections

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Under certain conditions, an error in temperature indication can occur as the result of a high temperature background, such as a boiler wall (behind the instrument), reflecting off of a reflective target surface and contributing to the apparent temperature of the target. Most instrument manufacturers provide a background temperature correction to compensate for this condition. Often, in practice, the troublesome component is T, the energy transmitted through a non-gray target from sources behind the target. A discussion of solutions to this type of problem is included in section A.4. A.3.4 The Transmitting Medium The transmission characteristics of the medium in the measurement path between the target and the instrument need to be considered in making non-contact thermal measurements. No loss of energy is encountered when measuring through a vacuum. For short path lengths, a few feet for example, most gases including the atmosphere, absorb very little energy and can be ignored (except where measurements of precision temperature values are required). As the path length increases to hundreds of feet, or as the air becomes heavy with water vapor, the absorption might become a factor. It is then necessary to consider the infrared transmission characteristics of the atmosphere. Figure A-10 illustrates the spectral transmission characteristics of 0.3 km of ground level atmosphere. Two spectral intervals can be seen to have very high transmission. These are known as the 1–5 µm and the 8–14 µm atmospheric windows, and almost all infrared sensing and scanning instruments are designed to operate in one or the other of these windows. Usually, the difficulties encountered with transmitting media occur when the target is viewed by the instrument through another solid object such as a glass or quartz viewing port in a process.

Figure A-10 Infrared Transmission of 0.3 km of Sea Level Atmosphere

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Figure A-11 shows transmission curves for various samples of glass and quartz. Upon seeing these, our first impression is that glass is opaque at 10 µm where ambient (30°C) surfaces radiate their peak energy. This impression is correct and, although in theory, infrared measurements can be made of 30°C targets through glass, it is hardly practical. The first approach to the problem is to attempt to eliminate the glass, or at least a portion of it, through which the instrument can be aimed at the target. If, for reasons of hazard, vacuum, or product safety, a window must be present; a material that transmits in the longer wavelengths might be substituted.

Figure A-11 Infrared Spectral Transmission of Glass

Figure A-12 shows the spectral transmission characteristics of several of these materials, many of which transmit energy past 10 µm. These materials are often used as lenses and optical elements in low-temperature infrared sensors. Of course, as targets become hotter and the emitted energy shifts to the shorter wavelengths, glass and quartz windows pose less of a problem and are even used as elements and lenses in high-temperature sensing instruments.

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Figure A-12 Characteristics of IR Transmitting Materials

The characteristics of the window material will always have some effect on the temperature measurement, but the attenuation can always be corrected by pre-calibrating the instrument with a sample window placed between the instrument and a target of known temperature. In closing the discussion of the transmitting medium, it is important to note that infrared sensors can only work when all of the following spectral ranges coincide or overlap:

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The spectral range over which the target emits

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The spectral range over which the medium transmits

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The spectral range over which the instrument operates

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A.3.5 The Measuring Instrument Figure A-13 shows the necessary components of an infrared radiation thermometer. Collecting optics (an infrared lens, for example) is necessary in order to focus the energy emitted by the target onto the sensitive surface of an infrared detector, which, in turn, converts this energy into an electrical signal.

Figure A-13 Components of an Infrared Radiation Thermometer

When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, it collects energy within a collecting beam, the shape of which is determined by the configuration of the optics and the detector. The cross-section of this collecting beam is called the field of view of the instrument, and it determines the size of the area (spot size) on the target surface that is measured by the instrument. On thermal imaging instruments, this is called the instantaneous field of view (IFOV) and becomes one picture element on the thermogram. Infrared optics are available in two general configurations, refractive and reflective. Refractive optics (lenses), which are at least partly transparent to the wavelengths of interest, are used most often for high-temperature applications where their throughput losses can be ignored. Reflective optics (mirrors), which are more efficient but somewhat complicate the optical path, are used more often for low-temperature applications, where the energy levels cannot warrant throughput energy losses. An infrared interference filter is often placed in front of the detector to limit the spectral region or band of the energy reaching the detector. The reasons for spectral selectivity will be discussed later in this section. The processing electronics unit amplifies and conditions the signal from the infrared detector and introduces corrections for such factors as detector ambient temperature drift and target surface emissivity. Generally, a meter indicates the target temperature and an analog output is provided. The analog signal is used to record, display, alarm, control, correct, or any combination of these. Figure A-14 illustrates the configuration of a typical instrument employing all of the elements outlined. The germanium lens collects the energy from a spot on the target surface and focuses it A-23

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on the surface of the radiation thermopile detector. The 8–14 µm filter limits the spectral band of the energy reaching the detector so that it falls within the atmospheric window. The detector generates a dc emf proportional to the energy emitted by the target surface. The auto-zero amplifier senses ambient temperature changes and prevents ambient drift errors. The output electronics unit conditions the signal and computes the target surface temperature based on a manual emissivity setting. The analog output terminals accept a 15–30 VDC loop supply and generate a 4–20 milliampere signal, proportional to target surface temperature. All infrared detector-transducers exhibit some electrical change in response to the radiant energy impinging on their sensitive surfaces. Depending on the type of detector this can be an impedance change, a capacitance change, the generation of an emf (voltage), or the release of photons. Detectors are available with response times as fast as nanoseconds or as slow as fractions of seconds. Depending on the requirement, either a broadband detector or a spectrally limited detector can be selected.

Figure A-14 Typical Infrared Radiation Thermometer Schematic

Infrared detectors fall into two broad categories: thermal detectors, which have broad, uniform spectral responses, somewhat lower sensitivities, and slower response times (on the order of milliseconds), and photodetectors, (or photon detectors), which have limited spectral responses, higher peak sensitivities, and faster response times (on the order of microseconds). Thermal detectors will generally operate at or near room temperature, while photodetectors are generally cooled to optimize performance. The mercury-cadmium-telluride (HgCdTe) detector, for example, is a photodetector cooled to 77 K for 8–14 µm operation and to 195 K for 3–5 µm operation. Because of its fast response, this detector is used extensively in high-speed scanning and imaging applications. The radiation thermopile, on the other hand, is a broadband thermal detector operating uncooled. It is used extensively for spot measurements of cool targets. It generates a dc emf proportional to the radiant energy reaching its surface and is ideal for use in portable, battery-powered instruments. Figure A-15 illustrates the spectral responses of various infrared detectors.

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Figure A-15 Spectral Sensitivity of Various Infrared Detectors

Point-sensing instruments for measuring very hot targets, usually operate in shorter wavelengths (0.9–1.1 µm, for example), and instruments for measuring cooler targets usually operate in longer wavelengths (3–5 µm or 8–14 µm, for example). Most infrared thermal imagers operate in either the 3–5 µm or 8–14 µm spectral region. A.3.6 Introduction to Thermal Scanning and Imaging Instruments When problems in temperature monitoring and control cannot be solved by the measurement of one or several discrete points on a target surface, it becomes necessary to spatially scan (that is, to move the collecting beam (field of view) of the instrument relative to the target). This can be accomplished by inserting a movable optical element into the collecting beam, or by employing a multi-detector array or mosaic, and scanning the array electronically. A brief overview of scanning and imaging instruments follows. A more detailed overview can be found in section 2. A.3.6.1

Line Scanning

The purpose of spatial scanning is to derive information concerning the distribution of radiant energy over a target scene. Quite often, a single straight line scanned on the target is all that is necessary to locate a critical thermal anomaly. The instantaneous position of the scanning A-25

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element (or the position of the element in the linear array) is controlled or sensed, so that the radiometric output signal can be accompanied by a position signal output and be displayed on a chart recorder, an oscilloscope, or some other recording device. A typical high-speed commercial line scanner develops a high-resolution thermal map by scanning normal to the motion of a moving target, such as a paper web or a strip steel process. The resulting output is a thermal strip map of the process as it moves normal to the scan line (as illustrated in Figure A-16). The output signal information is in real-time computer compatible format and can be used to monitor, control or predict the behavior of the target.

Figure A-16 Scanning Configuration of an Infrared Line Scanner

A.3.6.2

Two-Dimensional Scanning

The purpose of spatial scanning is to derive information concerning the distribution of infrared radiant energy over a target scene. Scanning can be accomplished either opto-mechanically or electronically. Opto-mechanical scanning can be done by moving the target with the instrument fixed, or by moving (translating or panning) the instrument, but it is more practically accomplished by inserting movable optical elements into the collected beam. Although an almost infinite variety of scanning patterns can be generated using two moving elements, the most common pattern is rectilinear, and this is most often accomplished by two elements, each scanning a line normal to the other. A typical rectilinear scanner employs two rotating prisms behind the primary lens A-26

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system (refractive scanning). An alternate configuration uses two oscillating mirrors behind the primary lens (reflective scanning). This is also commonly used in commercial scanners, as are combinations of reflective and refractive scanning elements. Now, electronically scanned thermal imaging is accomplished by means of an infrared focal plane array (IRFPA), whereby a two-dimensional staring array of detectors collects radiant energy from the target and is digitally scanned to produce the thermogram. In the case of the line scanner (Figure A-16), the opto-mechanical scanning approach is gradually being superceded by replacement of the single-element detector with an electronically scanned linear focal plane array (a line of detectors), thus eliminating the scanning mechanism entirely. At the time of this writing, focal plane array imagers have all but completely replaced optomechanically scanned imagers in manufacturers’ inventory and product literature. Because many opto-mechanically scanned line scanners and imagers are still in use throughout the predictive maintenance community, the following discussion is included in this appendix. A typical commercial rectilinear opto-mechanical scanner is shown schematically in Figure A-17. It employs two oscillating mirrors (reflective scanning) behind the primary lens and is commonly used in commercially available scanners. This approach has the advantage of a broad spectral response limited only by the spectral characteristics of the detector and the primary lens system. The main disadvantage is that the elements and their associated drive mechanisms must be arranged so that there is no optical or mechanical interference. This makes compact design more difficult. An alternate approach to scanning employs two rotating prisms behind the primary lens system. This instrument, using refractive scanning elements, has the advantage of compact design, because all of the scanning elements can be arranged in a line. It has the disadvantage of spectral limitation in that each element must transmit the entire portion of the infrared spectrum for which the instrument was designed. Some energy is absorbed by each refractive element, reducing the throughput somewhat, and the rather high cost of infrared transmitting materials add to the instrument cost. It should be pointed out that opto-mechanical scanners can employ refractive or reflective scanning elements or even combinations of both elements.

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Figure A-17 Schematic of a Typical Opto-Mechanically Scanned Imager

Electronic scanning involves no mechanical scanning elements—the surface is scanned electronically. The earliest type of electronically scanned thermal imager is the pyrovidicon. Pyrovidicon thermal imagers (pyroelectric vidicons) or thermal video systems are devices in which charge proportional to target temperature is collected on a single pyroelectric detector surface within an electronic picture tube, and scanning is accomplished by an electronic scanning beam. The pyrovidicon is a video camera tube that operates in the infrared (2–14 µm) region instead of in the visible spectrum. Electronically scanned thermal imaging systems based on pyrovidicons and operating in the 8–14 µm atmospheric window are in common use today. They provide qualitative thermal images and are classified as thermal viewers. Focal plane array (FPA) imagers have, over the last decade, become the imagers of choice over opto-mechanically scanned imagers, replacing them in virtually all commercial applications. Manufacturers of FPA imagers offer a wide choice of both cooled and uncooled detector arrays, with a wide selection of spectral ranges for both measuring (quantitative) and non-measuring (qualitative) applications. A more detailed discussion of focal plane array imagers can be found in Section 2. Published performance characteristics of currently available infrared commercial thermal imaging systems, including detailed discussions of diagnostic software and image recording methods, can also be found in Section 2, Table 2-1. A-28

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Figure A-18 is a schematic of a typical focal plane array based thermal imager.

