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“LINGAYAS INSTITUTE OF
MANAGEMENT AND TECHNOLOGY”
PRACTICAL FILE OF
“ELECTRONIC MEASURMENT AND
INSTRUMENTATION”
SUBMITTED BY:
INDEX
S.No.
EXPERIMENTS
DATE
SIGNATURE
EXPERIMENT NO. 1
AIM: Measurement of displacement using LVDT
APPARATUS: LVDT trainer kit, multimeter .
THEORY: the basic construction of differential transformer is shown in fig .at three
different core positions. The linear variable differential transformer consists of a primary
and 2 secondary coils,axially spaced & wound on a cylindrical coil former,with rod shaped
magnetic core positioned a preffered centrally inside a the coil assembly providing a
preffered path for magnetic flux linking the coil . the displacement to be measured is
transferred to the magnetic core through suitable linkages.When 1ry is energized with an
a/c carrier signal wave,voltage is induced in each 2ndrysection, exact value depending upon
position of magnetic core w.r.to the centre of coil assembly.If coil is symmetrically
placed(electrically) w.r.to 2 2ndry coils,equal voltages are induced in 2ndry coils ,when
these 2 coil output are connected in opposition,the magnitude of resultant voltage tend to 0
value. Such a balance point is turned as null position. In practice, a small residual voltage
is present at a null position due to presence of harmonic in the excitation signal and stray
capacitance coupling pt the 1ry& 2ndry winding,when the core is now displacedfrom null
position,the induced voltage in secondary towards which the core has moved increase
while that in other 2ndry decreases this results in differential voltage output from
transformer.
PROCEDURE
1. Power on the switch, the front LED glow with which indicates the power available on
instrument.
2. Give sometime to stabilize the instrument for stabilization.
3. Balance the pressure cell through the corresponding “0” ten turn timeout.
4. Take at least 10 readings.
5. Draw graph between error and displacement.
Observation table and calculations
Graph:
RESULT:
QUESTIONS:
Q1 What is difference between LVDT and ordinary transformer?
A:
Q2 Why is it called transducer?
A:
Q3 How many coils are there in LVDT?
A:
EXPERIMENT NO .2
AIM: Measurement of speed by photoelectric pick up
APPARATUS: Trainer kit, CRO, connecting wires.
THEORY: This method consists of mounting an opaque disc on rotating shaft.The disc has
no .of equidistant holes in its periphery . At 1 side of the disc a light fixed & on the other
side of the disc ,on the line with the light source,light sensor such as phototube or some
photosensitive semiconducting device is placed.When the opaque portion of the disc is
between the light source and lightsensor ,the lattice is unilluminated & produces no o/p.
But when a hole appears between the 2,light falling upon sensors produces an o/p pulse.
The frequency at which these pulses are produced depends upon no of holes in the disc and
its speed of rotation.Since the no of holes is fixed,the pulse rate is function of speed of
rotation.pulse rate are measured by an electronic counter that can be directly calibrated in
terms of speed in “rpm” .
PROCEDURE:
1. Connect o/p of photoelectric pick up ckt to the i/p of wave shaper ,CRO & digital
voltmeter.
2. Observe reading of frequency counter &also a pattern on CRO.
3. Take different readings.
Observation table and calculation:
RESULT:
EXPERIMENT NO. 3
AIM: Measurement of torque using torque transducer
APPARATUS: Torque measuring training kit,multimeter.
THEORY: Strain gauge are bonded to torque sensitive diaphragm the transducer in a single
body piece m/c from special steel treated for maximum stability. The design ensure high
inherent linearity while maintaining low hysteresis and good ultimate safety factors.The
design uses a full bridge strain gauge configuration. The transducers are well suited for
static and dynamic torque measurement.
PROCEDURE:
1 .Switch on the power. The front LED glow with indicate the poweravalable to device.
2 .leave for sometime to stabilize instrument for stabization.
3.Balance pressure corresponding cell by corresponding o then turn time pot.
4. Take at least 10 readings.
Observation and calculation:
RESULT:
EXPERIMENT NO 4
AIM: To study strain measurement using strain gauge and cantilever assembly.
APPARATUS: Strain gauge trainer kit
THEORY:
If a metal conducter is stressed or compressed,its resistance changes on
account of fact that both length and diameter of conductor changes. Also these cause a c
hange in resistivity.This property is called piezoelectric effect and condcucter is called
piezoelectric material.
