MESB333 Lab Manual (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

Lab No. 7

Strain Measurement Prelab Questions Experiment I: Getting to know the equipment  Experiment II: The Bending System Experiment III : The Torsion System Experiment IV : The Tension System

3 4 5 6  7

9 10  16

Determining fluid (air) velocity and Discharge Coefficient Prelab Questions Experiment I: Velocity Measurement 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 Thermocoupl e Experiment III: Humidity Measurement 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

60

Experiment: Flow Rate Measurement Devices

61

Introduction to PID Controller Prelab Questions Experiment: PID Controller

66 67

Free and Damped Vibration Prelab Questions Experiment I: Spring Coefficient (Stiffness) Experiment II: Natural Frequency Experiment III: Free and damped damped Vibration

66 67

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Laboratory Syllabus 

Lab 1 : Strain Measurement Measurement The experiments are related to the field of mechanics of deformable solid. The 1 st  experiment is on  bending of a cantilever beam. The 2nd experiment involves involves loading weighs on a circ circular ular 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.

I nforma nformall r epor t is i s re r equi uirr ed fo forr this lab lab..

Lab 2 : Determining fluid fluid (air) velocity and Discharge Discharge Coefficient There are two experiments in this lab. l ab. These experime experiments nts are related to the field of Fluid Dynamics of st air. Both experiments use the same apparatus. 1  experiment is to measure air flow velocity. Pressure along the test pipe will be measured to determine air flow velocity using Bernoulli’s equation. 2 nd  experiment is to measure the discharge coefficient of an orifice plate and a nozzle. An orifice plate will  be inserted along along the test pipe.

F or mal re r eport iiss re r equi uirr ed for this lab lab.. Lab 3 : Temperature Measurement

This experimentmeasurement is related to the field of Heattype Transfer and Thermodynamics. experiment consists of temperature using different of measuring devices: Pt 100This resistance thermometer, liquid filled thermometer  thermometer  and NTC temperature probe etc. The apparatus consists of rice cooker, oven, amplifier, and temperature indicator indicator and so on connected in a simple circuit. Understanding the working principle of resistance thermometer is important to students in order to design their own procedures/steps to achieve the objectives and how to capture the t he results. The student creativity and learning process in class is applied.

F or mal re r eport iiss re r equi uirr ed for this lab 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 ffalls alls on a material, current current that corresponds to the light intensity will be generated generated using transducer. Photocell, circuit box and light source aare re the important devices in this experiment. The current that is produced at different level of light intensity will be measured. measured.

I nforma nformall r epor t is i s re r equi uirr ed fo forr this lab 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 

I nforma nformall r epor t is i s re r equi uirr ed fo forr this lab lab..

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Lab 6 : Process Control Unit This experiment is related to the field of Process Control. A system with different controllers will be studied for it response to the controllers. The controllers are proportional controller, integrative controller and derivative controller. The flow rate of water in a continuous loop is to be studied as a system. This system is connected to computer software that enables the gain of each controller to be set, and enables the result to be plotted. In this lab, the function of different controllers will be noticed. The function of different controllers and working principle will be noticed by the students in order to design their own procedures/steps to achieve the objectives and how to capture the results. The student creativity is applied.

I nforma nformall r epor t is i s re r equi uirr ed fo forr this lab lab.. Lab 7. Vibration

In this lab, the students are to measure the stiffness of helical springs and its natural frequency. To expose to free and damped vibration system with their characteristic that are related to the theory learn in class.

LABORATORY & REPORTS: AN OVERVIEW

All experiments in the Engineering Measurements Laboratory require either a laboratory labora tory 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 sta ted 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. 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 : Khairul Anwar Bin Derahman Tel:

03- 8921 2020 ext. 6324

Laboratory Time:

Section 1A: Section 1B: Section 2A: Section 2B: Section 3A: Section 3B:

Thursday Friday Wednesday Tuesday Monday Tuesday

-

1600-1900 (BL-0-003) 800-1100 (BL-0-003) 800-1100 (BL-0-003) 900-1200 (BL-0-003) 800-1100 (BL-0-003) 1500-1800 (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.

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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. Experimentt 2: Determining fluid (air) velocity and Discharge Coefficie Experimen Coefficient. nt. –   –  Group  Group Report -5% Experimentt 1: Temperature Measurement.Experimen Measurement.- Individual Report Report –   –  7%  7% Duration of one-week period is provided for formal report and should be submitted during the t he next lab. Report should be submitted to the lab technician personally. Grade will be deducted from the late l ate report as follows (except (except with valid reason) reason) : Late submission submission penalty penalty : Late 1 day 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 improvement in future report writing. Please use tthe he 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 experiment group consists of 3-5 students. Group number consists of Section number, follows with number appointed. 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 experimen experimental tal 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 label of small small title etc. With references references if giv given en

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Format for Formal Report

General Instructions: Font type: Arial or Time New Roman

Paper size: A4

Font size: 12 pt

Ink colour: black

Spacing: 1.5

Graph: computer generate 

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 bri bri ef d de escri scri pti on of w wha hatt the exp xpe eri ment is d de emons nsttr ating ing.. 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 theoretical results. Answer to question if i f 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 label of small small title etc. With references references if given

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MESB 333 LAB NO.1 : STRAIN MEASUREMENT PRELAB QUESTIONS

Name: ________________________SID: ________________________SID: ______________Group:______ ______________Group:______ Date:____________ Date:_______________ ___

1.  What is stress? Strain? What is the relationship between between stress and strain?

2.  What is the principle used in strain gauge measurements? measurements?

3.  What is the different between quarter, half and full bridge?

4.  How to eliminate error due to temperature changes? changes?

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

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MESB 333 Lab No.1 Strain Measurement  _____________________________________  _____________________ ________________________________ _________________________________ _______________________ ______ 1.  Theory

material will bein deformed to certain extend external forces act onproduced it. This deformation willAcause changes length and diameter of when the material. The strain is directly  proportional to the stress at at a limited region, which which is called the limit of proportio proportionality nality (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 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 mathem atical 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  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

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)   ……………………………………………..(2)

where, R

:

electrical resistance

   

:

specific resistance of material 10

 

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. 2. Calculation of axial strain

Theoretically, the strain value can be calculated using the theory of bending at the Theoretically,  point of attachment attachment of the strain gauge. gauge. For a re rectangular ctangular cross-sectional cross-sectional area area cantilever cantilever beam, M

 



I

y

E

 

My

R 

I

………………………………..(3)   ………………………………..(3)

Where, M

:

bending moment = (Applied load X moment moment arm) 3

I

:

second moment of area of cantilever

=

 

:

axial axial stress

y

:

half the thickness of the cantilever

E

:

modulus of elasticity

R

:

radius of curvature of cantilever due to M

 bd 

12

(Width b and thickness t hickness d)

=½d

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

 

y



L

R 

……………………………………………………………….(4)   ……………………………………………………………….(4) From the theory of bending 1



R 

M EI

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



y

My

R  

EI

……………………………………………………………(6)   11

 

From the dimension of cantilever beam, M = 420* Load (N.mm)

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

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

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 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 att ached 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. gauge. Now consider a hollow round tube used as a cantilever.

Figure 3. Cantilever round bar exert with torsion. In bending there is a neutral axis at the horizontal axis, so any gauge fixed symmetrically symmetricall y 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 compensation

(2)

Net axial strain effect is zero for either A or B

(3)

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

12

 

The meter will therefore indicate twice the diagonal strain from which the stress can  be derived using the modulus of elasticity. 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

T r 

 

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

 

: angular twist over length L

D 32   

4 o

 

D

4 1

 

The shear stress  acts circumferentially and has to be accompanied by a system of complementary stresses including diagonal tensile and compressive stresses, which are

13

 

perpendicular to each other. Hence there are equal direct strains along opposing 45 0  helices on the surface of the tube given by

 

q

Tr 





 E 

 EJ    …………………………………… (9)

and the meter will indicate 2* 2* .

3 Wheatstone Bridge B

R1

R2 

Figure 1 Wheatstone bridge

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 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 Normally it is i s 12 volts. External zeroing is applied in Wheatstone Bridge Bridge.. External zeroing means the meter M will show zero reading. reading. This is done by having a variable variable resistor at D. Zeroing can be done done by varying the variable resistor. Zeroing is required because factor like weight of the material can affect the results.

Refer to the strain gauge trainer manual in the moodle for more detail how to perform this experiments. 14

 

MESB 333 LAB NO. 2: VELOCITY MEASUREMENT AND DETERMINATION OF DISCHARGE COEFFICIENT PRELAB QUESTIONS

Name: _____________________SID: _____________________SID: ______________Group:______ Date:______________ Date:______________

1.  Draw a diagram and explain briefly how to measure pressure 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 measuring flowrate?

15

 

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

1.  Experiment I

Velocity Measurement 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 differe difference nce of the moving air in tthe he 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 difference..

v

2 p

or 

2 gh'

 

(1)

  

 p   p  The p pressure ressure difference difference between between the pitot tube and the wall wall pressure pressure tapping measured measured using manometer bank provided (    g  x where x is the the level of fluid used used in the manome manometer). ter). h’  

The pressure difference expressed as a 'head' of the fluid being measured (air) 

The air density at the atmospheric pressure pressure and temperture of that day.(kg/m3)   g   gravitational acceleration 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.

16

 

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 fluid's density, the size size of the obstacle, obstacle, and the fluid's fluid's speed, and inversely  proportional to the fluid's fluid's viscosity (viscosity (viscosity is the measure measure of a fluid's fluid's "thickness"--for "thickness"--for example, example, honey has a much larger viscosity than water does). Re

  vd  vd  

 

 

fluid density v

: fluid velocity

d

: obstacle size coefficientt of fluid dynamic viscosity coefficien

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 t ogether as a cohesive material. 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 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 t o calculate pressure differences, h and pressure heads in all these experiments. Starting with the basic equation of hydrostatics:

 p = gh

(2) 17

 

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

Manometer tubes

1(static ‘pressure’*)  ‘pressure’*) 

2(stagnation ‘pressure’)  ‘pressure’) 

Liquid surface readings (mm)

X1

X2

 A  Angle ngle of inc inclina linatti on, = 0 ‘pressure’ term is used since this reading is in i n mm of manometer fluid and not the pressure of unit Pa. Therefore the equivalent vertical separation of liquid levels in manometer manometer tubes, h = (x1 - x2)cos x2)cos 

(3)

If k  is the density of tthe he kerosene in the manometer, the equivalent pressure difference  p is:  p = k  g  gh = k  g(x1  g(x1 - x2) cos cos 

(4)

The value for kerosene is k  =  = 787 kg/m3 and g = 9.81 m/s2. If x1 and x2 are read in mm, then: x2)cos  p = 7.72(x1 - x2)cos   [N/m2]

(5)

The  p obtained is then then used in second second equation (1) to obtain obtain the velocity 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    ( x1   x2 ) . . cos      air  1000  





[N/m2]

(6)

18

 

1.5  Apparatus 

Figure 1 Experime Experiment nt apparatus 1.6  Procedure

a)  Five mounting positions are provided for the pitot the pitot tube assembly. assembly. These are: 54 mm, 294 mm, 774 mm, 1574 mm and 2534 mm from the pipe inlet  b)  Ensure that the standard inlet nozzle is fitted for this experiment and that the orifice plate is removed from the pipe break line. c)  Set the manometer such that the inclined position is at 00. d)  Mount the pitot the pitot tube assembly assembly at  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. e)   Note that there is a pipe wall static pressure pressure tapping near to the position where the pitot tube assembly is placed. The static pressure p ressure tapping is connected to a manometer tube. Position the pitot tube with the traverse poisition of 0mm. Start the t he fan with the outlet throttle opened. g)  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. h)  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. f) 

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1.7  Results

D at ata a Shee Sheett for V eloc locii ty Mea Measur sure ement Usi Using ng Pi to tott Tube

Traverse Position

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

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

(mm) Stagnation 'Pressure' Reading (mm)

x (mm)

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

x (mm)

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

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

x (mm)

 p (N/m2)

Velocity (m/s)

0 10 20 30 40 50 60 70 80

20

 

Pitot Tube at 2534 mm Static 'Pressure' 'Pressure' Reading Reading ____________(mm) ____________(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 likely occurred by the third or fourth position. position.   Give your comments on the velocity profiles.   Include error analysis. 

21

 

2 

Experiment II Determination Determina tion 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 at the flanged flanged joint approximately approximately half way way along its length. length. The multi-tube multi-tube manometer manome ter 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 experime experimentally ntally 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 C D 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. downstream. The pressure difference between the two sides of the plate is i s related to the t he

 jet velocity, and therefore the discharge, by the energy equation: Q  A v  A C v  A C C 2gh  j  j o c  j o c v 

where

Q = A j = Ao = v j  = Cc = Cv = g = h =

 



discharge (volume/time) (volume/time) jet cross-section cross-section area at minim minimum um contraction (vena contracta) 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 acceleration (9.81 ms -2) pressure difference 'head' of air across orifice (refer to equation (6) of Exp. I)

These two(1) coefficients are normally combined to give a single coefficient of discharge: C D = Cc.Cv Equation 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

 



'

AiC   D 2gh i

(4)

22

 

If hi = the drop in i n pressure head across across the inlet, the discharge = ( (k /air  )*  )* (x before nozzle  – xafter nozzle): nozzle –  2 in which Ai = standard nozzle cross-s cross-section ection area (= d /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. atmosphere.

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

C  D

Qo



 Ao

2 gho

……………………………(5)   ……………………………(5) Where

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

2.5  Apparatus

Figure 2 Experiment Diagram 2.6  Procedure

(a) Insert the orifice orifice plate in in position (taking care to observe observe the instructions as to) in which the surface should face the approaching airflow. (b) Connect all the static pressure pressure tapping points to the manometer manometer tubes en ensuring suring 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 with low airflow (damper (damper plate closed) an and d read all manometer manometer tubes, tubes, including any open to the air (reading should be taken after the fan is on). (d) Gradually increase increase air flow by increas increasing ing the damper damper opening to 100%, and take read at at all opening. 23

 

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

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

25%

Points

50%

75%

100%

mm of kerosene

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

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

25%

50%

75%

100%

mm of kerosene

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

24

 

  From table 5.1using equation (4) calculate the Q i, then using equation (3) where Q=Qi calculate the CD for orifice plate for each damper damper opening.   For data in table 5.2, using similar si milar procedures, procedures, but this time using the t he 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: 

vd

Re 



……………………………………..(6)   ……………………………………..(6) where

 

:

the coefficient of dynamic viscosity of the air air density

v

:

is the mean pipe velocity (Qi/A p)

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.





obstruction such as anororifice platedata would cause pressure drop but by   Any analyzing the graph below from your youactually should see thata the reading in mm of kerosene is increased. Explain.

Pressure Drop across Orifice Plate

  e   n   e   s   o   r   e    K  

Air Flow

  m   m

Tapping position along test pipe

25

 

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 resistance thermometer? i) ________________________________________ ii) ________________________________________ iii) _________________________________________

4.

Gives two examples where where PTC thermistors are generally used? i) ________________________________________ ii) _______________________________________  

26

 

MESB 333 Lab No. 3 Temperature Measurement  ____________  ______ ______________ ______________ ____________ _____________ _____________ ____________ _________ ___ 1

Experiment I Time Constant

1.1

Objective

Design your experiment in order: 1. To compare the time constant of different type of temperature measuring device devicess with reference to mercury filled thermometer thermometer (smallest time constant). 2. To understand the relationship between resistance and temperature.

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 Centigrade))

0 0C

100 0C

Fahrenheit

32 0F

212 0F

Kelvin (Absolute Scale)

273 K

373 K

In this experiment experiment you will be familiarized with the following temperatur t emperaturee measurement measurement devices: a) Resistance thermometer

(TYPE K)

 b) Thermistor

(NTC)

1.4  The Liquid Filled Thermometer

This type of thermometer depends on the expansion of a liquid associated with an increase in temperature. The most common type is the mercury-in-glass thermo meter. This thermometer consists of a capillary tube with a bulbous end . clean , dry mercury is introduced and the 27

 

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 scale along along the tube, calibrated in units of temperature, temperature, gives a direct reading reading of temperature. The mercury-in-glass thermometer thermometer is an accurate device but is very fragile and care should be exercised in use. This type of thermom t hermometer eter should not be used in applications such as the food industry where mercury 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 lower temperatures than mercury. A mercury-in-glass mercury-in -glass thermometer is supplied with the Temperature Measurement Measurement Bench due to its it s stable and accurate performance. For accurate measurement measurement of temperature using a liquid filled thermo meter, it is important that the thermometer is immersed into the medium being measured 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 independent of filling or range

1.5  The Vapor Pressure Manometer

For industrial applications, the liquid-in-glass thermometer thermometer is far from suitable due to its fragility and the difficulty 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 thermo meter. meter. This consists of a metal bulb partially filled fill ed with fluid, which is connecte connected d to the sensing element of a Bourdon gauge. The space above the fluid is filled with vapor of the fluid, the pressure of which is display 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 temperature increases increases.. For For this reason, the vapor vapor  pressure thermometer thermometer is suitable only for for operation over short ranges ranges of temperature temperature and suffers from lack of sensitivity at low readings. In service, the range should be selected so that the gauge remains within operational limits with the normal operating point at approximately two thirds of fullscale reading.thermometers offer the advantage of remote reading. The thermometer may be Vapor pressure 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 thermometer supplied with the bench has the Bourdon gauge connected directly to the stem f or case of operation

1.6

The Bi-Metal Thermometer

Expansion of solids may be used to measure temperature temperature but direct measure measurement ment is im impractical practical due to the very v ery sma small ll move movem ments involved inv olved.. However, if two thin met  et aall str strips, ips, havi ng d iif  f  ff  erent coeff  iicients cients of linear linear expre expr ess ssion, ion, are ar e mechanically echanic ally f astened astened together, the result is a strip which bends signif icantly icantly when when  heated. heated.   This combinatio combination n is called a BiBi-metal metal strip and the sensitivity may be increased by coiling the strip int into o a spiral. One end of the strip is f  iixed xed to the case and a  po  pointer inter is attached to the other end. L iinear near sscale cale may be obtain obtain  eed d by suitable cho cho  ice 28

 

of metals. This type of thermo thermomete meterr is very ver y rrobust obust and has has many applications througho throughout ut industry where accuracy of measurement is not imp imp  ortant. The  bi-  meta The bimetall thermo thermometer meter supplied w ith the be the bench nch is mounted on th th  e back-boa back-board rd and gives a direct reading of am amb bient air te temperature. mperature.

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 thermometer is platinum. Nickel is used in general operation and monitoring. Copper is also suitable but only in a restricted temperature 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 t he 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 of this function function is m = R/ R/ T. R = m mT

Knowing that,

(2)

R(T) = Ro + R, thus: R(T) = Ro + mT = Ro (1 + m/Ro T) = Ro (1 +

R  / R o T

= Ro (1 + 1T)

 T)

(3)

where, 1 =

R  / R o T

 

29

 

450

 

400 350 300      W       /       R

Ni 100

250

Pt100

200 150

Cu100

100 50 0 -200

0

200

400

600

800

1000

0

T/ C

Figure 3.1

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

R(T)

R

Ro = R(To)

 per degree. degree.  Figure 3.2

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 coefficient 1 , also the square temperature coefficients coefficients 2, and for very large temperature changes T also the cubic temperature coefficients coefficients 3, and if necessary the biquadratic value 4.





R (T)  R o 1  1T   2   T2  ... .. . n Tn  

where,

T    T  T

o

(4)

 

30

 

1.8  Thermal Response

The therma thermall response of a thermo thermo  meter to changes in te  te mperature peratur e is is probab  probably ly the most important characteristic to consider when selecting instrumentat instrumentat  ion f  or or a part particular icular applicat application. ion. A thermo thermo  meter may be extrem ex tremely ely accur ac curate ate and s table in perf  in  perf ormance ormance but totally unsuitab unsuitab  llee f  or or use in a dynamic dynamic situation, due to a ti me la lag g between system temperature and thermo thermometer meter reading. The d iagra  iagra m below show showss typical response curves f  or or a thermo thermo  meter when step s tep changes in te tem mperatur per aturee are applied applied  . The response of the thermo thermo  m meter eter is def  iined ned by the t i me ta ta  ken f  or or the te mperature te mperature reading to change by 63.2% of the step change. For any thermo thermometer, meter, this time will be a constant value irrespective of step change and is def  iined ned as the "t  "t iime me constant" f  or or the thermo thermometer. meter. Th  Th e ti tim me constant and response  profil  profilee  f  or or a thermo thermom meter will change if the sys s ystem tem is modif  iied. ed. For example, t h hee speed of res ponse of a thermometer thermometer wi will ll be slowed slowed down down if it is protected pr otected from the system bei system  being ng measured by a ther  mo meter. The res response ponse will also be af  f ected ected by the therma thermall contact between between the thermomet thermometer er and pocket, f  luid f  iilling lling of the pocket poc ket result resulting ing in a reduction in time constant.

Th Thee response of the thermo thermometer meter is def  iined ned by the t i me taken taken f  or or the te te  mperature peratur e reading readi ng to change c hange by 63.2% of the step change. For any thermo thermometer, meter, this time will will be a constant c onstant value irrespective irres pective of step change and is def  ined ined as the "time "time constant" f  or or the thermo thermo  meter. Th  Th e ti me constant and rer e- sponse  prof  ile ile  f or or a thermo thermometer meter will change if the system is modif ied. ied. For example, the speed of response of a therm thermometer ometer will be slowed slowed down down if it is protected pr otected from the system system bein  being g measured by a thermo thermometer. meter. The response will also be af  ff  ected by the therma thermall contact between between the thermomet thermometer er and pocket, f  luid f   illing of the pocket result resulting ing in a reduction in time time constant.

31

 

Figure 3.3 Experiment apparatus setup

32

 

1.9

Apparatus Setup

Note: To discharge the hot water from the pot, request assistant from lab technician. Base on Figure 3.3, construct the experiment procedure in order to achieve the objective.

33

 

2

Experiment II Type K thermocouple

2.1

Objective

Design the experiment in order:

-

2.2

To investigate the working principle of Type K Thermocouple To find the sensitivity of the 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 temperature.. It possesses a negative temperature coefficient, which is the reason why these t hese sensors are called NTC resistors. If the CuO2  is mixed with the ingredients of a ferroelectric material (e.g. BaTi), the temperature coefficient 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 sensors possess a high high sensitivity, sensitivity, which which is easily 10 times times higher higher than than that that of metal resistance thermometers. The non-linearity of NTCs and their broad manufacturers' tolerances exclude them from use for precision instruments. In the ttempera emperature ture range between -60oC and +150oC they are frequently used in the area of household appliances and medical technology  because of their their high sensitivity 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 rapidl y by the sudden cancelling of a uniform orientation of all magnetic forces in the ferroelectric 34

 

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.

2.4  Temperature function and temperature coefficient of NTC thermometers

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

R T = Ae

(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 R T:

R(To) = R o 

= AeB/To 

A = R oe-B/To 

(6)

Subsitute (6)into equation (5)

R T = R oeB(1/T - 1/To) 

(7)

Construct the experiment procedure procedure in order to achieve the objective.

35

 

3

Experiment III Humidity

3.1

Objective

Design the experiment in order:

-

Understanding of whirling pyschorometer pyschorometer (hygrometer) Understanding of wet and dry bulb thermometer thermometer Measurement Measurem ent 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  water vapor in a parcel a parcel of  air  air to the saturated vapor saturated vapor pressure of water vapor at a prescribed temperature.  temperature.  Humidity may also be expressed as specific humidity. Relative humidity is an important i mportant metric  metric used in forecasting in forecasting weather. Humidity weather. Humidity indicates the likelihood of  precipitation, dew,  precipitation,  dew, or   or   fog. High 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 effect is calculated calculated in aa heat  heat index table Hygrometers are instruments used for measuring humidity. measuring humidity. A  A simple form of a hygrometer is specifically known as a psychrometer and consists of two  two thermometers, thermometers, one  one of which includes a dry bulb and the other of which includes a bulb that is kept wet to measure wet-bulb measure wet-bulb temperature. Modern temperature.  Modern electronic devices use temperature of condensation, changes in in electrical  electrical resistance, and resistance,  and changes in electrical capacitance electrical capacitance to measure humidity changes. Hygrometers measure humidity while psycrometers measure measure realative humidity in the air. In a psychrometer, there are two thermometers, thermometers, one with a dry bulb and the other with a wet bul bulb. b. Evaporation from the wet bulb lowers the temperature, the  temperature, so  so that the wet-bulb thermometer usually shows a lower temperature than that of the dry-bulb thermometer, which measures dry-bulb temperature. When 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 temperatures on a  psychrometric  psychrome tric chart. One chart. One device that uses the wet/dry bulb method is the sling psychrometer, where the thermometers thermometers are attached to a handle or length of rope and spun around in the air for a few minutes. minutes. 

36

 

Your are given a whirling hygrometer for humidity humidity measurement apparatus, write down the  procedure to achieve the objectives and to measure the Humidity of the Engineering Measurement Lab.

Figure 3.3 Whirling hygrometer

37

 

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.

38

 

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 character istic that are related to Inverse Square Law and Lambert’s Cosine Law.

1.1

Objective

To understand understand the photo transducers transducers effect and its relations with Inverse Inverse Squa Square re Law and Lambert’s Lambe rt’s Cosine Law. Students will measure the effect of the t he incident inci dent light on the behavior of a photodiode, phototransistor and photo conductive cell. 1.2

Theory

When of light falls onto certain material, energywill willbecome be givenenergy up as being by the  principle photo-electric transducer. Theitsenergy in the described 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 electric current caused by the light. In this experimen experiment, t, you will learn to use photoelectric 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 t he 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 wavelength is given in the equation 

v f 

f  

1 

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 meas measured ured experimentally as shown below.

39

 

Table 4.1Spectrum for light COLOR Violet Blue Blue-Green Green Yellow-Green Yellow Orange Red Deep-Red

WAVELENGTH (mm) 440 470 490 520 550 580 600 690 700

Light is a form of electromagnetic 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, waveleng th, the higher hi gher will be the frequency. With the relationship that energy is directly  proportional to the frequency frequency of light, light, higher frequency frequency will translate translate to higher energy. energy. Therefore, Therefore,  blue light has a higher energy that red light because because the wavelength 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 m 2 but the illumination has now fallen to a quarter of its previous value as the luminous flux is spread over four times the area.

    E



d

2

40

 

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

1.4

 

=

luminous flux (lumen)

d

=

distance (m)

Lambert’s Cosine Law  Law 

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

 

 

Incident Light

1

 2

Figure 4.1

Thus the modification of the inverse square law becom becomes: es: E

1.5





  cos  2 d

The Photo-Conductive 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    but other materials and combinations of materials behave in a similar fashion. They are extensively used in semiconductor 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, semiconduc tors, 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 PHOTO-RESISTOR or a PHOTOCONDUCTOR, 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 41

 

 photons, or the intensity i ntensity 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 phenomenon are rather involved, but are given here to make the study complete. In an intrinsic (pure) semi-conductor crystal all the valence electrons 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 i nterest 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, specimen, several things may happen,  as shown in Fig 4.2 

Conduction band doNor Impurity

photon

excitation

Energy gap Intrinsic

Eg

excitation AccePtor 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).  These last two transitions are known as impurity excitations  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

42

 

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 eexperiment xperiment 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 between banana socket first before turn on the control box. 3. Do not connect the positive terminal terminal of the power supply to negative terminal terminal of the power supply without connecting to any load between them. 4. Make sure the connection between the measurement measurement point and the measurem measurement ent meter are in correct polarity. 5. Make sure the connection connection of the lamp to the power power source are in corre correct ct polarity. 6. If the experiment is conducted conducted during day light, take the reading aass 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 reflections of light onto the transducers. 7. While the lamp is turn on, avoid touching the lamp’s body.  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. 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 accessories needed for the experiment.

43

 

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 plug from the banana terminal first first before assembling assembling out the circuit. circuit. 3. Start connecting connecting the circuit circuit using banana banana plug to respective respective banana socket, socket, by using circuit diagram below as reference.

Fig. 4.3 - Schematic for the photodiode experiment 4. Make sure all the wiring wiring connection is according according to the circuit diagram. 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 sur e sur e the  polarity is correct. correct. 6. Adjust the position position of the photo transducer transducer box so that its angular angular scale of the photodiode photodiode facing the light source is 0°. 7. Ensure the hole of the photo transducer transducer box is not facing facing other light source, affecting affecting your your reading value during experiment. 8. Turn on the mains mains switch, wait wait all the measurement measurement meter meter initialized first first before start conducting experiment. 9. Switch on the lamp’s power supply, check whether whether the lamp got light up or not.  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  Law 

1. With the circuit circuit of Part Part 1 still connected, connected, return the photo transducer transducer box box and lamp lamp to their starting positions (distance 1 meter) 2. Switch on the lamp again. 3. Rotate the angular angular scale shown on the photo photo transducer transducer box to 30° anti-clockwise and record the reading. 4. Repeat the the procedure procedure 3 for for the angles as as shown in the table below. below.

44

 

5. After finish the experiment, experiment, switch off the lamp power supply and the main main power supply 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 voltage:_____________Volt  Distance (m)

Current (μA)  (μA) 

Resistance (Ω)  (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 = V dc/I  What is the t he 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 t he value of applied voltage. Discuss the shape of the graph.

45

 

Part 2: Photo diode - Lambert’s Cosine Law  Law 

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

Angle (Degrees) (Degrees)

Current (μA)

Resistance (Ω)  (Ω) 

30 (ACW) 25 20 15 10 5(CCW) 0 5 (CW) 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 disadvantages of the Photo diode.

46

 

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 plug from the banana terminal first first before assembling assembling out the circuit. 3. Start connecting connecting the circuit circuit using banana banana plug to respective respective banana socket, socket, by using circuit diagram below as reference:

Fig. 4.4 - Wiring Diagram for Photo Conductive Cell Experiment 4. Make sure all the wiring wiring connection is according according to the circuit diagram. diagram. Before switch on the power supply, let the lab instructor to check the connection of circuit. 5. Check the potentiometer potentiometer (VR) control knob on the Operational Operational Amplifier section 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. correct. 7. Adjust the position of the photo transducer box so that its angular scale scale of of the photodiode facing the light source is 0°.

8. Ensure the hole of the photo transducer transducer box is not facing facing other light source, affecting affecting your your reading value during experiment. 9. Adjust the multimulti-meter’s 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 lamp holder again at the distance of 1m 1meter. eter. 12. Adjust the potentiometer to get 10mA. 10mA. Record down the voltage and this value should be constant for the experiment. 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 offConductive the lamp andCell take: the reading again corresponding to ambient light illumination. Part 2: Photo Lambert’s Cosine Law  Law  

47

 

1. With the circuit circuit of Part Part 1 still connected, connected, return the photo transducer transducer box box and lamp lamp to their starting positions. 2. Switch on the lamp again and slowly adjust adjust the potentiometer potentiometer (VR) until the multi-meter multi-meter reads about 10mA initial value. 3. Rotate the angular angular scale shown on the photo transducer transducer box to 30° anti-clockwise and and record the reading. 4. Repeat the procedure 3 for the angles angles as as shown shown in table below. 5. After finish the experimen experiment, t, switch off the lamp power supply and the main power 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)   (Ω)

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

-

Plot, discussion, analysis and conclusion.

48

 

Part 2: Photo Conductive Cell - Lambert’s Cosine Law  Law 

Table 4.5 Experiment Result of Photo Conductive Cell Lambert’s Cosine Law  Law 

Angle (Degrees) (Degrees)

Current (μA)

Resistance (Ω)  (Ω) 

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

Plot, discussion, analysis and conclusion.

49

 

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 plug from the banana terminal terminal first before assembling assembling out out the circuit. 3. Start connecting connecting the circuit circuit using banana banana plug to respective respective banana socket, by using circuit diagram below as reference r eference::

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

50

 

Part 2 Phototransistor - Lambert’s Cosine Law: 

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

-

Plot, discussion, analysis and conclusion.

51

 

Part 2: Phototransistor - Lambert’s Cosine Law  Law 

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

Angle (Degrees) (Degrees)

Current (μA)

Resistance (Ω)  (Ω) 

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

52

 

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

Name: _____________________SID: ______________ Group:______ Date:_______________

1. What are the examples examples of of flow measurement 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 measurement device?  ___________________  __________ ___________________ ___________________ ___________________ ___________________ __________________ ________________ _______

4. What is discharge coefficient ? What are C d for orifice plate and venturi meter meter ? What does the Cd value tells us ?  ___________________  _________ ___________________ ___________________ ___________________ ___________________ ___________________ _______________ ______  ___________________  _________ ___________________ ___________________ ___________________ ___________________ ___________________ _______________ ______ 5.

What does smaller discharge coefficient tells us?  

53

 

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

V22

P1

P2

2g  g  Z1  2g  g  Z2

For same elevation, Z1 = Z2   

2

V1

2g



P1 g

2



V2

P2



2g

g

 

Carry the velocity to the right and pressure to the left: P1 g



P2 g

2



V2

2g

2



V1

2g

     

1

 

1

P1  P2   V22  V12 g 2g For  an ideal flow : Q  A1V1  A 2V2 V1 

A2

 

V2

A1 SubstituteV1 int o

1 g

( p1   p 2 ) 

1 2g

2

( V2



2

V1 )gives :

2   A 2   2   2    ( p  p )  V  V g 1 2 2g  2   A1   2     2 V22   A 2        p1   p 2  1  2    A1     

1

1

Now, we will write the above in term of V 2: V22



2( p1   p 2 )

  A   2  1   2  

 A1        2( p1   p 2 ) V2    A   2  1   2      A1    

54





 

Knowing that Qideal = A2V2, thus: 2( p1   p 2 )

Qideal  A 2

 

 A 2  2  1       A1     

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

Where, Cd  Q  A2  A1  P

: : : : :

  p 2 )

   A   2    1   2      A1     

discharge coefficient volume flowrate (m3/s) /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)

C d  d    values assumed to be:

1.2

2( p1

C d  d   = 0.98 for the venturi meter C d  d   = 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.

55

 

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, mete r, variable area meter and orifice orific e 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 7.92 x 10-4 m2  15 mm 1.77 x 10-4 m2  21 0 inclusive 14 0 inclusive

Orifice plate Upstream pipe diameter hence A1  Orifice diameter

= = =

hence A2

= 3.14 x 10-4 m2 

31.75 mm 7.92 x 10-4 m2 20 mm

Procedure

1. Observe that the apparatus is placed on the hydraulic b bench. ench. 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. 3. Switch on the pump then slowly open the hydraulic bench inlet valve. 4. At the same ti time me 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 a and nd 56

 

6.

7. 8. 9. 1.5

prime manometer and tappings. When done, close back the air bleed screw. Switch off the pump and adjust the levels of the manometer by adjusting the air bleed screw screw.. Try to get initial manometer level at a comfortable comf ortable level so that when experiment is carried out there will be enough room for the water column in the manometer to m move ove up and down. Close back the air bleed screw when done. Switch on the pump again. 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. Measure a certain volume of the reservoir, using stop watch measure the time taken to fill that portion. Repeat step 7 to get another set of data.

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

Seconds

8

12 15 18 20 22 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 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)  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. these se calculated values and and the reading on the v variable ariable area meter with the actual   Compare the 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 viscosity = 8.937 x l0 -4 Pa.s and D is the diameter of the holes. Question for discussion r eading for p2 is taken at the venturi   When calculating (p1 - p2 ) for the venturi meter, why is the reading 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 you think occur on the venturi meter and the orifice plate?   Why the heights should different in relation to the others in the manometer?   Why velocity at P2 and P7 are different?  

57

 

  Which flow meters devices as the smallest error? Include error analysis. 

Flowrate comparision table  Variable Conversion Meter to Flow rate (Liter/min) m3/s 2

Venturi Flowrate

Oriface Flowrate

m3/s

m3/s

Flowrate using stopwatch m3/s

5 10 12 15 18 20 22

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

Velocity at P2 m/s

Reynolds Number at P7

5 10 12 15 18 20 22

58

 

 

 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 m main ain test signals : step, ramp, sinusoidal sinusoidal

3. Describe wh what at do you understand understand about the control control actions: proportional, proportional, derivative aand nd Integral.

4.  Draw an example of a system response with depict peak overshoot, settling time, rise time t ime 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

Design the experiment in order: 1. To investigate and learn the importance i mportance of the vital system characteristics in the assessm assessment ent of control loop efficiency. efficiency. 2. To evaluate the PID control elements using the PCU computer controlled flow cycle.

1.1

Theory

 A. Introduction to Control 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 param parameters eters (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

Controller

Control

Process  

(desired behavior)

Output (actual behavior)

Figure 6.1 Open Loop Loop Strategy Strategy

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

Controller

Control

Process

Output

Figure 6.2 The Feed Forward Strategy

The most common control strategy is feedback or closed loop control, as illustrated in figure fi gure 6.3. Here the process output is monitored, and control actions are taken to counteract deviations 48

 

 

 Lab No.6

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.

Disturbances

Input Controller

Control

(desired behavior)

Process

Output (actual behavior)

Measure

Figure 6.3 the Closed-loop (feedback) (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 Mathematically , Mp =PG(SP-MV)+C = PG e(t) +C Where, PG = SP = MV = C =

Mp = Controller Output Proportional Gain Set point measured value Output with zero error

e(t)

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 t he 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:

M i( t ) 

PG



  e( t )dt

IAT The integral Action time is defined as the time taken t aken for the integral action to duplicate the 49

 

 

 Lab No.6

 proportional action of the controller, controller, if the error error remains remains constant constant during this perio period. d. It is used commonly common ly to remove any steady state errors incurred when using a proportional controller. 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 t aken for the proportional action to duplicate    DAT de( t ) M d  PG dt

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 characte ristics of the response is shown in Figure 6.5.

Figure 6.4

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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% 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.

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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 sufficie sufficient nt water in the bottom reservoir tank before con conducting ducting the experiments. 2. Make sure there are no leakages leakages in the piping system before conducting conducting the eexperime xperiments. nts. 3. Open the bypa bypass ss valve before before switching on the the water pump pump and close it only after the flow is fully circulated through the entire system for a brief period.

MANUAL SETUP

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

MAINTENANCE

1. Please chec check k for signs of leakage leakage in the piping system from time to time. time. Besides that there is no major maintenance required for this apparatus 2. Kindly seek the assistance from the manufactur manufacturer er 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. microcomputer. On the Process Control Unit the temperature at the sump, flowline and process tank are measured thermometers. Thesignal flowrate is measured by Computer an in-line flowmeter.using Theseplatinum analogueresistance signals are fed back to the conditioners on the Control Module (CCM) from where they are sampled by the microcom microcomputer puter 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 i mpeller 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 therefore produced for one revolution of the rotor, thus  producing a frequency frequency output 'w 'which hich is proportional to the flowrate.

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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 displacem displacement ent 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

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, program, follow the instructions instructions in section 1 to fam familiarize iliarize yourself w with ith the program. program.

1.3.1 Section 1: Assessment of System Performance 1.  By operating the controls in the Process Control Unit, the vital characteris characteristics tics can be easily demonstrated demonstrate d by varying the values of the PID controller. 2.  Select the Flow Control tab and in the Control select select the Closed Loop tab 3.  Set the “Set point” to 4 liter/min 4  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, response, introduce a disturbance 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.

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1.3.2

 Lab No.6

Section 2: Evaluation of the PID Control Elements Elements The PID control elements may be easily evaluated using the PCU computer controlled flow cycle.

Characteristic selection of PID elements: el ements:

The selection range of the PID elements is: Proportional Gain: Between 1 to 10 Integral Action: Between 0 to 1 Derivative Action: Between 0 to 1

Base on Software operation in 1.3, construct the experiment procedure in order to achieve the objective.

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 Lab No.6

MESB 333 Lab No. 7 Free and Damped Vibration  _____________________________________  _____________________ ________________________________ _________________  _  

Introduction

In this lab, the students are to be expose to several type of free and damped vibration system with their characte characteristic ristic that are related to the theory learn learn in class. 1.1  Theory Underdamped Syatem

The displacement solution for this kind of system is:

An alternate but equivalent solution is given by:

The displacement plot of an underdamped system would appear as:

 Note that the displacement amplitude decays exponentially (i.e the natural logarithm of the amplitude ratio for any two diaplacements seperated in time by a constant ratio is a constant)

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, Td is the period of the damped vibration. Critically Damped System

The displacement displacement solution for this system is:

The critical damping, C c can be interpreted as the minimum damping that results in non-periodic non -periodic motion (i.e sample decay). The displacement displacement plot of a critically-damped critically-damped system with positive initial displacement displacem ent and velocity would appear as,

The displacement displacement decay to a negligible level after one natural period, T n. Note that if the initial velocity V 0 is negative while the initial displacement displacement X   X 0 is positive , there will exist one overshoot of the resting position in the displacement plot. Overdamped System The displacement solution for this kind of system is:

The displacement plot of an overdamped system would appear as:

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The motion of an overdamped system is non-periodic, regardless of the initial conditions. The larger the damping, the longer the time to decay from an initial disturbance. If the system is heavily damped, ζ > 1, the displacement solution takes takes the approximate form:

EXPERIMENT I 1

Objective To determine the spring coefficient and to investigate the deflection of the spring at certain load.

1.2 

Procedure

1.3 

Result and Discussion

1.  Find out the spring constant, k for spring T1, T2, T3. 2.  Plot a graph of force against deflection, where the spring coeffiecient is the slope, m of the graph. The k value is in unit kg/mm or N/mm.

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EXPERIMENT II 1.1

Objective   Objective

To determine the spring coefficient and the natural frequency of single degree freedom.

1.2 

Procedure

1.3 

Calculation:

Use the formula below to calculate the natural frequency.

where, k =stiffness =stiffness (N/m) m=mass (kg) RPM of the motorized chart recorder = 5 rpm Diameter of drum collector = 27.00mm and the circumference=84.82    =



   Where,

T:time (seconds)taken to complete one cycle.

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1.4 

 Lab No.6

Result and Discussion:

1.  Compare natural frequency of the system s ystem between the calculated from plotted graph and formula. 2.  Find out the spring constant, k from Experiment 1. 3.  Repeat the experiment an and d observe the behav behaviour iour of different type of spring.

EXPERIMENT III  1.1

Objective  Objective 

1. To demonstrate the oscillation of single degree freedom system 2. To investigate the behaviors for free vibration and damped vibration 

1.2 

1.3

Procedure

Calculation:

Calculate the natural frequency of the system as experiment 2.

, The damping ratio can be obtained from the formula above

1.3 

Result and Discussion:

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 Lab No.6

Do discuss if the damper is underdamped, critically damped or overdamped system.

**Please do download the details manual from the Moodle. **