Figure A-18 Schematic of a Typical FPA-Based Thermal Imager

A.4

Performance Parameters of Thermal-Sensing Instruments

To select an instrument suitable to a particular application, the thermographer needs to understand how to determine and specify its required performance. This section provides information regarding the performance parameters of point-sensing instruments and scanning and imaging instruments. A.4.1 Point-Sensing Instruments For point-sensing instruments (infrared radiation thermometers), the following performance parameters should be considered:

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Temperature range: The high and low limits over which the target temperature can vary

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Absolute accuracy: As related to the National Institute of Standards and Technology (NIST) standard

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Repeatability: How faithfully a reading is repeated for the same target

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Temperature sensitivity: The smallest target temperature change that the instrument needs to detect

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Speed of response: How fast the instrument responds to a temperature change at the target surface

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Target spot size and working distance: The size of the spot on the target to be measured, and its distance from the instrument

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Output requirements: How the output signal is to be used

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Spectral range: The portion of the infrared spectrum over which the instrument will operate

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Temperature range and absolute accuracy will always be interrelated; for example, the instrument might be expected to measure a range of temperatures from 0 to 200°C with an absolute accuracy ± 2°C over the entire range. This could alternately be specified as ± 1% absolute accuracy over full scale. On the other hand, we might require the best accuracy at some specific temperature, say 100°C. In this case, the manufacturer should be so informed. The instrument can then be calibrated to exactly match the manufacturer's laboratory calibration standard at that temperature. It is difficult for a manufacturer to comply with a tight specification for absolute accuracy because absolute accuracy is based on traceability to the National Institute of Standards and Technology (NIST) standard. An absolute accuracy of ±0.5°C ± 1% of full scale is about as tight as can be reasonably specified. Repeatability, on the other hand, can be more easily assured by the manufacturer, and is usually more important to the user. Temperature sensitivity is also called thermal resolution or noise equivalent temperature difference. It is the smallest temperature change at the target surface that must be clearly sensed at the output of the instrument. This is almost always closely associated with the cost of the instrument, so unnecessarily fine temperature sensitivity should not be specified. An important rule to remember is that, for any given instrument, target sensitivity will improve for hotter targets where there is more energy available for the instrument to measure. We should specify temperature sensitivity, therefore, at a particular target temperature, and this should be near the low end of the range of interest. We might, for example, specify temperature sensitivity to be 0.25°C at a target temperature of 25°C, and be confident that the sensitivity of the instrument will be at least that for targets hotter than 25°C. Speed of response is generally defined as the time it takes the instrument output to respond to 95% of a step change at the target surface. Figure A-19 shows this graphically. Note that the sensor time constant is defined by convention to be the time required to reach 63% of a step change at the target surface. Instrument speed of response is about 5 time constants, and is generally limited by the detector used. As previously discussed, this limit is on the order of microseconds for photodetectors and milliseconds for thermal detectors. There is, however, a tradeoff between speed of response and temperature sensitivity. As in all instrumentation systems, as the speed of response becomes faster (wider information bandwidth), the sensitivity becomes poorer (lower signal-to-noise ratio). We learn from this that the speed of response should not be over-specified.

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Figure A-19 Instrument Speed of Response and Time Constant

Target spot size (also called spatial resolution) and working distance can be specified as just that (1 cm at 1 meter, for example), or we can put it in more general terms such as field of view angle (10 milliradians, 1 degree, 2 degrees) or a field of view (spot size-to -working distance) ratio (D/15, D/30, D/75). A D/15 ratio means that the instrument measures the emitted energy of a spot one-fifteenth the size of the working distance (3 cm at 45 cm, for example). Figure A-20 illustrates the fields of view for several instruments and how an instrument can be selected based on the spot size and working distance required. An examination of the collecting beams of the instruments shown also shows that, at very close working distances, this simple ratio does not always apply. If close-up information is not clearly provided in the product literature, the instrument manufacturer should be consulted. For quick reference, a method of approximating spot size based on manufacturer-provided information is illustrated in Appendix C, Plate 2.

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Figure A-20 Fields of View of Infrared Radiation Thermometers

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The output requirements are totally dependent on the user's needs. If a readout indicator is required, a wide selection is usually offered. An analog output suitable for recording, monitoring, and control is commonly provided. In addition, most manufacturers offer a broad selection of output functions including digital (BCD coded) outputs, high, low, and proportional set-points, signal peak or valley sensors, sample and hold circuits, and even closed-loop controls for specific applications. Many currently available instruments, even portable hand-held units, include microprocessors that provide many of the above functions on standard models. As previously noted, the operating spectral range of the instrument is often critical to its performance. For cooler targets, up to about 500°C, most manufacturers offer instruments operating in the 8–14 µm atmospheric window. For hotter targets, shorter operating wavelengths are selected, usually shorter than 3 µm. One reason for choosing shorter wavelengths is that this enables manufacturers to use commonly available and less expensive quartz and glass optics, which have the added benefit of being visibly transparent for more convenient aiming and sighting. Another reason is that estimating effective emissivity incorrectly will result in smaller temperature errors when measurements are made at shorter wavelengths. A good general rule to follow, particularly when dealing with targets of low or uncertain effective emissivities, is to work at the shortest wavelengths possible without compromising sensitivity or risking susceptibility to reflections from visible energy sources. Spectrally selective instruments employ interference filters to allow only a very specific broad or narrow band of wavelengths to reach the detector. (A combination of a spectrally selective detector and a filter can also be used.) This can make the instrument highly selective to a specific material whose temperature is to be measured in the presence of an intervening medium or an interfering background. For example, for measuring the temperature of objects from 200°C to 1000°C inside a heating chamber with a glass port, or inside a glass bell jar, an instrument operating in the 1.5 to 2.5 µm band will see through the glass and make the measurement easily. A very important generic example of the need for spectral selectivity is in the measurement of plastics in the process of being formed into films and other configurations. Thin films of many plastics are virtually transparent to most infrared wavelengths but do emit at certain wavelengths. Polyethylene, polypropylene, and other related materials, for example, have a very strong, though narrow, absorption band at 3.45 µm. Polyethylene film is formed at about 200°C in the presence of heaters that are at about 700°C. Figure A-21 shows the transmission spectra of 1.5mil thick polyethylene film and the narrow absorption band at 3.45 µm. The instrument selected for measuring the surface of the film has a broadband thermal detector and a 3.45 µm spike band pass filter. The filter makes the instrument blind to all energy outside of 3.45 µm, and enables it to measure the temperature of the surface of the plastic film without seeing through the film to the heaters.