Let strain gaugewith no strain have length=l,area=a,diameter=d,then
R=pl/a
p=resistivity
When subjected to strain, length changes to dl, area to da and diameter to dd.Also the
length increases and are of cross section decreases.
/
POISSON’S ratio =lateral strain /longitudinal strain=-dd/d dl/l
E=strain=Δl/l
Gauge factor= ΔR/R /Δl/l
PROCEDURE:
1. Switch on the trainer kit.
2. Observe reading of display.
3. If reading is not zero then adjust offset null.,
4. Place weight of 5gm on cantilever and observe the display.It will be 10 raise to power -6
5. Calculate theoretical strain by formula: (6 X F X L /(w X T X T X Y))
Where F=mg, force (N); m=mass
G=gravity, T=thickness, Y=young”s modulus
OBSERVATION TABLE AND CALCULATION:
RESULT:
QUESTIONS:
Q1 Why strain gauge is also called piezoelectric strain gauge?
A:
Q2 What are different type of strain gauge?
Q3 To obtain good result, what should be value of G and why?
Q4 How does temperature effect operating characteristics of strain gauge?
EXPERIMENT NO 5
AIM: To study characterstic of k-type thermocouple.
APPARATUS: k-type thermocouple trainer kit.
THEORY: The operation of thermocouple is based on see back effect that states that if a
ckt is formed out of 2 dissimilar metallic conductors,a current flows in the circuit if
junction is at higher temp then there are no of pair of metal that exhibit this process.these
metals are arranged in a series by see back so that in the cktmade up of any 2 metals.
Direction of current is from hot to cold junction.
PROCEDURE:
1.
(a):The + o/p of thermocouple to B i/p of instrumentation amplifier.
(b): The -o/p to A i/p of instrumentation amplifier .
(c): O/P of instrumentation amplifier to i/p of X 100 amp.
(d): This o/p to i/p to d.c. amplifier.
(e):Connect voltmeter on 200V d.c. range between dc amp and ground
2. Switch on power and set effect control of amp as under:(a):Short ckt i/p connection to amp and adjust offset control for zero indication on
voltmeter.
(b): Reconnect thermometer out to instrumentation amp.The o/p voltage should be 0 with
hot and cold junction at same temperature.
3. Find temperature of inside and outside of ends of cold junction by using digital
multimeter on 20V from o/p socket i.e. temperature sensor and then from RFT o/p socket of
LM 335 provide on the type “k” thermometer.
4. Record values.
5. Connect 12V supply to heater and at 1 min. interval note value of thermocouple o/p
voltage(mV) and voltage representing temp.
6. Record value in table.
7. Switch off power supply and disconnect the heater element supply(+10).
8 Construct graph of thermocouple o/p voltage against temperature difference “hot” and “
cold” junction.
OBSERVATION TABLE:
RESULT:
EXPERIMENT NO 6
AIM: Measurement of temperature using RTD
APPARATUS: Trainer kit,connecting leads.
THEORY:
1. Resistance wire thermometer have a higher degree of accuracy.Precision laboratory
instrument may be calibrated for measuring to within ±0.01°C.industrail instrument called
”resistance temperature detector (RTD)” can be collaborated to detect the actual
temperature to within ±0.25°C up & ±.5 from 120°C to 550°C.
2. Resistance thermometers are normally designed for fast,as well as accuracy to provide
close control of processes in which narrow ranges or small temp spans must be maintained.
PROCEDURE:
1. Switch the heater and wait for 10-15 min ,a gradient is now established from holes A to
E.
2. Set meter selecter to RTD.
3. Set thermometer RTD switch to RTD position.
4. Insert RTD probe into hole marked A and observe Reading of DPM in °C.
Measurement of Resistance:
5. Connect Ω socket located near RTD sensor.
6. Set motor switch to 100Ω position.
7. Set temp/RTD toggle switch to the thermistor position
Meter now reads resistance of RTD in ohms.
8. likewise measure temp resistance of all 4 from A to E and plot Graph.
Observation table and calculation:
RESULT AND INFERENCE:
QUESTIONS:
Q1 What is RTD?Explain its working principle.
A:
Q2 Which material is used in RTD?
A:
Q3 What are various applications of RTD?
Q4Draw characterstics of RTD.
EXPERIMENT NO 7
AIM:To study characterstics of NTC thermistor.
APPARATUS:NTC trainer kit.
THEORY:
Thermistor is used for compensation of temp resistances.Although temp coeff of unit
exhibits increase in the value of frequeny with increase in temp are avialable , vast
thermistor have (+ve ) temperature coeff i.e. there resistance decreases with increase in
temp.In some materials resistance at room temp may increase as much as 6% to 10% rise in
temp.This high sensitivity to temp change make the thermistor extremely well suited to
precision temp measurement.Therefore especially in low temperature range of 100c-300c or
to detect very small change in temp which cant be observed with RTDor
thermocouple.Thermistors are composed of a sintered mix of metal oxides e.g.
Mn,Ni,Co,Cu and Fe.
There resistance range from .5 -75 ohms & are availanle in large variety of sizes and
shapes.
PROCEDURE
1. a: The o/p of NTC thermistor to C sockets 10 turn pot.
B:Connect a digital multimeter ads voltmeter b/w socketB of 10 turn pot and ground.
C:connect socket a of 10 turn pot at N.
2. switch on power suppy and adjust 10 turn potN until V indication by v meter 2.5V then
note dail reading and temp.
3. Record value of dail reading temp.
4. Connect 12V supply to heater element i/p socket and at 1 min interval note value of dail
reading to procedure 2-5 V across res & temp from sensor.
5 Switch off the power supply and disconnect the feature elment supply.
6 Plot graph b/w thermistor and resistance temp.
Observation and calculation:
Result:
EXPERIMENT NO 8
AIM: Measurement of speed using magnetic pick up.
APPARATUS: Trainer kit, CRO, connecting wires
THEORY: This method consists of mounting an opaque disc on rotating shaft.The disc
has no .of equidistant holes in its periphery . At 1 side of the disc a light fixed & on the
other side of the disc ,on the line with the light source,light sensor such as phototube or
some photosensitive semiconducting device is placed.When the opaque portion of the disc
is between the light source and lightsensor ,the lattice is unilluminated & produces no o/p.
But when a hole appears between the 2,light falling upon sensors produces an o/p pulse.
The frequency at which these pulses are produced depends upon no of holes in the disc and
its speed of rotation.Since the no of holes is fixed,the pulse rate is function of speed of
rotation.pulse rate are measured by an electronic counter that can be directly calibrated in
terms of speed in “rpm” .
PROCEDURE:
1. Connect o/p of magnetic pick up ckt to the i/p of wave shaper ,CRO & digital voltmeter.
2. Observe reading of frequency counter &also a pattern on CRO.
3. Take different readings.
Observation table and calculation:
RESULT:
EXPERIMENT NO 9
OBJECTIVE: To study working of cathode-ray oscilloscope.
APPARATUS: Cathode-ray oscilloscope, multimeter, and oscillator.
INTRODUCTION: The cathode-ray oscilloscope (CRO) is a common laboratory
instrument that provides accurate time and aplitude measurements of voltage signals
over a wide range of frequencies. Its reliability, stability, and ease of operation make
it suitable as a general purpose laboratory instrument. The heart of the CRO is a
cathode-ray tube shown schematically in Fig. 1.
The cathode ray is a beam of electrons which are emitted by the heated cathode
(negative electrode) and accelerated toward the fluorescent screen. The assembly of
the cathode, intensity grid, focus grid, and accelerating anode (positive electrode) is
called an electron gun. Its purpose is to generate the electron beam and control its
intensity and focus. Between the electron gun and the fluorescent screen are two pair
of metal plates - one oriented to provide horizontal deflection of the beam and one
pair oriented ot give vertical deflection to the beam. These plates are thus referred to
as the horizontal and vertical deflection plates. The combination of these two
deflections allows the beam to reach any portion of the fluorescent screen. Wherever
the electron beam hits the screen, the phosphor is excited and light is emitted from
that point. This coversion of electron energy into light allows us to write with points
or lines of light on an otherwise darkened screen.
In the most common use of the oscilloscope the signal to be studied is first amplified and
then applied to the vertical (deflection) plates to deflect the beam vertically and at the
same time a voltage that increases linearly with time is applied to the horizontal
(deflection) plates thus causing the beam to be deflected horizontally at a uniform
(constant> rate. The signal applied to the verical plates is thus displayed on the screen as
a function of time. The horizontal axis serves as a uniform time scale.
