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Mumbai University Electrical (Semester -III)
1 |www.brainheaters.in
Solution for Electrical and
Electronic Measurements
May 2016
Index
Q.1)
a) …………………………………………………………………………. 2
b) …………………………………………………………………………. 2
c) …………………………………………………………………………. 3-4
d) …………………………………………………………………………. 5-6
e)………………………………………………………………………….. 6
Q.2)
a) …………………………………………………………………………. 7-11
b) …………………………………………………………………………. 11-16
Q.3)
a) …………………………………………………………………………. 17-20
b) …………………………………………………………………………. 21-22
Q.4)
a) …………………………………………………………………………. 23-25
b) …………………………………………………………………………. 25-27
Q.5)
a) …………………………………………………………………………. N.A
b) …………………………………………………………………………. 28-31
Q.6)
a) …………………………………………………………………………. 31-33
b) …………………………………………………………………………. 34-35
c) …………………………………………………………………………. 35-37
d) …………………………………………………………………………. 37-38
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Q1)
(a) Differentiate between indicating and integrating instrument.
Ans:
(b) Explain the resolution and sensitivity of digital meter.
Ans:
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(c) Explain piezo electrical transducer
Ans:
Different modes of piezoelectric transducer.
A B
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Piezoelectric transducer.
Mumbai University Electrical (Semester -III)
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(d) Explain a suitable bridge to measure medium resistance.
Ans:
Mumbai University Electrical (Semester -III)
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(e) Differentiate between Active and Passive transducers
Ans:
Mumbai University Electrical (Semester -III)
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Q2
(a) Explain working principle ,construction of D.C permanent.
Magnet moving coil type meter and hence derive the torque equation.
Ans:
Mumbai University Electrical (Semester -III)
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In order to obtain longer movement of the pointer and a longer angular swing of
the coil, a concentric magnet construction shown in the figure is used. Since
magnet is concentric type ,it produces a radial flux pattern which extends over
250 0 or more .This type of construction is used for many panel type and some
portable instruments.
In recent years, the magnetic system shown in the figure is developed .It uses
magnetic material like Alnico .In this system the magnet itself serves as the core
.The moving coil moves over the magnet .The active sides of the moving coil
are located in the uniform radial field between the pole pieces and steel yoke.
This system has advantages of being unaffected by the external magnetic fields
.It also eliminates the magnetic shunning effects and needs for magnetic
shielding in the form of iron cases.
Mumbai University Electrical (Semester -III)
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Mumbai University Electrical (Semester -III)
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Mumbai University Electrical (Semester -III)
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(b) Describe construction, working principle ,and theory of dyno meter
Type of wattmeter.
Ans:
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Mumbai University Electrical (Semester -III)
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TORQUE EQUATION:
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Mumbai University Electrical (Semester -III)
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If the position of zero mutual inductance is at the mid-scale ,the scale
will will be uniform over 80 0 to 1000 which covers almost the entire scale
range.
ERRORS IN ELECTRODYNAMOMETER:
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Mumbai University Electrical (Semester -III)
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Q3
(a) Explain the block diagram Ramp type digital voltmeter.
Ans:
BLOCK DIAGRAM OF LINEAR RAMP TYPE DVM
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The sample rate multivibrator determines the rate of measurement cycle .The
oscillation of the multivibrator is usually adjusted by a front panel control
named “RATE” ,from few cycles per second to as high a 1000 cycles per
second .The typical value is 5 cycles/second with the accuracy of ± 0.005% of
the reading
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STAIR CASE RAMP TYPE DVM
Basic Principle :
The basic principle is that the input signal is compared with internally
generated voltages which is increased in steps starting from zero.
The number of pulses counted by the counter in the time interval which
staircase voltage takes to reach unknown input voltage is displayed as the
ouput.
The figure above represents DVM
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Mumbai University Electrical (Semester -III)
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(b) Explain Kelvin’s double bridge to measure low resistance and hence
derive the equation of unknown resistance using the above bridge.
Ans:
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The known resistance R3 is adjusted such that galvanometer indicates
zero and then using Equation Rx can be calculated .
Advantages
1) In a typical Kelvin’s double bridge the range of resistance covered is 1Ω
to 10µΩ with an accuracy of ± 0.05% to ± 0.2% .
2) The resistance of the connecting lead Ry has no effect on measurement
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Q4
(a) Explain the Maxwell’s induction bridge to measure self induction and
hence derive the equation self induction using the above bridge draw
the phasor diagram.
Ans:
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(4) It is useful for measurement of a wide range of inductance at power
And audio frequencies
(5) It can measure inductance from 1 H to 1000 H with ± 2 % error.
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(b) Explain the construction and working of D.C. Crompton type of
potentiometer.
Ans:
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Mumbai University Electrical (Semester -III)
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Q5
(a) A moving coil instruments give a full scale deflection pf 10mA when
the potential difference across its terminal is 100mV. Calculate.
i) Shunt resistance for a full scale deflection corresponding to 100A.
ii) The series resistance for full scale reading 100V.
Calculate the power dissipation for each.
Ans: N.A
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(b) Explain the construction and working of LVDT.
Ans:
It is a variable inductance displacement transducer .The construction of LVDT
is as shown in fig.
CONSTRUCTION OF LVDT
The two secondary winding are connected in series opposition as shown in fig.
(a) .Hence the voltage induced into these windings are of opposite polarities.
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The output voltage is given by,
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Performance characteristics of LVDT
(vi) Dynamic response:
This indicates how fast the LVDT responds to the displacement of the
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Core. Dynamic response is dependent on the excitation frequency and
the core weight.
Advantages of LVDT
Q6 Write short note on any three
(a) Moving iron instrument
Ans:
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Mumbai University Electrical (Semester -III)
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Repulsion type moving iron instrument
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(b) Megger
Ans:
MEGGER CIRCUIT
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(c) Tachometer
Ans:
PHOTOELECTRIC TACHOMETER
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VARIABLE RELUCTANCE TACHOMETER
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(d) Reed moving coil type frequency meter:
Ans:
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CONSTRUCTION AND WORKING: