lab manual measurement

8/9/2019 Lab Manual Measurement

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DEPARTMENT OF MECHANICAL ENGINEERING

COLLEGE OF ENGINEERINGTENAGA NASIONAL UNIVERSITY

MALAYSIA

ENGINEERING MEASUREMENT

LAB. MANUAL

MESB 333


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Table of Contents

Laboratory Syllabus 3Overview 4Laboratory Time 5

Format for Logbook 6Format for Formal Report 7

Lab No.1: Strain Measurement

Prelab Questions 9Experiment I: Axial Strain 10Experiment II: Torsion Strain 16

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

Prelab Questions 20

Experiment I: Velocity Measurement Using Pitot Tube 21

Experiment II: Determination of Discharge Coefficient 26

Lab No.3 Temperature Measurement

Prelab Questions 31Experiment I: Time Constant 32Experiment II: Type K Thermocouple 39Experiment III: Humidity Measurement 42

Lab No.4 Photo TransducerPrelab Questions 45Experiment I: Photo Diode 51Experiment II: Photo Conductive Cell 54Experiment II: Photo Transistor 57

Lab No. 5 Flow Rate Measurement

Prelab Questions 60

Experiment: Flow Rate Measurement Devices 61

Lab No. 6 Introduction to PID Controller

Prelab Questions 66

Experiment: PID Controller 67


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Laboratory Syllabus

Lab 1 : Strain Measurement

There are two experiments in this lab. The experiments are related to the field of mechanics ofdeformable solid. The 1

st experiment is on bending of a cantilever beam. The 2

ndexperiment involves

loading weighs on a circular bar to create torsion. Strain gauge is used to convert the value of bodydeformation to corresponding electric signal for analog reading. Simple calculation for strain isrequired using basic bending theory.

I nformal report is required for thi s lab.

Lab 2 : Determining fluid (air) velocity and Discharge Coefficient

There are two experiments in this lab. These experiments are related to the field of Fluid Dynamics ofair. Both experiments use the same apparatus. 1stexperiment is to measure air flow velocity. Pressure

along the test pipe will be measured to determine air flow velocity using Bernoullis equation. 2nd

experiment is to measure the discharge coefficient of an orifice plate and a nozzle. An orifice platewill be inserted along the test pipe.

Formal report is requir ed for th is lab.

Lab 3 : Temperature Measurement

This experiment is related to the field of Heat Transfer and Thermodynamics. This experimentconsists of temperature measurement using different type of measuring devices: Pt 100 resistancethermometer, liquid filled thermometerand NTC temperature probe. The apparatus consists of ricecooker, oven, amplifier, and temperature indicator and so on connected in a simple circuit.Understanding the working principle of resistance thermometer is important.


Lab 4 :Photo-electric TransducerThis lab is related to the field of physics, the behavior of light. Light intensity can be measured bymeasuring the effect of the light on a device. When light falls on a material, current that corresponds

to the light intensity will be generated using transducer. Photocell, circuit box and light source are theimportant devices in this experiment. The current that is produced at different level of light intensitywill be measured.


Lab 5 : Flow rate Measurement

This experiment is related to the field of fluid dynamics. This experiment involves the study of liquidflow rate. Water is used as the fluid in this experiment. Three flow rate measurement devices: orificeplate, variable area meter and venturi meter are used. The orifice plate and venturi meter requirecalculation using Bernoulli equation to give the flow rate reading while variable area meter gives

reading directlyI nformal report is required for thi s lab.


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Lab 6 : Flow rate Measurement

This experiment is related to the field of fluid dynamics. This experiment involves the study of liquidflow rate. Water is used as the fluid in this experiment. Three flow rate measurement devices: orificeplate, variable area meter and venturi meter are used. The orifice plate and venturi meter requirecalculation using Bernoulli equation to give the flow rate reading while variable area meter givesreading directly.


LABORATORY & REPORTS: AN OVERVIEW

All experiments in the Engineering Measurements Laboratory require either a laboratory

report (Logbook) or a formal laboratory report for selective experiments, unless it is stated

otherwise. The reports should be simple and clearly written. Laboratory reports (logbook) are

due after all of the experiments are performed, unless it is stated otherwise. Final reportsshould be submitted a week after the experiments day, unless it is stated otherwise. Any late

submission will not be entertained, unless there are concrete and unavoidable reasons.

The laboratory reports (log book) should be in hand writing and any graphs needed should be

drawn in either an appropriate graph paper or drawn using EXCEL, whichever suitable.

However, for final laboratory reports, it should be computer-generated and any graphs should

be drawn using EXCEL.

The formal laboratory reports should be submitted into pigeon hole in front the lab or to the

instructor directly.

The pre-lab questions in this lab manual should be answered and submitted during the first 5

minutes before you start your experiment accordingly.


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Laboratory Session

Lab Technician : Muhammad Faizal Bin Rahim

Tel: 03- 8921 2020 ext. 6324

Laboratory Time:

Section 1A: Wednesday - 800-1100 (BL-0-003)Section 1B: Wednesday - 1500-1800 (BL-0-003)Section 2A: Monday - 1400-1700 (BL-0-003)Section 2B: Thursday - 1100-1400 (BL-0-003)Section 3A: Tuesday - 1500-1800 (BL-0-003)Section 3B: Thursday - 1500-1800 (BL-0-003)

Section 4A: Monday - 900-1200 (BL-0-003)

Attendance:

Please sign attendant sheet upon arrived to lab. Mark will be given depending on time of arrival.

Student who comes 15 minutes after the lab begins will get 0 mark. Absence due to illness should beproven by medical certificates (MC).

Prelab:

Turn in prelab at the beginning of each lab. No prelab will be accepted 15 minutes after the labbegins. 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 signedat 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 theresults from each experiment. The logbook MUST be presented to the instructor and signed at the endof each laboratory session. Marks will be given for each experiment done in the session. Collect thelab 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 throughoutthe course. The formal reports should be written for the following experiments.

Experiment 2: Velocity Measurement.

Experiment 6: PID Controller.

Duration of one-week period is provided for formal report and should be submitted during the next

lab. Report should be submitted to the lab technician personally. Grade will be deducted from the latereport as follows (except with valid reason) : Late submission penalty : Late 1 day : 90%, Late 2

days : 80 %, Late 3 days : 70%, More than 3 days: 50% of earned mark.

Plagiarismis not acceptable. It will result in half of the total grade being deducted or zero grade forthe lab report or for the whole course. In addition, poor reportwriting will result in meeting theinstructor for improvement in future report writing. Please use the font of Arial or Times NewRomanonly.

Before submitting your hardcopy formal report to the instructor, you need to upload your

softcopy report into TURNITIN program, to check for similarity (report with silmilarity higher

than 50% will not be accepted). You will be given ID and password to upload the softcopy of

your formal report by the respective instructors.

Experiment Group:

Students will perform experiment in-group. Each experiment group consists of 3-5 students.Group number consists of Section number, follows with number appointed. For example, the first

group from section 1A will have group number of 1A1; the second group in the same section will bedesignated as 1A2 and so on.

Report must be submitted using front page supplied.


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Format for LOGBOOK

No. Criteria

1 Title PageWith name, SID, group no., lab no., date performed, date submitted.

2 Statement of Purpose or ObjectiveWith clear, specific purpose statement

3 Data, Observation and ResultsWith results clearly, orderly presented in either graph, spreadsheet, table etc withlabeled. Sample calculation if calculation is involved. Error calculation

4 Analysis and DiscussionWith specific comment, explanation, support on the results based on theory. Errorand uncertainty analysis ie. Error source, comparison between the experimentaland theoretical results. Answer to question if given.

5 ConclusionSummary of the experiment. Conclusion drawn from results in the light of thestated objective.

6 Overall report presentationNeat, Clear label of small title etc. With references if given


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Format for Formal Report

No. Criteria

1 Title Page

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

2 Table of Content

3 Summary/AbstractThe concise overview of the report.

4 Statement of Purpose or Objective

A br ief descri ption of what the experiment is demonstrati ng.

5 TheoryWith brief but clear background and theory related to the experiment.

6 EquipmentDiagram of the apparatus and specification.

7 ProcedureA step by step explanation of what was done in the lab and why each step was

performed.

8 Data, Observation and ResultsWith results clearly, orderly presented in either graph, spreadsheet, table etc

with labeled. Sample calculation if calculation is involved. Error calculation

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

10 ConclusionSummary of the experiment. Conclusion drawn from results in the light of thestated objective.

11 Overall report presentationNeat, Clear label of small title etc. With references if given


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MESB 333 LAB NO.1 :

STRAIN MEASUREMENT

PRELAB QUESTIONS

Name: ________________________SID: ______________Group:______ Date:_______________

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

2. What is the mechanical equipment used to measure small changes in length? What is the principle

used in strain gauge, theoretical formula to calculate strain and explain the terms in the formula?

3. Why is zeroing required before measurement is done?

4. How to eliminate error due to temperature changes?

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


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MESB 333 Lab No.1

Strain Measurement

____________________________________________________________________________

1. Experiment IMeasurement of Axial Strain

1.1 Objective

This experiment student will learn to measure strain of a cantilever beam. In addition, student

will be able to understand the relationship between stress, strain, and Youngs Modulus ofElasticity.

1.2 Theory

A material will be deformed to certain extend when external forces act on it. This deformationwill cause changes in length and diameter of the material. The strain produced is directlyproportional to the stress at a limited region, which is called the limit of proportionality (i.e. thereis linear relation between the two). The stress-strain graph is a straight line in this region. In thisexperiment, we are going to study the performance of an electrical resistance strain gauge as wellas to verify its accuracy on measuring the strain of a bending material.

Hooke's Law, which relates stress and strain, can be applied in the limit of proportionality

region. Young's Modulus of Elasticity is the gradient of straight line in the stress-strain graph.

The mathematical relationship is:

EEA

P

L

dL(1)

where,

dL : change in length L

: strainP : force on cross section area A

E : Youngs Modulus of Elasticity: axial stress

Equipment used to measure dL is called extensometer. It is a mechanical method to measuredL where change in length can be magnified. However, a better way to measure dL is by usingthe electronic measurement. Longitudinal strain is associated to the changes in length of amaterial. 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

Poissons ratio( ) = lateral contraction per unit breadth

Longitudinal extension per unit length


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

A

LR

..(2)

where,

R : electrical resistance

: specific resistance of material

L : length

A : cross sectional area

From the relationship, it is clear that the resistance will increase when the material isstretched. Conversely, compression will cause the resistance to decrease. Strain gauge usesthis principle to measure the strain.

1.3 Calculation of axial strain

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

..(3)

Where,

M : bending moment = (Applied load X moment arm)

I : second moment of area of cantilever =12

bd3

(Width b and thickness d)

: axial stress

y : half the thickness of the cantilever = d

E : modulus of elasticity

R : radius of curvature of cantilever due to M

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

I

My

R

E

yI

M


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.(4)

From the theory of bending

.(5)

Hence, the theoretical strain value is

(6)

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

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

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

1.4 Wheatstone Bridge

Figure 1 Wheatstone bridge

B

R1 R2

R

y

L

dL

EI

M

R

1

EI

My

R

y


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R1 will be the strain gauge attached to the material. It is also called an active gauge. R2 is asimilar strain gauge to R1. But, it is attached to an unstressed part of the material. The effect oftemperature 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 digitalmeter and a zeroing circuit. Voltage applied to A and C is a constant DC voltage. Normally it is

1-2 volts. External zeroing is applied in Wheatstone Bridge. External zeroing means the meter Mwill show zero reading. This is done by having a variable resistor at D. Zeroing can be done byvarying the variable resistor. Zeroing is required because factor like weight of the material canaffect the results.

1.5 Apparatus

Figure 2. Experiment apparatus

The apparatus above is a direct read-out strain meter in a base box to which a pillar carryingan aluminum alloy cantilever has been fixed.An electrical resistance strain gauge has been fixedto the top surface of the cantilever 150 mm from the loading point . The cross section of thecantilever is 25.4 x 3.2mm. The modulus of elasticity of the cantilever is 69 000 N/mm

2. A

temperature compensation (dummy) gauge is supplied fixed to a small piece of aluminum alloy.

The basic circuit of the Wheatstone bridge is laid out on top of the base, showing the use of azeroing control. An analogue meter with a center zero scale has been designed to read true strain

in units of micro-strain.


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1.6 Procedure

1. Connect the strain gauge leads from the cantilever strip and dummy gauge leads to theterminals, switch on the apparatus.

2. Adjust the zero offset knob (variable resistor) on the apparatus to zero the meter.3. Note whether any drift of the zeroed reading occurs as the strain gauges warm up4. To show the effect of temperature, warm the temperature compensation gauge by placing

one's finger on it.5. Suspend the C hook and load hanger in the groove at the end of the cantilever.6. You may need to re-zero the meter. Record the meter reading.7. Press downward on the end of the cantilever and observe the direction in which the meter

reads in the reverse direction. You should notice that the polarity of the reading indicateswhether the gauge is in tension or compression.

8. Load the cantilever to 30 N by 5 N increments. Read and record the meter reading at eachincrement

9. Unload the cantilever from 30 N to 0N and record the readings at each decrements.

10.Repeat step 8 and 9 and record the second set of reading in order to obtain the average of thereadings.

1.7 Results

Table 1 Cantilever experiment result

Load (N)

Theoretical Average Meter Reading

Strain ( )

Actual

Stress

(N/mm2

)

(Increasing

Load )

Strain

( )

Stress

(N/mm2)

IncreasingLoad

%ErrorDecreasing

Load%Error

0

5

10

15

20

25

30

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

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

%100theory

erimentexptheory

error%


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Plot the strain( ) against axial stress( ) for the theoretical and experimental values on the samegraph. Draw the best fit linear line and find its slope. What can you relate the gradient of the line

and Youngs Modulus of Elasticity?

Discuss the results. Are the readings for increasing and decreasing load the same? Why?

Why the system was connected to the dummy gauge ?

Include error analysis.


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2 Experiment II

Measurement of Torsion Strain

2.1 Objective

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

2.2 Theory

Having studied the use of a strain gauge for measuring tensile(axial) strain and stress,

a more complicated application can now be considered. Reverting to the diagram of thestandard bridge there are further ways of exploiting the measuring technique. In this

experiment, we are going to study the measurement of torsion strain.

Suppose the temperature compensation gauge used as R, can be attached to the structuralelement 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 knownas reversed active strain gauging. This could have been done in the case of bending by attachinga strain gauge on the underside of the cantilever where the compression due to bending equals thetension where the top surface gauge is fixed. The leads from the underside gauge would thenreplace the leads from the dummy gauge. Now consider a hollow round tube used as a cantilever.

Figure 3. Cantilever round bar exert with torsion.


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In bending there is a neutral axis at the horizontal axis, so any gauge fixed symmetricallyabout this neutral axis will not record a strain, By applying torque at the free end of thecantilever, a uniform shear is induced along the whole length. This in turn produces diagonaltension and compression stresses of equal value along the corresponding 45

0helical directions.

Hence by fixing two strain gauges at A and B as shown the following conditions are satisfied:

(1) Temperature compensation

(2) Net axial strain effect is zero for either A or B

(3) Gauge A is subjected to diagonal tension while gauge B is in diagonal compression, orvice versa.

The meter will therefore indicate twice the diagonal strainfrom which the stress can bederived using the modulus of elasticity.

2.3 Calculation of torsion strain

Hookes Law

..(7)

For the torsion specimen the comparable theoretical equation is

J

Tr

L

G

rJ

T

..(8)

where

T : torsion = (Applied Load X eccentricity)

J : polar moment of inertia of tube = 414

o DD32

Do : outside diameter

Di : inside diameter

: surface shear stress

r : outside radius of tube

G : modulus of rigidity

: angular twist over length L

E


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The shear stress acts circumferentially and has to be accompanied by a system ofcomplementary stresses including diagonal tensile and compressive stresses, which areperpendicular to each other. Hence there are equal direct strains along opposing 45

0helices on

the surface of the tube given by

EJ

Tr

E

q

(9)

and the meter will indicate 2* .

2.4 Apparatus

The torsion accessory consists of an aluminum alloy tube 9.5 mm O/D and 6.3 mm I/Dwith a loading arm welded across one end. A clamp is provided to enable the tube to replacethe clever strip used above, the loading arm being set horizontally. A load hanger can besuspended on the vertical axis of the tube, or at horizontal eccentricities of 50 or 100 mm. The

strain gauge leads from the strip cantilever and the dummy gauge are removed from theterminals so that the pairs of leads from the torsion specimen can be connected instead.

2.5 Procedure

1. Connect the two pairs of leads from the torsion tube to the pairs of terminals.2. Switch on the apparatus and adjust the offset knob to zero the meter. Re-zero if drift

occurs as the gauges warm up.3. Place the load hanger at zero eccentricity and add two 10 N weights. Note any meter

reading, and check that the meter returns to zero when the loads are removed.4. Move the load hanger to 50 mm offset. Zero the meter. Record the strain readings as the

30 N load is added by 5 N increments to the hanger. Repeat the readings as the weights areremoved. Use a table of results as shown.

5. Repeat the above for 100 mm offset. It will be necessary to hold the base box to prevent itbeing toppled over by the eccentric load.

6. Repeat step 4 and 5 and record the second set of reading to get the average.


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2.6 Results

Table 2.1 Diagonal Strains on a Torsion Specimen

Eccentricity

(mm)

Load

(N)

Theoretical

( )

Diagonal Strain( ) Actual

Shear

StressStrain Shear

stress

Average Meter

Reading

IncreaseLoad

DecreaseLoad

Increaseload

0 10

20

30

50 5

10

15

20

25

30

100 5

10

15

20

25

30

Calculate the theoretical value for the diagonal/torsion strain and compare with the meterreadings by stating the percent error. (Remember, the meter reading is twice the actual value.)

Plot a graph of strain vs. shear stress (increase load only) for theoretical and actual on the

same graph and use the best fit straight lines to determine the relationship between shearstress and torsion strain.

Why the diagonal strain at eccentricity 0 mm are zero?

How successful is the technique (two strain gauges) for eliminating bending stress from thereadings?

Why used two strain gauges?

What the system is not connected to dummy gauge?



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MESB 333 LAB NO. 2:

VELOCITY MEASUREMENT

AND DETERMINATION OF DISCHARGE COEFFICIENT

PRELAB QUESTIONS

Name: _____________________SID: ______________ Group:______ Date:______________

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

2. What is coefficient of discharge?

3. What is Reynolds number?

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

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


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MESB 333 Lab No.2

Determining fluid(air) velocity and Discharge Coefficient

1. Experiment IVelocity Measurement Using Pitot Tube

1.1. ObjectiveThis experiment allows student to learn the method of measuring air flow velocity using pitottube. 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. TheoryA pitot tube is used to explore the developing boundary layer in the entry length of a pipe whichhas 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 inthe pipe can be obtained by first measuring the pressure difference of the moving air in the pipeat two points, where one of the points is at static velocity. The Bernoulli equation is then appliedto calculate the velocity from the pressure difference.

'22

ghorp

v (1)

p The pressure difference between the pitot tube and the wall pressure tapping measured

using manometer bank provided ( g x where x is the level of fluid used in the manometer).

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

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

g gravitational acceleration constant (9.81 m/s2)

When fluid flows past a stationary solid wall, the shear stress set up close to this boundary due to

the relative motion between the fluid and the wall leads to the development of a flow boundarylayer. The boundary layer may be either laminar or turbulent in nature depending on the flowReynolds number.

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


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

1.3. Reynolds Number

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

vdRe

fluid density

v : fluid velocity

d : obstacle size

coefficient of fluid dynamic viscosity

A small Reynolds number refers to a flow in which the fluid has a low density so that it respondseasily to forces, encounters a small obstacle, moves slowly, or has a large viscosity to keep itorganized. 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'sviscosity--it's tendency to move smoothly together as a cohesive material.

A large Reynolds number refers to a flow in which the fluid has a large density so that it doesn't

respond easily to forces, encounters a large obstacle, moves rapidly, or has too small a viscosityto keep it organized. In such a situation, the fluid can't get around the obstacle without breakingup into turbulent swirls and eddies. You can describe such turbulent flow as dominated by thefluid's inertia--the tendency of each portion of fluid to follow a path determined by its ownmomentum.

The transition from laminar to turbulent flow, critcal flow, occurs at a particular range ofReynolds number (usually around 2500). Below this range, the flow is normally laminar; above it,the flow is normally turbulent.

1.4. Calculation of air flow velocity

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

p = gh (2)


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we can follow this procedure through using the following definitions:

Example:

Manometer tubes 1(static pressure*) 2(stagnation pressure)

Liquid surface readings(mm)

X1 X2

Angle of inclination, = 0

pressure term is used since this reading is in mm of manometer fluid and not the pressure of unitPa.

Therefore the equivalent vertical separation of liquid levels in manometer tubes,

h = (x1 - x2)cos (3)

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

p = kg h = kg(x1 - x2) cos (4)

The value for kerosene isk= 787 kg/m

3and g = 9.81 m/s

2. If x1 and x2 are read in mm, then:

p = 7.72(x1 - x2)cos [N/m2] (5)

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

To use the first equation (1), convert this into a 'head' of air, h. Assuming a value of 1.2 kg/m3

for this gives:

cos.1000

)(.' 21

xxh

air

k [N/m

2] (6)


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1.5 Apparatus

Figure 1 Experiment apparatus

1.6 Procedure

a) Five mounting positions are provided for the pitot tube assembly. These are: 54 mm, 294

mm, 774 mm, 1574 mm and 2534 mm from the pipe inletb) 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 tube assemblyat 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 aconvenient manometer tube. Make sure that the tip, the L-shape metal tube of the pitot tubeis facing the incoming flow.

e) Note that there is a pipe wall static pressure tapping near to the position where the pitot tubeassembly is placed. The static pressure tapping is connected to a manometer tube.

f) Position the pitot tube with the traverse poisition of 0mm. Start the fan with the outletthrottle 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 thetraveverse position touching the top of the pipe.

h) Repeat the velocity traverse for the same air flow value at the next positon with the pitottube assembly. Make sure that the blanking plugs is placed at the holes that are not in use.


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1.7 Results

Data Sheet for Veloci ty Measurement Using Pitot Tube

TraversePosition

(mm)

Pitot Tube at 54 mm

Static 'Pressure' Reading____________(mm)

Pitot Tube at 294 mm


Stagnation'Pressure'Reading

(mm)

x(mm)

p(N/m2)

velocity(m/s)


(mm)

x(mm)

p(N/m2)

Velocity(m/s)

0

10

20

30

40

50

60

70

80

TraversePosition

(mm)






(mm)

x

(mm)

p

(N/m2)

velocity(m/s)


(mm)

x

(mm)

p

(N/m2)

Velocity(m/s)

0

10

20

30

4050

60

70

80


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Static 'Pressure' Reading ____________(mm)

TraversePosition

(mm)

Stagnation'Pressure'

Reading(mm)

x(mm)

p(N/m

2)

velocity(m/s)

0

10

20

30

40

50

6070

80

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 developedpipe flow most likely occurred by the third or fourth position.

Give your comments on the velocity profiles. Include error analysis.


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2 Experiment IIDetermination of Discharge Coefficient

2.1ObjectiveThis 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 dischargefor the flow of liquids or gases through a pipe. The orifice provided can be inserted into thesuction pipe at the flanged joint approximately half way along its length. The multi-tubemanometer provided is used to measure the pressure drop across the orifice and this is related tothe discharge determined independently.

In this experiment, we are going to determine the discharge coefficient experimentally for an

orifice plate in an airflow pipe. Also using the static pressure tapings provided, we aredetermining the pressure distribution along the pipe downstream of the orifice plate. From the

obtained CDof the orifice plate, we will determine the CDof a small nozzle.

2.3TheoryThe orifice plate meter forms a jet, which expands to fill the whole pipe, some diameter

distance downstream. The pressure difference between the two sides of the plate is related tothe jet velocity, and therefore the discharge, by the energy equation:

where Q = discharge (volume/time)A

j= jet cross-section area at minimum contraction (vena contracta)

Ao = orifice cross-2/4: d = orifice size)

vj = jet velocity at minimum contraction (vena contracta)Cc= coefficient of contraction of jetCv= coefficient of velocity of jetg = gravitational acceleration (9.81 ms

-2)

h = pressure difference 'head' of air across orifice (refer to equation (6) of Exp.I)

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

(2)

If Q can be determined independently, then the discharge coefficient can be determined asfollows:-

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

(3)

(4)

2ghv

Cc

Co

Ajv

cC

oA

jv

jAQ

gh2A

QC

o

D

ghAo 2CQ D

iD'

ii gh2CAQ


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If hi= the drop in pressure head across the inlet, the discharge = ( k/ air)* (xbefore nozzlexafter nozzle):

in which Ai= standard nozzle cross-section area (= d2/4) and CDassumed to be 0.97. Values of

h I are obtained from the manometer tube levels connected to the pipe inlet pressure tapping andopen to the atmosphere.

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

(5)

Where ho = ( k/ air)*( x across orifice)

Ao = cross section area of orifice plate hole

2.5Apparatus

Figure 2 Experiment Diagram

2.6Procedure

(a) Insert the orifice plate in position (taking care to observe the instructions as to) in which thesurface should face the approaching airflow.

(b) Connect all the static pressure tapping points to the manometer tubes ensuring that onemanometer tube remains unconnected to record room air pressure and that one is attached tothe first tapping point adjacent to the standard inlet nozzle which should be fitted.

(c) Turn on fan with low airflow (damper plate closed) and read all manometer tubes, includingany open to the air (reading should be taken after the fan is on).

(d) Gradually increase air flow by increasing the damper opening to 100%, and take read at allopening.

oo

oD

ghA

QC

2


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Measure the diameter of the orifice plate, and the pipe for computing the cross sectional

area and Reynolds number.

2.7Results

Table 5.1 Static Pressure Readings when using Standard Nozzle (80 mm)

Damper Openings (% Openings)

0% 25% 50% 75% 100%

Points mm of kerosene

Roompressure

After nozzle

54mm

294mm

774mm

Before

After Orifice

1574mm

2534mm

Table 5.2 Static Pressure Readings when using Small Nozzle (50 mm)

Damper Openings (% Openings)

0% 25% 50% 75% 100%

Points mm of kerosene

Room

After nozzle

54mm

294mm

774mm

Before

After Orifice

1574mm

2534mm


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From table 5.1using equation (4) calculate the Qi, then using equation (3) where Q=Qicalculate the CDfor orifice plate for each damper opening.

For data in table 5.2, using similar procedures, but this time using the value of CD fororifice found previously, you need to calculate the CDfor small orifice for each damperopening.

For each case, plot values of CD obtained against corresponding values of Reynoldsnumber (Re) obtained using the relationship:

..(6)

where : the coefficient of dynamic viscosity of the air air density

v : is the mean pipe velocity (Qi/Ap)

d : the pipe diameter.

Also plot longitudinal pressure profiles for both tables from the manometer readings.(mm kerosene against tapping position)

Discuss what happen as the air flow past through the orifice plate. Discuss the CD obtained for orifice and small nozzle. What happen to the CDwhen you increase the damper opening? What happen to the manometer reading when the damper opening changes. Discuss. Any obstruction such as an orifice plate would actually cause a pressure drop but by

analyzing the graph below or from your data you should see that the reading in mm of

kerosene is increased. Explain.

Air Flow

vdRe

mmKerosene

Tapping position along test pipe

Pressure Drop across Orifice Plate


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MESB 333 LAB NO. 3TEMPERATURE MEASUREMENT

PRELAB QUESTIONS

Name: _____________________SID: ______________ Group:______ Date:______________

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

2. What is time constant?

3. What are the materials commonly used for resistance thermometer?

i) ________________________________________

ii) ________________________________________

iii) _________________________________________

4. Gives two examples where PTC thermistors are generally used?

i) ________________________________________

ii) _______________________________________


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MESB 333 Lab No. 3

Temperature Measurement

______________________________________________________

1 Experiment I

Time Constant

1.1 Objective

To compare the time constant of differnet type of temperature measuring devices with reference

to mercury filled thermometer. Understanding the concept of resistance thermometer (or RTD)

and thermistor using the PT100 and NTC probes. Students should be able to understand the

relationship between resistance and temperature, and main difference between resistance

thermometer and thermistor.

1.3 Theory

Temperature is a measure of hotness. Together with a measure of thermal mass of a body

it gives an indication of the total thermodynamics energy that body contains. There are many

scales for the comparison of temperatures, the most important is with their corresponding

values for melting ice and boiling water (which are common reference temperatures) being

given in the table below.

Scale Melting Ice Boiling Water

Celsius (or Centigrade) 00C 100

0C

Fahrenheit 320F 212

0F

Kelvin (Absolute Scale) 273 K 373 K

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

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 w ith an increase intemperature. The most common type is the mercury-in-glass thermo meter. This thermometer


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consists of a capillary tube with a bulbous end . clean , dry mercury is introduced and the

thermometer heated to drive off the air. The end is then scaled leaving mercury and mercury

vapour only.

On heating, the mercury expands relative to the glass container and a column is pushed along

the bore of the tube. A scale along the tube, calibrated in units of temperature, gives a directreading of temperature. The mercury-in-glass thermometer is an accurate device but is very

fragile and care should be exercised in use. This type of thermometer should not be used in

applications such as the food industry where mercury poisoning could occur in the event of

breakage.

The mercury may be replaced by other fluids according to the application. For example,

alcohol is cheaper and may be used at low er temperatures than mercury. A mercury-in-glass

thermometer is supplied with the Temperature Measurement Bench due to its stable and

accurate performance.

For accurate measurement of temperature using a liquid filled thermo meter, it is important thatthe

thermometer is immersed into the medium being measured by the correct amount. The depth of

immersion is usually stated on the stem of the thermo meter and defines the condition under

which calibration is maintained. The immersion depth may be partial or total and is

independent of filling or range

1.5 The Vapor Pressure Manometer

For industrial applications, the liquid-in-glass thermo meter is f ar f rom suitable due to itsfragility and the dif f iculty in reading. In these applications the glass is replaced by a metalcontainer and mechanical indication is substituted. One example of this type of thermo meter isthe vapor pressure thermo meter.This consists of a metal bulb partially f illed with f luid, w hich is connected to the sensing e lement of aBourdon gauge. The space above the fluid is filled with vapor of the fluid, the pressure ofwhich is displaye on the Bourdon gauge . The gauge is calibrated directly in units oftemperature corresponding to the equivalent , pressure of the vapor but calibration is far fromlinear due to the pressure increasing more and more rapidly as the temperature increases. For

this reason, the vapor pressure thermometer is suitable only for operation over short ranges oftemperature and suff ers from lack of sensitivity at low readings. In service, the range should beselected so that the gauge rema ins within operatio nal limits w ith the normal operating point atapproximately two thirds of f ullscale reading.Vapor pressure thermometers off er the advantage of remote reading. The thermometer may beordered with a metal capillary tube connecting the bulb to the gauge, permitting remote

operation overdistances up to sixty meters. Correct orientation of the bulb and gauge should be preserved f or

accurate results.The vapor pressure thermo meter supp lied w ith the bench has the Bourdon gauge connecteddirectly to the stem f or case of operation


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1.6 The Bi-Metal Thermometer

Expansion of solids may be used to measure temperature but direct measurement isimpractical due

to the very small movements involved. How ever, if two thin metal strips, having different coefficients of linear expression, are mechanically fastened together, the result is a strip whichbends significantly whenheated. This combination is called a Bi-metal strip and the sensitivitymay be increased by coiling the strip into a spiral. One end of the strip is fixed to the case andapointer is attached to the other end. Linear scale may be obtained by suitable choice of metals.

This type of thermometer is very robust and has many applications throughout industry whereaccuracy of measurement is not important.

Thebi-metal thermometer supplied w ith thebench is mounted on the back-board and gives adirect reading of ambient air temperature.

1.7 Resistance Thermometer

The resistance of a material changes with temperature. Resistance thermometer uses this

relationship in measuring the temperature. If high accuracy is required, the material used in

resistance thermometer is platinum. Nickel is used in general operation and monitoring. Copper

is also suitable but only in a restricted temperature range of approximately 250oC, because

copper tends to corrode more severely when subjected to oxidation.

Figure 3.1 shows the resistance change of the metals as a function of the temperature T.

They have a positive temperature coefficient . For the purpose of comparison a resistance

characteristics of a thermistor (NTC) was added, which runs much more non-linearly, and in

contrast to the metals, demonstrates a negative coefficient .

For small temperature ranges we may assume that linear relationships exist between

resistance and temperature. From figure 3.2 one can deduce the temperature-dependent

resistance ratio R(T) causedby the resistance change R is:

R(T) = Ro + R (1)

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

R = m T (2)

Knowing that, R(T) = Ro + R, thus:


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R(T) = Ro + m T

= Ro (1 + m/Ro T)

= Ro (1 +

T

R/R o T) (3)

= Ro (1 + 1 T) where, 1 =T

R/R o

Figure 3.1

1 is the linear temperature coefficient of the resistive material. It provides the relative change in

resistance ( R/ Ro) for a certain temperature change ( T), for example 0.4% change in resistance

per 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 1 , also the square temperature coefficients 2, and

Ni 100 Pt100

Cu100

R(T)

R Ro = R(To)


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for very large temperature changes T also the cubic temperature coefficients 3, and if

necessary the biquadratic value 4.

nn

2

21o T...TT1R)T(R (4)

where, oTTT

1.8 Thermal Response

The thermal response of a thermometer to changes in temperature is probably the mostimportant characteristic to consider w hen selecting instrumentation for a particular application.

A thermometer may be extremely accurate and stable inperformance but totally unsuitable foruse in a dynamic situation, due to a time lag betw een system temperature and thermometerreading.

The diagram below shows typical response curves for a thermometer when step changes in te

m- perature are applied.

The response of the thermometer is defined by the time taken for the temperature reading tochange by 63.2% of the step change. For any thermometer, this time will be a constant valueirrespective of step change and is defined as the "time constant" for the thermometer. Thetime constant and response profilefor a thermometer will change if the system is modified.For example, the speed of response of a thermometer will be slowed down if it is protected from the systembeing measured by a thermometer. The response will also be affected by thethermal contact between the thermometer and pocket, fluid filling of the pocket resulting in areduction in time constant.


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The response of the thermometer is defined by the time taken for the temperature reading to change

by 63.2% of the step change. For any thermometer, this time will be a constant value irrespective ofstep change and is defined as the "time constant" for the thermometer. The time constant and re-sponse profile for a thermometer will change if the system is modified. For example, the speed ofresponse of a thermometer will be slowed down if it is protected from the systembeing m easured by athermometer. The response will also be affected by the thermal contact between the thermometer andpocket, fluid filling of the pocket resulting in a reduction in time constant.

Figure 3.3 Experiment apparatus

setup


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1.9 Setup

1.10 Procedure

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


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1.6 Result

Table 1. Temperature measurements result

Plot the graph of Tagainst time for each type of temperature measuring devices.

Calculate and plot the time constant for each thermometer.

Discuss on the plotted graph? Which type of temperature measuring device hassmallest time constant?

2 Experiment II

Type K thermocouple

2.1 Objective

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

2.2 Thermistor

Thermistors consist of semi-conducting polycrystalline material. In the production of

temperature sensors copper dioxide (CuO2) is preferred. It demonstrates a sever (non-linear)

drop in resistance for an increase in temperature. It possesses a negative temperature

coefficient, which is the reason why these sensors are called NTCresistors.


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If the CuO2 is mixed with the ingredients of a ferroelectric material (e.g. BaTi), the

temperature coefficient is initially negative only for low temperatures. After reaching a

threshold temperature the temperature coefficient becomes very strongly positive in a narrow

temperature range. For even higher temperatures the temperature coefficient reverts back to

negative. Because of the clearly delineated positive temperature coefficient range, these sensors

are called PTCresistors. They are mainly used for trigger purposes.

2.3 Features of NTC and PTC thermistors

NTC sensors possess a high sensitivity, which is easily 10 times higher than that of

metal resistance thermometers. The non-linearity of NTCs and their broad manufacturers'

tolerances exclude them from use for precision instruments. In the temperature range between -

60oC and +150oC they are frequently used in the area of household appliances and medical

technology because of their high sensitivity and corresponding simple circuitry.

The effect of NTCs, whereby the resistance lowers as the temperature increases, is

explained by the semiconductor mechanism. In semi-conductors (as opposed to metal

conductors) the valency electrons have relatively strong bonds to the atomic nuclei of the

crystal lattice. A rise in temperature loosens this bond and more and more electrons enter into

the conduction band, where they are available for charge transport (i.e. for increased current),

thus reducing the ohmic resistance.

PTCs behave in the same manner below the threshold temperature. The

resistance lies only somewhat higher than for NTCs, because, due to the mixture of a

ferroelectric material to the semiconductor material an additional resistance of both

components results (series connection). However, with increasing temperature a

strong increase in resistance is observed within a narrow temperature range, which is

caused so rapidly by the sudden cancelling of a uniform orientation of all magnetic

forces in the ferroelectric material. Through thermal motion an amorphous crystal

structure is produced, which results in a considerable prolongation of the current

paths, on which the electrons move through the PTC. If this transition is completed,

the resistance then drops again as the rise in temperature continues. Thus the

function R(T) of the PTC follows the characteristic of its semiconductor components,

supplemented by the characteristics of its ferroelectric components.

They are generally intended for applications where a considerable change of

esistance is required as a function of themperature, or of dissipated power, for

example: heating elements, temperature indication, control or alarm, time-delay of

relays, circuit protection etc.


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2.4 Temperature function and temperature coefficient of NTC thermometers

The resistance R(T) = RTof NTC materials can be described as a function of the

temperature using the following equation:

RT= AeB/T (5)

The material constant B is given in Kelvin, e.g. B = 3800 K. The constant A gives

the resistance for infinitely high temperature. As the sensor cannot register this

temperature, the constant A cannot be used as a practical parameter. The

requirements for practical application can be better satisfied with the following

dependency RT. For this the reference temperature To = 20oC is used, for which the

resistance has its nominal value Ro. Due to the fact that in the above equation only A

is unknown, the equation is then solved for A, which is inserted into RT:

R(To) = Ro = AeB/To

A = Roe-B/To (6)

Subsitute (6)into equation (5)

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

(7)


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2.4 Procedure

2.5 Result

Table 2.1 Type K experiment result

Type K

Time (min) Voltage(mV) Temp(oC)

0

2

4

6

8

10

12

14

Explain the results of this measurement. How does the temperature effect thevoltage output?

Plot the temperature against time and voltage against temperature.

Is the graphs linear? If it is a linear get the slope of the best fit line.



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3 Experiment III

Humidity

3.1 Objective

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

3.2 Introduction

Humidity is the amount of water vapor in the air. Relative humidity is defined as the ratio of thepartial pressure ofwater vapor in aparcel ofair to the saturatedvapor pressure of water vapor ata prescribed temperature. Humidity may also be expressed as specific humidity. Relativehumidity is an importantmetric used in forecasting weather.Humidity indicates the likelihoodof precipitation, dew, or fog.High humidity makes people feel hotter outside in the summer

because it reduces the effectiveness ofsweating to cool the body by reducing theevaporation ofperspiration from the skin. This effect is calculated in aheat index table

Hygrometers are instruments used for measuringhumidity.A simple form of a hygrometer isspecifically known as a psychrometer and consists of twothermometers,one of which includes

a dry bulb and the other of which includes a bulb that is kept wet to measurewet-bulbtemperature.Modern electronic devices use temperature of condensation, changes inelectricalresistance,and changes in electricalcapacitance to measure humidity changes. Hygrometersmeasure humidity while psycrometers measure realative humidity in the air.

In a psychrometer, there are two thermometers, one with a dry bulb and the other with a wetbulb.Evaporation from the wet bulb lowers the temperature,so that the wet-bulb thermometerusually shows a lower temperature than that of the dry-bulb thermometer, which measuresdry-bulb temperature.When the air temperature is below freezing, however, the wet bulb is coveredwith a thin coating of ice and yet may be warmer than the dry bulb. Relative humidity iscomputed 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. Relativehumidity can also be determined by locating the intersection of the wet- and dry-bulbtemperatures on a psychrometric chart.One device that uses the wet/dry bulb method is thesling psychrometer, where the thermometers are attached to a handle or length of rope and spunaround in the air for a few minutes.
http://en.wikipedia.org/wiki/Partial_pressurehttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Air_parcelhttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Vapor_pressurehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Metric_(mathematics)http://en.wikipedia.org/wiki/Weather_forecastinghttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Dewhttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Sweatinghttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Heat_indexhttp://en.wikipedia.org/wiki/Humidityhttp://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Wet-bulb_temperaturehttp://en.wikipedia.org/wiki/Wet-bulb_temperaturehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Capacitancehttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Dry-bulb_temperaturehttp://en.wikipedia.org/wiki/Dry-bulb_temperaturehttp://en.wikipedia.org/wiki/Relative_humidityhttp://en.wikipedia.org/wiki/Psychrometricshttp://en.wikipedia.org/wiki/Psychrometricshttp://en.wikipedia.org/wiki/Relative_humidityhttp://en.wikipedia.org/wiki/Dry-bulb_temperaturehttp://en.wikipedia.org/wiki/Dry-bulb_temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Capacitancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Wet-bulb_temperaturehttp://en.wikipedia.org/wiki/Wet-bulb_temperaturehttp://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Humidityhttp://en.wikipedia.org/wiki/Heat_indexhttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Sweatinghttp://en.wikipedia.org/wiki/Foghttp://en.wikipedia.org/wiki/Dewhttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Weather_forecastinghttp://en.wikipedia.org/wiki/Metric_(mathematics)http://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Vapor_pressurehttp://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Air_parcelhttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Partial_pressure


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3.2 Procedure

Table 3.1 Wet and Dry Bulb and Humidity Measurement

Wet Bulb Dy Bulb

Initial Reading

Final Reading

Humiditiy from psychrometeric

Chart

Humidity reading from dail gage

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

- Error analysis


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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 Lamberts Cosine Law?

4. What is the Inverse square Law?

5. Give three type of photo transducer?

a.

b.

c.


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MESB 333 Lab No.4

Photo Transducer

1 Introduction.In this lab, the students are to be expose to several type of photo transducer with their

characteristic that are related to Inverse Square Law and Lamberts Cosine Law.

1.1 Objective

To understand the photo transducers effect and its relations with Inverse Square Law and

Lamberts Cosine Law. Students will measure the effect of the incident light on the behavior of

a photodiode, phototransistor and photo conductive cell.

1.2 Theory

When light falls onto certain material, its energy will be given up as being described by theprinciple of photo-electric transducer. The energy will become energy in the form of electriccurrent. Human eyes is an example of a photo-electric transducer. Eyes act as a transducer byconverting light energy to signals that will be sent to the brain for further process.

Experimentally, one can know the intensity of the light falls on an object by measuring the

corresponding electric current caused by the light. In this experiment, you will learn to use

photo-electric transducer to measure the intensity of light in relation to the induced current andresistance.

The variety of colors existing in this world is due to the fact that sun-light has differentcomponents of light. Color of light is determined by its frequency, which in turn proportional tothe reciprocal of its wavelength. The relationship between light frequency, speed of light and

wavelength is given in the equation

Where, f = frequency

v = speed of light, 3 x 108m/s

= wavelength

= time to complete a cycle of wave

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

1f

f

v


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Table 4.1Spectrum for light

COLOR WAVELENGTH (mm)

Violet 440

Blue 470Blue-Green 490

Green 520

Yellow-Green 550

Yellow 580

Orange 600

Red 690

Deep-Red 700

Light is a form of electromagnetic radiation. Alternatively, light can be considered as consistingof 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 thewavelength, the higher will be the frequency. With the relationship that energy is directly

proportional to the frequency of light, higher frequency will translate to higher energy. Therefore,blue light has a higher energy that red light because the wavelength for blue light is shorter than

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 cm2of 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 m

2, in proportion to the

square of the radius. The luminous flux over this area is still 1 m2but the illumination has now

fallen to a quarter of its previous value as the luminous flux is spread over four times the area.

vf

f

v


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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 = luminous flux (lumen)

d = distance (m)

1.4 Lamberts Cosine Law

If there is an angle of between the surface of the transducer and the oncoming light, theluminous flux falling on the transducer surface is exactly the same as that which would fall on anormal surface (Figure 5.1). However,

Area surface 1 = cos = Illumination surface 1Area surface 2 Illumination surface 2

Figure 4.1

Thus the modification of the inverse square law becomes:

1.5 The Photo-Conductive Cell

A semiconductor, as its name implies is a material with an electrical conductivity inbetween that of an insulator conductor and a conductor. Typical materials of interest areGermanium and Silicon,but other materials and combinations of materials behave in a similarfashion. They are extensively used in semiconductor devices, e.g diodes and transistors.

Electrical conduction in such a material occurs when free charge carriers, e.gelectrons, are available in the material to move when an electric field is applied. It happens that

in certain semiconductors, light energy falling on them is of the correct order of magnitude to

release charge carriers which will increase the flow of current produced by an applied voltage.This is known as the PHOTO-CONDUCTIVE effect, and device is called a PHOTO-

2d

E

1 2

Incident

Light

cos

d

E2


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RESISTOR or a PHOTO-CONDUCTOR, or sometimes a LIGHT DEPENDENT RESISTOR,as incident light will effectively vary its resistance.

The current, or the number of charge carriers would expect to be related to the number of

photons, or the intensity of the incident light, and will be investigated. The colour of the light

will affect the response, due to the different energies of the photons. Small number of charge

carriers are also produced at room temperature by thermal effects, and this will also contribute

to the current.

The physical effects which cause this phenomenon are rather involved, but are given here to

make the study complete. In an intrinsic (pure) semi-conductor crystal all the valence electrons

have covalent bonds together with their neighbours. There may be represented on a diagram of

energy bands. It is found that there is a forbidden energy gap of the order of an electron volt

(1eV) between the valence band (where the electrons are bound to their parent atoms) and the

conduction band the electrons are now free charge carriers). This corresponds to the minimum

energy necessary to break a covalent bond and form a hole/electron pair. The electron is raisedinto the conduction band and contributes to conduction as well as the hole left in the valence

band. This theory is fully described most standard textbooks. It is of interest to us now if this

energy can be supplied by light photons.

Consider first the effect of impurities in the semiconductor. Very small amounts of the

correct impurities can introduce either extra holes (P type) or extra electrons (N type) because

atomic structure. These will appear on our energy diagram as energy levels just below the

conduction band (doNor Ievel for N type) or just above the valence band (accePtor level for P

type). If photons of the correct energy illuminate such a specimen, several things may happen, as shown in Fig 4.2

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).

photon Impurity

excitation Intrinsic

excitation

Conduction band

doNor

AccePtor

Energy gap

Eg

Valence band


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These last two transitions are known as impurity excitations and require less energy thanintrinsic excitations. However, the density of states in the conduction and valence bands greatlyexceeds the density of impurity states. At room temperature, most of the impurity atoms areionised in any case. Thus, photoconductivity is due principally to intrinsic excitation. Impuritieshowever do have advantages as discussed later. Our transducer is actually an N-type semi-conductor.

The carriers generated by the photo-excitation will move if an external voltage is applied tothe device. This superimposes a regular drift on their random diffusion motion colliding withothers. They may however, recombine with an available hole or electron before they reach theedges of the material. This may affect the response time of the device, cut down the availablecurrent (loss of sensitivity) or introduce non-linearities. Those carriers remaining will constitutethe device current which thus depends initially on the number of photons.

The actual process is extremely complicated and depends on several factors, including the

density of the states in the energy bands, the probability that a photon will excite an electron,

and other factors, including carrier lifetime and mobility which depends upon recombinations

and trappings. Thermal effects also play a part.

1.6 SAFETY & PRECAUTION

1. Only plug the banana plug into the banana socket according to the experiment manual when

doing experiment, plugging the plug into the wrong socket may damage the electronics

component inside the control box.

2. Check the wiring connection between banana socket first before turn on the control box.

3. Do not connect the positive terminal of the power supply to negative terminal of the power

supply without connecting to any load between them.

4. Make sure the connection between the measurement point and the measurement meter are

in correct polarity.

5. Make sure the connection of the lamp to the power source are in correct polarity.

6. If the experiment is conducted during day light, take the reading as soon as possible in case

the day light varies. Also keep your hand away from the rig when taking readings in case

they cause unwanted reflections of light onto the transducers.

7. While the lamp is turn on, avoid touching the lamps 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 isconnected to correct terminal of the multi-meter.

Pre-experiment procedure

1. Read the safety instruction given before conducting the experiment.

2. Read and understand the theory of photo transducer before lab session.

3. Read and understand the theory of Inverse Square Law and Lamberts Cosine Law before

lab session.

4. Prepare the accessories needed for the experiment.


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2 Experiment 1: Photodiode

2.1. PROCEDURES

Part 1: Photo diode - Inverse Square Law

1. Make sure the control boxs main switch is turn off first before start doing wiring

connection.

2. Unplug all the banana plug from the banana terminal first before assembling out the

circuit.

3. Start connecting the circuit using banana plug to respective banana socket, by using

circuit diagram below as reference.

4. Make sure all the wiring connection is according to the circuit diagram. Before switch on

the power supply, let the lab instructor to check the connection of circuit.

5. Plug in the lamps banana plug into the Lamps power supply banana socket, make sure

the polarity is correct.

6. Adjust the position of the photo transducer box so that its angular scale of the photodiode

facing the light source is 0.

7. Ensure the hole of the photo transducer box is not facing other light source, affecting your

reading value during experiment.

8. Turn on the mains switch, wait all the measurement meter initialized first before start

conducting experiment.

9. Switch on the lamps power supply, check whether the lamp got light up or not.

10. Adjust the position of the light facing the photo transducer box, while carefully adjustingthe 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 - Lamberts Cosine Law

1. With the circuit of Part 1 still connected, return the photo transducer box and lamp to

their starting positions (distance 1 meter)

2. Switch on the lamp again.

3. Rotate the angular scale shown on the photo transducer box to 30 anti-clockwise andrecord the reading.

Fig. 4.3 - Schematic for the photodiode experiment


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4. Repeat the procedure 3 for the angles as shown in the table below.

5. After finish the experiment, switch off the lamp power supply and the main power supply

switch on the control box.

2.2. RESULT AND DISCUSSION

Part 1:Photo diode - Inverse Square Law

Table 4.2 Experiment Result of Photo diode response

Applied voltage:_____________Volt

Distance (m) Current (A) Resistance ()

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 Ohms law anddividing the applied voltage by the current flowing, R = Vdc/I

What is the relationship between resistance and distance at constant voltage?

Why the current did not become zero when the lamp is switch off?

How can you relate the result obtained with Inverse Square Law? Plot graph if required?

Plot a graph of current flowing against distance. Label your graph with the value of appliedvoltage. Discuss the shape of the graph.


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Part 2: Photo diode - Lamberts Cosine Law

Table 4.3 Experiment Result of Photo diode- Lamberts Cosine Law

Angle (Degrees) Current (A) Resistance ()

30 (ACW)

25

20

15

10

5

0

10 (CW)

5

10

15

20

25

30

Plot a graph of current flowing against angle.

Does the graph follow accurately the cosine law?

Suggest the principal advantages and disadvantages of the Photo diode.


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3 Experiment 2: Photo Conductive Cell

3.1 Procedure

Part 1: Photo Conductive Cell - Inverse Square Law

1. Make sure the control boxs main switch is turn off first before start doing wiringconnection.

2. Unplug all the banana plug from the banana terminal first before assembling out the

circuit.


circuit diagram below as reference:


the power supply, let the lab instructor to check the connection of circuit.

5. Check the potentiometer (VR) control knob on the Operational Amplifier section of the

control box is set to minimum first.

6. Plug in the lamps banana plug into the Lamps power supply banana socket, make sure

the polarity is correct.

7. Adjust the position of the photo transducer box so that its angular scale of the photodiode

facing the light source is 0.

8. Ensure the hole of the photo transducer box is not facing other light source, affecting your

reading value during experiment.

9. Adjust the multi-meters rotary switch into the correct range. i.e. 200mA range for currentmeter 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 lamps power supply, check whether the lamp got light up or not. After

that, position the lamp holder again at the distance of 1meter.

12. Adjust the potentiometer to get 10mA. Record down the voltage and this value should be

constant for the experiment.

13. Leave the equipment like this for at least 5 minutes. This is to ensure the necessary pre-

conditioning of the device is carried out.

14. Move the lamp backwards to vary the distance and the affect on the transducer. Record

the voltage and current value at each step.

15. Switch off the lamp and take the reading again corresponding to ambient lightillumination.

Fig. 4.4 - Wiring Diagram for Photo Conductive Cell Experiment


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Part 2: Photo Conductive Cell : Lamberts Cosine Law

1. With the circuit of Part 1 still connected, return the photo transducer box and lamp to

their starting positions.

2. Switch on the lamp again and slowly adjust the potentiometer (VR) until the multi-meter

reads about 10mA initial value.

3. Rotate the angular scale shown on the photo transducer box to 30 anti-clockwise and

record the reading.

4. Repeat the procedure 3 for the angles as shown in table below.

5. After finish the experiment, switch off the lamp power supply and the main power supply


3.2 RESULT AND DISCUSSION

Part 1: Photo Conductive Cell- Inverse Square Law

Table 4.4 Experiment Result of Photo Conductive Cellresponse

Distance (mm) Current (mA) Voltage

(Volt)

Device Resistance

()

1000

900

800

700

600

500

400

300

200

100

Off of the lamp


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Part 2: Photo Conductive Cell - Lamberts Cosine Law

Table 4.5 Experiment Result of Photo Conductive Cell Lamberts Cosine Law


30 (ACW)

25

20

15

10

5

0

5

10

15

20

25

30


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4 Experiment 3: Phototransistor

4.1 Procedure

Part 1: Phototransistor - Inverse Square Law

1. Make sure the control boxs main switch is turn off first before start doing wiringconnection.

2. Unplug all the banana plug from the banana terminal first before assembling out thecircuit.


circuit diagram below as reference:


the power supply, let the lab instructor to check the connection of circuit.5. Check the potentiometer (VR) control knob on the Operational Amplifier section of the

control box is set to minimum first.

6. Plug in the lamps banana plug into the Lamps power supply banana socket, make surethe polarity is correct.

7. Adjust the position of the photo transducer box so that its angular scale of the photodiodefacing the light source is 0.

8. Ensure the hole of the photo transducer box is not facing other light source, affecting yourreading value during experiment.

9. Adjust the multi-meters 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 lamps power supply, check whether the lamp got light up or not. After that,

position the lamp holder again at the distance 1 meter.12. Adjust the potentiometer to get different voltage.13. Leave the equipment like this for at least 5 minutes. This is to ensure the necessary pre-

conditioning 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.

Fig. 4.5 - Wiring Diagram for Photo-transistor Experiment


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Part 2 Phototransistor - Lamberts Cosine Law:

1. With the circuit of Part 1 still connected, return the photo transducer box and lamp totheir starting positions corresponding to 100% relative illumination.

2. Switch on the lamp again and slowly adjust the potentiometer (VR) until the multimeterreads about 10mA initial value.

3. Rotate the angular scale shown on the photo transducer box to 30 anti-clockwise and

record the reading.4. Repeat the procedure 3 for the angle of 20, 10 until 0 up to 30 clockwise.5. After finish the experiment, switch off the lamp power supply and the main power supply


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


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Part 2: Phototransistor - Lamberts Cosine Law

Table 4.7 Experiment Result of Phototransistor - Lamberts Cosine Law


30 (ACW)

25

20

15

10

5

0

5

10

15

20

25

30

Plot graph and write the analysis according to the objective of the experiment.


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MESB 333 LAB NO. 5 :

FLOW RATE MEASUREMENT

PRELAB QUESTIONS

Name: _____________________SID: ______________ Group:______ Date:_______________

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

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

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

_________________________________________________________________________

4. What is discharge coefficient ? What are Cdfor orifice plate and venturi meter ? What

does the Cd value tells us ?

________________________________________________________________________

________________________________________________________________________

5. What does smaller discharge coefficient tells us?


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MESB 333 Lab No. 5

Flow Rate Measurement

1 Objective

In this experiment, students will learn different types of flow meters devices to measureliquid (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 theadvantages and accuracy of each device.

1.1 Theory

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

Applying Bernoulli equation:

For same elevation, Z1= Z2

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

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

22

22

11

21 Z

g

P

g2

VZ

g

P

g2

V

g

P

g2

V

g

P

g2

V 2221

21

21

2221

212221

VVg2

1PP

g

1

g2

V

g2

V

g

P

g

P

:gives)VV(g2

1)pp(

g

1ointVSubstitute

VA

AV

VAVAQ

:flowidealanFor

21

22211

21

21

2211

22

22

21

22

2

1

22221

A1

Vpp

VA

AV

g2

1)pp(

g

1

2

1

2

212

2

1

2

2122

A

A1

)pp(2V

A

A1

)pp(2V


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Knowing that Qideal=

lab manual measurement

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