The linear deflection or sweep of the beam horizontally is accomplished by use of a
sweep generator that is incorporated in the oscilloscope circuitry. The voltage output
of such a generator is that of a sawtooth wave as shown in Fig. 2. Application of one
cycle of this voltage difference, which increases linearly with time, to the horizontal
plates causes the beam to be deflected linearly with time across the tube face. When
the voltage suddenly falls to zero, as at points (a) (b) (c), etc...., the end of each sweep the beam flies back to its initial position. The horizontal deflection of the beam is
repeated periodically, the frequency of this periodicity is adjustable by external
controls.
To obtain steady traces on the tube face, an internal number of cycles of the unknown
signal that is applied to the vertical plates must be associated with each cycle of the
sweep generator. Thus, with such a matching of synchronization of the two
deflections, the pattern on the tube face repeats itself and hence appears to remain
stationary. The persistance of vision in the human eye and of the glow of the
fluorescent screen aids in producing a stationary pattern. In addition, the electron
beam is cut off (blanked) during flyback so that the retrace sweep is not observed.
CRO Operation: A simplified block diagram of a typical oscilloscope is shown in Fig.
3. In general, the instrument is operated in the following manner. The signal to be
displayed is amplified by the vertical amplifier and applied to the verical deflection
plates of the CRT. A portion of the signal in the vertical amplifier is applied to the
sweep trigger as a triggering signal. The sweep trigger then generates a pulse
coincident with a selected point in the cycle of the triggering signal. This pulse turns
on the sweep generator, initiating the sawtooth wave form. The sawtooth wave is
amplified by the horizontal amplifier and applied to the horizontal deflection plates.
Usually, additional provisions signal are made for appliying an external triggering
signal or utilizing the 60 Hz line for triggering. Also the sweep generator may be
bypassed and an external signal applied directly to the horizontal amplifier.
CRO Controls
The controls available on most oscilloscopes provide a wide range of operating
conditions and thus make the instrument especially versatile. Since many of these
controls are common to most oscilloscopes a brief description of them follows.
CATHODE-RAY TUBE
Power and Scale Illumination: Turns instrument on and controls illumination of the
graticule.
Focus: Focus the spot or trace on the screen.
Intensity: Regulates the brightness of the spot or trace.
VERTICAL AMPLIFIER SECTION
Position: Controls vertical positioning of oscilloscope display.
Sensitivity: Selects the sensitivity of the vertical amplifier in calibrated steps.
Variable Sensitivity: Provides a continuous range of sensitivities between the
calibrated steps. Normally the sensitivity is calibrated only when the variable knob is
in the fully clockwise position.
AC-DC-GND: Selects desired coupling (ac or dc) for incoming signal applied to
vertical amplifier, or grounds the amplifier input. Selecting dc couples the input
directly to the amplifier; selecting ac send the signal through a capacitor before going
to the amplifier thus blocking any constant component.
HORIZONTAL-SWEEP SECTION
Sweep time/cm: Selects desired sweep rate from calibrated steps or admits external
signal to horizontal amplifier.
Sweep time/cm Variable: Provides continuously variable sweep rates. Calibrated
position is fully clockwise.
Position: Controls horizontal position of trace on screen.
Horizontal Variable: Controls the attenuation (reduction) of signal applied to
horizontal aplifier through Ext. Horiz. connector.
TRIGGER
The trigger selects the timing of the beginning of the horizontal sweep.
Slope: Selects whether triggering occurs on an increasing (+) or decreasing (-) portion
of trigger signal.
Coupling: Selects whether triggering occurs at a specific dc or ac level.
Source: Selects the source of the triggering signal.
INT
(internal)
from
signal
on
vertical
amplifier
EXT - (external) - from an external signal inserted at the EXT. TRIG. INPUT.
LINE - 60 cycle triger
Level: Selects the voltage point on the triggering signal at which sweep is triggered. It
also allows automatic (auto) triggering of allows sweep to run free (free run).
CONNECTIONS FOR THE OSCILLOSCOPE
Vertical Input: A pair of jacks for connecting the signal under study to the Y (or
vertical) amplifier. The lower jack is grounded to the case.
Horizontal Input: A pair of jacks for connecting an external signal to the horizontal
amplifier. The lower terminal is graounted to the case of the oscilloscope.
