Instrumentation Multiple Choice Questions Answers PDF

61. Which one of the following is the most sensitive device ?

(a) Thermocouple
(b) RTD
(c) Thermistor
(d) Pyrometer

62. Which of the following should be incorporated in the RTD to make a temperature sensing bridge most sensitive to temperature?

(a) Platinum.
(b) Nickel.
(c) Thermistor.
(d) Copper.

63. Consider the following statements : The causes of error in the measurement of temperature using a thermistor are

1. Self heating.
2. Poor sensitivity.
3. Non-linear characteristics.

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

64. A fixed resistor of suitable value is usually connected across a thermistor to

(a) decrease its resistance.
(b) increase its sensitivity.
(c) compensate its self-heating effect.
(d) improve linearity.

65. Thermocouples

(a) are most commonly employed for indication of rapidly changing temperature and for use in localized and in otherwise accessible positions.
(b) need reference junction compensation.
(c) have a low output voltage level.
(d) all of the above.

66. The drawbacks of thermocouples are that

(a) they are less accurate than RTDs and thermistors.
(b) they need compensating leads.
(c) reference junction compensation is required in thermo-couples.
(d) all of the above.

67. For a thermocouple pair (A, B) the extension wires (C, D)

(a) should be identical pair elements.
(b) should be identical temperature emf relationship.
(c) can be of any two dissimilar materials.
(d) should have very small temperature emf sensitivity.

68. Which one of the following thermocouples has the highest temperature measuring range ?

(a) Copper-Constantan.
(b) Iron-Constantan.
(c) Alumel-Chromel.
(d) Platinum Rhodium-Platinum.

69. A thermocouple arrangement is to be used to measure temperature in the range of 700 – 800°C. Point out the pair that would be most suitable for this application.

(a) Copper-constantan.
(b) Iron-constantan.
(c) Chromel-alumel.
(d) Platinum-platinum rhodium.

70. For surface temperature measurement one can use

(a) strain gauge.
(b) diaphragm.
(c) RTD.
(d) thermocouple.

71. What is a differential transformer?

(a) Constant pressure transducer.
(b) Variable pressure transducer.
(c) Constant displacement transducer.
(d) Variable inductance transducer.

72. Inductive transducers are employed in differential configurations because differential outputs are less affected by

(a) external magnetic fields.
(b) temperature variations.
(c) variations of bridge supply voltage and frequency.
(d) all of the above.

73. LVDT can be used for

(a) vibration measurement.
(b) angular velocity measurement.
(c) force measurement in a beam.
(d) load measurement on a column.

74. The principle of operation of LVDT is based on variation of

(a) self-inductance.
(b) mutual inductance.
(c) reluctance.
(d) permeance.

75. LVDT has following advantage(s)

(a) infinite resolution, high sensitivity and very high output.
(b) low hysteresis, good repeatability and capability of tolerating shock and vibrations.
(c) good dynamic response.
(d) both (a) and (b).

76. Consider the following statements about LVDT as a transducer.

1. The relationship between input displacement and output voltage is almost linear.
2. The range of displacement that can be measured is wide.
3. It does not form a loading on the mechanical system.

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

77. A linear variable differential transformer (LVDT) has

1. One primary winding.
2. two exactly similarly secondary windings.
3. A toroidal magnetic core.

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

78. In an LVDT, there are two secondary coils which are connected for a single output. Which one of the following is correct ?

(a) The coils are in series and in phase opposition.
(b) The coils are in parallel and in phase opposition.
(c) The coils are in series and in the same phase condition.
(d) The coils are in parallel and in the same phase condition.

79. In a LVDT, the two secondary voltages

(a) are independent of the core position.
(b) vary unequally depending on the core position.
(c) vary equally depending on the core position.
(d) are always in phase quadrature.

80. Sensitivity of LVDT is mainly due to

(a) magnetic shielding of the core.
(b) permeability of the core.
(c) exact cancellation of secondary voltages.
(d) insulation used in the winding.

81. In an LVDT, the output quantity

(a) is algebraically summed to zero.
(b) is difference of the two currents flowing in the two secondaries.
(c) depends upon its rating.
(d) none of the above.

82. For applications requiring large torques and high accuracies we use

(a) torque transmission type servosystems.
(b) control or error detecting type synchros.
(c) either (a) or (b).
(d) none of the above.

83. Consider the following statements regarding constructional features of synchros :

1. Synchro repeater has a three phase stator and a three phase rotor.
2. Disc shaped rotor of the synchro control transformer offers a low resistance to the magnetic path.
3. Synchro transmitter has a frictionless bearing.

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

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