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Figure A-21 Spectral Filtering for Polyethylene Temperature Measurement

Figure A-22 shows a similar solution for 0.5-mil thick polyester (Mylar) film under about the same temperature conditions. Here, the strong polyester absorption band, from 7.7 to 8.2 µm, dictates the use of a 7.9 µm spike filter placed in front of the same broadband detector.

Figure A-22 Spectral Filtering for Polyester Temperature Measurement

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A.4.2 Scanners and Imagers—Qualitative and Quantitative The parameters used for assessing the performance of infrared thermal imaging scanners are complex and the methods used for testing performance have generated some controversy among manufacturers and users of these instruments. A thermal image is made up of a great number of discrete point measurements, however, many of the performance parameters of infrared thermal imagers are the same as those of radiation thermometers (point-sensing infrared radiometers that read out in temperature). Others derive from, or are extensions of, radiation thermometer performance parameters. Qualitative (non-measuring) thermal imagers, also called thermal viewers, differ from quantitative (measuring) thermal imagers, also called imaging radiometers, in that thermal viewers do not provide temperature or thermal energy measurements. It should be noted, therefore, that for users requiring qualitative rather than quantitative thermal images, many of the parameters discussed herein are of no importance. A.4.3 Performance Parameters of Imaging Radiometers The Environmental Research Institute, Michigan (ERIM) Infrared Handbook [13] provides an extensive table of terms and definitions (section 19.1.2) and a list of specimen specifications (section 19.4.1). The section of the Handbook covering infrared imaging systems does not, however, deal with the imager as a quantitative measurement instrument, and so the performance parameters related with temperature measurement need to be added. Some simplifications can be made, which result in some acceptable approximations. Bearing these qualifications in mind, the following definitions of the key performance parameters of infrared thermal scanners are offered:

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Total field of view (TFOV): the image size, in terms of scanning angle. (example: TFOV = 20°V x 30°H)

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Instantaneous field of view (IFOV): the angular projection of the detector element at the target plane; imaging spatial resolution. (example: IFOV= 2 milliradians )

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Measurement spatial resolution (IFOVmeas): the spatial resolution describing the minimum target spot size on which an accurate temperature measurement can be made. (example: IFOVmeas = 5 milliradians)

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Frame repetition rate: The number of times every point on the target is scanned in one second. (example: Frame rate = 30 /second)

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Minimum resolvable temperature (MRT): The smallest blackbody equivalent target temperature difference that can be observed; temperature sensitivity (example: MRT=0.1°C @ 30°C target temperature)

MRT and the terms relating to spatial resolution are interrelated and cannot be considered independently. Other parameters, such as spectral ranges, target temperature ranges, accuracy and repeatability, and focusing distances, are essentially the same as those defined previously for infrared radiation thermometers, although they can be expressed differently. Dynamic range and reference level range, for example, are the terms that define the target temperature ranges for A-35

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thermal imagers. While the operating spectral range of a radiation thermometer is often critical to its performance, the spectral range of operation of a thermal imager is not usually as critical to the user, except for a few specialized applications. Most commercial thermal imagers operate in either the 2–5 µm or the 8–12 µm atmospheric window, depending on the manufacturer's choice of detector. Filter wheels or slides are usually available to enable users to insert special interference filters and perform spectrally selective measurements when necessary. Despite some manufacturers' claims to the contrary, there is usually little difference in overall performance between an imager operating in the 2–5 µm band and an imager operating in the 8–12 µm band, all other parameters being equal. For a specific application, however, there might be a clear choice. One example of this would be selecting an imager operating in the 2 –5 µm band to observe a target through a quartz window. There would be no alternative because quartz is virtually opaque in the 8–12 µm region. Another example would be selecting an imager operating in the 8–12 µm band to observe a cool target through a long atmospheric path. The choice would be obvious because long-path atmospheric absorption is substantially greater in the 2–5 µm window than in the 8–12 µm window. For qualitative (non-measuring) thermal viewers, parameters relating to temperature range are only applicable in the broadest sense. Absolute accuracy and stability parameters are not applicable. MRT is applicable only as an approximation because stability cannot be assured. IFOVmeas is not applicable. Secondary features, such as field uniformity and spatial distortion, are design parameters and are assumed to be handled by responsible manufacturers. A discussion of the significant performance parameters (figures of merit) follows. A.4.3.1

Temperature Sensitivity, Minimum Resolvable Temperature Difference (MRTD) or Minimum Resolvable Temperature (MRT)

Temperature sensitivity, also called thermal resolution or noise equivalent temperature difference (NETD) for a radiation thermometer, is the smallest temperature change at the target surface and can be clearly sensed at the output of the instrument. For an imaging system, the MRT or MRTD defines temperature sensitivity but also implies spatial resolution (IFOV). MRTD is expressed as a function of angular spatial frequency. Testing for MRTD is usually accomplished by means of a subjective procedure developed by the Department of Defense community. This involves selecting the smallest (highest frequency) standard periodic test pattern (four bars, 7:1 length-to-width aspect ratio) that can be distinguished as a 4 bar contrast target by the observer, and recording the smallest detectable element-to-element temperature difference between two blackbody elements on this pattern. Unlimited viewing time and optimization of controls is allowed and the target is oriented with the bars normal to the horizontal scan line. Figure A-23 illustrates the setup using an ambient pattern and a heated background. The MRTD curve shown is a function of spatial frequency (cycles/mRad). Additional points on the curve are achieved by changing the pattern size or the distance to the scanner.

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Figure A-23 Test Setup for MRTD Measurement, MRTD Curve

A.4.3.2

Spot Size, Instantaneous Field of View (IFOV), Imaging Spatial Resolution, Measurement Spatial Resolution (IFOVmeas)

For thermal imagers, the instantaneous field of view (IFOV) expresses spatial resolution for imaging purposes but not for measurement purposes. Measurement instantaneous field of view (IFOVmeas) expresses spatial resolution for measurement purposes. The modulation transfer function (MTF) is a measure of imaging spatial resolution. Modulation is a measure of radiance contrast and is expressed: Modulation = Lmax- Lmin Lmax + Lmin

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Modulation transfer is the ratio of the modulation in the observed image to that in the actual object. For any system, MTF will vary with scan angle and background, and will often be different when measured along the horizontal than it is when measured along the vertical. For this reason, a methodology was established and accepted by manufacturers and users alike to measure the MTF of an imager and, thereby, to verify the spatial resolution for imaging (night vision) purposes. A sample procedure follows for a system where IFOV is specified at 2.0 milliradians. This is shown in Figure A-24 and uses the same setup as illustrated in Figure A-23: A standard 4 bar (slit) resolution target (7:1 aspect ratio) with a 2-mm slit width is placed in front of a heated blackbody reference surface at a distance of 1 meter from the primary optic of the instrument. The ratio of the 2-mm slit width to the 1-meter working distance is 2 milliradians). The target is centered in the scanned field (oriented so that the horizontal axis is normal to the slit), and a single line scan output signal is monitored. The analog signal value of the 4 peaks (Vmax), as the slits are scanned, and the analog signal value of the 3 valleys (Vmin), are recorded using the bar target surface ambient temperature as a base reference. The MTF is expressed as a ratio equal to (Vmax -Vmin) / (Vmax + Vmin). If this ratio is at least 0.35, the 2 milliradian IFOV is verified. There are some disagreements among users and manufacturers regarding the acceptable minimum value of MTF to verify imaging spatial resolution, with values varying between 0.35 and 0.5, depending on the manufacturer and the purpose of the instrument. For most users, a tested value of MTF, equal to or greater than 0.35 for a slit width representing a specified spatial resolution is generally considered sufficient to demonstrate that spatial resolution for imaging purposes.

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Figure A-24 Modulation Transfer Function, Imager Spatial Resolution

Both MRTD and MTF are functions of spatial frequency for any given system. This is illustrated in Figure A-25, reprinted from J.M. Lloyd, Thermal Imaging Systems [14], for a typical system rated by the manufacturer to be 1 milliradian. The cut-off frequency is where the IFOV equals 1 cycle (one bar and one slit) so that the intersection of the two curves at the half-cut-off frequency represents the actual performance of the system for an MRTD of 1°C. MTF is seen to be about 0.22 for this system.

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Figure A-25 MRTD and MTF for a System Rated at 1.0 Milliradian

For measurement purposes, of course the slit width should, ideally, be increased until the modulation reaches unity. For this reason the MTF method was found to be unsatisfactory for commercial thermal imagers where quantitative temperature measurement and control are often necessary. Another procedure, called the Slit Response Function (SRF), was developed for this purpose and is generally accepted for measuring IFOVmeas. In this method, illustrated in Figure A-26, a single variable slit is placed in front of a blackbody source and the slit width is varied until the resultant single-line-scan signal approaches the signal of the blackbody reference. Because there are other errors in the optics, the 100% level of SRF is approached rather slowly, as shown in the curve of Figure A-26. The slit width at which the SRF reaches 0.9, divided by the distance to the slit (W/d), is usually accepted as the IFOVmeas of the instrument under test. Figures A-23 and A-26 are adapted from the Ohman paper, “Measurement Versus Imaging in A-40

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Thermography” [15], which provides a detailed description of the Slit Response Method, setup diagrams, and a discussion of imaging and measurement spatial resolution figures of merit. The step-by-step procedure for measuring SRF is described in detail in Appendix C, Plate 6.

Figure A-26 Setup and Curves for Slit Response Function Test

Note: Because FPA imagers have all but replaced opto-mechanically scanned imagers, many experienced thermographers suggest that the SRF measurement procedure be performed in both the horizontal and vertical scan-line direction. The larger of the two results is then accepted as the IFOVmeas of the imager under test. A.4.3.3

Speed of Response and Frame Repetition Rate

Speed of response of a radiation thermometer is generally defined as the time it takes the instrument output to respond to 95% of a step change at the target surface (about 5 time constants). This parameter is not applicable to thermal imagers.

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Frame repetition rate is the measure of the data update of a thermal imager. This is not the same as field repetition rate. (Manufacturers might use fast field rates with not all of the picture elements included in any one scan, and then interlace the fields so that it takes multiple fields to complete a full frame. This might produce a more flicker-free image and be more pleasing to the eye than scanning full data frames at a slower rate. Frame repetition rate is the number of times per second every picture element is scanned. A.4.4 Thermal Imaging Software In order to optimize the effectiveness of thermography measurement programs, the thermographer needs a basic understanding of thermal image processing techniques. The following is a broad discussion of thermal image processing and diagnostics. A detailed description of thermal imaging and diagnostic software currently available from manufacturers is provided in section 2. Thermal imaging software can be categorized into the following groupings:

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Quantitative thermal measurements of targets

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Detailed processing and image diagnostics

•

Image recording, storage, and recovery

•

Image comparison

•

Archiving and database* *Although data and image database development is not an exclusive characteristic of thermal imaging software, it should be considered an important part of the thermographer's tool kit.

With the introduction of computer-assisted thermal image storage and processing, thermography has become a far more exact science, and the ability to perform image analysis and trend analysis has greatly expanded its reach. Innovative software has been tailored specifically for detailed image and thermal data analysis, and has been rapidly updated and expanded. Most software packages for thermography image analysis and diagnostics offer a number of standard features. These include spot temperature readout, multiple X and Y analog traces, monochrome and multiple-color scale selection, image shift, rotation and magnification, area analysis with histogram display, image averaging and filtering, and permanent disk storage and retrieval. Some of these capabilities are offered as part of the basic instrument and some are found in a diagnostics package offered separately. The newest field-portable instruments allow the thermographer to store images to disc (or data card) during field measurements, and perform detailed image analysis upon return to home base (see Section 2 for details). The ability to perform differential thermography is a most powerful feature of thermographic software routines. This is the capability for archiving thermal images of acceptable operating components, and assemblies and mechanisms, and using these stored images as models for

A-42

EPRI Licensed Material The Science of Thermography (Practical Application of Thermographic and Thermal Sensing Equipment)

comparison to subsequently inspected items. Subtractive routines produce differential images, illustrating the deviation of each pixel (picture element) from its corresponding model. Another powerful routine that was recently introduced is an emissivity determination and correction program, which produces true surface-temperature thermograms of microelectronic devices and other very small targets. To perform this function, the unpowered device is heated sequentially to two known low-level temperatures, and the stored thermal images are used to allow the computer to calculate emissivity of each pixel. The device is then powered and the image produced is corrected, point by point, for the emissivities previously computed. There is great interest in applying this spatial emissivity correction to larger targets such as circuit cards. The difficulty in developing a reliable emissivity matrix lies in achieving tight control over the temperature and temperature uniformity while heating a target of this size. For the professional thermographer, the maintenance of an historical database is most critical, and thermography software allows this to be done systematically. The historical data included with stored images (time, date, location, ambient conditions, distance to target, estimated effective emissivity, scanner serial number, and additional stored comments) serve as important inputs and subsequent backup for the written report. New software to aid the thermographer in the efficient and rapid preparation of professionallooking reports is also available from most manufacturers of thermal imagers (see Section 2).

A-43

EPRI Licensed Material

B

MEASURING EMISSIVITY, REFLECTANCE, AND TRANSMITTANCE

B.1

Introduction

An infrared radiometer measures the sum of the emitted (We), reflected (Wr), and transmitted (Wt) energies coming from the target of interest. Figure B-1 (repeated from Appendix A, Figure A-8) demonstrates this graphically. The sum of We + Wr + Wt is called Exitance or Radiosity. To determine the temperature of the target, the emitted energy must first be subtracted from the reflected and transmitted energies. This value must then be corrected to account for the emissivity of the target and to obtain a blackbody equivalent value. The blackbody equivalent value is then converted to temperature by referencing a calibration curve. All of the techniques discussed below for measuring emissivity, reflectance, and transmittance assume that the user has a thermal imager. Also note that the values for emissivity, reflectance, and transmittance are valid only for the spectral range of that instrument [16].

Figure B-1 Target Radiosity

B-1

EPRI Licensed Material Measuring Emissivity, Reflectance, and Transmittance

B.2

Measuring Emissivity

There are several common techniques for the measurement of emissivity using a single band radiometer, two of which are illustrated below. The first technique, known as the reference emitter technique, is accomplished by direct comparison with a known emitter at the same temperature. The second technique, known as the reflective emissivity technique, is accomplished by calculating emissivity indirectly using measured values of reflectance (and transmittance if applicable). The reference emitter technique works well when the target is at a different temperature than the background, such as in the case of a steam inlet valve whose body is at system operating temperature, while the applied emissivity reference is at the same temperature as the target. The reflective emissivity technique works well for smooth surfaces such as an electrical connection. The reflective emissivity technique is independent of target temperature, although the temperature of the target must remain constant throughout the measurement. A third, field-type method for estimating the effective emissivity of a specific target under specific conditions, is described in Section 3.3.3 and is illustrated in Appendix C, Plate 5. B.2.1 Reference Emitter Technique The reference emitter technique assumes both that the transmittance through the target is zero, and that a constant temperature difference between the target and the background is maintained. Ideally, this temperature difference, either hotter or colder, should be in the range of at least 15°F to 25°F. If the target is colder than the background, it should be above the dew point so that condensation on the surface of the target cannot occur. The reference emitter technique will only work if a reference emitter is applied to the surface of the target. Good reference emitters are foot-powder, dye check developer, or black electrician's tape, as previously discussed in sections 4.1.2 through 4.1.4. The procedure for determining the effective emissivity of a target using the reference emitter is as follows (refer to Figure B-2): 1. Apply the reference emitter (E) to a portion of the target (an area of at least one square inch is normally adequate). 2. Set the imager to measure isotherm units. 3. Measure the background thermal level (B) adjacent to the target. Do this by placing a piece of cardboard to which is applied a crumpled, flattened piece of aluminum foil. Take this measurement over a large area of the foil. (An area of at least one square foot is normally adequate.) 4. Measure the target thermal level (T). 5. Measure the reference emitter level (R). The reference emitter must be in thermal equilibrium with the target. This thermal equilibrium condition will be apparent when the reference emitter thermal level is not changing. (In the case of dye check developer, its application B-2

EPRI Licensed Material Measuring Emissivity, Reflectance, and Transmittance

cools the surface as the propellant evaporates. Wait at least 15 minutes after application unless the target is very warm.) 6. Calculate the emissivity by using the equation: Emissivity=(T-B)/(R-B) 7. Measure the emissivity several times. Determine the final value by taking an average of all measured emissivity values.

Figure B-2 Using the Reference Emitter Technique

B.2.2 Reflective Emissivity Technique The reflective emissivity technique involves measuring the reflectance of the target and subtracting it from 1.0 (emissivity = 1 minus target reflectance). The procedure for determining emissivity using the reflective emissivity technique works best when dealing with highly reflected or mirrored surfaces, such as mirror insulation, and when dealing with pipes or electrical contacts. Some of these surfaces naturally have a low emissivity. In this technique, the target should not be coated with a reference emitter and must be kept at a constant temperature. Also, once a range is chosen for measuring temperature, both measurements must be made on that range. This technique is temperature independent. The emissivity, using the reflective emissivity technique, is calculated from the ratio of the thermal level differences. The procedure for determining the reflective emissivity technique follows (refer to Figure B-3). Note: The temperatures of the two sources must be constant and with a substantial spread between them (15°F to 25°F). B-3

EPRI Licensed Material Measuring Emissivity, Reflectance, and Transmittance

1. Establish that the two sources are at different temperatures and are thermally stable. This can be adequately accomplished with a hand-held contact pyrometer. The exact temperature of each surface does not need to be known, only the ∆T. The ∆T, however, is limited by the temperature range of the imager. 2. Aim the imager at each source and measure the direct isotherm levels (Sa and Sb). 3. Reposition the imager so that the sources are reflected off the target. Measure the reflected isotherm levels (Ta and Tb). In most situations, this requires reflecting one source at a time (the exception is when they are reflected off a large uniform surface). 4. Calculate the target reflectance: Reflectance = (Ta-Tb) /(Sa-Sb) To ensure that the data is reliable, take the average of several of these measurements over several parts of the surface, particularly if the surface is non-uniform in appearance. The exception to this is when an imager, either directly or through software, allows an area to be defined and averaged.

Figure B-3 Using the Reflective Emissivity Technique

B-4

EPRI Licensed Material Measuring Emissivity, Reflectance, and Transmittance

B.2.3 Transmittance Measurement The transmittance of non-opaque targets is measured similar to the reflectance measurement technique. As shown in Figure B-4, two sources are again used. In this case, the target is placed directly in front of the two sources rather than reflected off of it. To calculate transmittance, substitute the reflected levels in the equation cited previously for reflectance (Section B.2.2) with the transmitted thermal levels.

Figure B-4 Using the Transmittance Technique (Measuring Transmittance)

B-5

EPRI Licensed Material Measuring Emissivity, Reflectance, and Transmittance

B.2.4 Generic Emissivity Values Table B-1 lists broadband, generic normal emissivity values for several common materials (repeated from Section 4, Table 4-1. These values should only be used as references until the user can compile a library of values based on actual measurements. Table B-1 Normal Emissivity Values of Common Materials Material

Emissivity

Aluminum Highly polished plate 98.3% pure

0.039

Polished plate

0.040

Rough plate

0.55

Chromium

0.080

Copper Commercial, emeried, polished, with no pits remaining

0.030

Commercial, scraped, shiny but not mirror-like

0.072

Polished

0.023

Iron and Steel Cast iron, polished

0.21

Wrought iron, highly polished

0.28

Cast iron, newly turned

0.435

Oxidized surfaces

B-6

Iron plate, pickled then rusted red

0.612

Completely rusted

0.685

Rolled sheet steel

0.657

Steel oxidized at 110°

0.79

Cast plate, smooth

0.80

Cast plate, rough

0.82

EPRI Licensed Material

C

QUICK REFERENCE CHARTS AND PLATES

C-1

EPRI Licensed Material Quick Reference Charts and Plates

TEMPERATURE CONVERSION TCELSIUS

=

5/9 (TFAHRENHEIT – 32)

TFAHRENHEIT

=

9/5 TCELSIUS + 32

TRANKINE

=

TFAHRENHEIT + 459.7

TKELVIN

=

TCELSIUS + 273.16

DIFFERENTIAL TEMPERATURE: ∆TFAHRENHEIT OR RANKINE = 1.8 ∆TCELSIUS OR KELVIN

Plate 1 C-2

EPRI Licensed Material Quick Reference Charts and Plates

CALCULATING INSTANTANEOUS FIELD OF VIEW, QUICK CALCULATION

Plate 2 C-3

EPRI Licensed Material Quick Reference Charts and Plates

MTF DETERMINATION USING AN IR IMAGER

Plate 3 C-4

EPRI Licensed Material Quick Reference Charts and Plates

MINIMUM RESOLVABLE TEMPERATURE DIFFERENCE (MRTD) ESTIMATE USING AN IR IMAGER

Plate 4 C-5

EPRI Licensed Material Quick Reference Charts and Plates

MEASURING AND SETTING EFFECTIVE EMISSIVITY USING AN IMAGER OR A POINT SENSOR

Plate 5 C-6

EPRI Licensed Material Quick Reference Charts and Plates

MEASURING IFOVmeas OF AN IMAGER USING THE SLIT RESPONSE FUNCTION (SRF)

Plate 6 C-7

EPRI Licensed Material Quick Reference Charts and Plates

CLASSIFICATION OF FAULTS (GUIDELINES) RELATING TO 50% OF MAXIMUM LOAD CLASS

TEMPERATURE RISE

DESCRIPTION

I

Greater than 5°C

First stage of overheating—should be kept under control and repaired at the next scheduled maintenance.

II

5° to 30°C

Developed overheating—should be repaired at the first opportune moment with due consideration to loading conditions.

III

Greater than 30°C

Acute overheating—repair at once but with consideration to the load.

Joule’s Law: P = I2R. Use this to proportion the temperature rise to 50% of the load. For example: At 20% of load, an 8°C rise is seen. To proportion it to 50% of load, multiply by the square of the load ratio as follows: (50/20)² = 6.25; 6.25 x 8°C = 50°C equivalent temperature rise

Plate 7 C-8

EPRI Licensed Material

D

REFERENCES 1. H. Kaplan, Honeyhill Technical Co., “An Update on Commercial Infrared Sensing and Imaging Instruments,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE), SPIE Thermosense VI (1983). 446-34. 2. J. C. Krapez and P. G. Cielo, National Research Council Canada, X. Maldague, Laval University, Canada, “Subsurface Flaw Detection in Reflective Materials by ThermalTransfer Imaging,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1989). 1094-27. 3. S. D. Cowell, D. D. Burleigh, General Dynamic Space Systems Division, T. J. Murray, Army Materials Technology Lab, “Flash Lamp Heat Flux Requirements for Thermographic Inspection of Fiber Composite Laminates,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1989). 1094-29. 4. F. T. Caruso, Environmental Thermography & Testing Services, Inc., “Thermal Imaging for the Nuclear Power Industry,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1985). 581-26. 5. P.W. Hugo, U.S. Army Office for Test Measurement and Diagnostic Equipment, “Infrared Automatic Mass Screening (IRAMS) System for Printed Circuit-board Fault Detection,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1987). 780-23. 6. H. Kaplan, Honeyhill Technical Co., “Infrared Automatic Screening (IRAMS) Progress Report,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1988). 934-10. 7. G. E. Courville, Oak Ridge National Lab, “Current Status of Professionalism in Commercial Infrared Sensing,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1985). 581-01. 8. C. C. Roberts, Jr., C. Roberts Consulting Engineers, “The Misuse of Infrared Thermography,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1985). 581-03. 9. G. S. Baird, Thermal Services, Inc., “Questions of Quality in Thermographic Services,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1985). 581-04.

D-1

EPRI Licensed Material References

10. C. C. Roberts, Jr., C. Roberts Consulting Engineers, Inc., “Proposed Code Ethics for Infrared Thermographic Professionals,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1987). 780-40. 11. G. S. Baird, Baird Infrared Technology, Inc., D. R. Brooks, Northeast Utilities, Inc., “Certification, Qualification and Certificate of Completion: What is the Difference?” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1987). 934-02. 12. Richmond/Dewitt, Applications of Radiation Thermometry. American Society for Testing and Materials: 1984. ASTM STP 895. 13. Wolfe, Zissis, ERIM, ONR, Department of the Navy, The Infrared Handbook, 1978. 14. J. M. Lloyd. Thermal Imaging Systems. Plenum Press 1975. 15. C. Ohman, Agema Infrared Systems, “Measurement VS Imaging in Thermography, or What is Resolution?” Proceedings of the Fifth Infrared Information Exchange, New Orleans, LA Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1985). 16. R. B. Johnson, C. Feng, J. D. Fehribach, University of Alabama/Huntsville, “On the Validity and Techniques of Temperature and Emissivity Measurements,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) (1988). 934-37.

D-2

EPRI Licensed Material

E

BIBLIOGRAPHY 1. D. C. Baird. Experimentation: An Introduction to Measurement Theory and Experiment Design. Prentice-Hall, Inc. 1962. 2. G. S. Baird, “Infrared Detection Instruments and Techniques Boost Energy Management and Analysis Capability,” Electrical Energy Management (December/January 1981). 3. M. A. Bramson. Infrared Radiation. Plenum Press, New York 1968. 4. G. J. Burrer, N. B. Stetson, and M. C. Terrell, “Fast Scan Infrared Imaging Devices,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE), Bellingham, Washington (1975).

5. M. A. Burton. ABC's of Infrared. Howard W. Sams and Company, Inc. 1970. 6. E. Feit, “Insulation and Infrared Imaging: An Engineer's Perspective,” Insulation Outlook. (October 1986). 7. E. L. Grant, W. G. Ireson, and R. S. Leavensworth. Principles of Engineering Economy. Ronald Press, New York 1976. 8. R. B. Headley, Infrared Thermography Requirements Study for Energy Conservation. Prepared for the Energy Research and Development Administration by Aerodyne Research, Inc.: April 1977. CONS/2109-1. 9. C. W. Hurley and K. G. Kreider, “Applications of Thermography for Energy Conservation in Industry,” National Bureau of Standards. (October 1976). 10. F. R. Jack and R. L. Bowman, “Effective Aerial Thermography for Energy Conservation.” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) Thermosense II (1979). 11. J. A. Jamieson, R. H. McFee, G. N. Plass, R. H. Grube, and R. G. Richards. Infrared Physics and Engineering. McGraw-Hill, Inc. 1963. 12. H. Kaplan, ASNT Level III Study Guide: Infrared and Thermal Testing Method. ASNT 2001. 13. H. Kaplan, SPIE Tutorial Text TT34, Practical Applications of Infrared Thermal Sensing and Imaging Instruments Second Edition, Society of Photo-Optical Instrumentation Engineers (1999).

E-1

EPRI Licensed Material Bibliography

14. H. Kaplan, SPIE Mini-Course, Basics of Practical Infrared Radiation Measurements, Society of Photo-Optical Instrumentation Engineers (1980). 15. F. Kreith. Principles of Heat Transfer. Haddon Craftsmen, Inc., Pennsylvania 1967. 16. K. G. Krieder and P. T. Sheahen, “Use of Infrared Thermography to Industrial Heat Balance Calculation,” Proceedings of the Fourth Biennial Infrared Information Exchange, AGA Corporation. 17. A. S. Levens. Nomography. John Wiley and Sons, New York 1959. 18. J. M. Lloyd. Thermal Imaging Systems. Plenum Publishing Corporation 1975. 19. R. Lucier, “Non-Problems in Power Plants - A Primer on Correct Diagnosis,” Yankee Atomic Electric Company, Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) Thermosense IX, Orlando, Florida (1987). 20. R. P. Madding, “Fundamentals of Heat Transfer Through Structures,” Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE) Thermosense II (1979). 21. X. P. V. Maldague. Infrared and Thermal Testing Handbook, Third Edition, Volume 3. ASNT, 2001. 22. J. B. Nelson, “Life Cycle Costing, A Practical Use of Engineering Economy.” Engineering Extension Short Course Notebook (1980). 23. D. G. Newman. Engineering Economic Analysis. Engineering Press, California 1980. 24. R. L. Petritz, Fundamentals of Infrared Detectors. I.R.E., 1959. 25. W. M. Rohsenow and J. Hartnett (editors). Handbook of Heat Transfer. McGraw-Hill, Inc. 1973. 26. E. A. Saporetti and W. L. McCracken, Design Monograph Black Body Radiation Functions. Honeywell EO Center, Lexington, Massachusetts (1979). 27. Thermosense I, Proceedings. American Society of Photogrammetry, Virginia (1979). 28. Thermosense II, Proceedings. American Society of Photogrammetry, Virginia (1980). 29. Thermosense III, Proceedings. American Society of Photogrammetry, Virginia (1981). 30. H. Kaplan, editor, Thermosense VIII, Proceedings. Society of Photo-Optical Engineers, Cambridge, Massachusetts: 1985. 31. R. Madding, editor, Thermosense IX, Proceedings. Society of Photo-Optical Engineers,

Orlando, Florida: 1987.

E-2

EPRI Licensed Material Bibliography

32. U.S. Department of Energy. Energy Measures and Energy Audits. Code of Federal Regulations, Title 10, Part 450. 33. U.S. Department of Energy. Instructions for Energy Audits, Volumes 1 and 2. DOE/CS0041/12 and 13, September 1978. 34. U.S. Department of Energy. Status of Thermal Imaging as Applied to Conservation. HCP/M 4228-ON, December 1978. 35. J. A. White, M. H. Agee, and K. E. Case. Principles of Engineering Economic Analysis. John Wiley and Sons, New York 1977. 36. R. K. Willardson and A. C. Beer. Semiconductors and Semimetals, Volume 5, Infrared Detectors. Academic Press, Inc., New York 1970. 37. W. L. Wolfe and G. J. Zissis, The Infrared Handbook. Environmental Research Institute of Michigan (1973).

E-3

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