Process Control and Instrumentation

11. A constant volume gas thermometer employing _________ is used to measure sub-zero (i.e., <0°C) temperature.

  1. Helium
  2. Hydrogen
  3. Nitrogen
  4. None of these

Correct answer: (A)
Helium

12. A control system is unstable, if the open loop frequency response exhibits an amplitude ratio exceeding unity at the crossover frequency. This is _________ criterion.

  1. Bode stability
  2. Nyquist
  3. Routh stability
  4. None of these

Correct answer: (A)
Bode stability

13. A first order system with a time constant of 1 min is subjected to frequency response analysis. At an input frequency of 1 radian/min, the phase shift is

  1. 45°
  2. -90°
  3. -180°
  4. -45°

Correct answer: (D)
-45°

14. A first order system with unity gain and time constant η is subjected to a sinusoidal input of frequency w = 1/η. The amplitude ratio for this system is

  1. 1
  2. 0.5
  3. 1/√2
  4. 0.25

Correct answer: (C)
1/√2

15. A magnetic flowmeter is

  1. Based on the principle of Faraday's law
  2. Capable of measuring the flow rate of slurries and electrolytes
  3. Based on the linear relationship between the fluid flow rate and the induced voltage
  4. All (A), (B) and (C)

Correct answer: (D)
All (A), (B) and (C)

16. A manometer measures the _________ pressure.

  1. Atmospheric
  2. Absolute
  3. Gauge
  4. None of these

Correct answer: (C)
Gauge

17. A mercury barometer measures the _________ pressure.

  1. Atmospheric
  2. Gauge
  3. Vacuum
  4. Absolute

Correct answer: (A)
Atmospheric

18. A mercury thermometer cannot be used to measure the temperature below the freezing point of mercury, which is _________ °C.

  1. -38.9
  2. -11.9
  3. -60.9
  4. -80.9

Correct answer: (A)
-38.9

19. A negative gain margin expressed in decibels means a/an _________ system.

  1. Stable
  2. Unstable
  3. Critically damped
  4. None of these

Correct answer: (B)
Unstable

20. A non-linear chemical system is exemplified by a/an

  1. Isothermal CSTR
  2. Mixer
  3. Non-isothermal CSTR
  4. None of these

Correct answer: (C)
Non-isothermal CSTR

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