Full Lab Manual - Measurement (UNITEN)

DEPARTMENT OF MECHANICAL ENGINEERING COLLEGE OF ENGINEERING TENAGA NASIONAL UNIVERSITY MALAYSIA

ENGINEERING MEASUREMENT

LAB. MANUAL

MESB 333

1

Table of Contents Laboratory Syllabus Overview Laboratory Time Format for Logbook Format for Formal Report

Lab No.1:

Lab No. 2:

Lab No.3

Lab No.4

Lab No. 5

Lab No. 6

3 4 5 6 7

Strain Measurement Prelab Questions Experiment I: Axial Strain Experiment II: Torsion Strain

9 10 16

Determining fluid (air) velocity and Discharge Coefficient Prelab Questions Experiment I: Velocity Measurement Using Pitot Tube Experiment II: Determination of Discharge Coefficient

20 21 26

Temperature Measurement Prelab Questions Experiment I: Time Constant Experiment II: Type K Thermocouple Experiment III: Humidity Measurement

31 32 39 42

Photo Transducer Prelab Questions Experiment I: Photo Diode Experiment II: Photo Conductive Cell Experiment II: Photo Transistor

45 51 54 57

Flow Rate Measurement Prelab Questions Experiment: Flow Rate Measurement Devices

60 61

Introduction to PID Controller Prelab Questions Experiment: PID Controller

66 67

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Laboratory Syllabus Lab 1 : Strain Measurement There are two experiments in this lab. The experiments are related to the field of mechanics of deformable solid. The 1st experiment is on bending of a cantilever beam. The 2nd experiment involves loading weighs on a circular bar to create torsion. Strain gauge is used to convert the value of body deformation to corresponding electric signal for analog reading. Simple calculation for strain is required using basic bending theory. Informal report is required for this lab.

Lab 2 : Determining fluid (air) velocity and Discharge Coefficient There are two experiments in this lab. These experiments are related to the field of Fluid Dynamics of air. Both experiments use the same apparatus. 1st experiment is to measure air flow velocity. Pressure along the test pipe will be measured to determine air flow velocity using Bernoulli’s equation. 2nd experiment is to measure the discharge coefficient of an orifice plate and a nozzle. An orifice plate will be inserted along the test pipe. Formal report is required for this lab. Lab 3 : Temperature Measurement This experiment is related to the field of Heat Transfer and Thermodynamics. This experiment consists of temperature measurement using different type of measuring devices: Pt 100 resistance thermometer, liquid filled thermometer and NTC temperature probe. The apparatus consists of rice cooker, oven, amplifier, and temperature indicator and so on connected in a simple circuit. Understanding the working principle of resistance thermometer is important. Informal report is required for this lab.

Lab 4 : Photo-electric Transducer This lab is related to the field of physics, the behavior of light. Light intensity can be measured by measuring the effect of the light on a device. When light falls on a material, current that corresponds to the light intensity will be generated using transducer. Photocell, circuit box and light source are the important devices in this experiment. The current that is produced at different level of light intensity will be measured. Informal report is required for this lab.

Lab 5 : Flow rate Measurement This experiment is related to the field of fluid dynamics. This experiment involves the study of liquid flow rate. Water is used as the fluid in this experiment. Three flow rate measurement devices: orifice plate, variable area meter and venturi meter are used. The orifice plate and venturi meter require calculation using Bernoulli equation to give the flow rate reading while variable area meter gives reading directly Informal report is required for this lab.

3

Lab 6 : Flow rate Measurement This experiment is related to the field of fluid dynamics. This experiment involves the study of liquid flow rate. Water is used as the fluid in this experiment. Three flow rate measurement devices: orifice plate, variable area meter and venturi meter are used. The orifice plate and venturi meter require calculation using Bernoulli equation to give the flow rate reading while variable area meter gives reading directly. Informal report is required for this lab.

LABORATORY & REPORTS: AN OVERVIEW All experiments in the Engineering Measurements Laboratory require either a laboratory report (Logbook) or a formal laboratory report for selective experiments, unless it is stated otherwise. The reports should be simple and clearly written. Laboratory reports (logbook) are due after all of the experiments are performed, unless it is stated otherwise. Final reports should be submitted a week after the experiment’s day, unless it is stated otherwise. Any late submission will not be entertained, unless there are concrete and unavoidable reasons. The laboratory reports (log book) should be in hand writing and any graphs needed should be drawn in either an appropriate graph paper or drawn using EXCEL, whichever suitable. However, for final laboratory reports, it should be computer-generated and any graphs should be drawn using EXCEL. The formal laboratory reports should be submitted into pigeon hole in front the lab or to the instructor directly. The pre-lab questions in this lab manual should be answered and submitted during the first 5 minutes before you start your experiment accordingly.

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Laboratory Session Lab Technician : Muhammad Faizal Bin Rahim Tel:

03- 8921 2020 ext. 6324

Laboratory Time: Section 1A: Section 1B: Section 2A: Section 2B: Section 3A: Section 3B: Section 4A:

Wednesday Wednesday Monday Thursday Tuesday Thursday Monday

-

800-1100 (BL-0-003) 1500-1800 (BL-0-003) 1400-1700 (BL-0-003) 1100-1400 (BL-0-003) 1500-1800 (BL-0-003) 1500-1800 (BL-0-003) 900-1200 (BL-0-003)

Attendance: Please sign attendant sheet upon arrived to lab. Mark will be given depending on time of arrival. Student who comes 15 minutes after the lab begins will get 0 mark. Absence due to illness should be proven by medical certificates (MC).

Prelab: Turn in prelab at the beginning of each lab. No prelab will be accepted 15 minutes after the lab begins. Prelab will not be return to the students until the end of semester. The purpose of prelab is to encourage student to read through lab manual before coming to the lab.

Logbook: Students are required to prepare a logbook for the purpose of recording the data and discussing the results from each informal experiment. The logbook MUST be presented to the instructor and signed at the end of each laboratory session. Marks will be given for each experiment done in the session. Collect the lab front page cover from the lab technician if you are assigned to write a formal report.

Laboratory Assessment:

Students are required to prepare a logbook for the purpose of recording the data and discussing the results from each experiment. The logbook MUST be presented to the instructor and signed at the end of each laboratory session. Marks will be given for each experiment done in the session. Collect the lab front page cover from the lab technician if you are assigned to write a formal report.

5

Formal Reports: There are a total of 2 individual formal reports that need to be completed by each student throughout the course. The formal reports should be written for the following experiments. Experiment 2: Velocity Measurement. Experiment 6: PID Controller. Duration of one-week period is provided for formal report and should be submitted during the next lab. Report should be submitted to the lab technician personally. Grade will be deducted from the late report as follows (except with valid reason) : Late submission penalty : Late 1 day : 90%, Late 2 days : 80 %, Late 3 days : 70%, More than 3 days: 50% of earned mark.

Plagiarism is not acceptable. It will result in half of the total grade being deducted or zero grade for the lab report or for the whole course. In addition, poor report writing will result in meeting the instructor for improvement in future report writing. Please use the font of Arial or Times New Roman only. Before submitting your hardcopy formal report to the instructor, you need to upload your softcopy report into TURNITIN program, to check for similarity (report with silmilarity higher than 50% will not be accepted). You will be given ID and password to upload the softcopy of your formal report by the respective instructors.

Experiment Group: Students will perform experiment in-group. Each experiment group consists of 3-5 students. Group number consists of Section number, follows with number appointed. For example, the first group from section 1A will have group number of 1A1; the second group in the same section will be designated as 1A2 and so on. Report must be submitted using front page supplied.

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Format for LOGBOOK No.

Criteria

1

Title Page With name, SID, group no., lab no., date performed, date submitted.

2

Statement of Purpose or Objective With clear, specific purpose statement

3

Data, Observation and Results With results clearly, orderly presented in either graph, spreadsheet, table etc with labeled. Sample calculation if calculation is involved. Error calculation

4

Analysis and Discussion With specific comment, explanation, support on the results based on theory. Error and uncertainty analysis ie. Error source, comparison between the experimental and theoretical results. Answer to question if given.

5

Conclusion Summary of the experiment. Conclusion drawn from results in the light of the stated objective.

6

Overall report presentation Neat, Clear label of small title etc. With references if given

7

Format for Formal Report No.

Criteria

1

Title Page With name, SID, group no., lab no., date performed, date submitted.

2

Table of Content

3

Summary/Abstract The concise overview of the report.

4

Statement of Purpose or Objective A brief description of what the experiment is demonstrating.

5

Theory With brief but clear background and theory related to the experiment.

6

Equipment Diagram of the apparatus and specification.

7

Procedure A step by step explanation of what was done in the lab and why each step was performed.

8

Data, Observation and Results With results clearly, orderly presented in either graph, spreadsheet, table etc with labeled. Sample calculation if calculation is involved. Error calculation

9

Analysis and Discussion With specific comment, explanation, support on the results based on theory. Error and uncertainty analysis ie. Error source, comparison between the experimental and theoretical results. Answer to question if given.

10

Conclusion Summary of the experiment. Conclusion drawn from results in the light of the stated objective.

11

Overall report presentation Neat, Clear label of small title etc. With references if given

8

MESB 333 LAB NO.1 : STRAIN MEASUREMENT PRELAB QUESTIONS Name: ________________________SID: ______________Group:______ Date:_______________ 1. What is stress? Strain? What is the relationship between stress and strain?

2. What is the mechanical equipment used to measure small changes in length? What is the principle used in strain gauge, theoretical formula to calculate strain and explain the terms in the formula?

3. Why is zeroing required before measurement is done?

4. How to eliminate error due to temperature changes?

5. In measuring the torsion strain, how can the axial or bending strain be eliminated? Sketch to explain.

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MESB 333 Lab No.1 Strain Measurement ____________________________________________________________________________ 1.

