Temp. Measurement
Short Description
Temperature Measurement Course...
Description
ADMA-OPCO On-Site-Training
Instrumentation & Control
ADMA-OPCO ON-SITE-TRAINING PROGRAMME
TECHNICAL COURSES INSTRUMENTATION AND CONTROL
Temperature Measurement For Existing Instrument Technicians And Senior Instrument Technicians
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 1
ADMA-OPCO On-Site-Training
Instrumentation & Control
Temperature Measurement Short course details Objective
This course is designed for ADMA-OPCO existing instrument technicians, to provide hands on experience related to temperature measurement methods.
Content
This course reviews types of temperature measurements used in ADMA-OPCO oil and gas facilities, Selection, Principle of operations, Maintenance and troubleshooting.
Temperature sensing elements. Local and remote temperature control.
Topics
Pre-alarm and trip/ alarm switch-settings. Calibration of temp transmitters using standard temp charts Bench services of temperature instruments. Troubleshooting and maintenance.
Other
Technical Contact
IHRDC
Audience Prerequisites Location Duration Format
: : : : :
Instrument technicians & senior technicians. English comprehension and communication. ADMA-OPCO VTC, DAS Island 4 Days. Lecture, discussion and workshop practice.
IHRDC Job Advisor: Tel # 68030, Fax # 68033
TM – I – 06 (Rev. 0) 26.12.99
Page 2
ADMA-OPCO On-Site-Training
Instrumentation & Control
SAFETY REQUIREMENTS 1.GENERAL Participant must become thoroughly familiar with the following safety requirements and first aid procedures, and must observe the safety requirements at all times. Maximum safety of personnel is of primary importance, followed closely by protection of equipment from damage. Careful observation of these safety requirements will minimize hazards or injury to personnel and equipment. There are three types of Safety Requirements: Warning, Cautions, and Notes, which are intended to emphasize critical information. Safety Requirements also include procedures to be observed in the event of certain operating malfunctions and important precautions to be observed when personnel are working in a special environment (such as in an explosive atmosphere) or with a special substance. Warnings, Cautions, and Notes are listed in order of significance as follows: WARNING A WARNING points out a procedure, practice, condition, or precaution which, if not heeded, could result in personal injury or loss of life. CAUTION A CAUTION points out a precaution which, if not observed, could result in damage or destruction of equipment. NOTE A Note highlights information necessary to understand or follow a procedure, practice, condition, or description.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 3
ADMA-OPCO On-Site-Training
Instrumentation & Control
2. COURSE SAFETY REQUIREMENTS Participant has to use the following safety precautions during this course: -Coverall. -Safety helmet. -Safety shoes/boots. -Leather gloves.
COURSE CONTENTS IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 4
ADMA-OPCO On-Site-Training
Instrumentation & Control
1. Objectives
P. 06
2. Course Outline
P. 07-08
3. Equipment / Resources
P. 09
4. Course Manual (Handout for the participant)
P. 10-54
5. Training aids
P. 55
6. Lesson plans
P. 56-59
7. Course Final Test
P. 60
Attachments: 1) Manufacturer’s instruction Manuals for Temperature Transmitter-Pneumatic 2) Manufacturer’s instruction Manuals for Temperature Transmitter-Electronic 3) Manufacturer’s instruction Manuals for temperature Switch
Objectives Upon completion of this course the participant IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 5
ADMA-OPCO On-Site-Training
Instrumentation & Control
will be able to do the following: 1. Describe the temperature scales and conversions 2. Describe the sensing elements and thermowells 3. Perform the response check of RTDs 4. Perform the response check on Thermocouples 5. Proper use of Conversion tables, T/c and RTD simulators 6. Calibration of a temperature transmitter 7. Calibration of a SMART temperature transmitter 8. Setting of a temperature switch 9. Trouble shoot the temperature measuring instruments
COURSE OUTLINE - This course is designed for the instrument technicians of ADMA-OPCO working at offshore or onshore. - Duration of this course is 4 working days (40 hr). The maximum number of participant in a batch shall be four IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 6
ADMA-OPCO On-Site-Training
Instrumentation & Control
- This course can be conducted in the class rooms and work shops of ADMAOPCO vocational training center at DAS island. - Course time plan: Every day 07.00 Hr to 17.00 Hr - Total instruction-time
16 Hr
- Total work shop time:
20 Hr
- Total Assessment time:
2 Hr
- Total Tea/ snack/ Prayer:
3 Hr
Day –1 Time (Hr.) 4 Hr
5 Hr 0.5 Hr
IHRDC
Activities / Topics Introduction Temp scales Mechanical sensors Temperature switch Temperature transmitter calibration Temperature switch calibration Assessment
TM – I – 06 (Rev. 0) 26.12.99
Location Class room
workshop classroom
Page 7
ADMA-OPCO On-Site-Training
Instrumentation & Control
DAY :02 Time
Activities
Location
4 Hr
Thermo EMF Cold Junction Compensation Thermocouples
Classroom
5 Hr
Thermocouple Verification. Calibration of a transmitter Assessment
Workshop
0.5 Hr
Workshop
DAY : 03 Time
Activities
Location
4 Hr
Wheatstone bridge Resistance temperature detectors Wiring configurations
Classroom
5 Hr
Resistance table verification Smart TT calibration Assessment
Workshop
0.5 Hr
Workshop
DAY –04 Time 4 Hr
5 Hr 0.5 Hr
IHRDC
Activities
Location
Burn out protection Trouble shooting Measuring lags Derivative term of a controller Verification of burnout protection Derivative action verification.
Classroom
Assessment
Work shop
TM – I – 06 (Rev. 0) 26.12.99
Work shop
Page 8
ADMA-OPCO On-Site-Training
Instrumentation & Control
EQUIPMENT & RESOURCES The following test equipment and tools are required to conduct the short courses: -
Thermocouple type K, J, T . any one
-
Resistance temperature detector Pt 100
-
Filled system temperature indicating controller
-
Temperature bath
-
mV calibration
-
Resistance decade box
-
Temperature transmitter (RTD or TC input)
-
Smart transmitter
-
HART communication
-
Reference tables (RTD, T/C)
-
Digital multimeter
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 9
ADMA-OPCO On-Site-Training
Instrumentation & Control
4. Course Manual HANDOUT FOR THE COURSE PARTICIPANT
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 10
ADMA-OPCO On-Site-Training
Instrumentation & Control
TEMPERATURE MEASUREMENT Temperature Scales Heat is a from of stored energy. Temperature is the Measurement of intensity of heat. It is like measuring the pressure of a gas in cylinder, irrespective of the volume of the cylinder. Temperature measurement is very important in oil and processing industries the components in the crude oil and gas may vary in composition due to the variations in temperature while they are treated in processing units. The Machinery like pumps Compressors and equipment like the heating furnaces need to be monitored carefully on their heat generating parts in order to safe guard them from over heating there by preventing the damage of components and expensive break down. Temperature is expressed in degree. There are few temperature scales commonly used in Industrial measurement the centigrade the Fahrenheit and the Kelvin are most popular scales. The centigrade scale zero starts at the ice point of pure water and divided into 100 graduations at the temperature of boiling point of pure water each division is known as a degree centigrade. The Fahrenheit scale zero starts below ice point. It is divided into 10 equal graduations in between pure water ice point and boiling point. The ice point is 32ºF and the boiling point is 212ºF. The absolute or the Kelvin scale zero reference starts from a point which is theoretically derived, where all the particles in the matter stops moving and seizes to a stand still. It is 273.15 degrees below the ice point in centigrade scale. Hence, the ice point on a Kelvin scale is 273.15ºK and the boiling point is 373.15ºK. Temperature value on a given scale can be converted to express on other Scales: Deg C = (Deg. F-32) x 5/9 Deg F = (Deg. C x 95) + 32 Deg K = (Deg. C x 273.15)
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 11
ADMA-OPCO On-Site-Training
Instrumentation & Control
Example:1 Convert 100ºC into Fahrenheit Scale? ºF = ºC x 9/5 + 32 9 i e = (100 x
) + 32 = 212 ºF 5
Example: 2. Convert 122ºF into degrees centigrade? 5 ºC = (ºF-32) x 9 5 i e = (122-32) x
= 50 ºC 9
Example: 3 Convert -40ºC in degrees Fahrenheit? 9 ºF = (ºC x
) + 32 5 9
i e = (-40 x
) + 32 = -40 5
Hence -40ºC = -40ºF !
