Jawaharlal Nehru Engineering College

Laboratory Manual

SENSOR TECHNOLOGY-I

For

Second Year Students

Author JNEC INSTRU DEPT., Aurangabad

This manual is intended for the second year students of instrumentation in thE

subjectInstrumentation-1. Manual typically contains practical/Lab Sessions related

Measurement System fundamentals covering various aspects related the subject to enhanced

understanding.

Students are advised to thoroughly go though this manual rather than only topics

mentioned in the syllabus as practical aspects are the key to understanding and conceptual

visualization of theoretical aspects covered in the books.

Good Luck for your enjoyable laboratory sessions.

DOs and DON’T DOs in Laborary:

1. Do not handle any equipment before reading the instructions/Instruction manuals

2. Read carefully the power ratings of the equipment before it is switched on whether ratings

230 V/50 Hz or 115V/60 Hz. For Indian equipments, the power ratings are normally

230V/50Hz. If you have equipment with 115/60 Hz ratings, do not insert power plug, as our

normal supply is 230V/50 Hz, which will damage the equipment.

3. Observe type of sockets of equipment power to avoid mechanical damage

4. Do not forcefully place connectors to avoid the damage

5. Strictly observe the instructions given by the teacher/Lab Instructor

Instruction for Laboratory Teachers::

1. Submission related to whatever lab work has been completed should be done during the

next lab session. The immediate arrangements for printouts related to submission on the day

of practical assignments.

2. Students should be taught for taking the printouts under the observation of lab teacher.

3. The promptness of submission should be encouraged by way of marking and evaluation

patterns that will benefit the sincere students.

INDEX

1. Characterization of strain gauge indicator and weight measurement using

Load Cell.

2. Measurement of Displacement using LVDT.

3. Study of Encoder as displacement sensor.

4. To plot the characteristics of

a) J/K/R/S/T Thermocouples (any two types)

b) Thermocouple simulator

5. To plot the characteristics of

a) RTD Pt100/Pt500/Pt1000 (any two)

b) RTD simulator

6. Measurement of Pressure using Bellows, Bourdon gauge, Diaphragm.

7. Study of different types of Proximity switches.

8. Study of Dead Weight Tester.

9. Study of Vacuum Gauge Tester.

10. Measurement of sound level.

EXPERIMENT NO.1

FORCE - MEASUREMENT

Aim: To study characteristics of strain gauge indicator and weight measurement using Load cell . Apparatus:

1) Force Measurement Trainer

2) Strain gauge with cantilever beam,

2) Digital multi meter.

3) Standard Weights Theory: Whatever be the principle of operation of the force measuring device ,it is invariably

possible to callibrate it against fundamental standards of mass.The measurement of force

can be achieved with both mechanical as well as electrical sensors.

Cantilever Beam :

A cantilever cofiguration is in wide use , particularly for loads upto 10 Kg. On the application of a

force F at the end of the cantilever beam , bending moment proportional to the force is devloped in

the beam.Strain gauges are attached at the top and bottom surface of the beam near the fixed end

to sense the stresses so devloped. With the direction of force as shown , tensile strains devloped

on the top surface are sensed by strain gauge SG1 ,while compressive strains devloped at the

bottom surface are sensed by strain gauge SG2.

SG1

q F

i

o δ SG2

t

b i

The maximum deflection due to load will occur at the free end of the beam , while

maximum strain will be developed at the fixed end .Thus either the deflection ‘ δ ‘

or strain ‘ ε ‘ can be measured as function of the applied force F. 6 F l

= ------------- ( at fixed end )

E b t2

6 F l3

= ----------------------------- ( at the free end ) E b t

3

Here again , to obtain a perticular value of stress for a given nominal load , length ‘l’ is

increased or width ‘b’ and thickness ‘t’ are reduced. This puts a limitation on the lower

nominal loads that can be measured.

STRAIN GAUGE

The resistance of a conductor is given by ,

ρ l R = -------------- ------------- (1)

A

Where ρ = Specific Resistance of the material

l = Length of the conductor

A = cross section area

If uniform stress is applied to this wire along its length , the resistance R will

change because of dimensional changes. Differentiating the

equation (1) and rearranging it ,

R l A ρ −−−−−= −−−− − −−− + −−− −−−−−−(2) R l A ρ Thus the total change in resistance due to the finite stress variation is because of

fractional change in length l / l , fractional change in cross sectional area A/A

and the fractional change in resistivity / .

The equation (2) can be more simplified to ,

R/R / −−−−−=1 + 2 v + ----------- = Gauge Factor l / l l / l

where v = poisson’s ratio.

Gauge Factor - This is the ratio of change in resistance per unit resistance per

unit strain. It is the measure of the sensitivity of the gauge. Measurement of change in Resistance in strain gauge :

Wheatstone Bridge circuit is the usual method for the measurement of change in

Resistance in strain gauge.

1) Quarter bridge :

In this configuration on arm of the bridge is starin gauge and the other three arms contain

fixed resistors.

If SG = R1 and R2 = R3 =R4 are the fourarms of the Wheatstone Bridge ,

E G ε1 E R1

the output voltage of the bridge , e = --------- =-- -------

4 4 R1

where E = Excitation voltage

ε1 = starin devloped

2) Half Bridge : Two arms of the bridge R1 and R2 are active strain gauges ( SG1 = SG2 ) , one in tension and

the othe in compression while the othe two arms are the fixed

resistors of identical values.

SG1 = SG2 ( R1 = R2 ) & G1 = 2 & ε1 = ε2

E R1

the output voltage of the bridge , e = ---------------

2 R1

Thus the sensivity of the Half Bridge is twice that of Quarter Bridge . 3) Full

Bridge :

All the four arms of the bridge are active straing gauges and

R1

the output voltage of the bridge , e =E ----------

R1

APPLICATION OF STRAIN GAUGE

FORCE - MEASURING SENSOR - LOAD CELL

The load cell is an electromechanical sensor employed to measure static and dynamic forces. The

device can be designed to handle a wide range of operating forces with high level of reliability, and hence it

is one of the most popular transducer in industrial

measurements . The load cell derives its output from the deformation of an elastic mem-ber

having high tensile strength . The elastic member is made of homogeneous materials ,

preferably steel alloys, manufactured to very close tolerences. The basic design param-eters

include size and shape, material density and modulus of elasticity, strain sensitivity ,

deflection, and dynamic response.

Through a careful choice of the material and structural configuration, a linear relationship

between a dimensional change and measured force can be achieved. The materials so

chosen should possess the following properties : (a) linear stress strain relationship up to a fairly large elastic strain limit (typically 5000 micro-strains) ;

(b) low strain hysteresis over repeated loading ( < 2 micro - strains ) ; (c) very low creep over long periods of loading ( < 5 micro - strains) ; and (d) very low plastic flow due to

strain . In addition , many other material properties , such as the modulus of elasticity and its variations with

temperature , ultimate strength , linearity of stress developed with force, and ease of fabrication are to be

considered while selecting the most appropriate material for the elastic element. The various elastic

materials suitable for the purpose are medium to high carbon steels of chromium molybdenum , and precipi-

tate - hardened stainless steel (such as S 94 - 98 , EN 24 and EN 28) . It is essential to

harden the material with heat treatment to the required level for a specific application to keep

the hysteresis and creep low and to obtain good repeatability.

COLUMN - TYPE DEVICES :- The simplest method for measuring unidirectional forces is to use a column or rod

in tension or compression . The stress developed due to the force on loading is measured

with electrical strain gauges attached to the body as shown in figure.

The strain gauges 1 and 3 , which are fixed on the opposite sides are aligned to measure

axial strains only , whereas gauges 2 and 4 will measure the circumferential strains due to

applied force. The strain values can be expressed as , σ F F ε1 = ε3 = ----------- = ------------ and ε2 = ε4 = −ν -------- E A E A E

where ε1 to ε4 = the strains sensed by the strain gauges ,

s = strain devloped in the column ,

F = axial force ,

A = cross sectional area of the column , E = modulus of

elasticity and

ν = poisson’s ratio of the material of the rod.

PROVING RINGS : An alternative to the column -type load cell is the proving ring which is better suited for lower load ranges. An

arrangement of the proving ring type load cell, also known as the ring dynamometer is known in figure. The

forces applied across the ring , as shown in the figure, develop circumferential stresses. Such a loading

causes compressive strains on the inner surfaces and tensile strains on the outer surfaces with maximum

stresses

occurring at 90 0 points of arc in either direction from the point of application of force .

The strain levels are sensed by strain gauges R1, R2, R3, and R4 bonded onto the sur-face. Since

both tensile and conpressive strains are equal , a relatively higher output can result from the

measuring bridge when compared to the axially - loaded columns.

Referring to Figure , for a thin - walled ring, the bending couple Mθ at an angle θ from the direction of force can be expressed as

Fr 2

Mθ = -------- (sin θ - ------)

2 π

Where r is the mean radius of the ring. The equation is valid only when the top and

bottom of the ring are restrained from rotation.

The maximum stress σ and maximum strain ε in the thin walled ring are related by ,

Mθ t σ σ = ---------- ε = -----------

2 I E

where Mθ = bending couple at an angle t

t = thickness of the wall

I = Moment of Inertia about the axis of bending E =

Young’s modulus of the material

1.092 F r

Substituting for M and I Strain magnitude becomes , ε = ------------------ (t << r)

E b t2

EXPERIMENT NO.2

FORCE - MEASUREMENT AIM: To study the proving ring and measurement of force using proving ring.

APPRATUS:

1) Proving ring Trainer.

2) Weights

THEORY:

Fundamental Concepts of Force

When we push or pull on a body, we are said to exert a force on it. Forces can

also be exerted by inanimate objects. For example, a locomotive exerts a force

on a train it is pulling or pushing. Similarly, compressed air in a container exerts a

force on the wall of the container. The force may produce motion of the body or

may cause the body to deform. Energy may be expended in the process, or the

applied force may be balanced by an opposing force so that no energy is

expended. The distortion or the displacement that occurs when a body is

subjected to a force occurs in accordance with Hooke's and Newton's laws

governing the behavior of elastic and non-elastic bodies.

Newton was the first to state the basic laws of motion of bodies. He

postulated three fundamental principles:

First Law: A body remains at rest or continues to move in a straight line with

uniform velocity if there is no unbalanced force acting on it.

Second Law: An unbalanced force acting on a body will cause that body to

accelerate in the direction of the force with an acceleration inversely

proportional to the mass of the body.

Third Law: For every action there is an equal and opposite reaction.

During the same era, Robert Hooke observed that when an elastic body is

subjected to stress its dimension or shape changes in proportion to the applied

stress over a range of stresses. This led to Hooke's law which states that strain,

the relative change in dimension, is proportional to stress. If the stress applied

to a body goes beyond a certain value known as the elastic limit, the body does

not return to its original state once the stress is removed. Hooke's law applies

only in the region below the elastic limit. Because measurement of distortion or

of motion provides the means of determining the magnitude of a force, Newton's

and Hooke's laws are key concepts in force measurement.