Experiment I Measurement of Axial Strain

1.1 Objective This experiment student will learn to measure strain of a cantilever beam. In addition, student will be able to understand the relationship between stress, strain, and Young’s Modulus of Elasticity. 1.2 Theory A material will be deformed to certain extend when external forces act on it. This deformation will cause changes in length and diameter of the material. The strain produced is directly proportional to the stress at a limited region, which is called the limit of proportionality (i.e. there is linear relation between the two). The stress-strain graph is a straight line in this region. In this experiment, we are going to study the performance of an electrical resistance strain gauge as well as to verify its accuracy on measuring the strain of a bending material. Hooke's Law, which relates stress and strain, can be applied in the limit of proportionality region. Young's Modulus of Elasticity is the gradient of straight line in the stress-strain graph. The mathematical relationship is: dL L

where, dL : : P : E : :

P EA

E

…………………………………………(1)

change in length L strain force on cross section area A Young’s Modulus of Elasticity axial stress

Equipment used to measure dL is called extensometer. It is a mechanical method to measure dL where change in length can be magnified. However, a better way to measure dL is by using the electronic measurement. Longitudinal strain is associated to the changes in length of a material. While diametral strain is associated to the changes in the diameter of a material. Poisson's ratio is the ratio of longitudinal strain to diametral strain or can be given as Poisson’s ratio( ) =

lateral contraction per unit breadth Longitudinal extension per unit length

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When the length and the diameter of a material change, the electrical resistance of the material will change too. The relationship between the change in the dimension to the electrical resistance of the material can be related mathematically as equation shown:

R

L A ……………………………………………..(2)

where, R

:

electrical resistance

:

specific resistance of material

L

:

length

A

:

cross sectional area

From the relationship, it is clear that the resistance will increase when the material is stretched. Conversely, compression will cause the resistance to decrease. Strain gauge uses this principle to measure the strain. 1.3 Calculation of axial strain Theoretically, the strain value can be calculated using the theory of bending at the point of attachment of the strain gauge. For a rectangular cross-sectional area cantilever beam, M I

y

E R

My I

………………………………..(3)

Where, M I

:

bending moment = (Applied load X moment arm)

bd 3 = (Width b and thickness d) 12

:

second moment of area of cantilever

:

axial stress

y

:

half the thickness of the cantilever

E

:

modulus of elasticity

R

:

radius of curvature of cantilever due to M

=½d

Strain is defined as change in length per unit length, that is

11

dL L

y R

……………………………………………………………….(4)

From the theory of bending 1 R

M EI

……………………………………………………………….(5) Hence, the theoretical strain value is y R

My EI

……………………………………………………………(6) From the dimension of cantilever beam, M = 150* Load (N.mm)

*150 mm is the distance from the load point to strain gauge.

Measurement of the resistance is usually done using the Wheatstone Bridge. The gauge is attached to the material using a high-grade adhesive. Since temperature will affect the resistance, this factor must be taken into consideration too

1.4 Wheatstone Bridge B

R1

A

R2

M

C

+

_

Figure 1 Wheatstone bridge R3

R4

D

12

R1 will be the strain gauge attached to the material. It is also called an active gauge. R2 is a similar strain gauge to R1. But, it is attached to an unstressed part of the material. The effect of temperature on R1 and R2 will be similar. R3 and R4 are high stability resistors of equal value. M is a digital voltmeter or a purpose designed high stability high gain amplifier with a digital meter and a zeroing circuit. Voltage applied to A and C is a constant DC voltage. Normally it is 1-2 volts. External zeroing is applied in Wheatstone Bridge. External zeroing means the meter M will show zero reading. This is done by having a variable resistor at D. Zeroing can be done by varying the variable resistor. Zeroing is required because factor like weight of the material can affect the results.

1.5 Apparatus

Figure 2. Experiment apparatus

The apparatus above is a direct read-out strain meter in a base box to which a pillar carrying an aluminum alloy cantilever has been fixed. An electrical resistance strain gauge has been fixed to the top surface of the cantilever 150 mm from the loading point. The cross section of the cantilever is 25.4 x 3.2 mm. The modulus of elasticity of the cantilever is 69 000 N/mm2. A temperature compensation (dummy) gauge is supplied fixed to a small piece of aluminum alloy. The basic circuit of the Wheatstone bridge is laid out on top of the base, showing the use of a zeroing control. An analogue meter with a center zero scale has been designed to read true strain in units of micro-strain.

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1.6 Procedure

1. Connect the strain gauge leads from the cantilever strip and dummy gauge leads to the terminals, switch on the apparatus. 2. Adjust the zero offset knob (variable resistor) on the apparatus to zero the meter. 3. Note whether any drift of the zeroed reading occurs as the strain gauges warm up 4. To show the effect of temperature, warm the temperature compensation gauge by placing one's finger on it. 5. Suspend the C hook and load hanger in the groove at the end of the cantilever. 6. You may need to re-zero the meter. Record the meter reading. 7. Press downward on the end of the cantilever and observe the direction in which the meter reads in the reverse direction. You should notice that the polarity of the reading indicates whether the gauge is in tension or compression. 8. Load the cantilever to 30 N by 5 N increments. Read and record the meter reading at each increment 9. Unload the cantilever from 30 N to 0N and record the readings at each decrements. 10. Repeat step 8 and 9 and record the second set of reading in order to obtain the average of the readings. 1.7 Results Table 1 Cantilever experiment result Theoretical

Average Meter Reading Strain (

Load (N)

Strain Stress (

)

2

Increasing Load

Actual Stress

)

(N/mm2) %Error

(N/mm )

Decreasing Load

%Error

(Increasing Load )

0 5 10 15 20 25 30

Calculate the theoretical strain and stress for each load and then compare the theoretical result with experimental result for both increasing-load and decreasing-load result. Compare your

%error

theory exp eriment 100% theory

results by calculating the % error between the theoretical and the experimental values. 14

Plot the strain( ) against axial stress( ) for the theoretical and experimental values on the same graph. Draw the best fit linear line and find its slope. What can you relate the gradient of the line and Young’s Modulus of Elasticity? Discuss the results. Are the readings for increasing and decreasing load the same? Why? Why the system was connected to the dummy gauge ? Include error analysis.

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2

Experiment II Measurement of Torsion Strain

2.1 Objective

In this experiment, student will learn to measure torsion strain and understand the relationship between torque and strain.

2.2 Theory Having studied the use of a strain gauge for measuring tensile(axial) strain and stress, a more complicated application can now be considered. Reverting to the diagram of the standard bridge there are further ways of exploiting the measuring technique. In this experiment, we are going to study the measurement of torsion strain. Suppose the temperature compensation gauge used as R, can be attached to the structural element being tested in such a way it is subjected to an equal but opposite strain to the R, gauge. This will double the meter reading while providing the temperature compensation and is known as reversed active strain gauging. This could have been done in the case of bending by attaching a strain gauge on the underside of the cantilever where the compression due to bending equals the tension where the top surface gauge is fixed. The leads from the underside gauge would then replace the leads from the dummy gauge. Now consider a hollow round tube used as a cantilever.

Figure 3. Cantilever round bar exert with torsion.

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In bending there is a neutral axis at the horizontal axis, so any gauge fixed symmetrically about this neutral axis will not record a strain, By applying torque at the free end of the cantilever, a uniform shear is induced along the whole length. This in turn produces diagonal tension and compression stresses of equal value along the corresponding 450 helical directions. Hence by fixing two strain gauges at A and B as shown the following conditions are satisfied:

(1)

Temperature compensation

(2)

Net axial strain effect is zero for either A or B

(3)

Gauge A is subjected to diagonal tension while gauge B is in diagonal compression, or vice versa.

The meter will therefore indicate twice the diagonal strain from which the stress can be derived using the modulus of elasticity. 2.3 Calculation of torsion strain Hooke’s Law

E ……………………………………………………..(7) For the torsion specimen the comparable theoretical equation is

T J

r

G L

Tr J

……………………………………..(8) where T

:

torsion = (Applied Load X eccentricity)

J

:

polar moment of inertia of tube =

Do

:

outside diameter

Di

:

inside diameter

:

surface shear stress

r

: outside radius of tube

G

: modulus of rigidity

32

Do

4

D1

4

: angular twist over length L

17

The shear stress acts circumferentially and has to be accompanied by a system of complementary stresses including diagonal tensile and compressive stresses, which are perpendicular to each other. Hence there are equal direct strains along opposing 45 0 helices on the surface of the tube given by

q E

Tr EJ ……………………………………(9)

and the meter will indicate 2* . 2.4

Apparatus

The torsion accessory consists of an aluminum alloy tube 9.5 mm O/D and 6.3 mm I/D with a loading arm welded across one end. A clamp is provided to enable the tube to replace the clever strip used above, the loading arm being set horizontally. A load hanger can be suspended on the vertical axis of the tube, or at horizontal eccentricities of 50 or 100 mm. The strain gauge leads from the strip cantilever and the dummy gauge are removed from the terminals so that the pairs of leads from the torsion specimen can be connected instead.

2.5

Procedure

1. Connect the two pairs of leads from the torsion tube to the pairs of terminals. 2. Switch on the apparatus and adjust the offset knob to zero the meter. Re-zero if drift occurs as the gauges warm up. 3. Place the load hanger at zero eccentricity and add two 10 N weights. Note any meter reading, and check that the meter returns to zero when the loads are removed. 4. Move the load hanger to 50 mm offset. Zero the meter. Record the strain readings as the 30 N load is added by 5 N increments to the hanger. Repeat the readings as the weights are removed. Use a table of results as shown. 5. Repeat the above for 100 mm offset. It will be necessary to hold the base box to prevent it being toppled over by the eccentric load. 6. Repeat step 4 and 5 and record the second set of reading to get the average.

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2.6

Results Table 2.1 Diagonal Strains on a Torsion Specimen Theoretical Load Eccentricity

(N)

(mm)

( Strain

Diagonal Strain(

Actual Shear

) Shear

Average Meter Reading

Stress

stress Increase Load

0

)

Decrease Load

Increase load

10 20 30

50

5 10 15 20 25 30

100

5 10 15 20 25 30

Calculate the theoretical value for the diagonal/torsion strain and compare with the meter readings by stating the percent error. (Remember, the meter reading is twice the actual value.) Plot a graph of strain vs. shear stress (increase load only) for theoretical and actual on the same graph and use the best fit straight lines to determine the relationship between shear stress and torsion strain. Why the diagonal strain at eccentricity 0 mm are zero? How successful is the technique (two strain gauges) for eliminating bending stress from the readings? Why used two strain gauges? What the system is not connected to dummy gauge? Include error analysis.

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MESB 333 LAB NO. 2: VELOCITY MEASUREMENT AND DETERMINATION OF DISCHARGE COEFFICIENT PRELAB QUESTIONS Name: _____________________SID: ______________ Group:______ Date:______________

1. Draw a diagram and explain briefly how to measure pressure using pitot tube?

2. What is coefficient of discharge?

3. What is Reynolds number?

4. Describe three different flow characteristics and what determines each characteristic?

5. What is orifice plate is use for ? Gives 2 examples UNITS for measuring flowrate?

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MESB 333 Lab No.2 Determining fluid(air) velocity and Discharge Coefficient

1.

Experiment I Velocity Measurement Using Pitot Tube

1.1. Objective This experiment allows student to learn the method of measuring air flow velocity using pitot tube. The student will understand the working principle of pitot tube as well as the importance of Bernoulli equation in deriving and calculating the velocity. 1.2. Theory A pitot tube is used to explore the developing boundary layer in the entry length of a pipe which has air drawn through it. With pitot tube, the velocity distribution profiles can be determined at a number of cross-sections at different locations along a pipe. With pitot tube, air flow velocities in the pipe can be obtained by first measuring the pressure difference of the moving air in the pipe at two points, where one of the points is at static velocity. The Bernoulli equation is then applied to calculate the velocity from the pressure difference.

v

2 p

or

2 gh'

(1)

p The pressure difference between the pitot tube and the wall pressure tapping measured using manometer bank provided ( g x where x is the level of fluid used in the manometer). h’ The pressure difference expressed as a 'head' of the fluid being measured (air) The air density at the atmospheric pressure and temperture of that day.(kg/m3) g gravitational acceleration constant (9.81 m/s2)

When fluid flows past a stationary solid wall, the shear stress set up close to this boundary due to the relative motion between the fluid and the wall leads to the development of a flow boundary layer. The boundary layer may be either laminar or turbulent in nature depending on the flow Reynolds number.

The growth of this boundary layer can be revealed by studying the velocity profiles at selected cross-sections, the core region still outside the boundary layer showing up as an area of more or less uniform velocity.

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If velocity profiles for cross-sections different distances from the pipe entrance are compared, the rate of growth of the boundary layer along the pipe length can be determined. Once the boundary layer has grown to the point where it fills the whole pipe cross-section this is termed "fully developed pipe flow".

1.3. Reynolds Number

The Reynolds number is a measure of the way in which a moving fluid encounters an obstacle. It's proportional to the fluid's density, the size of the obstacle, and the fluid's speed, and inversely proportional to the fluid's viscosity (viscosity is the measure of a fluid's "thickness"--for example, honey has a much larger viscosity than water does).

vd

Re fluid density v

: fluid velocity

d

: obstacle size coefficient of fluid dynamic viscosity

A small Reynolds number refers to a flow in which the fluid has a low density so that it responds easily to forces, encounters a small obstacle, moves slowly, or has a large viscosity to keep it organized. In such a situation, the fluid is able to get around the obstacle smoothly in what is known as "laminar flow." You can describe such laminar flow as dominated by the fluid's viscosity--it's tendency to move smoothly together as a cohesive material.

A large Reynolds number refers to a flow in which the fluid has a large density so that it doesn't respond easily to forces, encounters a large obstacle, moves rapidly, or has too small a viscosity to keep it organized. In such a situation, the fluid can't get around the obstacle without breaking up into turbulent swirls and eddies. You can describe such turbulent flow as dominated by the fluid's inertia--the tendency of each portion of fluid to follow a path determined by its own momentum. The transition from laminar to turbulent flow, critcal flow, occurs at a particular range of Reynolds number (usually around 2500). Below this range, the flow is normally laminar; above it, the flow is normally turbulent.

1.4. Calculation of air flow velocity The manometer tube liquid levels must be used to calculate pressure differences, h and pressure heads in all these experiments. Starting with the basic equation of hydrostatics:

p=

gh

(2) 22

we can follow this procedure through using the following definitions: Example:

Manometer tubes

1(static ‘pressure’*)

2(stagnation ‘pressure’)

Liquid surface readings (mm)

X1

X2

Angle of inclination,

=0

‘pressure’ term is used since this reading is in mm of manometer fluid and not the pressure of unit Pa. Therefore the equivalent vertical separation of liquid levels in manometer tubes, h = (x1 - x2)cos

If

k

(3)

is the density of the kerosene in the manometer, the equivalent pressure difference p is: p=

k

g h=

The value for kerosene is

k

g(x1 - x2) cos

k

(4)

= 787 kg/m3 and g = 9.81 m/s2. If x1 and x2 are read in mm, then:

p = 7.72(x1 - x2)cos

[N/m2]

(5)

The p obtained is then used in second equation (1) to obtain the velocity.

To use the first equation (1), convert this into a 'head' of air, h’. Assuming a value of 1.2 kg/m 3 for this gives:

h'

k air

.

( x1 x2 ) . cos 1000

[N/m2]

(6)

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1.5 Apparatus

Figure 1 Experiment apparatus 1.6 Procedure a) b) c) d)

e) f) g)

h)

Five mounting positions are provided for the pitot tube assembly. These are: 54 mm, 294 mm, 774 mm, 1574 mm and 2534 mm from the pipe inlet Ensure that the standard inlet nozzle is fitted for this experiment and that the orifice plate is removed from the pipe break line. Set the manometer such that the inclined position is at 00. Mount the pitot tube assembly at position 1 (at 54mm, nearest to the pipe inlet). Note that the connecting tube, the pressure tapping at the outer end of the assembly, is connected to a convenient manometer tube. Make sure that the tip, the L-shape metal tube of the pitot tube is facing the incoming flow. Note that there is a pipe wall static pressure tapping near to the position where the pitot tube assembly is placed. The static pressure tapping is connected to a manometer tube. Position the pitot tube with the traverse poisition of 0mm. Start the fan with the outlet throttle opened. Starting with the traverse position at 0mm, where the tip is touching the bottom of the pipe, read and record both manometer tube levels of the wall static and the pitot tube until the traveverse position touching the top of the pipe. Repeat the velocity traverse for the same air flow value at the next positon with the pitot tube assembly. Make sure that the blanking plugs is placed at the holes that are not in use.

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1.7 Results Data Sheet for Velocity Measurement Using Pitot Tube

Traverse Position (mm)

Pitot Tube at 54 mm Static 'Pressure' Reading ____________(mm) Stagnation 'Pressure' Reading (mm)

x (mm)

Pitot Tube at 294 mm Static 'Pressure' Reading ____________(mm)

velocity Stagnation p 2 'Pressure' (N/m ) (m/s) Reading (mm)

x (mm)

p (N/m2)

Velocity (m/s)

0 10 20 30 40 50 60 70 80

Traverse Position (mm)

Pitot Tube at 774 mm Static 'Pressure' Reading ____________(mm) Stagnation 'Pressure' Reading (mm)

x (mm)

Pitot Tube at 1574 mm Static 'Pressure' Reading ____________(mm)

velocity Stagnation p 'Pressure' (N/m2) (m/s) Reading (mm)

x (mm)

p (N/m2)

Velocity (m/s)

0 10 20 30 40 50 60 70 80

25

Pitot Tube at 2534 mm Static 'Pressure' Reading ____________(mm) Traverse Position (mm) 0 10 20 30 40 50 60 70 80    

Stagnation 'Pressure' Reading(mm)

x (mm)

p (N/m2)

velocity (m/s)

Calculate air velocity at each point using equations (1), (5) or (6). Plot the traverse velocity profiles in one graph (Velocity against traverse position). Note that the boundary layer grows in the pipe to fill the whole cross-section; fully developed pipe flow most likely occurred by the third or fourth position. Give your comments on the velocity profiles. Include error analysis.

26

2

Experiment II Determination of Discharge Coefficient

2.1 Objective This experiment will ask student to determine the discharge coefficients, CD for orifice plate and the small nozzle. 2.2

Introduction An orifice plate meter forms an accurate and inexpensive device for measuring the discharge for the flow of liquids or gases through a pipe. The orifice provided can be inserted into the suction pipe at the flanged joint approximately half way along its length. The multi-tube manometer provided is used to measure the pressure drop across the orifice and this is related to the discharge determined independently. In this experiment, we are going to determine the discharge coefficient experimentally for an orifice plate in an airflow pipe. Also using the static pressure tapings provided, we are determining the pressure distribution along the pipe downstream of the orifice plate. From the obtained CD of the orifice plate, we will determine the CD of a small nozzle.

2.3 Theory The orifice plate meter forms a jet, which expands to fill the whole pipe, some diameter distance downstream. The pressure difference between the two sides of the plate is related to the jet velocity, and therefore the discharge, by the energy equation: Q

where

A jv j

Q = Aj = Ao = vj = Cc = Cv = g = h = I)

A oCc v j

A oCc Cv 2gh

discharge (volume/time) jet cross-section area at minimum contraction (vena contracta) 2 orifice cross/4: d = orifice size) jet velocity at minimum contraction (vena contracta) coefficient of contraction of jet coefficient of velocity of jet gravitational acceleration (9.81 ms -2) pressure difference 'head' of air across orifice (refer to equation (6) of Exp.

These two coefficients are normally combined to give a single coefficient of discharge: CD = Cc.Cv Equation (1) now becomes Q

C D Ao 2 gh

(2) If Q can be determined independently, then the discharge coefficient can be determined as follows:-

CD

Q A o 2gh

(3)

Values of Qi can be determined if the standard nozzle is fitted at the pipe inlet.

Qi

A i C ' D 2gh i

(4)

27

If hi = the drop in pressure head across the inlet, the discharge = ( k/ air )* (xbefore nozzle –xafter nozzle): in which Ai = standard nozzle cross-section area (= d2 /4) and C’D assumed to be 0.97. Values of h I are obtained from the manometer tube levels connected to the pipe inlet pressure tapping and open to the atmosphere.

2.4 Calculating the CD of orifice plate: From equation (4), with the Qi obtained from standard nozzle where CD of standard nozzle is assumed to be 0.97, we can calculate the CD of orifice plate. Assuming that Qi across standard nozzle and Qo across orifice plate is the same, apply equation (3) CD

Qo Ao 2 gho

……………………………(5) Where

ho = ( k/ air)*( x across orifice) Ao = cross section area of orifice plate hole

2.5 Apparatus

Figure 2 Experiment Diagram 2.6 Procedure (a) Insert the orifice plate in position (taking care to observe the instructions as to) in which the surface should face the approaching airflow. (b) Connect all the static pressure tapping points to the manometer tubes ensuring that one manometer tube remains unconnected to record room air pressure and that one is attached to the first tapping point adjacent to the standard inlet nozzle which should be fitted. (c) Turn on fan with low airflow (damper plate closed) and read all manometer tubes, including any open to the air (reading should be taken after the fan is on). (d) Gradually increase air flow by increasing the damper opening to 100%, and take read at all opening. 28

Measure the diameter of the orifice plate, and the pipe for computing the cross sectional area and Reynolds number.

2.7 Results Table 5.1 Static ‘Pressure’ Readings when using Standard Nozzle (80 mm) Damper Openings (% Openings) 0%

25%

Points

50%

75%

100%

mm of kerosene

Room “pressure” After nozzle 54mm 294mm 774mm Before Orifice After Orifice 1574mm 2534mm

Table 5.2 Static ‘Pressure’ Readings when using Small Nozzle (50 mm) Damper Openings (% Openings) 0% Points

25%

50%

75%

100%

mm of kerosene

Room “pressure” After nozzle 54mm 294mm 774mm Before Orifice After Orifice 1574mm 2534mm

29



From table 5.1using equation (4) calculate the Qi, then using equation (3) where Q=Qi calculate the CD for orifice plate for each damper opening. For data in table 5.2, using similar procedures, but this time using the value of C D for orifice found previously, you need to calculate the CD for small orifice for each damper opening. For each case, plot values of CD obtained against corresponding values of Reynolds number (Re) obtained using the relationship:

 

Re

vd

……………………………………..(6) where

    

the coefficient of dynamic viscosity of the air air density

v

:

is the mean pipe velocity (Qi/Ap)

d

:

the pipe diameter.

Also plot longitudinal pressure profiles for both tables from the manometer readings. (mm kerosene against tapping position) Discuss what happen as the air flow past through the orifice plate. Discuss the CD obtained for orifice and small nozzle. What happen to the CD when you increase the damper opening? What happen to the manometer reading when the damper opening changes. Discuss. Any obstruction such as an orifice plate would actually cause a pressure drop but by analyzing the graph below or from your data you should see that the reading in mm of kerosene is increased. Explain.

Pressure Drop across Orifice Plate

mm Kerosene



:

Air Flow

Tapping position along test pipe

30

MESB 333 LAB NO. 3 TEMPERATURE MEASUREMENT PRELAB QUESTIONS Name: _____________________SID: ______________ Group:______ Date:______________

1. Describe the working principle of a thermistor and resistance thermometer. What are the differences?

2. What is time constant?

3. What are the materials commonly used for resistance thermometer? i) ________________________________________ ii) ________________________________________ iii) _________________________________________ 4. Gives two examples where PTC thermistors are generally used? i) ________________________________________ ii) _______________________________________

31

MESB 333 Lab No. 3 Temperature Measurement ______________________________________________________ 1

Experiment I Time Constant

1.1

Objective

To compare the time constant of differnet type of temperature measuring devices with reference to mercury filled thermometer. Understanding the concept of resistance thermometer (or RTD) and thermistor using the PT100 and NTC probes. Students should be able to understand the relationship between resistance and temperature, and main difference between resistance thermometer and thermistor.

1.3

Theory

Temperature is a measure of hotness. Together with a measure of ‘thermal mass’ of a body it gives an indication of the total thermodynamics energy that body contains. There are many scales for the comparison of temperatures, the most important is with their corresponding values for melting ice and boiling water (which are common reference temperatures) being given in the table below.

Scale

Melting Ice

Boiling Water

Celsius (or Centigrade)

0 0C

100 0C

Fahrenheit

32 0F

212 0F

Kelvin (Absolute Scale)

273 K

373 K

In this experiment you will be familiarized with the following temperature measurement devices:

1.4

a) Resistance thermometer

(TYPE K)

b) Thermistor

(NTC)

The Liquid Filled Thermometer This type of thermometer depends on the expansion of a liquid associated w ith an increase in temperature. The most common type is the mercury-in-glass thermo meter. This thermometer 32

consists of a capillary tube with a bulbous end . clean , dry mercury is introduced and the thermometer heated to drive off the air. The end is then scaled leaving mercury and mercury vapour only. On heating, the mercury expands relative to the glass container and a column is pushed along the bore of the tube. A scale along the tube, calibrated in units of temperature, gives a direct reading of temperature. The mercury-in-glass thermometer is an accurate device but is very fragile and care should be exercised in use. This type of thermometer should not be used in applications such as the food industry where mercury poisoning could occur in the event of breakage. The mercury may be replaced by other fluids according to the application. For example, alcohol is cheaper and may be used at low er temperatures than mercury. A mercury-in-glass thermometer is supplied with the Temperature Measurement Bench due to its stable and accurate performance. For accurate measurement of temperature using a liquid filled thermo meter, it is important that the thermometer is immersed into the medium being measured by the correct amount. The depth of immersion is usually stated on the stem of the thermo meter and defines the condition under which calibration is maintained. The immersion depth may be partial or total and is independent of filling or range

1.5

The Vapor Pressure Manometer For industrial applications, the liquid-in-glass thermo meter is f ar f rom suitable due to its fragility and the dif f iculty in reading. In these applications the glass is replaced by a metal container and mechanical indication is substituted. One example of this type of thermo meter is the vapor pressure thermo meter. This consists of a metal bulb partially f illed with f luid, w hich is connected to the sensing e le ment of a Bourdon gauge. The space above the fluid is filled with vapor of the fluid, the pressure of which is displaye on the Bourdon gauge . The gauge is calibrated directly in units of temperature corresponding to the equivalent , pressure of the vapor but calibration is far from linear due to the pressure increasing more and more rapidly as the temperature increases. For this reason, the vapor pressure thermometer is suitable only for operation over short ranges of temperature and suff ers from lack of sensitivity at low readings. In service, the range should be selected so that the gauge rema ins within operatio nal limits w ith the normal operating point at approximately two thirds of f ullscale reading. Vapor pressure thermometers off er the advantage of remote reading. The thermometer may be ordered with a metal capillary tube connecting the bulb to the gauge, permitting remote operation over distances up to sixty meters. Correct orientation of the bulb and gauge should be preserved f or ac- curate results. The vapor pressure thermo meter supp lied w ith the bench has the Bourdon gauge connected directly to the stem f or case of operation

33

1.6

The Bi-Metal Thermometer

Expansion of solids may be used to measure te mperature but direct measure ment is impractical due to the very small move ments involved. How ever, if two thin met al strips, having d if f erent coeff icients of linear expression, are mechanically fastened together, the result is a strip which bends significantly when heated. This combination is called a Bi-metal strip and the sensitivity may be increased by coiling the strip int o a spiral. One end of the strip is f ixed to the case and a pointer is attached to the other end. L inear scale may be obtain ed by suitable cho ice of metals. This type of thermometer is very robust and has many applications throughout industry where accuracy of measurement is not imp ortant. The bi- metal thermometer supplied w ith the bench is mounted on th e back-board and gives a direct reading of ambient a ir temperature.

1.7

Resistance Thermometer The resistance of a material changes with temperature. Resistance thermometer uses this relationship in measuring the temperature. If high accuracy is required, the material used in resistance thermometer is platinum. Nickel is used in general operation and monitoring. Copper is also suitable but only in a restricted temperature range of approximately 250 oC, because copper tends to corrode more severely when subjected to oxidation.

Figure 3.1 shows the resistance change of the metals as a function of the temperature T. They have a positive temperature coefficient . For the purpose of comparison a resistance characteristics of a thermistor (NTC) was added, which runs much more non-linearly, and in contrast to the metals, demonstrates a negative coefficient .

For small temperature ranges we may assume that linear relationships exist between resistance and temperature. From figure 3.2 one can deduce the temperature-dependent resistance ratio R(T) caused by the resistance change R is:

R(T) = Ro + R

(1)

The rise of this function is m = R/ T. R =m T

Knowing that,

(2)

R(T) = Ro + R, thus: 34

R(T) = Ro + m T = Ro (1 + m/Ro T) = Ro (1 +

R / Ro T

T)

= Ro (1 + 1 T)

Ni 100

(3)

where, 1 =

R / Ro T

Pt100

Cu100

Figure 3.1

1 is the linear temperature coefficient of the resistive material. It provides the relative change in NTC resistance ( R/ Ro) for a certain temperature change ( T), for example 0.4% change in resistance

R(T) R per degree.

Ro = R(To) T=T-To (To=00C)

Ro T Figure 3.2

R=R(T)-Ro

From Figure 3.1 we can see that for large measurement ranges no linear relationship between resistance R and temperature T can be assumed. In this case we must take into consideration, apart from the linear temperature coefficient 1 , also To T the square temperature coefficients 2, and 35

for very large temperature changes T also the cubic temperature coefficients 3, and if necessary the biquadratic value 4.

R (T)

Ro 1

1

T

2

T2 ...

n

Tn

(4)

where, T T To

1.8

Thermal Response The thermal response of a thermo meter to changes in te mperature is probably the most important characteristic to consider w hen selecting instrumentat ion f or a particular application.

A thermo meter may be extremely accurate and stable in performance but totally unsuitab le f or use in a dynamic situation, due to a time lag betw een system temperature and thermometer reading.

The d iagra m below shows typical response curves f or a thermo meter when step changes in te m- perature are applied .

The response of the thermo meter is def ined by the t ime ta ken f or the te mperature reading to change by 63.2% of the step change. For any thermometer, this time will be a constant value irrespective of step change and is def ined as the "t ime constant" f or the thermometer. Th e time constant and re- sponse profile f or a thermometer will change if the system is modif ied. For example, t he speed of response of a thermometer will be slowed down if it is protected f rom the system being measured by a ther mo meter. The response will also be af f ected by the thermal contact between the thermometer and pocket, f luid f illing of the pocket resulting in a reduction in time constant.

36

The response of the thermometer is def ined by the t ime taken f or the te mperature reading to change by 63.2% of the step change. For any thermometer, this time will be a constant value irrespective of step change and is def ined as the "time constant" f or the thermo meter. Th e time constant and response prof ile for a thermometer will change if the system is modified. For example, the speed of response of a thermometer will be slowed down if it is protected from the system being m easured by a thermometer. The response will also be af f ected by the thermal contact between the thermometer and pocket, f luid f illing of the pocket resulting in a reduction in time constant.

Figure 3.3 Experiment apparatus setup

37

1.9

Setup

1.10 Procedure

Note: To discharge the hot water from the pot, request assistant from lab technician.

38

1.6

Result

Table 1. Temperature measurements result

Plot the graph of T against time for each type of temperature measuring devices. Calculate and plot the time constant for each thermometer. Discuss on the plotted graph? Which type of temperature measuring device has smallest time constant?

2

Experiment II Type K thermocouple

2.1

Objective

-

2.2

To investigate the working principle of Type K Thermocouple To investigate the relation between voltage output and temperature

Thermistor

Thermistors consist of semi-conducting polycrystalline material. In the production of temperature sensors copper dioxide (CuO2) is preferred. It demonstrates a sever (non-linear) drop in resistance for an increase in temperature. It possesses a negative temperature coefficient, which is the reason why these sensors are called NTC resistors.

39

If the CuO2 is mixed with the ingredients of a ferroelectric material (e.g. BaTi), the temperature coefficient is initially negative only for low temperatures. After reaching a threshold temperature the temperature coefficient becomes very strongly positive in a narrow temperature range. For even higher temperatures the temperature coefficient reverts back to negative. Because of the clearly delineated positive temperature coefficient range, these sensors are called PTC resistors. They are mainly used for trigger purposes.

2.3

Features of NTC and PTC thermistors

NTC sensors possess a high sensitivity, which is easily 10 times higher than that of metal resistance thermometers. The non-linearity of NTCs and their broad manufacturers' tolerances exclude them from use for precision instruments. In the temperature range between 60oC and +150oC they are frequently used in the area of household appliances and medical technology because of their high sensitivity and corresponding simple circuitry.

The effect of NTCs, whereby the resistance lowers as the temperature increases, is explained by the semiconductor mechanism. In semi-conductors (as opposed to metal conductors) the valency electrons have relatively strong bonds to the atomic nuclei of the crystal lattice. A rise in temperature loosens this bond and more and more electrons enter into the conduction band, where they are available for charge transport (i.e. for increased current), thus reducing the ohmic resistance.

PTCs behave in the same manner below the threshold temperature. The resistance lies only somewhat higher than for NTCs, because, due to the mixture of a ferroelectric material to the semiconductor material an additional resistance of both components results (series connection). However, with increasing temperature a strong increase in resistance is observed within a narrow temperature range, which is caused so rapidly by the sudden cancelling of a uniform orientation of all magnetic forces in the ferroelectric material. Through thermal motion an amorphous crystal structure is produced, which results in a considerable prolongation of the current paths, on which the electrons move through the PTC. If this transition is completed, the resistance then drops again as the rise in temperature continues. Thus the function R(T) of the PTC follows the characteristic of its semiconductor components, supplemented by the characteristics of its ferroelectric components. They are generally intended for applications where a considerable change of esistance is required as a function of themperature, or of dissipated power, for example: heating elements, temperature indication, control or alarm, time-delay of relays, circuit protection etc.

40

2.4

Temperature function and temperature coefficient of NTC thermometers

The resistance R(T) = RT of NTC materials can be described as a function of the temperature using the following equation:

RT = AeB/T

(5)

The material constant B is given in Kelvin, e.g. B = 3800 K. The constant A gives the resistance for infinitely high temperature. As the sensor cannot register this temperature, the constant A cannot be used as a practical parameter. The requirements for practical application can be better satisfied with the following dependency RT. For this the reference temperature To = 20oC is used, for which the resistance has its nominal value Ro. Due to the fact that in the above equation only A is unknown, the equation is then solved for A, which is inserted into RT:

R(To) = Ro

= AeB/To

A = Roe-B/To

(6)

Subsitute (6)into equation (5)

RT = RoeB(1/T - 1/To)

(7)

41

2.4

Procedure

2.5

Result Table 2.1 Type K experiment result

Type K Time (min)

Voltage(mV)

Temp(oC)

0 2 4 6 8 10 12 14

Explain the results of this measurement. How does the temperature effect the voltage output? Plot the temperature against time and voltage against temperature. Is the graphs linear? If it is a linear get the slope of the best fit line. Include error analysis.

42

3

Experiment III Humidity

3.1

Objective

-

Understanding of whirling pyschorometer (hygrometer) Understanding of wet and dry bulb thermometer Measurement of ambient humidity using dry and wet bulb.

3.2 Introduction

Humidity is the amount of water vapor in the air. Relative humidity is defined as the ratio of the partial pressure of water vapor in a parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature. Humidity may also be expressed as specific humidity. Relative humidity is an important metric used in forecasting weather. Humidity indicates the likelihood of precipitation, dew, or fog. High humidity makes people feel hotter outside in the summer because it reduces the effectiveness of sweating to cool the body by reducing the evaporation of perspiration from the skin. This effect is calculated in a heat index table Hygrometers are instruments used for measuring humidity. A simple form of a hygrometer is specifically known as a psychrometer and consists of two thermometers, one of which includes a dry bulb and the other of which includes a bulb that is kept wet to measure wet-bulb temperature. Modern electronic devices use temperature of condensation, changes in electrical resistance, and changes in electrical capacitance to measure humidity changes. Hygrometers measure humidity while psycrometers measure realative humidity in the air. In a psychrometer, there are two thermometers, one with a dry bulb and the other with a wet bulb. Evaporation from the wet bulb lowers the temperature, so that the wet-bulb thermometer usually shows a lower temperature than that of the dry-bulb thermometer, which measures drybulb temperature. When the air temperature is below freezing, however, the wet bulb is covered with a thin coating of ice and yet may be warmer than the dry bulb. Relative humidity is computed from the ambient temperature as shown by the dry-bulb thermometer and the difference in temperatures as shown by the wet-bulb and dry-bulb thermometers. Relative humidity can also be determined by locating the intersection of the wet- and dry-bulb temperatures on a psychrometric chart. One device that uses the wet/dry bulb method is the sling psychrometer, where the thermometers are attached to a handle or length of rope and spun around in the air for a few minutes.

43

3.2 Procedure

Table 3.1 Wet and Dry Bulb and Humidity Measurement Wet Bulb

Dy Bulb

Initial Reading Final Reading Humiditiy from psychrometeric Chart Humidity reading from dail gage

- Compare the humidity measurements between hunidity dail gage and the psycrometric chart - Error analysis

44

MESB 333 LAB NO. 4 : PHOTO ELECTRIC TRANSDUCER PRELAB QUESTIONS Name: _____________________SID: ______________ Group:______ Date_______________

1. How to measure the intensity of a light?

2. What is the principle of photo electric transducer?

3. What is the Lambert’s Cosine Law?

4. What is the Inverse square Law?

5. Give three type of photo transducer?

a.

b.

c.

45

MESB 333 Lab No.4 Photo Transducer 1

Introduction. In this lab, the students are to be expose to several type of photo transducer with their characteristic that are related to Inverse Square Law and Lambert’s Cosine Law.

1.1

Objective

To understand the photo transducers effect and its relations with Inverse Square Law and Lambert’s Cosine Law. Students will measure the effect of the incident light on the behavior of a photodiode, phototransistor and photo conductive cell. 1.2

Theory

When light falls onto certain material, its energy will be given up as being described by the principle of photo-electric transducer. The energy will become energy in the form of electric current. Human eyes is an example of a photo-electric transducer. Eyes act as a transducer by converting light energy to signals that will be sent to the brain for further process. Experimentally, one can know the intensity of the light falls on an object by measuring the corresponding electric current caused by the light. In this experiment, you will learn to use photo-electric transducer to measure the intensity of light in relation to the induced current and resistance. The variety of colors existing in this world is due to the fact that sun-light has different components of light. Color of light is determined by its frequency, which in turn proportional to the reciprocal of its wavelength. The relationship between light frequency, speed of light and

f

v f 1

wavelength is given in the equation Where,

f

= frequency

v

= speed of light, 3 x 108 m/s = wavelength = time to complete a cycle of wave

The spectrum for light with its wavelength has been measured experimentally as shown below.

46

Table 4.1Spectrum for light COLOR WAVELENGTH (mm) 440 Violet Blue 470 Blue-Green 490 Green 520 Yellow-Green 550 Yellow 580 Orange 600 Red 690 Deep-Red 700 Light is a form of electromagnetic radiation. Alternatively, light can be considered as consisting of little packets of energy, called photons, and the energy of each photon is directly proportional to the frequency of light. From the light wavelength and frequency relationship, the smaller the wavelength, the higher will be the frequency. With the relationship that energy is directly proportional to the frequency of light, higher frequency will translate to higher energy. Therefore, blue light has a higher energy that red light because the wavelength for blue light is shorter than

f

v f v

the red light as shown in table 5.1. Luminous intensity for light has unit of candela, cd. 1 cd equals to 1/60 of luminous intensity coming from an area of 1 cm2 of platinum melting at 2046 K. Light can be described in term of luminous flux with a unit called LUMEN. A lumen is a luminous flux from a point source of 1 candela within a solid angle of 1 steradian. Luminous flux can be thought of as light power, or the energy (number of photons) emitted per second.

Another definition is illumination. An illumination at any point on the surface is defined as the luminous flux per unit area falling perpendicular to the surface. When a luminous flux of 1 lumen falls onto a surface area of 1 m2 , it is called an illumination of 1 LUX (lx)

1.3

The Inverse Square Law

If the radius of an imaginary sphere is increased from 1 m to 2 m, the area subtended on the surface by the solid angle of 1 Sr is increased from 1 m2 to 4 m2, in proportion to the square of the radius. The luminous flux over this area is still 1 m2 but the illumination has now fallen to a quarter of its previous value as the luminous flux is spread over four times the area.