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 12
ADMA-OPCO On-Site-Training
Instrumentation & Control
Bimetallic Elements Most substances expand when the temperature increases and contract when the temperature decreases, but different sub-stances expand and contract at different rates for a given material, the increase length per unit length per degree of temperature increase is called the coefficient of thermal expansion for that material. If two materials with different coefficients of thermal expansion are bonded together increase in temperature will cause the free end to bend toward the material with the lower coefficient of thermal expansion. A bimetallic element can be formed in spiral or helix to increase the amount of motion available for a given temperature change. The spiral form of bimetallic element is convenient for housing in a circular flat case and is typically used is dial thermometers that measure ambient temperature. The helical form is well suited for housing in a narrow tube (stem) for insertion into a fluid directly or housing within a thermowell with a small bore. Thermometers Filled system thermometers have a bulb filled with an expanding substance, (usually an inter gas) and a dial, which is controlled by a bourbon tube. The bulb is connected by a capillary tube, which can be up to about 50 feet (15 meters) long, to the dial mechanism. Their accuracy is about the same as a bimetallic thermometer and they are much more expensive. Therefore, filled system thermometers are not usually unless remote installation of the gauge is desired. Figure shows filled system thermometers. Schematic illustrating concept of bimetallic temperature elements
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 13
ADMA-OPCO On-Site-Training
Instrumentation & Control
Schematic of a typical bimetallic dial thremometer Bimetallic thermometers are available in convenient range increments for measurements between -80ºF (-50ºC) and 1000ºF (500ºC). A range should be chosen so that the normal operating temperature is near the centre and both the high and low temperatures of interest are covered. They are not very susceptible to damage from over-or under ranging. Dial calibrations are available in either Fahrenheit or Celsius or with both calibrations. An external adjustment screw is usually provided so that the thermometer can be calibrated at a single point, but there is usually no adjustment for span. Sectional View of An Industrial Bimetallic Thermometer
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 14
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 15
ADMA-OPCO On-Site-Training
Instrumentation & Control
Electric Temperature Switches An electric temperature switch is a device, which causes a contact to open or close with a change in temperature. Most switches can be used as either high temperature or low temperature sensors, depending on how they are calibrated and electrically connected. Mechanically operated temperature switches are used more frequently in production facilities most mechanically operated temperature switches use a vapour-filled system or a liquid-filled system to operate pressure switch. Gas-filled systems generally do not develop enough power for switch use. Filled system switches are available for both local and remote mounting. The local mounting type has the bulb rigidly attached to the switch mechanism and housing. The assembly has a threaded connection so that it can be screwed into and be supported by a thermowell. The remote mounting type has the bulb connection to the switch mechanism by a capillary tube from 6 feet (2 meters) to 25 feet (8 meters) or more long. The local mounting type is less expensive to purchase and install, while the remote mounting type provides isolation of the switch from process vibration and more convenient access. The switch cannot be separated from the bulb in the field for either these designs.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 16
ADMA-OPCO On-Site-Training
Instrumentation & Control
Schematics illustraating types of compensaating sysTems for filled system deuices
Thermowells
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 17
ADMA-OPCO On-Site-Training
Instrumentation & Control
A thermowell is a protective sheath, which protects a thermal sensor from the process fluid. Almost all temperature sensors in production facilities, with the exceptions stack temperature and pilot flame sensors are installed in thermowells. This relatively simple device will be discussed first because a thermowell is often apart of other types of devices.
Typical thermowells
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 18
ADMA-OPCO On-Site-Training
Instrumentation & Control
Most thermowells used in production facilities are machined from a solid piece of material in a fabrication process generally referred to as drilled or bar-stock construction. They can also be made by cutting a piece of drown tubing, welding the construction end closed, and then welding on the process connection. This second type is generally known as welded, drawn, or tubing Drilled construction more expensive than welded construction, but is more reliable and durable. A very large majority of operating companies insist on drilled construction.
