solution for electrical and electronic measurements › uploads › 2 › 6 › 0 › 3 › 26031536...

Mumbai University Electrical (Semester -III)

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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



Q1)

(a) Differentiate between indicating and integrating instrument.

Ans:

(b) Explain the resolution and sensitivity of digital meter.

Ans:



(c) Explain piezo electrical transducer

Ans:

Different modes of piezoelectric transducer.

A B



Piezoelectric transducer.



(d) Explain a suitable bridge to measure medium resistance.

Ans:



(e) Differentiate between Active and Passive transducers

Ans:



Q2

(a) Explain working principle ,construction of D.C permanent.

Magnet moving coil type meter and hence derive the torque equation.

Ans:



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.



(b) Describe construction, working principle ,and theory of dyno meter

Type of wattmeter.

Ans:



TORQUE EQUATION:



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:



Q3

(a) Explain the block diagram Ramp type digital voltmeter.

Ans:

BLOCK DIAGRAM OF LINEAR RAMP TYPE DVM



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



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



(b) Explain Kelvin’s double bridge to measure low resistance and hence

derive the equation of unknown resistance using the above bridge.

Ans:



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



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:



(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.



(b) Explain the construction and working of D.C. Crompton type of

potentiometer.

Ans:



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



(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.



The output voltage is given by,



Performance characteristics of LVDT

(vi) Dynamic response:

This indicates how fast the LVDT responds to the displacement of the



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:



Repulsion type moving iron instrument



(b) Megger

Ans:

MEGGER CIRCUIT



(c) Tachometer

Ans:

PHOTOELECTRIC TACHOMETER



VARIABLE RELUCTANCE TACHOMETER



(d) Reed moving coil type frequency meter:

Ans:



CONSTRUCTION AND WORKING:

solution for electrical and electronic measurements › uploads › 2 › 6 › 0 › 3 › 26031536...

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