47

E

d2

Hence, the illumination on a surface is inversely proportional to the square of its distance from the source. The illuminance, E (lux) is given as,

Where d

1.4

=

luminous flux (lumen)

=

distance (m)

Lambert’s Cosine Law If there is an angle of between the surface of the transducer and the oncoming light, the luminous flux falling on the transducer surface is exactly the same as that which would fall on a normal surface (Figure 5.1). However, Area surface 1 = cos Area surface 2

Incident Light

= Illumination surface 1 Illumination surface 2

1

2

Figure 4.1

Thus the modification of the inverse square law becomes:

E 1.5

d2

cos

The Photo-Conductive Cell A semiconductor, as its name implies is a material with an electrical conductivity in between that of an insulator conductor and a conductor. Typical materials of interest are Germanium and Silicon, but other materials and combinations of materials behave in a similar fashion. They are extensively used in semiconductor devices, e.g diodes and transistors. Electrical conduction in such a material occurs when free charge carriers, e.g electrons, are available in the material to move when an electric field is applied. It happens that in certain semiconductors, light energy falling on them is of the correct order of magnitude to release charge carriers which will increase the flow of current produced by an applied voltage. This is known as the PHOTO-CONDUCTIVE effect, and device is called a PHOTO48

RESISTOR or a PHOTO-CONDUCTOR, or sometimes a LIGHT DEPENDENT RESISTOR, as incident light will effectively vary its resistance. The current, or the number of charge carriers would expect to be related to the number of photons, or the intensity of the incident light, and will be investigated. The colour of the light will affect the response, due to the different energies of the photons. Small number of charge carriers are also produced at room temperature by thermal effects, and this will also contribute to the current. The physical effects which cause this phenomenon are rather involved, but are given here to make the study complete. In an intrinsic (pure) semi-conductor crystal all the valence electrons have covalent bonds together with their neighbours. There may be represented on a diagram of energy bands. It is found that there is a forbidden energy gap of the order of an electron volt (1eV) between the valence band (where the electrons are bound to their parent atoms) and the conduction band the electrons are now free charge carriers). This corresponds to the minimum energy necessary to break a covalent bond and form a hole/electron pair. The electron is raised into the conduction band and contributes to conduction as well as the hole left in the valence band. This theory is fully described most standard textbooks. It is of interest to us now if this energy can be supplied by light photons. Consider first the effect of impurities in the semiconductor. Very small amounts of the correct impurities can introduce either extra holes (P type) or extra electrons (N type) because atomic structure. These will appear on our energy diagram as energy levels just below the conduction band (doNor Ievel for N type) or just above the valence band (accePtor level for P type). If photons of the correct energy illuminate such a specimen, several things may happen, as shown in Fig 4.2

Conduction band doNor level photon

Impurity excitation

Intrinsic excitation

Energy gap Eg

AccePtor level Valence band

Figure 4.2 Effect of photons in energy bands of a semiconductor with both P & N type impurities

An electron/'hole pair may be generated by a high energy photon as described above. The electron ‘jumps’ the gap into the conduction band. This is called intrinsic excitation. An electron in the doNor level" (for N type) may be excited into the conduction band. A valence electron may fill a hole in the accePtor level (for P type). 49

These last two transitions are known as impurity excitations and require less energy than intrinsic excitations. However, the density of states in the conduction and valence bands greatly exceeds the density of impurity states. At room temperature, most of the impurity atoms are ionised in any case. Thus, photoconductivity is due principally to intrinsic excitation. Impurities however do have advantages as discussed later. Our transducer is actually an N-type semiconductor. The carriers generated by the photo-excitation will move if an external voltage is applied to the device. This superimposes a regular drift on their random diffusion motion colliding with others. They may however, recombine with an available hole or electron before they reach the edges of the material. This may affect the response time of the device, cut down the available current (loss of sensitivity) or introduce non-linearities. Those carriers remaining will constitute the device current which thus depends initially on the number of photons. The actual process is extremely complicated and depends on several factors, including the density of the states in the energy bands, the probability that a photon will excite an electron, and other factors, including carrier lifetime and mobility which depends upon recombinations and trappings. Thermal effects also play a part. 1.6

SAFETY & PRECAUTION

1. Only plug the banana plug into the banana socket according to the experiment manual when doing experiment, plugging the plug into the wrong socket may damage the electronics component inside the control box. 2. Check the wiring connection between banana socket first before turn on the control box. 3. Do not connect the positive terminal of the power supply to negative terminal of the power supply without connecting to any load between them. 4. Make sure the connection between the measurement point and the measurement meter are in correct polarity. 5. Make sure the connection of the lamp to the power source are in correct polarity. 6. If the experiment is conducted during day light, take the reading as soon as possible in case the day light varies. Also keep your hand away from the rig when taking readings in case they cause unwanted reflections of light onto the transducers. 7. While the lamp is turn on, avoid touching the lamp’s body. 8. Before using the multi-meter to do voltage/current measurement, make sure the correct measurement range is selected on the multi-meter. Also make sure the banana plug is connected to correct terminal of the multi-meter.

Pre-experiment procedure 1. Read the safety instruction given before conducting the experiment. 2. Read and understand the theory of photo transducer before lab session. 3. Read and understand the theory of Inverse Square Law and Lambert’s Cosine Law before lab session. 4. Prepare the accessories needed for the experiment.

50

2

Experiment 1: Photodiode 2.1.

PROCEDURES

Part 1: Photo diode - Inverse Square Law 1. Make sure the control box’s main switch is turn off first before start doing wiring connection. 2. Unplug all the banana plug from the banana terminal first before assembling out the circuit. 3. Start connecting the circuit using banana plug to respective banana socket, by using circuit diagram below as reference.

Fig. 4.3 - Schematic for the photodiode experiment 4. Make sure all the wiring connection is according to the circuit diagram. Before switch on the power supply, let the lab instructor to check the connection of circuit. 5. Plug in the lamp’s banana plug into the Lamp’s power supply banana socket, make sure the polarity is correct. 6. Adjust the position of the photo transducer box so that its angular scale of the photodiode facing the light source is 0°. 7. Ensure the hole of the photo transducer box is not facing other light source, affecting your reading value during experiment. 8. Turn on the mains switch, wait all the measurement meter initialized first before start conducting experiment. 9. Switch on the lamp’s power supply, check whether the lamp got light up or not. 10. Adjust the position of the light facing the photo transducer box, while carefully adjusting the position of the lamp with distance 1 meter. 11. Move the bulb to get different distance. 12. At each value of different distance, record down the values of the voltage and current on your table. Part 2: Photo diode - Lambert’s Cosine Law 1. With the circuit of Part 1 still connected, return the photo transducer box and lamp to their starting positions (distance 1 meter) 2. Switch on the lamp again. 3. Rotate the angular scale shown on the photo transducer box to 30° anti-clockwise and record the reading. 51

4. Repeat the procedure 3 for the angles as shown in the table below. 5. After finish the experiment, switch off the lamp power supply and the main power supply switch on the control box. 2.2.

RESULT AND DISCUSSION

Part 1: Photo diode - Inverse Square Law Table 4.2 Experiment Result of Photo diode response Applied voltage:_____________Volt Distance (m)

Current (μA)

Resistance (Ω)

1000 900 800 700 600 500 400 300 200 100 Switch Off the lamp For each distance, calculate the resistance of the transducer by applying Ohm’s law and dividing the applied voltage by the current flowing, R = Vdc/I What is the relationship between resistance and distance at constant voltage? Why the current did not become zero when the lamp is switch off? How can you relate the result obtained with Inverse Square Law? Plot graph if required? Plot a graph of current flowing against distance. Label your graph with the value of applied voltage. Discuss the shape of the graph.

52

Part 2: Photo diode - Lambert’s Cosine Law Table 4.3 Experiment Result of Photo diode - Lambert’s Cosine Law

Angle (Degrees)

Current (μA)

Resistance (Ω)

30 (ACW) 25 20 15 10 5 0 10 (CW) 5 10 15 20 25 30

Plot a graph of current flowing against angle. Does the graph follow accurately the cosine law? Suggest the principal advantages and disadvantages of the Photo diode.

53

3

Experiment 2: Photo Conductive Cell 3.1 Procedure Part 1: Photo Conductive Cell - Inverse Square Law 1. Make sure the control box’s main switch is turn off first before start doing wiring connection. 2. Unplug all the banana plug from the banana terminal first before assembling out the circuit. 3. Start connecting the circuit using banana plug to respective banana socket, by using circuit diagram below as reference:

Fig. 4.4 - Wiring Diagram for Photo Conductive Cell Experiment 4. Make sure all the wiring connection is according to the circuit diagram. Before switch on the power supply, let the lab instructor to check the connection of circuit. 5. Check the potentiometer (VR) control knob on the Operational Amplifier section of the control box is set to minimum first. 6. Plug in the lamp’s banana plug into the Lamp’s power supply banana socket, make sure the polarity is correct. 7. Adjust the position of the photo transducer box so that its angular scale of the photodiode facing the light source is 0°. 8. Ensure the hole of the photo transducer box is not facing other light source, affecting your reading value during experiment. 9. Adjust the multi-meter’s rotary switch into the correct range. i.e. 200mA range for current meter and 20V for voltage meter. 10. Turn on the mains switch, wait all the measurement meter initialized first before start conducting experiment. 11. Switch on the lamp’s power supply, check whether the lamp got light up or not. After that, position the lamp holder again at the distance of 1meter. 12. Adjust the potentiometer to get 10mA. Record down the voltage and this value should be constant for the experiment. 13. Leave the equipment like this for at least 5 minutes. This is to ensure the necessary preconditioning of the device is carried out. 14. Move the lamp backwards to vary the distance and the affect on the transducer. Record the voltage and current value at each step. 15. Switch off the lamp and take the reading again corresponding to ambient light illumination. 54

Part 2: Photo Conductive Cell : Lambert’s Cosine Law 1. With the circuit of Part 1 still connected, return the photo transducer box and lamp to their starting positions. 2. Switch on the lamp again and slowly adjust the potentiometer (VR) until the multi-meter reads about 10mA initial value. 3. Rotate the angular scale shown on the photo transducer box to 30° anti-clockwise and record the reading. 4. Repeat the procedure 3 for the angles as shown in table below. 5. After finish the experiment, switch off the lamp power supply and the main power supply switch on the control box. 3.2 RESULT AND DISCUSSION Part 1: Photo Conductive Cell- Inverse Square Law Table 4.4 Experiment Result of Photo Conductive Cell response Distance (mm)

Current (mA)

Voltage (Volt)

Device Resistance (Ω)

1000 900 800 700 600 500 400 300 200 100 Off of the lamp

55

Part 2: Photo Conductive Cell - Lambert’s Cosine Law Table 4.5 Experiment Result of Photo Conductive Cell Lambert’s Cosine Law