Unit of Force

The unit of force is derived from a fundamental quantity, mass. The fundamental

unit of mass is the kilogram (kg). The unit of force is the Newton (N). By

definition, the newton is the force required to give a onekilogram mass an

acceleration of one meter per second squared.

The Proving Ring

The proving ring was invented primarily because scientists needed a precise way

to test the durability of various materials. When scientists create new materials

for building or use in products, sometimes there is a concern about the

tolerances of the materials. Engineers who are designing machines or architects

designing buildings may need to know exactly how much weight a material can

withstand before using it in a

particular part of the design. If this data is not precise enough, there is the

possibility of a costly or dangerous accident. The proving ring allows for a very

precise and reliable definition of force tolerance for nearly any material, which

can help avoid these kinds of accidents. A proving ring is a device used to

measure force. It consists of an elastic ring in which the deflection of the ring

when loaded along a diameter is measured by means of a micrometer screw and a

vibrating reed. Scientists and engineers often use proving rings as a way to

measure force. The devices are made using a ring of metal with a spring-like

consistency. Inside the ring there is a screw attached to a dial with

measurements on it and a plate that vibrates after being struck with something.

The contraption in the center works to show the ring's diameter after it has

been compressed or stretched, which produces a reliable force measurement

that can be used for other purposes. To use a proving ring, a person will exert

force on the ring in some way—generally either pushing from both ends or pulling

it apart—and then strike the plate to start vibrations. At this point, the screw is

generally turned until it touches the plate and stops it from vibrating. When the

vibration stops, the number on the dial will show exactly how much force was used

on the ring. The metal used to make the rings is often quite thick, so any flexing

will often be very slight, which facilitates the need for precise measurement

tools. Proving rings are often used to calibrate the amount of force used within

various force-testing devices. Once the calibration is set, other materials are

placed in the devices, and it is possible to see if they can withstand the same

force that was being applied to the proving ring. In this way, scientists can

determine the exact strengths of various materials.

Design and Construction of the Proving Ring

The proving ring is a device used to measure force. It consists of an elastic ring

of known diameter with a measuring device located in the center of the ring.

Proving rings come in a variety of sizes. They are made of a steel alloy.

Manufacturing consists of rough machining from annealed forgings, heat

treatment, and precision grinding to final size and finish. Proving rings can be

designed to measure either compression or tension forces. Some are designed to

measure both. The basic operation of the proving ring in tension is the same as in

compression. However, tension rings are provided with threaded bosses and

supplied with pulling rods which are screwed onto the bosses. The proving ring

consists of two main elements, the ring itself and the diameter-measuring

system. Forces are applied to the ring through the external bosses. The resulting

change in diameter, referred to as the deflection of the ring, is measured with a

micrometer screw. The micrometer screw is attached to the internal bosses of

the ring. In modern rings, the upper and lower internal and external bosses are

machined as an integral part of the ring to avoid mechanical interferences during

the application of the force

PRECAUTIONS:

1. Ensure delicate handling of the trainer. Dial gauge is very sensitive and very

precise

instrument, requires at most attention while operation.

2. Ensure the instrument is firmly placed and properly leveled.

3. Extreme care needs to be taken while loading and unloading of weights on the

trainer tray.

CALIBRATION:

1. Place instrument on flat, horizontal, sturdy surface.

2. With no weights on top tray, ensure following settings on dial gauge.

3. Ensure the big pointer of dial gauge is at ‘12’ indicating position.

4. Ensure the small pointer of dial gauge is at ‘5’ indicating position.

5. Gently tap on the dial gauge centre and observe the pointer of dial gauge takes

small jurk.

PROCEDURE:

1. Ensure dial gauge pointers are positioned at 12 and 5 positions as above.

2. Carefully place the weight on top tray. Dumping weights in the tray may

permanently

damage the dial gauge or likely chances to loose dial gauge accuracy.

3. Note down the dial gauge reading. Take the difference from 12 position.

4. Increase the weights and repeat the procedure.

5. Unload the weights

OBSERVATION : 9.8 gravitational Acceleration in m/s2

Calculations : 1 division of dial gauge = 7.66N = 0.781Kg ;

For given settings of dial 1Kg = 9.8N

Force N = 7.66 x dial gauge reading in divisions

Sr.No.

Mass in

Kg

Actual Force in

N ( Kg x g )

Dial Gauge

reading In µm

Calculated

Force

in N

1.

2.

3.

4.

5.

6.

GRAPH: Plot graph .

CONCLUSION:-

EXPERIMENT NO.3

TEMPERATURE MEASUREMENT Aim: To study the temperature measurement Using Thermocouple, it’s characteristics . Apparatus: Thermocouple Trainer , Thermometer, Digital Multimeter etc.

Theory:

Temperature measurement is done by devices such as,

1) Resistance Thermometers :- Resistance of metal changes with temperature.

2) Semiconductor Thermometers :- Semicondutor materials like germanium crystals.

3) Thermocouple :- When two metals having different work functions are placed

together, a voltage is generated at the junction which is nearly

proportional to temperature.

4) Radiation Pyrometers :- Thermal radiations are used to measure very

high temperature

Here we are using Theromcouple for measurment of

temperature. Emf produced in a thermocouple circuit is given by,

E = a ( t ) + b ( t)

Where t = difference in temperature between the hot thermocouple junction & the

reference junction of thermocouple.

a, b = constants.

a is very large compared to b and therefore , we can approximate the equation as ,

E = a ( T)

The thermocouples are used for measurement of temperature upto 1400 0 C.

In industrial application, the choice of materials used to make up thermocouple

depends upon , the temperature range to be measured, the kind of atmosphere to

which the material will be exposed, output emf and its stability , mechanical

strength & the accuracy required in measurements.

Thermocouple materials are divided into two catagories,

1) Rare material type using platinum, rhodium &

2) Base material type.

MEASUREMENT OF THERMOCOUPLE OUTPUT

The output emf of a thermocouple as a result of difference between temperature

of measuring junction & reference junction can be measured by -

1) Millivoltmeter directly

2) Using potentiometric Null deflection method.

3) By amplifying the output and then measuring it.

The voltage generated by thermocouple is conditioned and amplified to get

the output voltage proportional to temperature.

The output voltage is to be adjusted such that 0 - 2 Volt DPM ( Digital Panel

Meter ) should read directly the temperature of thermocouple.

CIRCUIT DESCRIPTION :

Thermocouple output is buffered by amplifier A1.

At higher ambient temp. thermocouple produces low output voltage. To

compensate this effect, PN junction is used across amplifier A2 whose output

increases at higher ambient temp. Thus cold junction compensation is provided to

make thermocouple output nearly linear at high ambient temp.

The output of amplifier A1 & A2 is added at A3 and the output of adder A3

after buffer amplifier A4 is displayed on DPM which reads temp directly.

CALLIBRATION :

Before using the unit for measurement of temperature , callibration of the

unit is required.

A) Standard callibration instruments are available for thermocouple & RTD

sensors. Connect callibration box of thermocouple to the unit.

a) Set callibration instruments for zero & adjust the zero adjust pot of the

unit to read DPM zero.

b) Step by step change the temp setting knob of callibration instrument &

adjust the DPM reading by span adjust potmeter of the unit.

Repeat steps a & b to get optimum setting of SPAN & ZERO adjust potmeter.

B) If callibration instrument is not available, then get the ice cold

water. ( Or as cold as available in laboratory )

a) Place the sensor and thermoter in water & adjust zero adjust potmeter

to read the actual temp of water as observed on thermometer.

b) Get water heated to 60 0 C & place the sensor in bath and adjust

SPAN (GAIN) potmeter to display 600C on DPM.

Repeat the the steps a & b for getting optimum setting of the SPAN and

ZERO adjust potmeter.

Procedure B is to be used for callibration for this unit.

PROCEDURE :

1. Connect 230 volt AC mains supply to the water heater. 2. Connect thermocouple pin , at input socket of signal conditioner circuit. 3. Take sufficient amount of cold water in water bath ( so that heater coil is fully

immersed in water ) 4. Put Thermocouple in waterbath. To read the temp of water in waterbath , put

mercury thermometer along with thermocouple in water bath. Make mains ON. Note the thermometer reading & DPM reading. Observation Table:

S.No. 0 DPM Reading ( Volt)

Thermometer Reading ( C )

Graph:

Plot the graph of thermometer reading against output voltage Thermocouple used is type K.

i.e. Chromel (+) / Alumel (-)

Sensitivity = 40 - 55 uV / 0 C.

Range : -18 to 10000 C.

V+

R1

THERMOCOUPLE

TEMP

SP

V+ P8

SP

ADJUST

ZERO V+

GAIN

q

ADJUST ADJUST

q

V+

V-

R3

V+

-

A -

VOUT

+ A3

R2

V-

+

BUFFER

V-

AMPLIFIER AMPLIFIER

TEMP 230 V AC

R6

V+ q

_ POWER

R7 A 3 CONTROL

+ RELAY

V-

q

P3

POWER OUTPUT TO

HEATER

CONTROLLER

EXPERIMENT NO.4

TEMPERATURE MEASUREMENT Aim: To study the temperature measurement of RTD, it’s characteristics . Apparatus: RTD Temperature measurement Trainer , Thermometer, Digital Multimeter

etc.

Theory:

Temperature Measurement Using RTD:

Metallic materials are basically structured molecules having free electrons. These

free electrons in metal gives rise to conductivity to metals. When heated these free

electrons collide with each other & lattice structure creating resistance to free motion of

electrons & hence resistance of metal increases with increrase in temp.

The range of temp over which this phenomenon occurs depends on temp.

coefficient of resistance, chemical inertness & its crystal structure. In general the

resis-tivity of materail increases with increase in temp (positive coefficient of temp).

Where as in other type of material (some seconducting materials) resistance decrease

with increase in temp.

Temperature measurement using resistance thermometry is most accurate having good

repeatability & hence reliable. We can achive an accuracy of 0.0001k. Where as at

high temp. accuracy is about 0.01K & In the range of 1200 K accuracy is 0.1K.

Major disadvantage is its large size requirement of sophisticated instrumentation.

Within small range of temp , temp-coefficient is constant & resistance at temp. ‘ T ‘

is

given by

Rt = Ro [1 + α (T -To) ]

= Ro (1 +α t)

Where Ro = Resistance at temp To

α = Temp coefficient of material

t = Temp differance (T - To )

R2 - R1

Temp. Coefficient , α = ---------------------

R1 T2 - R2 T1

Where R1 & R2 are resistance at temp. T1 & T2 respectively , depends on

material, its purity & heat treatment.

Among the base material, copper has highest temp. Coefficient & good linearity

& its resistivity is low & hence rarely used for this purpose .Temp. sensors made from

Nickel are good for temp range 1000 to 4500 K. Platinum resistance element is the

best element as it gives very good accuracy and reproducibility. It is used as

international standard for temp. measurement.

For pure, strain free annealed platinum , equation for temp is

given by callender’s equation.

1 Rt t

t = -----

- [

-------

- 1 ] + δ [

---------

- 1]

α Ro R100

Where t is temp in oC , Ro , Rt and R100 are resistance values at respective

temperature for platinum.

CALLIBRATION :

1. Make power on to the unit.

2. Plug in 100 ohm jack pin in RTD socket.

3. Adjust zero adjust potmeter to read 0 on DPM.

4. Remove 100 ohm jack pin & plug in 138.5 ohm jack pin in RTD socket.

5. Adjust gain adjust pot meter to read 100 on DPM.

6. Repeat step 2 to 5 till we get optimum settings of zero adjust and gain

adjust potmeter.

MESUREMENT OF TEMPERATURE USING RTD :

1. Plug in RTD pin ,in RTD socket.

2. Put the RTD sensor & mercury themometer in water bath.

3. Connect water heater power cord (A.C.mains power for heater) to the

output socket of control realy circult . (provided on right side of the

trainer unit.)

4. Fill the water bath 3/4th by water.

5. Make power on to the unit.

6. Place TEMP / SP selector switch on set point position (SP)and adjust set

point to 400 C by adjusting set point potmeter.

7. Change the selector switch to TEMP position.

8. Note the temp.of mercury thermometer and that read by DPM.

Also note the output voltage at the output of opamp A2 (Vout).

(Set point must be above the actual temp. of water to observe control action.) Observation Table:

S. No. Temperature DPM Reading Vout

(0C )

( Volt)

Plot the graph of temp. against DPM reading and Vout.

Vout

Temp 0C

RESISTANCE MEASUREMENT OF RTD :

1. Put the RTD and thermometer in water bath. 2. Make water heater ON. 3. Note the temp. of water bath by mercury thermometer and resistance of RTD

between upper tip and middle contact of jack pin of RTD.

Measure resistance at different temperature at an interval of 50 C and tabulate

the result.

Plot the graph of temperature against resistance of RTD.

Observation Table:

S.No. Temperature Resistance

Resistance (ohm)

R

T

Temp 0C

Graph of resistance of RTD against temp. in degree C. is straight line .

From the slope of the graph calculate the value of Resistance temp. Coefficient

for a given RTD.

EXPERIMENT NO.5

POTENTIOMETER AS ERROR DETECTOR

AIM: To study pot characteristics

To study pot as an error detector.

APPARATUS: Pot as error detector trainer, Digital multimeter etc

THEORY:

Potentiometer is the basic & very important Electric component widely used

in electronics industry. Potentiometer is variable resistance which varies

proportional to the angular displacement, the resistance varies is either

linear or logarithmic, to the angle position, depending upon the type of its

fabrication. In logarithmic potentiometer the change in resistance is the log

value of the angle. Like resistors, potentiometer are also with different

types depend on size, material of construction, manufacturing process,

power (wattage) required etc. Very accurate & precise potentiometers used

for sensing purpose. Normally a pot has mechanically angular displacement

from 00 to 2700 for single turn & 0- 3600 for multiturn. Multiturn pot can

take up to 10 turn & gives much more better result than single turn pots.

Diagram:

PRECAUTION:

1) As the pot is delicate component, use the trainer delicately& carefully.

2) Ensure pot minimum is at zero degree

3) Use proper selection on DMM.

PROCEDURE:

Pot Characteristics

1) Check & ensure the ‘pot as error detector trainer’ is proper.

2) Ensure the DMM works on volt range.

3) Connect the trainer to mains 230 V AC

4) Ensure the pot position is at 00

5) Connect DMM at GND & O/P terminal on volt range.

6) Turn on the trainer

7) Measure the o/p on DMM

8) Displace/rotate the pot by 50 & repeat step 7.

9) Repeat step 8 for various pot positions @ 50 increment

10) Draw pot characteristics

11) Repeat whole procedure for other pot B.

OBSERVATION TABLE: Pot Characteristics

Sr. No. Angle

in Degree

Output of

POT A

In Volt

Output of

POT B

In Volt

1.

2.

-

-

-

28.

GRAPH:

Pot as error detector:-

1. Select any pot position for pot B i.e. 1000

2. Place pot A at ‘0’ position.

3. Measure the error signal between two variable points i.e.

differential

Outputs of pot A & pot B.

4. Change pot A o/p position in increments of 100

5. Observe the differential o/p between pot A & pot B.

6. Repeat expt. for various pot position

7. Measure the o/p when both pot are at 1000

8. Repeat exercise even for pot A position beyond 1000

9. Observe the error signal.

10.Change the pot B to 2000 & repeat the expt.

OBSERVATION TABLE: Pot as error detector

Sr. No. Angle

in Degree

Output of

POT A

In Volt

Output of

POT B

In Volt

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

GRAPH: POT ERROR DETECTOR

CONCLUSION:

EXPERIMENT NO.6

PRESSURE MEASUREMENT Aim: To study Pressure transducers using Bellows, Bourdon gauge, Diaphragm and its measurement. Apparatus:

1) Pressure measurement Trainer.

2) Bellows,

3) Diaphragm

4) Bourdon gauge.

Theory: Pressure Transducers :

DIAPHRAGMS :

The most common type of pressure-sensing elastic element used in a transducer is

the diaphragm. The structure of the diaphragm may be flat or corrugated.

Diaphragms are widely used as a sensing element for high accuracy and good

dynamic response.

