TR Lab Manual To Be Uploaded - Final - With Units
TR Lab Manual To Be Uploaded - Final - With Units
TR Lab Manual To Be Uploaded - Final - With Units
LABORATORY MANUAL
TRANSDUCERS LAB (EE 385)
for
B.E. III/IV I-SEM EIE
www.mjcollege.ac.in
WITH EFFECT FROM THE ACADEMIC YEAR 2012 - 2013
EE 385
TRANSDUCERS LAB
Instruction 3 Periods per week
Duration of University Examination 3 Hours
University Examination 50 Marks
Sessional 25 Marks
Page
S.No. Name of the Experiment
No.
Measurement of Temperature by
2 a) Thermistor. 5
b) Thermocouple. 7
5 Measurement of Pressure. 19
Figure: 1
Figure: 2
Circuit Operation:-
In this setup, there is a toothed wheel having 20 teeth. When the motor runs at 1500
rpm (i.e. 25 revolutions/sec), the frequency of the pulse = 25 x 20 = 500 per second.
i.e. when the motor runs at 1500 rpm, the pickup works as pulse generating
transducer, producing 500 pulses per second. The circuit consists of 2 stages of AC
amplification giving a very high overall gain. The resultant output is fed into a
Schmitt trigger circuit using IC 555 Timer. The Schmitt trigger in turn triggers
monostable, which generates constant width, constant height pulses. These shaped
pulses are given to a panel meter for display through an additional amplifier.
A separate signal generator with a stable frequency of 500 Hz is provided for
calibration. (Set the selector switch in magnetic pickup).When the output of this
calibration source is connected to input of the amplifier stage and by using the
potentiometer marked „Max‟ the reading of the meter is adjusted to maximum speed
of 1500 rpm. With this calibration, the panel meter (DPM) directly reads the speed of
the motor in rpm.
Procedure:-
1) After calibration is done as given in the above section, set the selector Switch to
the magnetic pickup side.
2) Connect the motor terminal cable to the output terminals of DC supply. Ensure
that the dimmerstat knob is in zero position. Now switch on power supply for speed
controller section and slowly go on changing the speed of the motor.
3) Note the speed in the panel meter.
4) Check the speed by using precision Tachometer.
5) Tabulate the readings as shown below.
Rpm rpm
Graph:-
Draw the graph of Tachometer reading Vs DPM reading.
rpm rpm
Graph:-
Draw the graph of Tachometer reading Vs DPM reading.
Figure: 1
Circuit Operation:-
Study of Thermistor characteristics
When thermistor is connected between the terminals 2 and 6 of Op-amp, with pin no 2
of Op amp at virtual ground, a fixed current of minus 0.1 milliamps (100
microamperes) will be flowing through the Thermistor because of 50 KΩ resistances
and minus 5 volts supply.
Output pin 6 of the Op-amp will generate a potential which is exactly proportional to
the resistance of the device under study. If thermistor resistance is 1999 ohms,
Graph:-
Draw Resistance Vs Temperature.
Result:-
Measured the different temperatures using thermistor and studied its characteristics.
Figure: 1
Figure: 2
(0C) (0C)
The main problem with the resistance wire strain gauge is the extremely small change
in resistance as a result of change in the applied load. This makes the circuit operation
and strain gauge installation very critical. Moreover temperature effects are also
required to be taken care of.
Circuit Diagram:-
Figure: 1
Figure: 2
Circuit Operation:-
On a mild steel bar, two single element Bakelite strain gauges (R=350 Ω) are
mounted with the help of adhesive cement on the upper surface and the two are
mounted on the lower surface. When all the four gauges are used in the bridge we
have a four arm system. If only two gauges one from upper surface and one from
lower surface) are used, we have a two arm system with two resistances of 350 ohms
forming other two arms. The bridge is excited with the help of 5V supply using IC
7805. A 10 KΩ helical pot and 47 KΩ POT forms the coarse and fine balancing
controls respectively.
