Bengal Engineering and Science University 2007 B.E Electrical Engineering Electrical measurement-II - Question Paper
Ex/BESUS/ EE-401/07 B.E. (EE) Part-II 4th Semester Examination, 2007
Electrical Measurement-II (EE-401)
Time : 3 hours Full Marks : 70
Use separate answerscript for each half.
Answer SIX questions, taking THREE from each half.
Two marks are reserved for neatness in each half.
FIRST HALF
1. a) Define probable and random errors. What do you understand by resolution of
an instrument?
b) A set of independent 10 measurements were made to determine the weight of a lead shot. The weights in gramme were :
1.570, 1.597, 1.591, 1.562, 1.577, 1.580, 1.564, 1.586, 1.550, 1.576 Determine the (i) arithmetic mean, (ii) average deviation, (iii) standard deviation, (iv) probable error of one reading and (iv) probable error of the mean. [ill
2. a) What methods can be used for the measurement of frequency? Explain any
one frequency meter with its advantages and disadvantages.
b) In Grassot flux meter, prove that it has a uniform scale. [11]
3. a) Describe the expression for the deflection of Ballistic Galvanometer in terms
of its physical constants. Explain these constants.
b) The reluctance of a magnetic circuit excited by an mmf of 8000 A is 120,000 A/wb. A fluxmeter is used to measure the flux. If the fluxmeter scale has 120 divisions and the flux linkages required for a deflection of 1 division are 0.15 x 10 weber turn, calculate the resistance of the shunt required for use with the search coil. Number of turns of search coil is 1 and its resistance is 0.025 ohm. The measurement is made by switching off the excitation. [ll]
4. a) Describe the different methods used for digital tape recording. Explain its
advantages and disadvantages.
b) Supposing the following readings are obtained for one month of 30 days, find out the average monthly load factor and power factor. kVarh (reactive) meter advance = 83,830; kWh meter indicator = 1400, demand indicator = 1400 kW. (ll]
5. Write short notes on (any four) : [11]
a) Synchroscope
b) Maximum demand indicator
c) Hall effect
d) VTVM
e) Trivector meter.
SECOND HALF
6. a) How the inductance of a coil having Q value 2.5 (appox) is measured with
A.C. bridge? Draw the bridge circuit and derive the necessary expressions. Draw the modified bridge ckt for the above measurement if Q value of the coil is 25.
b) Discuss the influence of frequency term present in the expression of the above measurement. [ll]
7. a) How the value of unknown capacitor (loss free) is measured with A.C. bridge
when Rj, R2 are variable resistances and ps is the standard capacitor. [Other resistances R3, R4 etc and capacitors Cj, C2 etc may be used if necessary]
b) AB-BC-CD-DA are the four arms of AC bridge having impedances Zl5 Z2, Z4, Z3 respectively at balance condition. Find the magnitude and nature ofZ4 where
Z\ = 100Q < 80 (inductive)
Z2 = 250 Q (Res only)
Z3 = 400 Q <30 inductive are given.
Discuss the result if Zj = 100Q <-80. [11]
8. a) Compare (i) AC potentiometer with D.C. potentiometer and (ii) polar type
potentiometer with co-ordinate type potentiometer.
b) Explain the operating principle of d.c. potentiometer highlighting the necessary precautions taken. Describe Crompton Type Potentiometer. )ll]
9. a) How the frequency is measured using AC Bridge?
b) Write notes on : Lissajous figures and frequency measurement. [11]
10. Write notes on any two : [ll]
a) Drysdale Phase Shifting Instrument
b) Bridge used for comparison of Dissipation factors of two capacitors
c) Universal bridge.
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