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Posted By: arunkumar Member Level: Gold Posted Date: 30 May 2008
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2007 Anna University B.E Electronic Instrumentation and Control EI 237 — ELECTRICAL MEASUREMENTS AND INSTRUMENTS MODEL PAPER Question paper
M050
MODEL PAPER
B.E. DEGREE EXAMINATION.
Fourth Semester
Electronics and Instrumentation Engineering
EI 237 — ELECTRICAL MEASUREMENTS AND INSTRUMENTS
(Common to Instrumentation and Control Engineering)
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 ? 2 = 20 marks)
1. How are smaller currents measured with larger range ammeters?
2. What are the advantages of dynamometer type instruments?
3. What is meant by kVA rating and kVhr rating?
4. How is the creep effect in energy meters avoided?
5. Justify the application of potentiometers in instrumentation.
6. Comment on the effect of change of input frequency on the characteristics of a current transformer.
7. Why are Kelvin’s double bridges used for measuring low resistance?
8. What is the need for calibration of voltmeters?
9. Give the general equation for balance of a.c. bridges.
10. State the principle of Q meters.
PART B — (5 ? 16 = 80 marks)
11. Give the construction and principle of operation of a moving coil ammeter. List their advantages and disadvantages. Explain how measuring range is increased in ammeters. (16)
12. (a) Explain 2–wattmeter method of measuring 3–phase power with a neat circuit and give the vector diagram. (16)
Or
(b) (i) Explain briefly on the full load and low load adjustments of energy meters.
(ii) With a neat figure explain the operation of a single–phase energy meter. (8 + 8)
13. (a) Explain how potentiometers are used to calibrate ammeters and
resistances. Give the principle of operation of a typical a.c. potentiometer
with a neat figure. (16)
Or
(b) (i) Distinguish between operating conditions of a current transformer and potential transformer with regard to materials used, windings, operation and application.
(ii) A PT rated 33 kV/220 V and a CT of 100/5 A are used to measure the voltage and current in a transmission line. If the voltmeter shows 200 V and the ammeter shows 4 A, determine the voltage and current in the line. (12 + 4)
14. (a) Describe Price’s guard wire method of finding a high resistance and state the precautions. (16)
Or
(b) (i) A 4–terminal resistance of approximately 50 ?? is measured by using a Kelvin double bridge with the component resistances as given below :
Standard resistor = 100.03 micro ohm
Inner ratio arms = 100.31 ohm and 200 ohm
Outer ratio arms = 100.24 ohm and 200 ohm
Value of low resistance link = 700 micro ohm
Find the unknown resistance to the nearest of 0.01 ohm.
(ii) Give the constructional details and state the working of a Megger.
(4 + 12)
15. (a) (i) Explain the Maxwell’s bridge method for finding an unknown
inductance.
(ii) Derive the balance condition of a Schering bridge. (8 + 8)
Or
(b) Write briefly on any TWO of the following :
(i) Compensation methods in watt meters
(ii) Bridge configuration to measure mutual inductance
(iii) Measurement of high resistance by loss of charge method. (8 + 8)
———————
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