# UPTU Previous Year Exam Papers

# BE 3rd Sem

# Electrical Measurement and Measuring Instrument-2010-11

**Note : (1) Attempt all questions.**

**(2) All questions carry equal marks.**

**1. Attempt any four parts of the following :**

(a) Differentiate between electrical, electronics and mechanical instruments with suitable examples.

(b) What is standard ? Explain different types of standards.

(c) A resistance is measured by the voltmeter-ammeter method. The voltmeter reading is 123.4 V on the 250 V scale and the ammeter reading is 283.5 mA on the 500mA scale. Both meters are guaranteed to be accurate within ±1% of full scale reading. Calculate indicated value of resistance and limits within which the result can be guaranteed.

(d) A dc circuit can be represented by an internal voltage source of 50V with an output resistance of 100 k Q. In order to achieve accuracy better than 99% for voltage measurment across its terminals, calculate the resistance of voltage measuring device.

(e) The meter constant of a 230V, 20A single-phase energy meter is 1800 rev./KWh. The meter makes 200 revolutions in 120 seconds when tested at full load at 0.8 pf lag at the rated voltage. Determine the error in energy meter reading.

(f) A three phase, 400V load has power factor of 0.6 lagging. The two wattmeters read a total power of 20 KW. Find the reading of each wattmeter.

**2. Attempt any two parts of the following : **

(a) Describe the constructional detai Is and working of 3 -phase electrodynamic power factor meter. Describe why phase splitting is not necessary in this case.

(b) What are the different methods of measurement of speed ? Explain the construction and working principle of any one of them.

(c) Enlist the difference between power transformer and instrument transfarmer.

A current transformer with 5 primary turns has a secondary burden consisting of a resistance of 0.16 Q and an inductive reactance of 0.12 O, when the primary current is 200 A, the magnetizing current is 1.5 A and the iron loss current is 0.4A. Find the number of secondary turns needed to make the current ratio 100:1 and the phase angle. balance conditions and draw the phasor diagram under balance conditions.

(b) Describe the working principle of Q-meter with suitable circuit diagram.

The self capacitance of a coil is to be measured by Q-meter. The first measurement result is f=l .5 MHz and (^=550 pf. The second measurement result is f_{2}=3 MHz and new value of tuning capacitor is 110 pf. Find the distributed capacitance and inductance of the coil.

(c) What is three-terminal resistance ? Explain its use. What are the difficulties in measurement of high resistance ? Explain the use of guard circuits.

** 3. Attempt any two parts of the following:**

(a) Describe the construction and working of a co-ordinate type ac potentiometer. How is it standardized ? Explain how an unknown voltage can be measured with it.

(b) Explain ac Wattmeter method for determination of iron loss of test specimen of iron piece.

(c) A flux meter is connected to a search coil of 100 turns and the mean area of the coil is 5 cnr. The search coil is placed at the centre and a standard solenoid 1 .m long uniformly wound with 800 turns. When a current of 5A is reversed, a

deflection of 10 scale divisions is obtained with the fluxmeter. Calculate the calibration constant of the instrument in Wb-tums per division.

**4. Attempt any three parts of the following :**

(a) Describe the construction and working of dual trace CRO with suitable block diagram.

(b) Draw and explain the c ircuit of a ramp type digital voltmeter.

(c) Explain the function ing of a time-base generator in a CRO.

(d) Describe the construction and working of wave analyzers used for audio frequency and megahertz ranges.

(e) Explain briefly with the help of neat diagrams the use of electronic multimeter.