The output of the bridge which is in the range of few hundreds of micro volts is
amplified with the help of an instrumentation amplifier. Whose gain is adjusted by
means of Amplifier adjust POT (10 KΩ). In maximum clockwise position, the gain of
the amplifier is exactly 1000.The DPM used is 1.999 volt or 1999mV. Hence when
the gain adjust pot is in maximum clockwise position the DPM reading exhibits
directly the micro volts (neglecting the decimal points). The instrumentation amplifier
is having low drift, high stable gain.
Procedure:-
Connect the flexible wires provided with the strain gauge cantilever beam between
terminals 1-1, 2-2 and 3-3(special care must be taken to ensure proper connection of
terminal No 2).If terminals 1 and 3 are interchanged. Only the output polarity will be
changed.
𝐸𝑥𝑐 ∗ ∆𝑅
𝐸𝑜𝑢𝑡 =
2𝑅
∆𝑅
Where = 𝐺𝑓 ∗ 𝑠𝑡𝑟𝑎𝑖𝑛, gauge factor G f = 2
𝑅
𝑠𝑡𝑟𝑒𝑠𝑠 𝑠𝑡𝑟𝑒𝑠𝑠
𝑠𝑡𝑟𝑎𝑖𝑛 = =
𝑦 2∗10 6
𝑀 1
and 𝑠𝑡𝑟𝑒𝑠𝑠 = 𝑓 = where z = moment of cross section =
𝑧 6∗𝑏∗𝑡 2
Assuming G f = 2.
∆𝑅
= 𝐺𝑓 ∗ 𝑠𝑡𝑟𝑎𝑖𝑛= 2*52.378*10−6 = 105.315
𝑅
Hence
𝐸𝑥𝑐 ∗ ∆𝑅 5
𝐸𝑜𝑢𝑡 = = ∗ 105.315 ∗ 10−6 = 263.28 µ𝑉 = 0.263𝑚𝑉
2𝑅 2
Assuming G f = 2.
∆𝑅
= 𝐺𝑓 ∗ 𝑠𝑡𝑟𝑎𝑖𝑛= 2*52.65*10−6 = 105.315
𝑅
Hence,
𝐸𝑥𝑐 ∗ ∆𝑅
𝐸= = 5 ∗ 105.315 = 526.575 µ𝑉 = 0.526𝑚𝑉
𝑅
Graph:-
Plot the graph of the applied load versus the experimental output.
Result: - The known weights are measured by strain gauge and verified to be correct.
Discussion of Result:-
1. The student will be able to discuss the effect of dimensions of cantilever beam on
output voltage.
2. The student will observe the differences in output voltage between 2 arm and 4
arm configuration used for measuring weights.
0.36 ∗ 𝑇 ∗ 𝐿
𝜃=
3.14 ∗ 𝐷4 ∗ 𝐺
Procedure:-
1) Keep SW8 in speed position, SW9 in calibration position. The DPM should be 1500
RPM, confirming that speed circuit is in calibrated condition. Now keep SW 8 in
right position, the DPM should indicate 1800 plus or minus, ensuring that
electronic circuit is O.K. Now again take SW8 in speed mode and SW9 in Read
position.
2) Switch ON speed controller and increase the speed of the motor slowly about 1500
RPM as indicated by the DPM.
3) Take SW8 switch to Torque mode and torque should be indicated as 0.0 Kg-m.
4) If it is not zero, adjust Min POT to get zero condition.
5) Apply some load (5th hole in the loading rod).
Observations:-
Graph:-
Plot the graph of calculated torque Vs DPM reading as shown in expected graph
below.
MEASUREMENT OF PRESSURE
Aim: - To study and calibrate pressure transducer using Piezo resistive element.
Apparatus required: - DPM, Pressure measurement experiment setup, Foot pump.
Theory:-
Pressure transducers can be classified into gravitational and elastic types. In the
gravitational type, the familiar manometer is the simplest device. In elastic
transducers, the pressure exerts a force over the area of an elastic device. The force
responsive elastic member is in the form of a diaphragm, capsule, bellows or a
bourdon tube. The resultant displacement is measured with an appropriate electric
sensor. The most common type of pressure sensing element is the diaphragm. They
are rugged, have excellent stability, reliability and low hysteresis.
Principle:-
The Motorola pressure sensor is designed utilizing a monolithic silicon piezo resistor,
which generates a changing output voltage with variations in applied pressure. The
resistive element, which constitutes a strain gauge, is diffused or ion implanted on a
thin silicon diaphragm.