Sensing diaphragms are made from elastic metal alloys, such as bronze,Phosphor

broze, beryllium copper, and stainless steel or from proprietory alloys, such as

Monel, Inconel-X and Nickel-span-C( a ferrous-nickel alloy). The dia-phragms are

fabricated by pressing, stamping , or spinning from sheet stock or they are

integrally machined with their supporting wall from a bar. The main considerations

while selecting a suitable diaphragm material are the chemical nature of the fluid

which is expected to come in contact with the diaphragm, temperature range,

effects of shock and vibration, and frequency respose re-quirements. Ni-Span-C is

unique in that it has constant elastic properties over a wide temperature range.

BOURDON TUBE :

The bourdon tube is a curved or twisted tube having an elliptical cross-section , and

sealed at one end. The tube tends to straighten out on the application of pressure,

and the angular deflection of the free end is taken as a measure of the pressure.

The deflec-tion sensitivity is a function of the aspect ratio of the tube cross-

section. The main advantages are high sensitivity and good repeatability .The

different configurations mainly employed for this device are ‘C’ , helical,spiral, and

twisted tubes.

BELLOWS :

Bellows are thin walled cylindrical shells with deep convolutions , and are sealed at

one end. The sealed end moves axially when pressure is applied to the other end.

TRANSDUCTION METHODS :

Electrical pressure transducers based on the principle of variable capacitance ,

resistance, and inductance have been devloped for a variety of pressure measure-

ments, for converting the deflections or stresses developed in elastic elements

into corresponding electrical signals.

POTENTIOMETRIC DEVICE :

The Potentiometric - type pressure transducer in one of the earliest type of

electrical pressure sensors. In this, a diaphragm capsule, bellows, or bourdon tube

is linked to a free-sliding wiper contact moving on a resistive element . The wiper

is driven by the elastic element in response to the applied pressure, and the

changes in the voltage at the wiper point is related to the pressure.

SOLID - STATE DEVICES : Recent advances in microelectronic circuit technology have been sucessfully applied

for the development of solid-state transducers, especially for pressure

measurements . There are two varieties in this category. The first is based on the

piezojunction effect. The piezoresistive - type tranducer consists of a

monocrystalline silicon diaphragm with four piezoresistive strain gauges formed

integrally in a Wheatstone bridge configuration diffused on it to measure the

stresses developed due to the applied pressure.

The salient features of this device are :

(a) the mechanical properties of the mono-crystalline silicon show low hysteresis

and high repeatability , (b) piezoresistive semicon-ductor gauges formed on the silicon

diaphragm exhibit much higher sensitivity compared with conventional bonded or

unbonded wire gauges mounted on metal diaphragms, c) Piezoresistive gauges

diffused directly onto the diaphragm surface are not likely to suffer from the

creep and hystersis effects inherent in bonded strain gauges, d) Miniaturization of

the transducer is easy without any sacrifice in performance and , e)They exhibit

excellent thermal characteristics. The other type of solid-state pressure

transducer employs the piezojunction effect, i.e. the variation in the sensitivity of

the V - I (Volt - ampere) characteristics of a p - n junction to stress.

PLC APPLICATION :

Connect output from Presure Measurement unit VOUT to analog input of PLC.

Configure I :1. 0 as analog input (Analog I /O - 1: channel - 0 ) and analog output O

:3 .0 (Analog I/ O - 3 : channel 0).

B) 0 - 10 V DC input.

Raw or proportional format

C) 0 -10 V DC output

Raw or proportional format

Write ladder program as ,

Use MOV Instruction to get anlog input from channel-0 and store in temporary

variable N7:0

Compare for the pressure less than 10 PSI ( input < 0.5 Volt) . Alarm a under

pressure indicator . (say yellow pilot lamp).

For pressure above 15 PSI & bellow 20 PSI - nomal status indicator (Green pilot

lamp) & above 25 PSI- overload status indicator (Red pilot lamp).

Run & execute the program.

Use MOV instruction to display the load value on digital meter of PLC panel

through output channel O:3.0

PRESSURE MEASUREMENT

PRESSURE SENSOR V+

SG1 SG2

VIN

SG3 SG4

PRESSURE θ

INPUT

0 - 30 PSI

VOUT

INSTRUMENTATION To PLC

Analog Input

AMPLIFIER

θ

ZERO ADJUST GAIN ADJUST

Procedure:

1. Connect air pressure signal at the input pressure connector provided on left side of

unit .

2. Keep Air regulator knob fully anticlockwise so as to have zero pressure in the system. Check that the displacement on digital panel meter is zero and pressure on digital panel meter is zero. If not adjust the zero adjust of , LVDT and Pressure , provied on right side of unit. 3. Using foot pump devlop the pressure in tank to aprox 35 PSI. By slowly turning the knob of air regulator clockwise , increase the pressure applied to system to 30 PSI. Check that the displacement on digital panel meter is 10mm and pressure on digital panel meter is 30 PSI. 4. Now slowly increase the pressure in system in proper steps from zero to 30 PSI,and every time note 5. The angular position of the pointer attached to the mechanical amplifier system driven by free tip of Bourdon tube ‘B1’ . 6. Pressure indicated on dial gauge G1 7. Pressure indicated on digital presure gauge P1 . 8. Displacement of free tip of Bourdon tube in mm as indicated on digital meter ‘ d’ .

Observation Table:

S.No. Input Air Presure Angular Deflection Pressure indicated on Displacemet

Free tip of

G1 ( PSI ) of Bourdon tube Digital Pressure Gauge

Bourdon tube

B1 (degree) P1 ( PSI )

d (mm)

Graph: Conclusion:

Experiment No. 7

STUDY OF PROXIMITY SWITCHES

Aim: Study of proximity switches.

Theory: 1) Inductive proximity switch

2) Capacitive proximity switch

Inductive proximity switch :- These are based on Faradays laws of electromagnetic induction

which states that the emf is induced in a conductor placed in magnetic field whenever there is a

rate of change of flux linking the conductor. It produces the output voltage proportional to the

velocity of the moving object.

Inductive proximity switch produces high frequency alternating field at the sensing face. When any

metallic material enters in the sensing zone of the switch, the fieldget disturbed. A sensitive

detector circuit senses the change which is further processed by amplifier circuit to produce

output signal.

Construction: It consists of the coil which is wounded on a magnetic core, a high frequency current

source delivers current flows through coil.

Coil & a high frequency source is housed in a stainless steel metallic tube. Front end

of coil form sensing zone through which magnetic field is scattered around sensing zone.

External three wires are brought for connecting:

- Operating supply - Output Terminal

Dia:

Working:

When a high frequency attracting current passes through a coil, it produces magnetic

field surrounding the coil across face plate. If a metal piece is brought into this field in the vicinity

of the coil, eddy currents are induced in the metal piece. These eddy currents create their own

magnetic field that opposes the field of coil. Closer the metal piece to the coil, greater is the

opposition. The opposing magnetic field reduces the effective inductance of the coil which causes

the change in the magnitude & phase of the alternating current. The change in current is a measure

of detecting moving metal object into magnetic zone.

Applications:

1) Metal detector 2) Speed measurement 3) Flow measurement 4) Position sensing 5) Gauge measurement 6) Level sensing

Capacitive proximity switch:

When the object enters in the sensing zone of the switch,

capacitance between two plates of capacitor changes. As soon as the capacitance value crosses

the preset level, oscillator starts. This change is detected and resulted in an output signal.

Dia:

One plate is represented by electrode at sensing face of the switch & another by all

surrounding material, which is connected to the earth.

Applications:

1) Position sensing: Plastic pouches, tablets, cardboard boxes, bottles. 2) Level sensing: Solid, Liquids, Granules. 3) No. of bottles, Boxes, Pouches etc.

EXPERIMENT NO. 8

PROXIMITY

AIM: To study Proximity Magnetic Pick up , its principle of operation & characteristics.

APPRATUS:

a) Magnetic Pickup Trainer.

b) Oscilloscope with Probes.

c) 230 V AC 1Ø, 50 Hz mains supply.

THEORY:

Inductive sensor: An inductive sensor is an electronic proximity sensor, which

detects metallic objects without touching them. The sensor consists of an induction

loop. electric current generates a magnetic field, which collapses generating a

current that falls asymptotically towards zero from its initial level

when the input electricity ceases. The inductance of the loop changes according to

the inside it and since metals are much more effective inductors than other

materials, the presence of metal increases the current flowing through the loop.

This change can be detected by sensing circuitry which can be given as a signal to

other devices.

CALCULATION OF THE SPEED : RPM = pulses per sec x 60

No of teeth

PRECAUTIONS:

1) Ensure main supply is 230 V AC, 50 Hz, 1Ø Only. 2) Ensure the trainer is in proper condition, sensor is rigidly mounted & placed near

to gear teeth. 3) Turn the speed pot to anticlockwise ( min speed ) 4) Do not short the banana sockets. 5) Do not disturb/change the scale factor /DIP switches on indicator.

PROCEDURE:

1) Keep speed pot to min speed.

2) Connect the magnetic pickup trainer to 230 V AC mains.

3) Turn on mains. The motor will slowly gain the speed.

Note : There is speed ramp up circuitry, ensures smooth start.

4) Ensure the digital indicator is ON, Motor rotates and sensor LED Flickers.

5) Connect the oscilloscope to banana socket.

Connection details – Black - OV Ground.

- Red - Pulse O/P.

6) Observe the pulses on CRO

7) Slowly increase the motor speed.

8) Repeat step ‘ 7 ’ till full speed i.e.1500 RPM ( Pot to most clockwise )

9) Reduce the speed to min speed.

Note : Encoder generates 40 pulses/revolution.

BLOCK DIAGRAM OF SPEED MEASUREMENT SIGNAL CONDITIONIING CKT.

OBSERVATION TABLE :-

Sr.No.

Actual

Speed

Indicated

(in RPM)

Tachometer

Speed

(in RPM)

Calculated Speed

(in RPM)

Error in %

1.

2.

3.

4.

Graph: Conclusion:

EXPERIMENT NO. 9

DEAD WEIGHT TESTERS

AIM: To study Dead Weight Testers , its principle of operation & characteristics.

APPRATUS:

Nagman‘s Dead Weight Testers , Weight etc.

THEORY:

1. INTRODUCTION :

Nagman‘s Dead Weight Testers (DWT) Models H300/6000/6600 Series

provides a facility for testing pressure indicating instruments for calibration

accuracy. The design uses the piston gauge principle in which an applied pressure

within the system balances a known mass applied to a piston of known effective

area. In the comparison mode the DWT can be used to compare the readings of a

test instrument directly with that of a standard instrument.

The DWT comprises of

1. Instrument Housing.

2. Low piston & High piston assemblies

3. Test port ½ “ BSP (F) (Swivel Adaptor)

4. Fluid reservoir with needle valve.

5. Ram system

6. Priming pump

7. Spirit level.

8. Isolating valve

9. Weights

10. Leveling Adjustment Legs.

11. Weight Carrying case.

7 4 3 8 (Back side)

.

9

2

1

10

5 6 11

ACCESSORIES

Standard:

The instrument comes with the following Accessories.