Angle (Degrees)

Current (μA)

Resistance (Ω)

30 (ACW) 25 20 15 10 5 0 5 10 15 20 25 30

56

4

Experiment 3: Phototransistor 4.1 Procedure Part 1: Phototransistor - Inverse Square Law 1. Make sure the control box’s main switch is turn off first before start doing wiring connection. 2. Unplug all the banana plug from the banana terminal first before assembling out the circuit. 3. Start connecting the circuit using banana plug to respective banana socket, by using circuit diagram below as reference:

Fig. 4.5 - Wiring Diagram for Photo-transistor Experiment 4. Make sure all the wiring connection is according to the circuit diagram. Before switch on the power supply, let the lab instructor to check the connection of circuit. 5. Check the potentiometer (VR) control knob on the Operational Amplifier section of the control box is set to minimum first. 6. Plug in the lamp’s banana plug into the Lamp’s power supply banana socket, make sure the polarity is correct. 7. Adjust the position of the photo transducer box so that its angular scale of the photodiode facing the light source is 0°. 8. Ensure the hole of the photo transducer box is not facing other light source, affecting your reading value during experiment. 9. Adjust the multi-meter’s rotary switch into the correct range. i.e. 200mA range for current meter and 20V for voltage meter. 10. Turn on the mains switch, wait all the measurement meter initialized first before start conducting experiment. 11. Switch on the lamp’s power supply, check whether the lamp got light up or not. After that, position the lamp holder again at the distance 1 meter. 12. Adjust the potentiometer to get different voltage. 13. Leave the equipment like this for at least 5 minutes. This is to ensure the necessary preconditioning of the device is carried out. 14. Move the lamp backwards to vary the distance and affect on the transducer. Record the voltage and current value at each step. 15. Switch off the lamp and take the reading again corresponding to ambient light illumination.

57

Part 2 Phototransistor - Lambert’s Cosine Law: 1. With the circuit of Part 1 still connected, return the photo transducer box and lamp to their starting positions corresponding to 100% relative illumination. 2. Switch on the lamp again and slowly adjust the potentiometer (VR) until the multimeter reads about 10mA initial value. 3. Rotate the angular scale shown on the photo transducer box to 30° anti-clockwise and record the reading. 4. Repeat the procedure 3 for the angle of 20°, 10° until 0° up to 30° clockwise. 5. After finish the experiment, switch off the lamp power supply and the main power supply switch on the control box.

4.2 RESULT AND DISCUSSION Part 1: Phototransistor - Inverse Square Law Table 4.6 Experiment Result of Phototransistor - current Response Distance (mm) 1000

900

800

700

600

500

400

300

200

100

Voltage (V)

Current (mA)

0 1 2 5 10

58

Part 2: Phototransistor - Lambert’s Cosine Law Table 4.7 Experiment Result of Phototransistor - Lambert’s Cosine Law

Angle (Degrees)

Current (μA)

Resistance (Ω)

30 (ACW) 25 20 15 10 5 0 5 10 15 20 25 30 Plot graph and write the analysis according to the objective of the experiment.

59

MESB 333 LAB NO. 5 : FLOW RATE MEASUREMENT PRELAB QUESTIONS

Name: _____________________SID: ______________ Group:______ Date:_______________

1. What are the examples of flow measurement techniques that use obstruction.

2. Draw the cross section of a venturi meter and label the throat, upstream, and recovery cone.

3. Why is orifice plate is used as a fluid flow measurement device? _________________________________________________________________________

4. What is discharge coefficient ? What are Cd for orifice plate and venturi meter ? What does the Cd value tells us ? ________________________________________________________________________ ________________________________________________________________________ 5. What does smaller discharge coefficient tells us?

60

MESB 333 Lab No. 5 Flow Rate Measurement

1

Objective In this experiment, students will learn different types of flow meters devices to measure liquid (water) volume flow rate. The flow meters used on the apparatus are venturi meter, variable area meter and orifice plate. From these three devices, you will be able to compare the advantages and accuracy of each device.

1.1

Theory

The theory behind this experiment is similar to the air flow rig in experiment 2. From the pressure drop on the orifice or the venturi meter, the flowrate of the fluid can be calculated. Applying Bernoulli equation:

V12 2g For same elevation, Z1 = Z2

P1 g

V22

Z1

V12

V22

P1 g

2g

P2 g

2g

Z2

P2 g

2g

Carry the velocity to the right and pressure to the left: 2

2

P1 P2 V2 V1 g g 2g 2g 1 1 2 P1 P2 V g 2g 2 For an ideal flow :

V12

Q A1V1 A 2 V2 A2 V1 V2 A1 SubstituteV1 int o

1 (p1 g

1 (p1 g

p1

1 V2 2g 2

p2 ) V22

p2

1 (V 2 2g 2

p2 )

1

2

A2 A1

V12 )gives : A2 A1

2

V22

2

Now, we will write the above in term of V2:

V22

2(p1

2

A2 A1

1

V2

p2 )

2(p1 1

p2 ) A2 A1

2

61

Knowing that Qideal = A2V2, thus:

Qideal A 2

2(p1 p 2 ) 1

A2 A1

2

The above is for an ideal flow. For venturi tube and the orifice, the equation must be multiplied with the coefficient of discharge, Cd: Qactual

Cd Qideal

Qactual

Cd A 2

2( p1 1

Where, Cd Q A2 A1 P

: : : : :

A2 A1

2

discharge coefficient 3 volume flowrate (m /s) throat diameter for venturi, or orifice diameter for orifice plate upstream pipe diameter (P1-P2) pressure drop across the venturi meter or the orifice ( g h)

Cd values assumed to be:

1.2

p2 )

Cd = 0.98 for the venturi meter Cd = 0.63 for the orifice plate

Discharge Coefficient What is really a discharge coefficient? You have observed in the previous experiments on the airflow rig where the discharge coefficient is always used in relation to the orifice plate and the nozzle. Similarly, discharge coefficient will be applied to venturi tube too. Discharge coefficient basically tells how much the actual flow defers from the ideal flow: Cd

Qactual Qideal

A smaller value of discharge coefficient tells that the actual flow is smaller compare to the ideal or theoretical value. The discharge coefficient for the orifice plate is 0.63 while for the venturi meter it is 0.98. There is more resistance to the flow imposed by the orifice plate, and subsequently it causes some loses through the meter. This loss can be observed from the large pressure drop across the orifice compares to the pressure drop across the venturi meter.

62

1.3 Apparatus

Figure 1 Experiment apparatus

The hydraulic bench and the apparatus are as shown above. The flow meter apparatus is set up on top of the hydraulic bench. The apparatus above consists of venturi meter, variable area meter and orifice plate and 8 bank manometer. Pressure readings of the water flow will be taken from the 8 bank manometer. 1.3.1 Technical Data:

Venturi meter Upstream pipe diameter hence A1 Throat dia. hence A2 Upstream taper Downstream taper

1.4

= = = = = =

31.75 mm -4 2 7.92 x 10 m 15 mm -4 2 1.77 x 10 m 0 21 inclusive 0 14 inclusive

Orifice plate Upstream pipe diameter hence A1 Orifice diameter

= = =

hence A2

= 3.14 x 10-4 m2

31.75 mm -4 2 7.92 x 10 m 20 mm

Procedure

1. Observe that the apparatus is placed on the hydraulic bench. The inlet pipe of the apparatus is connected to the hydraulic bench supply, while the apparatus outlet pipe is connected to the pipe going to the volumeter tank. 2. Note that the hydraulic bench inlet valve is in shut position. 63

3. Switch on the pump then slowly open the hydraulic bench inlet valve. 4. At the same time open the flow control valve, the outlet valve on the apparatus. 5. To disperse air trapped in the flow system, close flow control valve, open air bleed screw and prime manometer and tappings. When done, close back the air bleed screw. 6. Switch off the pump and adjust the levels of the manometer by adjusting the air bleed screw. Try to get initial manometer level at a comfortable level so that when experiment is carried out there will be enough room for the water column in the manometer to move up and down. Close back the air bleed screw when done. Switch on the pump again. 7. Adjust the inlet and outlet valves so that variable meter gives the flow rate of 2 Liter/min. Record the manometer reading. Increase the flow rate until 22 Liter/min. 8. Measure a certain volume of the reservoir, using stop watch measure the time taken to fill that portion. 9. Repeat step 7 to get another set of data. 1.5

Results

Get the manometer readings for the respective flow rates of the variable meter. Table 1 Experiment Result Variable Meter Flow rate Manometer Readings (mm) (Liter/min) 1 2 3 4 5 6 7 2 5 10 12 15 18 20 22

8

Seconds

Note the followings: Manometer 1 minus Manometer 2 = Venturi Reading Manometer 1 minus Manometer 3 = Loss In Venturi Manometer 4 minus Manometer 5 = Loss In Variable Area Manometer 6 minus Manometer 7 = Orifice Plate Reading Manometer 6 minus Manometer 8 = Loss In Orifice Plate From the readings obtained on the Venturi meter and orifice plate calculate the volume flow rate using the basic equation with relevant Cd factor. Note that (p1 - p2) in the equation refers to Venturi Reading (Manometer 1 minus Manometer 2), and NOT Loss In Venturi (Manometer 1 minus Manometer 3). Similarly for Orifice Plate, use Orifice Plate Reading. Calculate the actual flow rate using the volume and time measured. Don't forget to change the manometer column readings from mm to m. Compare these calculated values and the reading on the variable area meter with the actual flow rate. Use same units. Calculate the velocity at point 2 (venturi meter) and 7 (orifice plate) (Use formula: velocity=volume flow rate/cross section area) and discuss. Also calculate the Reynolds number at these two points. Re d = Dv/ ,,where = absolute -4 viscosity = 8.937 x l0 Pa.s and D is the diameter of the holes. Question for discussion When calculating (p1 - p2) for the venturi meter, why is the reading for p2 is taken at the venturi throat and not at the tapping after the throat? How does the variable area meter work? How to calculate the volume flow rate using stop watch? What sort of losses do you think occur on the venturi meter and the orifice plate? 64

Why the heights should different in relation to the others in the manometer? Why velocity at P2 and P7 are different? Which flow meters devices as the smallest error? Include error analysis.

