Instrumentation Multiple Choice Questions Answers

41. Which one of the following is the main reason for insertion of two strain gauges in the adjacent arms of a bridge circuit ?

(a) Achievement of higher sensitivity.
(b) Elimination of radio-frequency interference.
(c) Elimination of effect of environmental temperature.
(d) To facilitate quick balancing of the bridge.

42. Why is strain gauge bridge sometimes excited with ac ?

(a) It has a stable performance with ac.
(b) Its sensitivity is more with ac.
(c) Power frequency pick-up can be avoided with ac.
(d) AC output can be easily amplified.

43. A load cell is an electromechanical device and is widely used for measurement of

(a) static forces.
(b) dynamic forces.
(c) both static and dynamic forces.
(d) temperature.

44. The factors to be considered in the selection of a load cell for a particular application are

(a) type of loading-tensile or compressive.
(b) required accuracy, loading conditions, environment, space available, scale capacity.
(c) desired output characteristics and number of cells required.
(d) all of the above.

45. Which of the following is not an element of electropneumatic pressure transmitter?

(a) LVDT.
(b) Bellows.
(c) Flapper-nozzle mechanism.
(d) Op-amp.

46. Which of the following transducers can be used for measurement of pressures as high as 100,000 atmosphere.

(a) Mcleod gauge.
(b) Pirani gauge.
(c) Bridgman gauge.
(d) Knudsen gauge.

47. The operation of Pirani gauge depends upon the

(a) variation of the thermal conductivity of a gas with the change in pressure.
(b) variation of the electrical conductivity of a gas with the change in pressure.
(c) variation in humidity of the medium with the change in pressure.
(d) none of the above.

48. Thermal conductivity gauges have the following shortcomings

(a) these gauges need individual calibration and frequent checking.
(b) these gauges burn out when exposed to atmospheric pressure during operation.
(c) these gauges get easily damaged by organic vapors.
(d) all of the above.

49. The working principle of a pirani gauge pressure transducer is based on which one of the following ?

(a) Humidity of the medium.
(b) Thermal conductivity of the medium.
(c) Combustibility of the medium.
(d) Electrical resistivity of the medium.

50. The ionization vacuum gauge, in construction, is similar to a

(a) vacuum diode.
(b) vacuum triode.
(c) thyratron.
(d) none of these.

51. The advantages of ionization vacuum gauges are

(a) linearity.
(b) interchangeability.
(c) that these can be used for measurement of vacuum pressure below 10^-10 torr.
(d) both (a) and (b).

52. Pick the odd one out

(a) Pirani gauge.
(b) Thermocouple gauge.
(c) Meleod gauge.
(d) Resistance-wire strain gauge.

53. Which one of the following statements is not correct ?

(a) Vacuum can act as a dielectric material.
(b) Piezoelectric materials can act as transducers.
(c) Quartz crystal is a ferroelectric material.
(d) The dielectric constant of dielectrics depends on the frequency of the applied field.

54. Which one of the following pressure transducers is suitable for measurement of high pressure ?

(a) Alphatron.
(b) Mcleod gauge.
(c) Pirani gauge.
(d) Bourdon gauge.

55. In strain gauge torque transducers, the strain gauges are mounted at which one of the following ?

(a) 0° to the shaft axis.
(b) 45° to the shaft axis.
(c) 90° to the shaft axis.
(d) at any angle with the shaft axis.

56. Which of the following can be used/modified for measurement of angular speed ?

1. LVDT. 2. Magnetic pick-up. 3. Tachogenerator. 4. Strain gauge.

Select the correct answer using the code given below :
(a) Only 1 and 2.
(b) Only 2 and 3.
(c) Only 3.
(d) Only 2, 3 and 4.

57. The generated emf of a dc tachogenerator is

(a) directly proportional to angular speed.
(b) inversely proportional to angular speed.
(c) proportional to square root of angular speed.
(d) proportional to square of angular speed.

58. AC tachometers are often built with thin metallic drag-cup rotor to

(a) reduce inertia.
(b) obtain low Q.
(c) make them suitable for high frequency (400 Hz) operation.

59. The commercial thermopiles arc formed by

(a) Series of Si-Al thermocouples in an IC by doping Al layers on p-type Si on n-type Si epitaxial layers.
(b) Series of Cu-W thermocouple strips.
(c) Piezoelectric material strips piled together.
(d) Series of bismuth-telluride couples.

60. In optical pyrometers temperature is measured by

(a) thermocouple effect.
(b) photocell principle.
(c) comparison of brightness of the source with that of a standard source.
(d) none of the above.