Free Process Control and Instrumentation MCQs with Answers
254 Process Control and Instrumentation MCQs from Chemical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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254 questions · page 8 of 13
- A. Open
- B. Closed
- C. Either A. or B.
- D. Neither A. nor B.
Explanation: The Bode method plots magnitude and phase of the open-loop loop-transfer function, usually G(s)H(s), to assess closed-loop stability…
Correct answer: Open- A. Has a non-zero slope at the origin
- B. Has a damped oscillatory characteristics
- C. Is overdamped
- D. Is unstable
Explanation: The characteristic equation has natural frequency √3 and damping ratio 1/√3, which is less than 1.
Correct answer: Has a damped oscillatory characteristics- A. 1/(S2 + 2)
- B. 1/(S2 - 2S + 3)
- C. 1/(S2 + 2S + 2)
- D. exp (-20 S)/(S2 + 2S - 1)
Explanation: A continuous system is stable when all poles lie in the left half of the s-plane.
Correct answer: 1/(S2 + 2S + 2)144. What is the dynamic error in a critically damped second order instrument for a ramp input (At) ?
- A. 2 AT
- B. 0.5 AT
- C. √(AT)
- D. 1.5 AT
Explanation: For a critically damped second-order instrument subjected to a ramp input At, the steady dynamic error is twice the instrument time…
Correct answer: 2 AT- A. Chromel-alumel
- B. Iron-constantan
- C. Platinum-rhodium
- D. Platinum-platinum + rhodium
Explanation: An iron-constantan thermocouple, type J, produces approximately 22 mV at 400°C with a 0°C reference.
Correct answer: Iron-constantan- A. 20
- B. -20
- C. 10
- D. -10
Explanation: For an amplitude ratio, decibels are calculated as 20 log₁₀(ratio). Thus 20 log₁₀(0.1) = 20(-1) = −20 dB, with the negative sign…
Correct answer: -20- A. eTS
- B. None of these
- C. 1/(Ts + 1)
- D. e-TS
Explanation: A pure transportation delay T shifts a signal in time without changing its shape, and its Laplace-domain transfer function is e^(−Ts).
Correct answer: e-TS- A. 8, 0.6, 0.08
- B. 12, 0.6, 0.12
- C. 8, 0.6, 0.12
- D. 12, 0.4, 0.08
Explanation: For the conservative largest-error case, each uncertain process parameter is taken at its upper 20% limit: gain 10(1.2) = 12, time…
Correct answer: 12, 0.6, 0.12- A. Oxygen
- B. Carbon dioxide
- C. Oxides of nitrogen
- D. Any of these
Explanation: Paramagnetic gas analysis is suitable for oxygen and nitrogen oxides because they exhibit paramagnetism.
Correct answer: Carbon dioxide- A. (T1S/(T2S + 1)
- B. (T1S + 1)/(T2S + 1)
- C. e-ηS
- D. (T1S + 1)/(T2S
Explanation: A pure time delay has transfer function e^(-τs), whose magnitude remains unity while its phase is -ωτ, becoming more negative linearly…
Correct answer: e-ηS- A. Kilo volts
- B. Micro volts
- C. Volts
- D. Milli volts
Explanation: Thermocouples generate a small thermoelectric voltage, normally measured in millivolts.
Correct answer: Milli volts- A. Differential pressure gage
- B. External float gage
- C. Gage glass
- D. None of these
Explanation: A differential-pressure gauge measures liquid level from the hydrostatic pressure difference between the tank bottom and the vapour space.
Correct answer: Differential pressure gage- A. Zero
- B. Second
- C. First
- D. Third
Explanation: A U-tube manometer contains liquid inertia and restoring action, with damping from flow resistance, so its dynamic model is generally…
Correct answer: Second- A. Polarograph
- B. Photo electric cell
- C. Thermal conductivity meter
- D. Chromatograph
Explanation: Smoke density reduces the intensity of a light beam passing through the flue gas, so a photoelectric cell can detect the resulting change…
Correct answer: Photo electric cell- A. Open
- B. Both A. and B.
- C. Closed
- D. Neither A. nor B.
Explanation: For a feedback system, the characteristic equation is obtained by setting the denominator of the closed-loop transfer function to zero…
Correct answer: Closed156. Measurement of sub-zero Celsius temperature in industry is done most commonly by __________________?
- A. Thermocouples
- B. Bi-metallic thermometers
- C. Gas thermometers
- D. Resistance thermometers
Explanation: Resistance thermometers, especially platinum RTDs, provide accurate and stable measurement over the sub-zero industrial range.
Correct answer: Resistance thermometers- A. < 1
- B. > 1
- C. 1
- D. None of these
Explanation: For a first-order system, the amplitude ratio is 1/√[1+(ωτ)²]. Thus it is less than unity for a sinusoid of nonzero frequency, because the…
Correct answer: < 1- A. Mercury in glass thermometer
- B. Resistance thermometer
- C. Thermocouple
- D. Vapor pressure thermometer
Explanation: A thermocouple provides a continuous electrical temperature signal and is rugged enough for industrial heat-exchanger service.
Correct answer: Thermocouple- A. 250
- B. 500
- C. 750
Explanation: Fibreglass insulation used around thermocouple wires is generally suitable up to about 500°C.
Correct answer: 500- A. All a, b & c
- B. Accuracy (± 1% of span)
- C. Speed of response
- D. Temperature measuring range (- 40°C to 450°C)
Explanation: Industrial bimetallic and mercury-in-glass thermometers can have broadly comparable ranges, accuracy, and response characteristics in…
Correct answer: All a, b & c