Applying pressure to the diaphragm, results in resistance change in the strain gauge,
which in turn causes a change in the output voltage proportional to the applied
pressure. The strain gauge is an integral of the silicon diaphragm. Hence there are no
temperature effects due to differences in thermal expansion of the strain gauge and the
diaphragm.
Circuit Diagram:-
Observations:-
S.No. Input DPM (𝐴 − 𝐸)
% 𝐸𝑟𝑟𝑜𝑟 = ∗ 100
Pressure(A) Reading (E) 𝐴
psi psi
Graph:-
Plot the graph of applied input pressure versus output pressure on Dpm.
Discussion of Result:-
The student will be able to discuss the characteristics of pressure transducer.
(∈ 𝑜 ∗∈ 𝑟 ∗ 𝐴)
𝐶=
𝑑
Where A = area of the plates.
d = distance between the plates
Є0 = Permittivity of free space.
Єr = Relative permittivity of the medium.
In this setup, the capacitor transducer works on the principle of variation of effective
area of the plates, other parameters are kept constant. A two- ganged condenser is
used here. The effective area between moving and stationary plates goes on changing
as the shaft of the capacitor is rotated. This arrangement is used to demonstrate the
measurement of the angular displacement.
Circuit Diagram:-
Figure: 1
Figure: 2
Principle of Operation:-
The basis of the angular displacement measurement with the help of capacitive
transducer is indicated in figure 1. The two sets of identical condenser form a part of
the Wien Bridge oscillator for which the frequency is
1
𝐹=
2.3 ∗ 3.14 ∗ 𝑅𝐶
(Assuming R1 = R2 = R and C1 = C2 = C)
So if C is varied typically between (550 pF to 50 pF), we get the frequency variation
in the range of 1: 10. On a separate PCB, signal generator and its allied circuitry is
mounted. There is a buffer stage associated with this oscillator. The waveform is
adjusted to be almost as a square wave. The amplification is done by IC741 and then
fed to Schmitt trigger circuit using IC 555 timer. The output of Schmitt trigger is used
to trigger the input of IC 555 monostable. The monostable output is of constant pulse
width, constant pulse height, so that the meter reading is strictly proportional to the
input frequency.
The output circuit is connected to a special bucking circuit, so that for zero angular
displacement, the DPM reading can be adjusted to be zero. The necessary bucking
voltage is obtained from a separate power supply. The pulse height is constant
because of the use of a regulated power supply.
Procedure:-
1) Keep the input angular displacement to zero position.
2) Check for the zero indication on the DPM. Otherwise by operating potentiometer
marked Min (P2) obtain zero indication.
3) Turn the shaft of the capacitive pickup to the fully clockwise position in a gentle
manner corresponding to 170 degrees. Adjust DPM indication to 170 degrees by
operating the knob marked Max (P1). Repeat the operation for consistent reading.
Graph:-
Plot the graph of input angular displacement on X –axis versus DPM reading on Y-
axis.
Figure: 1
Figure: 2
Note: For Resistance of Photoconductive cell, the Max POT must be in the fully
clockwise position.
Procedure:-
1) Connect the LDR to the input terminals on the front panel.
2) Connect the output terminals of the transducer circuit to the DPM, observing the
polarity.
3) Adjust the channel to which LDR is mounted, so that full-scale deflection is obtained
on the meter. If required use potentiometer marked Max on the panel.
4) Using the scale mounted on the bottom of C channel, measure the input
displacement and the resultant DPM readings.
5) Tabulate the reading as show
Observations:-
Result:-
Linear displacement is measured using LDR.
Discussion of Result:-
The student will be able to discuss the relation between input displacement and
resistance of LDR.
Figure: 1
Figure: 2
Figure: 3
Principle of Operation:-
The liquid column in a vessel exerts a pressure at the bottom surface of the vessel.
The liquid height and the pressure are related by
𝑝 𝑝
= =
𝑑 (𝑝𝑤 ∗ 𝑠𝑔𝑙)
Where h = height of the liquid in meters.
p = pressure in Kg/m3 or Kg/cm3.
d = density in Kg/m3 at the operating temperature.
pw = density of water at the same temperature.
sgl = specific gravity of liquid at operating temperature.
Figure: 1
Muffakham Jah College of Engg. & Tech. Page 33
Transducers Lab, EED
Figure: 2
Figure: 3
Circuit Operation:-
The primary winding of LVDT is excited by means of 4 KHz power source. The
Wein bridge oscillator circuit placed on a separate PCB generates a stable ac
excitation of 4 KHz. The output from signal generator card is given to complimentary
power transistors namely AD161 and AD162. The power amplifier in turn provides
excitation to primary winding of LVDT.
The output from secondary is amplified by means of an Op-amp741(IC-D).The POT
marked „Max‟ on the front panel controls the value of feedback resistance and in turn
gain of the amplifier. Separate Op-amp318(IC-B) converts the excitation signal into
square waves which serve to provide reference signal for phase sensitive detection.
A field effect transistor 2N3819 acts as an analog switch and a phase detected output
is generated. The output from the first stage amplification(IC-D) is passed through an
all pass network (consisting of IC-C) which facilitates proper phase adjustment with
the help of preset PR1. The output from this all pass filter is given to the phase
Figure: 1
Figure: 2
Graph:-
Draw the graph between measured temperature and output resistance.
Figure: 3
Figure: 1
Circuit operation:
The transducer in this set up is operating on the principle of variation of permeability
or reluctance of the magnetic circuit. The inductive coil is mounted on a micrometer
and as the steel bar of the micrometer moves in or out of the core of the coil, the
inductance increases or decreases accordingly. When a simple single coil is used as a
transducer element, the input usually changes the permeance of the flux path
generated by the coil, merely changing the inductance.
The inductive pickup has three distinct sections.
1. Bridge network.
2. Excitation source.
3. Bridge output amplifier and final indication (and bucking source).
Muffakham Jah College of Engg. & Tech. Page 41
Transducers Lab, EED
Excitation Source:
A sinusoidal excitation of 1 KHz is obtained by making use of 741 Op-amps in Wein
bridge oscillator circuit. This output is given to a voltage follower stage and an
amplifier before it is fed to the inductive bridge circuit.
Bridge Network:
The output of the excitation source is impressed across the primary of the transformer
and the secondary of it excites the inductive pickup. Two arms of the inductive bridge
are resistive and other two are inductive in nature. The coil mounted on the
micrometer works as a variable inductance element and there is dummy inductance
very close to isolating transformer inside the main instrument. The resistance is made
variable and is used to make Zero or Min adjustment.
Amplifier:
The output of the bridge is rectified and then filtered. The filtered output is further
amplified and connected to the DPM. The variable resistance marked Max is working
as POT and its output is given to DPM for final indication. For differential
measurements, additional bucking source is included.
PART-1 (Without Bucking Circuit)
Procedure:
1. Keep the micrometer circuit reading at 25 mm position.
2. Connect the output of the amplifier to the DPM input. Keep SW1 in the upward
position. Keep the Max POT in the mid position. Now adjust Min POT carefully to
get minimum reading on the DPM.
3. Now move the magnetic core gently away from the coil to position 35 mm and
adjust indication of 011 mill volts on the DPM corresponding to a displacement of 10
mm with the help of Max POT (indicating a resolution of 0.1mm).Now check back
for minimum reading at 25 mm position.
4. Enter the readings in the table as shown.
Observations:
Effective input Displacement DPM reading
S.No.
mm mm
Circuit Diagram:
Figure: 2
Procedure:
1. Repeat 1 and 2 as per the previous part of the experiment.
2. Now keep SW1 to downward position (Buck Position) and move the core to 30 mm
position.
3. Now adjust pot marked “Buck” to get zero output. Slightly disturb the Min POT
also if necessary. Now take the core to 35 mm position and adjust the Max POT to get
a reading of 50. Take the readings for various core positions and tabulate the readings
as shown.
Muffakham Jah College of Engg. & Tech. Page 43
Transducers Lab, EED
Observations:
S.No Effective input Displacement (mm) DPM Reading (mm)
Graph: Plot the graph between input displacement and DPM reading.