Instrumentation Multiple Choice Questions Answers

1. A synchrotransmitter consists of a

(a) salient pole rotor winding excited by an ac supply and a 3-phase balanced rotor winding.
(b) three phase balanced stator winding excited by a three phase balanced ac signal and rotor connected to a dc voltage source.
(c) salient pole, rotor winding excited by a dc signal.
(d) cylindrical rotor winding and a stepped stator excited by pulses.

2. A synchro is used to

(a) accelerate a rotating shaft.
(b) convert an angular position of a shaft into an electrical signal.
(c) convert linear motion into angular position.
(d) amplify low frequency signals.

3. Synchros and resolvers have the following advantages

(a) infinite resolution.
(b) much operating speeds.
(c) high reliability and accuracy.
(d) all of the above.

4. Which of the following statements is NOT true ?

(a) Potentiometric linear displacement can give high output signal.
(b) LVD transformer has low output impedance.
(c) Synchros and resolvers have low accuracy.
(d) Eddy current proximity transducers are non-contact type transducers.

5. Capacitive transducers have the advantages of

(a) very high input impedance, excellent frequency response, high sensitivity, and not being affected by stray magnetic fields.
(b) very high output impedance.
(c) both (a) and (b).
(d) none of the above.

6. The dynamic characteristics of capacitive transducers are similar to those of

(a) low pass filter
(b) high pass filter.
(c) notch filter.
(d) band stop filter.

7. Quartz and Rochelle salt belong to

(a) natural group of piezoelectric materials.
(b) synthetic group of piezoelectric materials.
(c) natural or synthetic group of piezoelectric materials provided they are properly polarized.
(d) none of the above.

8. Which one of the following materials is not used as a piezoelectric transducer?

(a) Rochelle salt.
(b) Lithium sulphate.
(c) Barium titanate
(d) Tungsten oxide.

9. Which of the following are piezoelectric substances ?

1. Barium titanate. 2. Lead titanate. 3. Lead zirconate. 4. Cadmium sulphate.

(a) 1, 2 and 4.
(b) 1, 3 and 4.
(c) 1, 2 and 3.
(d) 2, 3 and 4.

10. Piezoelectric crystals produce an emf

(a) when external mechanical force is applied to it.
(b) when external magnetic field is applied.
(c) when radiant energy stimulates the crystal.
(d) when the junction of two such crystals is heated.

11. Piezoelectric materials owe their property to the

(a) presence of a centre of symmetry.
(b) lack of a centre of symmetry.
(c) presence of axis of symmetry.
(d) lack of axis of symmetry.

12. Consider the following statements : Piezoelectric materials are useful for converting

1. mechanical energy into electrical energy.
2. electrical energy into mechanical energy.
3. mechanical energy into chemical energy.
4. chemical energy into mechanical energy.

Of these statements
(a) 1 and 2 are correct.
(b) 1, 2, 3 and 4 are correct.
(c) 1 alone is correct.
(d) 2, 3 and 4 are correct.

13. Consider the following statements: Piezoelectric materials serve as

1. A source of ultrasonic waves.
2. When electric field is applied, the mechanical dimensions of the substances are not at all altered.
3. Converts electrical energy to mechanical and vice versa.
4. Converts thermal energy to electrical energy.

Which of the above statements is/are correct?
(a) 1 only.
(c) 1 and 3 only.
(b) 2 and 3 only.
(d) 1, 2, 3 and 4.

14. Consider the following statements: Piezoelectric materials

1. Crystal can be shown as electrical equivalent circuit similar to an inductor and a capacitor (Tank circuit).
2. Quartz, Rochelle salt, tourmaline.
3. Used in voltage stabilizers.
4. This exhibits the reverse effect of electrostriction.

Which of the above statements are correct?
(a) 1, 2 and 4 only.
(b) 1 and 2 only.
(c) 2 and 4 only.
(d) 1, 2, 3 and 4.

15. The piezoelectric crystal voltage sensitivity is defined as

(a) Field developed per unit force.
(b) Field developed per unit stress.
(c) Voltage developed per unit stress.
(d) Voltage developed per unit force.

16. Piezoelectric crystal is generally employed for the measurement of which one of the following ?

(a) Flow.
(b) Velocity.
(c) Acceleration.
(d) Temperature.

17. Piezoelectric crystal can be used to measure

(a) static pressure only.
(b) dynamic pressure only.
(c) both static and dynamic pressures.
(d) none of the above.

18. Piezoelectric crystals are used for the measurement of

(a) temperature.
(b) velocity.
(c) sound.
(d) none of the above.

19. Piezoelectric transducers have the following advantage(s).

(a) These are small in size, light in weight and very rugged in construction.
(b) wide operating temperature range.
(c) very good frequency response and quite large output.
(d) all of the above.

20. Hall effect transducers have the drawbacks of

(a) high sensitivity to temperature variations.
(b) variation of Hall coefficient from plate to plate.
(c) poor resolution.
(d) both (a) and (b).