Schematics of threaded thermowells for screwed on connection
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 19
ADMA-OPCO On-Site-Training
Instrumentation & Control
Insertion Length is the length that is exposed to the process fluid. It is the distance from the bottom of the threads, bottom of the socket to the tip of the thermowell. Insertion length is also known as the U-dimension. Thread Allowance is the threaded length of the thermowell. This is usually 1 inch (25 mm). Thread allowance applies only to screwed thermowells. Wrench Allowance is the length of the wrench flats above the threads. This dimension is usually 3/4 inch (18 mm). Wrench allowance applies only to screwed thermowells. Lagging Extension (or log) is the length between the thread allowance and the wrench to allow the top of the well to be accessed when installed in an insulated pipe or vessel. The lagging extension is usually 3 inches (75mm) lagging extension is usually extension is usually only specified when insulation is present and applies only to screwed or socket-weld thermowells. The nozzle for mounting the flanged well will protrude through the insulation so that a lagging extension is not required. The lagging extension is also known as the "T" length. Flanged and Van stone flanged thermowells extend above the face to allow for installation of the flange, but there is no special name for this dimension. This dimension is usually about 21/4 inched (56 mm). Element Length is the depth of the measured from the very top of the well to bottom of the bore. Usually, this dimension will be 1/4 inch (6 mm) less than the overall length of the well. Thermocouples A thermocouple is a junction of dissimilar metals used to measure temperature. When two different metals come in contact with each other, thermal energy is converted into electrical energy. Any two metals can be used and the amount of electrical energy created is a direct function of the absolute temperature except in circumstances. Also the amount of energy converted depends on the metals selected. Certain combinations of metals have been identified which create enough energy in a sufficiently liner manner so that they can be used to measure temperature with a high degree of accuracy. Thermocouple, wires of the selected metals are joined together to make electrical contact.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 20
ADMA-OPCO On-Site-Training
Instrumentation & Control
The electrical limitations are that the junction, including any third metal, must be at the temperature to be measured, the wires must be insulated from each other from the junction to be receiver, and if the junction is grounded, there must be no other ground. The only physical limitation is that the wires must be able to stand the environment to which they are subjected.
Schematic depicting a copper-constantan thermocouple circuit with an external reference junction Connection of thermocouples does present some difficulty be-cause when the selected metals are connected to any other metal, such as copper wire, another thermocouple is created and the temperature of this connection will affect the measurement as much as the temperature of the primary junction. Figure shows a thermocouple constructed from copper (Cu) wire and a copper-nickel alloy wire named constant an (c) connected to a voltmeter made of copper. The constant an wire must be connected an wire must be connected to copper somewhere in addition to the thermocouple to complete the circuit, but this will form another thermocouple. This connection is made so that the temperature can be held constant at a known temperature and is called the cold junction or reference junction (J2) A temperature that is easy to create and duplicate is that of a bath formed by pure water and the ice that water, 32ºF (0ºC) by holding the reference junction at the ice point, the temperature of the primary junction (J 1) can be found by measuring the voltage it creates in reference to the voltage created by the reference junction.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 21
ADMA-OPCO On-Site-Training
Instrumentation & Control
Tables of the voltage created at temperature versus the ice point are published by the Untied National Bureau of Standards (NBS) and are used worldwide. By measuring the thermocouple voltage, the temperature can be found from the table. If the reference junction is located where the temperature is known or can be measured accurately, then the junction voltage for this temperature can be added to the measured voltage to find the temperature of the primary junction. All of the connections and the measurement are made to a thermally conductive, but electrical insulating material known as the isothermal block. This block is usually in the instrument case, but in large installations is sometimes done elsewhere by minimizing the thermocouple wire. If the temperature is computed circuit it is known as software compensation. If an electronic circuit is used to correct the reading, it is known as hardware compensation or an electronic ice point. The thermocouple is connected tp the isothermal block by wire made from the same metals as the thermocouple, called thermocouple extension wire. A thermocouple extension wire is usually a shielded, twisted pair with the shield grounded at the instrument to minimize interference pickup. Terminal strips constructed of thermocouple material are available and should be used if intermediate connections are required. Only a few mili-volts are produced by a thermocouple, so careful attention to proper wiring and shielding is essential to good measurement.
Schematic depicting a hardware compensated thermocouple assembly
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 22
ADMA-OPCO On-Site-Training
Instrumentation & Control
Three basic types of thermocouple assembly Some thermocouple assemblies are manufactured so that the thermocouple makes electrical contact with the sheath (called ground junction) and some are manufactured where the thermocouple is electrically insulated from the sheath (called ungrounded junction) A third option is where the thermocouple extends slightly beyond the heath (called exposed junction) Exposed junction offer the fastest response, but are not used in oil and gas processing because they are subject to physical damage. They would need to be installed without a thermowell to take advantage of this faster response. Grounded junction offer faster response than ungrounded junctions because the contact area which provides the electrical connection also provides good thermal conduction. Also, grounding at thermocouple provides the most nearly symmetrical circuit, which reduced interference picked up by the wires to a minimum. Grounded thermocouples should be selected unless other components of the circuit require that the ground be at some other point, or the process fluid and piping are not at ground potential.grounding any measurement loop at more than one point will usually cause
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 23
ADMA-OPCO On-Site-Training
Instrumentation & Control
measurement errors because of potential difference in the grounding system. These errors are more acute with low voltage signals such as generated by thermocouples. These statements do not preclude grounding the extension wire shield at the receiver, which is recommended. The most common and leat expensive thermocouple is iron versus constant an (ISA type J). Type can be used for measurement from -320°F (-195°C) to1400°F (760°C), but is normally limited to 32 to 1000°F (0-500°C). Type J is usually furnished when no specific type is specified Chromal versus alumal thermocouples (ISA type K) offer better corrosion resistance. Type K can be used for-310°F (-190°C) to 2500°F (1370°C) but usually limited to 32 to 2000°F (0 to 1000°C) Type K does not produce as much out put as type Copper versus constantan thermocouples (ISA type T) are usually used when temperatures below zero are to be measured. While the usable range for type T, 310 to 750 °F (- 190 to 400 °C), is the same for the lower limit and less for the higher limit than for types J and K, the recommended range is -290 to 700°F (-180 to 370°C). The materials used in type T behave more predictably at low temperatures than those used for types J and K. Chromel versus constant an thermocouples (ISA type E) provide the largest voltage change per temperature change for standard thermocouples. An output of 40 millivolts at 1000°F can be compared to 30 mv for type J and 22 mv for type K. type E can be used for 320 to 1830°F (-195 to 1000°() and is recommended for 32 to 1600°F (0 to 870°F). Some sources extend this range downward to -100°F (-73 °C), but type T is generally considered a better choice for below freezing temperature. Type E has more tendency to change characteristics with time than types J, K and T. These four types of thermocouples comprise the base metal thermocouples.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 24
ADMA-OPCO On-Site-Training
Instrumentation & Control
Output versus temperature curves for the four types of base metal thermocouples. (Types J, K, T and E) Other thermocouple types, called the noble metal types are available for measurements where the base metal types are not suitable. They are made from expensive metals such as platinum, rhodium, iridium and tungsten thus are more expensive. Also, they do not provide as much output as the base metal types. These noble metal thermocouples are used in laboratories, for molten metals and other applications, but are rarely used in production facilities.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 25
ADMA-OPCO On-Site-Training
Instrumentation & Control
A nipple-union-nipple extension assembly for installing an RTD or thermocouple element into a thermowell
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 26
ADMA-OPCO On-Site-Training
Instrumentation & Control
Resistance Temperature Detectors The resistance of a conductor usually increase as the temperature increase. If the properties of that conductor are known, the temperature can be calculated from the measured resistance. A resistance temperature detector (RTD) is a conductor of known characteristics constructed for insertion into the medium for temperature measurement. Any conductor can be used to construct an RTD, but a few have been identified as having more described characteristics than others. The characteristics which are desired include. 1. Stability in the temperature range to be measured. The material must not melt, corrode, embrittle or change electrical characteristics when subjected to the environment in which it will operate. 2. Linearity. The resistance change with temperature should be as liner as possible over the range of interest to simplify readout. 3. High resistively. Less material is needed to manufacture an RTD with a specified resistance when the material has a high characteristic resistively. 4. Workability. The material must be suitable for configuring for insertion the media.
into
The materials which have been identified as having acceptable characteristics are: copper, nickel, tungsten and platinum. Copper has good linearity, workability, and is able up to 250°F (120°C), but has low resistively, thus either a long conductor or one with a very small cross-sectional area is required for a reasonable resistance. Nickel and nickel alloys have high resistively, good stability and good workability, but have poor linearity. Tungsten is brittle and difficult to work with. Platinum has been accepted as the material which best fits all the criteria and has been generally accepted for industrial measurement between -300 and 1200 °F (-150 and 650°C). The effect of resistances inherent in the lead wires of the RTD circuit on the temperature measurement can be minimized by increasing the resistance of the sensor; however, the size of the sensor will also be increased. RTDS are commercially available with resistances from 50 to 1000 ohms at 32°F (0°C) and increase resistance 0.385 ohms for every °C of temperature rise.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 27
ADMA-OPCO On-Site-Training
Instrumentation & Control
This is called the European (E) standard and is in accordance with the DIN (Deutsche Institut fuer Normung) 43760 Standard. Chemically pure platinum has a rise of.392 ohms per °C for a 100 ohm RTD in accordance with the American (A) standard. The European standard is dominant,. Even in the United States the American standard is seldom used. When the resistance of the RTD is found by measurement, the temperature can be calculated: °C = (Ohms reading -100)/0.385 The accuracy of this calculation is determined primarily by the accuracy of the reading. Modem instruments can measure resistance very accurately and the temperature can be determined precisely if the resistance of the connecting circuit is insignificant or is known. Unfortunately, this resistances usually not negligible or known for most practical circuits. The wire thats usually used (16 AWG stranded copper) has a resistance of approximately 4 ohms per 100 feet (305 m). If it is assumed that the RTD is connected to the instrument by a 625- foot cable as shown in Figure, the total resiatance will be 5 ohms larger than the RTD resistance, which will cause a 23.4 °F (13°C) error. Furthermore, copper wire has a temperature coefficient of about 0.0039 ohms /°C/ so the reading will vary about a degree for every 20° change in ambient temperature. These errors can be compensated for by measuring the resistance of every loop and keeping track of the ambient temperature, but fortunately there are better methods.