Flowrate comparision table Variable Conversion Meter to Flow rate 3 (Liter/min) m /s 2 5 10 12 15 18 20 22

Venturi Flowrate 3

m /s

Oriface Flowrate 3

m /s

Flowrate using stopwatch 3 m /s

Percentage Different Relative to Variable Meter Variable Meter Flow rate (Liter/min) 2 5 10 12 15 18 20 22

Venturi %

Oriface %

Stopwatch %

Velocity at P7 m/s

Reynolds Number at P2

Velocity at p2 and p7. Variable Meter Flow rate (Liter/min) 2 5 10 12 15 18 20 22

Velocity at P2 m/s

Reynolds Number at P7

65

Lab No.6

MESB 333 LAB NO. 6: INTRODUCTION TO PID CONTROLLER PRELAB QUESTIONS

Name: _____________________

SID: ______________ Group:______ Date:____________

1. What is the difference between a open-loop control and close-loop control?

2. Draw the three main test signals : step, ramp, sinusoidal

3. Describe what do you understand about the control actions: proportional, derivative and Integral.

4. Draw an example of a system response with depict peak overshoot, settling time, rise time and steady state error.

5. What are the three types of response for a second order system?

47

Lab No.6

MESB 333 Lab No. 6 Introduction to PID Controller ______________________________________________________

1

Objective This experiment consists of two sections. In the first section, you will learn the importance of the vital system characteristics in the assessment of control loop efficiency. In the second section, you will learn to evaluate the PID control elements using the PCU computer controlled flow cycle.

1.1

Theory A. Introduction to Control System In the industrial world the field of control engineering is very crucial. Control systems are designed to achieve specified objectives within a given set of constraints. The three common control strategies are open-loop, feed forward and closed-loop control. The open-loop control cannot compensate for either disturbances to the system or changes in plant parameters (Figure 7.1). For example an open-loop speed control system cannot compensate for load variation (disturbance) and the bearings friction variation (plant parameter). Input (desired behavior)

Control

Output Process s Action (actual behavior) Figure 6.1 Open Loop Strategy

Controller

The feedforward control attempts to compensate for disturbances before they have any effect on the system output (Figure 6.2). This strategy can be effective if the disturbance can be measured. However it cannot compensate for changes of the plant parameters which cannot be measured and treated as a disturbance. Disturbances Measure Disturbances

Input (desired behavior)

Controller

Control

Process

Action

Output (actual behavior)

Figure 6.2 The Feed Forward Strategy The most common control strategy is feedback or closed loop control, as illustrated in figure 6.3. Here the process output is monitored, and control actions are taken to counteract deviations from the required behavior. In the case of motor speed control system, the speed is measured, and the applied voltage is modified as required. However in practice, feedback and feedforward are often combined in a single system.

48

Lab No.6

Disturbances

Input

Controller

(desired behavior)

Control Action

Process

Output (actual behavior)

Measure Output Figure 6.3 The Closed-loop (feedback) Control Strategy B. PID Controller The term PID controller refers to proportional, integral and derivative controller. PID controllers are the most common controller used in the industrial process control. I) Proportional Control Mode In this mode the output of the controller is proportional to the error between the set point and the measured value. Proportional control may be expressed as either proportional gain or proportional band. Mathematically , Mp =PG(SP-MV)+C = PG e(t) +C Where, PG = SP = MV = C = e(t) =

Mp = Controller Output Proportional Gain Set point measured value Output with zero error Error as a function of time.

The error band where the output is between 0% and 100% is called the proportional band (PB), and given by PB = 100/PG. Thus the higher the gain the smaller the band. This control mode rarely produce adequate control, where there usually an offset (permanent error). II) Integral Mode This mode of control is often used to remove proportional offsets errors. The integral mode determines an output based on the history of error. It is calculated by finding the net area under the error curve versus time and multiplying by a constant called the integral action time (IAT) in seconds. The controller output equation is:

Mi( t )

PG e( t )dt IAT

The integral Action time is defined as the time taken for the integral action to duplicate the proportional action of the controller, if the error remains constant during this period. It is used commonly to remove any steady state errors incurred when using a proportional controller. 49

Lab No.6

III) Derivative Control Mode Derivative control mode is often used to reduce the response time of the system, it is based on the time rate of the change of error. The time taken for the proportional action to

Md

PG DAT

de( t ) dt

duplicate the instantaneous output of the derivative element is called derivative action time (DAT). The controller output equation is: The derivative control mode is never used alone as there is no controller output corresponding to zero rate of change. So it is commonly used with Proportional controller (PD). However, it can also exaggerate high frequency noise in the system. C. System Response Figure 6.4 shows the typical system response of a control system. There are three types of response for a second order system, which are overdamped, underdamped, and critical damped response. The system response depends on the PID gains set in the experiment. The characteristics of the response is shown in Figure 6.5.

Figure 6.4

50

Lab No.6

Figure 6.5 Some of the important system performance parameters are: Peak overshoot : is often expressed as percent overshoot at the first peak and given by (Peak value- input value)/input value * 100 Settling time: The time taken to settle within 2% of the final value Rise time: The time taken for the system to respond to a fraction of the final value on the initial part. Typically 5-95% or 10-90%. Steady state error : Any error between the set point and the controlled variable once the system has stabilized. 1.2

Apparatus

1.2.1 The System Rig The System Rig is the hardware for the process, which is to be controlled by the microcomputer. This reflects a typical process control situation such as in the food and drink manufacturing petrochemical industry. Each feature on the System Rig has a manual or computer control option. Users may select either of the modes allowing a comparison between human and computer control operation to be made. This allows a rapid appreciation of the advantages and disadvantages under both modes of control.

51

Lab No.6

1.2.2 Description

Figure 6.6 Process control unit

LEGEND

A - Mains switch

G - Overflow pipe

B - Water pump switch

H - Proportional valve

C - Bottom reservoir tank

I - Water inlet port

D - Bypass valve

J - Water drain port

E - Return valve

K - Water pump

F - Water level tank

L - Control panel M - Level foot 52

Lab No.6

SAFETY / PRECAUTION 1. Ensure that there are sufficient water in the bottom reservoir tank before conducting the experiments. 2. Make sure there are no leakages in the piping system before conducting the experiments. 3. Open the bypass valve before switching on the water pump and close it only after the flow is fully circulated through the entire system for a brief period.

SETUP 1. Place the LS-33039 PID Controller Experiment Rig. on a level table and adjust the levelling foot if necessary. 2. Connect the main power plug to electrical supply. 3. Connect the RS-485 cable from the computer to the control box. 4. Run the Data Acquisition Software from the computer 5. Switch on the mains switch on the control box 6. Ensure there is enough water in the bottom reservoir tank before switching on the pump. 7. The LS-33039 apparatus is ready to be used.

MAINTENANCE

1. Please check for signs of leakage in the piping system from time to time. Besides that there is no major maintenance required for this apparatus 2. Kindly seek the assistance from the manufacturer if necessary.

1.2.3 Feedback Feedback is an essential requirement for the control of any process. It consists of various transducers measuring the conditions on the rig and feeding this information back to the controlling microcomputer. On the Process Control Unit the temperature at the sump, flowline and process tank are measured using platinum resistance thermometers. The flowrate is measured by an in-line flowmeter. These analogue signals are fed back to the signal conditioners on the Computer Control Module (CCM) from where they are sampled by the microcomputer via an analogue to digital converter (ADC). LED meters are used to display the temperatures and flowrate on the system rig. Indicators are provided for the cooler, tank full sensor and drain/divener solenoids, giving a status check when the Process Control Unit is in operation. 1.2.4

Flow measurement The flow rate of the fluid is measured by means of a flow meter of the impeller type. The fluid flows through the meter rotating the impeller, which has six blades. Mounted either side of the impeller is an infra red transmitter and receiver producing an infra red beam which is broken by the rotating impeller. Six pulses are therefore produced for one revolution of the rotor, thus producing a frequency output 'which is proportional to the flowrate.

53

Lab No.6

The approximate full-scale frequency is 570Hz (pulses/sec) which is converted to a voltage by the signal conditioning circuit. This voltage is used to drive the flowrate LED display on the rig and also converted into a digital word by the Data Acquisition circuit.

Figure 6.8 1.2.5

Pump The pump used is a centrifugal type. It is not a positive displacement type and thus its output is not necessarily linearly proportional to speed, though variation in speed will, of course, vary the output flow rate. Activating Voltage : 12V D.C; Maximum Continuous Current: 6 Amps

1.2.6

Water Drain Port This is used to drain the bottom reservoir tank

1.3 Procedure 1.3.1 Software Operation a) Turn on both the computer system and the process control unit. b) In the Windows desktop, select the LS-330390 PID icon. c) In the program, follow the instructions in section 1 to familiarize yourself with the program.

1.3.2 Section 1 : Assessment of System Performance 1. By operating the controls in the Process Control Unit, the vital characteristics can be easily demonstrated by varying the values of the PID controller. 2. Select the Flow Control tab and in the Control select the Closed Loop tab 3. Set the “Set point” to 6 liter/min and set the controller setting as in the table below. 4. Click the Enabled button to start the flow. 5. Set the PID controller using the given values. Use your own values to complete the table. 6. Print out your results and observe the graphs. Label the graphs. 7. To study the effect of load change on the PID controller. Based on the plotted response from Table 1, select the best PID controller response, introduce a disturbance by opening the by-pass valve 30% when it has reached the stabile flow rate. Observe the response of the controller and comment on the behavior.

54

Lab No.6

1.3.3 Results Controller Settings

Table 1. Characteristics of print out results Peak Settling Rise Overshoot Time Time

Steady state error

Under damped/ over damped/ Critical

Proportional

Integra l

Derivative

1

0.1

1

3.5

0.01

0

7

0.05

0.5

Gain

Question : Comment on the difference between under damped, over damped and critical?

1.4

Section 2 : Evaluation of the PID Control Elements The PID control elements may be easily evaluated using the PCU computer controlled flow cycle. Identify the best PID value to control the flow rate at 6 liter/min.

General Guidelines The selection range of the PID elements is: Proportional Gain: Between 1 to 10 Integral Action: Between 0 to 5 Derivative Action: Between 0 to 10 Compare and discuss the function of different types of controller. Which type of controllers or combination of controller will give ideal control system that you will recommend? What is the optimum tuned PI controller? Include error analysis.

55