# Mumbai University Previous year question papers

## Electronic and Electrical Measuring Instruments and Machine

N.B. (1) Question No.1 is ‘compulsory.

(2) Answer any four out of remaining six questions

(3) Assumesuitable datawherever required and state clearly.

(4) Answers to the questions should be grouped and written together.

1. (a) Explain the necessity of Controlling torgue in an indicating instrument.

(b) What ‘is back emf? Explain the significance of back emf.

(c) What is the necessity of a starter in a d.c. motor? 5

(d) What happens if the secondary of current transformer is open Circuited while the primary carries valid current.

2. (a) Explain different methods for the speed controi of d.c. motor? 10

(b) A dc shunt motor drives a centrifugal pump whose torque varies as the square of the speed. The motor is fed from a 200V supply and takes 50A when running at 1000 rpm. What resistance must be inserted in the armature circuit in order to reduce the speed to 800 rpm? The armature and the field resistance of the motor are 0.1Q and 100 Q respectively.

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3. (a) Draw and explain the torCjue slip characteristics of a 3-phase Induction Motor? 10

.(b) A50 Hz, 8 pole-Induction motor has Full load slip of 4%. The rotor resistance/phase is 0.01 Q and stand still reactance/phase is 0.1 Q. Find the ratio of maximum full load torque and the speed at which maximum torque occurs. .,

4. (a) With a neat s~etch explain the construction and workingof a single phase inductiontype energymeter and show that the total .number of revolutions made by the disc during a particular time is proportional to the energy consumed.

(b) What are the essential requirements of indicating type instruments? Explain each of them.

5. (a) Explain the working and principal of a D.C. potentiometer with a neat sketch and state the meaning of standardization?

.(b). Explain with the help of neat diagram the working of Anderson Bridge. Drawthe phasor diagram at the balance condition of the bridge?

6.(a) Describe the working principle of an Induction type Wattmeter and with a neat sketch explain the  construction of this instrument?

(b) Explain the construction and principle of anyone type of Stepper Motor?

7. Write short notes on (any three)

(a) PMMCinstruments

(b) Paramagnetism and Ferromagnetism

(c) Extension of range for Voltmeters arid Ammeters

(d) CT and P.T.