Schematic two-wire RTD circuit
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 28
ADMA-OPCO On-Site-Training
Instrumentation & Control
Schematic of four-wire RTD circuit The most accurate method for connecting the RTD is with four wires as shown in Figure 8. A constant current source forces a known current through the RTD, which for this discussion will be assumed to be 2.6 milliamperes. The resistance of the wires conducting this current does not need to be known. By Ohm's law, the voltage across the RTD will be this current multiplied by the resistance of the RTD. This voltage is measured by a high-impedance voltmeter on the other set of wires. The voltmeter will read 260 millivolts when the temperature of the RTD is 32°F (0°C) and its resistance is 100 ohms. For every 1.8 °F (1°C) of temperature rise, the resistance of the RTD will increase 0.385 ohms, which when multiplied by the 2.6 milliamperes flowing increases the voltage b 1 millivolt and the temperature in °C can be read by subtracting 260 from the reading. The resistance of the leads is not important, even in relation to each other as long as the current can be maintained and the resistances of the leads are small compared to the resistance of the voltmeter. Use of 4-wire RTD circuits is usually limited to laboratories and situations where very high accuracy is desired because less expansive 3-wire circuits almost always provide the needed accuracy.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 29
ADMA-OPCO On-Site-Training
Instrumentation & Control
Schematic of Three-wire RTD circuit with a balanced bridge A compromise connection method for RTDS that uses three wires and a balanced bridge circuit is shown above. For this circuit, Rl and R2 are selected to be the same resistance so that the voltage at the negative terminal of the voltmeter is one half o the supply voltage. R3 is selected to be the same resistance as the RTD at the base temperature, 100 ohms if 0°C is used as the base. For this circuit, it is important that wire A and wire B have the same resistance. The usual practice is to run the three wires as a shielded raid, thus they will all be the same length and the same resistance within manufacturing tolerance. At the base condition, the positive terminal will also see one-half of the supply voltage and the reading will be zero. If 5.2 volts is used to power the bridge, the voltage will be 2.6 at each terminal of the voltmeter at the base temperature. When the temperature of the RTD is raised one degree C, the voltage reading will increase to one millivolt. The symmetry will be upset as the reading moves away from the base temperature and the one millivolt per degree will not continue to be exact, but various schemes of completion are available to give an acceptable reading. The proceeding paragraphs are intended to explain the basis of two, three and four wire RTD connections. The selection of resistors and compensation schemes are left to the manufacturer of the instrument, but the facilities engineer selects which of the connection methods to use.
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 30
ADMA-OPCO On-Site-Training
Instrumentation & Control
The three wire method is the proper selection for virtually all production facility applications. Resistance temperature detectors (RTDS) are the most frequently used electronic temperature sensors for production facilities. The industry has standardized on RTDS that are calibrated to Din standard 43760 which is also known as the European standard RTDS which meet this standard measure 100 ohms at 0°C, are made of platinum and exhibit a resistance increase of 0.385 ohms per °C temperature increase. Another standard, called the American Standard, is available but is not in wide use, even in the United States. Typical RTDS are shown in Figure.
Various methods for attaching an RTD or thermocouple sheath to a thermowell fitting
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 31
ADMA-OPCO On-Site-Training
Instrumentation & Control
RTDS are usually purchased as a probe assembly consisting of the RTD sensor installed in a type 304 stainless steel sheath. The sheath is held in the thermowell by a fitting which is threaded on both ends for attachment to the thermowell and the head so that the tip of the sheath touches or is very near the end of the well. The preferred method of attachment of the sheath to the fitting is with a spring assembly which allows the fitting to be screwed into the thermowell as the spring is compressed. The spring holds the sheath firmly against the bottom of the well for good heat transfer. Another method is to sliver solder the sheath into the fitting which makes a good firm assembly, but requires a small clearance from the bottom of the well. The third popular method is with a comparison fitting so that the sheath can be pushed against the bottom of the well after the fitting is screwed into the well. The compression nut is then tightened to hold the sheath. The compression fitting allows use of a universal probe in different lengths of thermowells. The head of the assembly is a chamber where the leads from the RTD and the leads to the receiver instrument can be terminated and connected to each other. Temperature Transmitters Temperature transmitters are used when it is necessary to convert the signal from a temperature sensor to one of the standard signals for transmission over a long distance or interface with other instruments. The signal is usually 4 to 20 ma. For electronic transmission and 3 to 15 psig (20 to 100 Kpa) for pneumatic if a transmitter is used. Other signals can be used if required by the receiver, but these are the most common and should be used if possible. It is also possible to bring a temperature measurement into a control room without using a transmitter A thermocouple RTD can be wired directly to an instrument in the control room and this is acceptable practice. Temperature transmitters for new installations are predominantly electronic with 4 to 20 ma. Outputs and inputs from thermocouples or RTDS. These transmitters can be mounted in the field and on the thermowell or in the field on a support and connected to the sensor by a cable. Temperature transmitter mounted in the field must be protected from the elements by an appropriate housing. A weatherproof (INEMA 4) housing is adequate for m most applications, even in Division 2 hazardous area because there are no arching contacts in a typical temperature transmitter. An explosion- proof (NEMA 7) housing is required for Division I area unless the installation is certified intrinsically safe. The energy level required in temperature transmitters is such that they can be used in intrinsically safe installations if isolated from the power supply and receiver by approved barriers and approved by an agency recognized in the country where installed. Burn Out Protection IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 32
ADMA-OPCO On-Site-Training
Instrumentation & Control
As the temperature sensors are continuously subjected to process temperature, there is a likely chance of failure due to excess temperature or mechanical damage. In either event, the RTD or thermocouple circuit will be open, discontinuing the electrical path. This is called bum out. It is a facility provided within the receiving instruments like the recorders, indicating, controllers, to respond for such loss of input signals. Burn out Protection Up Scale. When the input to the instrument is disconnected the instrument shows a range maximum value. Burn out Protection Down Scale When the input signal wiring to the instrument is disconnected. The instrument shows scale minimum value. The associated circuits with the above instrument like switches- alarm, shutdown logic fail safe option is selected in Bum Out Protection.
Heat / Temperature
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 33
ADMA-OPCO On-Site-Training
Instrumentation & Control
Temperature scales
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 34
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 35
ADMA-OPCO On-Site-Training
Instrumentation & Control
Sensors
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 36
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 37
ADMA-OPCO On-Site-Training
Instrumentation & Control
Thermo EMF
Thermocouples IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 38
ADMA-OPCO On-Site-Training
Instrumentation & Control
Temp Renges of T. C
Thermocouple Pair Iron-Constantan
CopperConstantan Chromel Alumel Chronel Constantan
IHRDC
Type
Positive Insulation BS/ANSI
J
Iron (magnetic) :yellow White
T
K
E
Copper (By Color) :White/ Blue Chromel (shiny) Brown/ Yellow Chromel (shiny) Brown/ Purple
TM – I – 06 (Rev. 0) 26.12.99
Negative Insulation BS/ANSI Constantan (dull) :Blue/ Red
Useful Range 0-800ºC
Constantan (dull) :Blue/ Red
-200 to +400ºC
Alumel (Magnetic) Blue Red
0-1100ºC
Constantan (dull) Blue/ Red
0-800ºC
Page 39
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 40
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 41
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 42
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 43
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 44
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 45
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 46
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 47
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 48
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 49
ADMA-OPCO On-Site-Training
IHRDC
Instrumentation & Control
TM – I – 06 (Rev. 0) 26.12.99
Page 50
ADMA-OPCO On-Site-Training
Instrumentation & Control
Cables-color code
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 51
ADMA-OPCO On-Site-Training
Instrumentation & Control
Transfer log
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 52
ADMA-OPCO On-Site-Training
Instrumentation & Control
Derivative action
5. Training Aids LIST OF TRANSPARENCIES
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 53
ADMA-OPCO On-Site-Training
Instrumentation & Control
T1
Objectives
T2
Heat-Energy transfer
T3
Temperature Scales
T4
Sensors
T5
Thermowells
T6
Thermocouples
T7
Temp Ranges of T.C
T8
Promac Calibrator
T9
Calibration hook up
T10
T. C Verification
T11
Bridge circuit
T12
Resistance temperature Detector
T13
RTD wiring options
T14
RTD conversion tables
T15
Decade Resistance box
T16
RTD verification
T17
SMART transmitters
T18
Cold Junction
T19
Burn protection
T20
Cables-color code
T21
Transfer lag
T22
Derivative action
6. LESSON PLANS Instructor 's guide LESSON I IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 54
ADMA-OPCO On-Site-Training
Instrumentation & Control
Introduction
-
Introduce your self and speak to the participants to gauge their language
Objectives
- Show transparency Tl read all the course objectives
Course out line
- Show transparency T2 Read the course plan
Heat/ Temperature
-
Temperature scales Conversion
Show transparency T4 - Explain Ice point and Steam point. About deg.centigrade, about deg. fahrenheit, about deg.kelvin or Absolute scale.
Sensors
- Show transparency T5 Explain Bimetallic sensors Filled system bulbs
Thermowells
- Show transparency T6 Discuss thermo wells screwed, flanged, length etc.
Temperature bath
- Show transparency T7 Explain how to use the equipment
Show transparency T3 Explain about heat as an energy Explain that temperature is the intensity of heat
Lesson 2 Thermo EMF
IHRDC
- Show transparency T8 Explain seebeck, Peltier and Thomson effects
TM – I – 06 (Rev. 0) 26.12.99
Page 55
ADMA-OPCO On-Site-Training
Instrumentation & Control
Thermocouples
- Show transparency T9 Explain different types of thermo couples, Temperature ranges
Conversion tables
-
Test equipment
- Show transparency Tl1 explain the features of promac calibrator
Calibration Hook-up
- Show Transparency T12 Discuss the methods to simulate the mv signal
Thermocouple Verification
- show Transparency T13 Discuss the hook up
IHRDC
Show transparency Tl0 Explain the use of tables
TM – I – 06 (Rev. 0) 26.12.99
Page 56
ADMA-OPCO On-Site-Training
Instrumentation & Control
LESSON 3 Wheatstone bridge
Show transparency T14 - Explain the bridge balancing
RTD
- Show transparency Tl5 Function of an RTD Explain various symbols Pt 100, Cu 500
Wiring
- Show transparency Tl6 Explain 2 wire, 3 wire and 4 wire connections
Conversion table
Show transparency Tl7 - Explain the use of tables
Decade resistance box
RTD verification Smart transmitters
IHRDC
- Show transparency Tl8 Discuss the simulation method Explain wiring - Show transparency T19 Explain hook up method and verification - Show transparency T20 Discuss smart communications
TM – I – 06 (Rev. 0) 26.12.99
Page 57
ADMA-OPCO On-Site-Training
Instrumentation & Control
Lesson 4 CJC
Burn out Protection
-
Show transparency T21 Explain reference junction Discuss ambient temperature
- Show transparency T22 Explain reasons for bum out Discuss fail safe circuit Explain up scale / down scale
Cables
-
Transfer lag
- - Show transparency T24 Discuss the energy transfer
Derivative action
- Show transparency T25 Explain the need for a prediction Explain how the controlers work
IHRDC
Show transparency T23 Explain extension leads Discuss compensating cables
TM – I – 06 (Rev. 0) 26.12.99
Page 58
ADMA-OPCO On-Site-Training
Instrumentation & Control
7. Assessment Q, 1. A temperature transmitter was calibrated for 0-100°C (a) what will be the output when the process temperature is 348.15°K? (output range is 3 to 15 psig). (b) what will be the local temperature gauge reading if the scale is in °F? Q.2. A temperature transmitter uses type T thermocouple, write down the procedure to calibrate the instrument for a rang of -50 to +150°C at a room temperature of 25°C. (a) Using thermocouple simulator. (b) Using mV source and conversion tables. Q.3. On a process line, RTD sensor resistance measured as 138.5 ohms. The transmitter gives an output signal of16 mA. The process temperature was brought down to 122°F by the operator. The transmitter gave an output of 8 mA. what is the calibrated range of the transmitter?
IHRDC
TM – I – 06 (Rev. 0) 26.12.99
Page 59
View more...
Comments