• Test port conversion Adaptors.

• Operating Fluid (½ litre)

• Set of Weights (SS/MS/Aluminium – as applicable)

• Dust cover.

• Wooden carrying case for weights.

• Spare seals.

• Test certificate.

• Instruction manual.

• Warranty certificate.

Optional :

• NPT (or) BSP adaptors ⅛”, ¼”, ⅜”, ½” (female thread) & ½” BSP (male).

• Incremental weight sets for smaller increments of pressure.

• Two gauge adaptor.

• Right angled adaptor.

• Spanners (30-32, 25-28) ( 2nos)

• Screw Drivers (2 nos)

• Pointer Puller (1 NO.).

• Pointer Punch (2 nos).

• Extra special conversion adaptors.

• Quick-release couplings.

UNIT IDENTIFICATION:

Unit is identified by the following way.

H ABCD – EF - GHI - J

ABCD indicates the model no. 3000/6000/6600

EF indicates no piston – Single (SP) Or Dual (DP).

GHI indicates the range of the instrument eg. 350,700 etc

J indicates the calibration unit 1 – bar, 2 – Kg/cm², 3 –Psi

TECHNICAL SPECIFICATION:

• Ranges : 1-700 BAR (maximum range)

Parameter H3000 H6000 H6600

accuracy 0.1%of reading 0.05% of reading 0.025% of reading.

0.015% of reading

• Piston : Single/Dual

• Weight:

� Instrument : 18Kg.

� Weights : 8 to 33 Kg.

• No. of weights : 12 -14.

• Dimension : 470×325×100mm (L×W×D)

• Operating Fluid : Chemoleum oil (HD22).

Pressure Ranges

OPERATING METHOD:

PRIMING:

1. Open the oil reservoir needle valve & cover (4) (Refer Fig.1)

2. Rotate the RAM (5) in anti-clockwise direction

3. Open the isolating valve (8).

4. Operate the priming pump (6) so that the air bubbles come out in the reservoir.

5. Repeat point no1-4 until all the air trappes in comes out of the reservoir.

6. Now rotate the RAM in clockwise and in anti-clockwise direction and ensure that

no air bubbles comes out of the reservoir.

7. Fix the reservoir cover/spring/needle valve with the tank.

TEST PROCEDURE

1. Connect the test gauges on the test port with the suitable adaptors.

2. Ensure that the priming operation has been carried out.

LOW PRESSURE PISTON MODE:

1. Place the base weight (Low) on the top of the piston (2) pin.

2. Give initial pressure using priming pump and close the isolating valve.

Bar

Kg/Cm²

Psi

Single SP-35 1 to 35 1 to 35 15 to 500 25

SP-70 1 to 70 1 to 70 10 to 1000 35

SP-160 10 to 160 10 to 160 150 to 2500 13

SP-350 10 to 350 10 to 350 150 to 5000 20

SP-600 10 to 600 10 to 600 150 to 9000 31

SP-700 10 to 700 10 to 700 150 to 10000 35

Dual DP-160 1 to 160 1 to 160 15 to 2500 13

DP-350 1 to 350 1 to 350 15 to 5000 20

DP-600 1 to 600 1 to 600 15 to 9000 31

DP-700 1 to 700 1 to 700 15 to 10000 35

3. Rotate the RAM screw in clockwise direction to the required pressure for

calibration.

4. Select correct weight (9) according to the range of the instrument under test.

5. Apply the pressure until the weight floats & stop at the mark on the piston.

6. Rotate the weights gently by both the hands in clockwise direction.

7. With weights floating and spinning, the pressure generated in the Test will be the

pressure marked on the weights plus the pressure on the weight carrier.

8. Increase or decrease pressure by screwing the RAM IN or OUT.

9. To reduce pressure to zero, screw the RAM fully out and open the isolating valve

& oil tank valve.

10. Remove the weights from the weight carrier one by one slowly.

11. Remove the instrument under test.

HIGH PRESSURE PISTON MODE:

1. Repeat the same procedure followed for Low piston.

CORRECTION FACTORS:

The dead weight tester has been calibrated to the gravity, Temperature and air density

stated on the certificate. The following correction factor has to be applied if the Dead weight

tester is operated in the

environment conditions apart from the conditions stated in the certificate.

Temperature and Gravity Correction:

The value of gravitational acceleration (g) varies with latitude, height above sea level and

geological conditions at the location of the DWT. The following standard values are applied

during calibration unless otherwise requested by customer for special values.

Standard Gravitational Acceleration (G) …………… 9.80665 m/s2

Standard Temperature (T) …………… 20°C

DWT calibrated gravitational acceleration (g) …………… 9.78244215 m/s2

Coefficient of Linear Expansion (α) …………… 0.000025

P1 = P2 (1+α (T-t)) * g/G

Where:

P1 = Corrected Pressure

P2 = Applied Pressure

α = Co-efficient of Linear Expansion

T = DWT calibrated temperature °C

t = Temperature at position of DWT °C (Room Temperature)

g = Gravitational acceleration at position of DWT(Site Gravity)

G = DWT calibrated gravitational acceleration

For Example:

Weight Applied: 100 Bar

P1 = P2 (1+α (T-t)) * g/G

P1 = 100 (1+0.000025(20-27)) * (9.78244215/9.80665)

P1 = 100 (1+ 0.000025(-7)) * (0.997531486)

P1 = 100 (1+ (-0.000175)) * (0.997531486)

P1 = 100 (0.999825) * (0.997531486)

P1 = 100 * 0.997356917

P1 = 99.7356917