External Tigger Input: Input connector for external trigger signal.
Cal. Out: Provides amplitude calibrated square waves of 25 and 500 millivolts for use
in calibrating the gain of the amplifiers.
Accuracy of the vertical deflection is + 3%. Sensitivity is variable.
Horizontal sweep should be accurate to within 3%. Range of sweep is variable.
Operating Instructions: Before plugging the oscilloscope into a wall receptacle, set
the controls as follows:
(a)
Power
switch
(b)
Intensity
fully
(c)
Vertical
centering
in
(d)
Horizontal
centering
in
(e)
Vertical
(f) Sweep times 1
at
counter
the
center
the
center
at
off
clockwise
of
range
of
range
0.2
Plug line cord into a standard ac wall recepticle (nominally 118 V). Turn power on. Do
not advance the Intensity Control.
Allow the scope to warm up for approximately two minutes, then turn the Intensity
Control until the beam is visible on the screen.
WARNING: Never advance the Intensity Control so far that an excessively bright
spot appears. Bright spots imply burning of the screen. A sharp focused spot of high
intensity (great brightness) should never be allowed to remain fixed in one position on
the screen for any length of time as damage to the screen may occur.
Adjust Horizontal and Vertical Centering Controls. Adjust the focus to give a sharp
trace. Set trigger to internal, level to auto.
EXPERIMENT NO. 10
AIM: To measure voltage using load cell.
APPARATUS: Trainer kit,multimeter,etc.
THEORY:
A load cell is an electronic device (transducer) that is used to convert a force into an
electrical signal. This conversion is indirect and happens in two stages. Through a
mechanical arrangement, the force being sensed deforms a strain gauge. The strain
gauge converts the deformation (strain) to electrical signals. A load cell usually
consists of four strain gauges in a Wheatstone bridge configuration. Load cells of one
or two strain gauges are also available. The electrical signal output is typically in the
order of a few millivolts and requires amplification by an instrumentation amplifier
before it can be used. The output of the transducer is plugged into an algorithm to
calculate the force applied to the transducer.
Although strain gauge load cells are the most common, there are other types of load
cells as well. In industrial applications, hydraulic (or hydrostatic) is probably the
second most common, and these are utilized to eliminate some problems with strain
gauge load cell devices. As an example, a hydraulic load cell is immune to transient
voltages (lightning) so might be a more effective device in outdoor environments.
Other types include piezo-electric load cells (useful for dynamic measurements of
force), and vibrating wire load cells, which are useful in geomechanical applications
due to low amounts of drift.
Every load cell is subject to "ringing" when subjected to abrupt load changes. This
stems from the spring-like behavior of load cells. In order to measure the loads, they
have to deform. As such, a load cell of finite stiffness must have spring-like behavior,
exhibiting vibrations at its natural frequency. An oscillating data pattern can be the
result of ringing. Ringing can be suppressed in a limited fashion by passive means.
Alternatively, a control system can use an actuator to actively damp out the ringing
of a load cell. This method offers better performance at a cost of significant increase in
complexity.
Load cell types

load button

inline rod end
parallel beam
diaphram
canister
double ended shear beam
single ended shear beam
single column
multi -column
membrane
torsion ring
bending ring
pancake
digital ElectroMotive Force
"S" type for hanging
shear beam
bending beam
proving ring
















Applications

electronic crane scales
finding the center of gravity of an object by weight
force measurement
tension measurement
in- motion dynamic check weighers check weigher
truck weighing
wireless crane scales
batching
monitor inventory
feedback control
impact measurement










OBSERVATION TABLE:
RESULT:
EXPERIMENT NO. 11
AIM:To measure voltage using pressure transducer
APPARATUS:
Trainer kit,multimeter.
THEORY:
A pressure transducer is a transducer that converts pressure into an analog electrical
signal. Although there are various types of pressure transducers, one of the most
common is the strain-gage base transducer. The conversion of pressure into an
electrical signal is achieved by the physical deformation of strain gages which are
bonded into the diaphragm of the pressure transducer and wired into a wheatstone
bridge configuration. Pressure applied to the pressure transducer produces a deflection
of the diaphragm which introduces strain to the gages. The strain will produce an
electrical resistance change proportional to the pressure.
OBSERVATION TABLE:
RESULT: