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 10 of 13
- A. Triple point of hydrogen and freezing point of antimony
- B. 13.81°K to 903.9°K
- C. Neither A. nor B.
- D. Both A. and B.
Explanation: The standard platinum resistance thermometer range extends from the triple point of hydrogen, 13.81 K, to the freezing point of antimony…
Correct answer: Both A. and B.- A. Critically damped
- B. Overdamped
- C. Underdamped
- D. Highly fluctuating
Explanation: A damping ratio of unity means the two characteristic roots coincide on the negative real axis, giving the fastest response without…
Correct answer: Critically damped- A. Flow rates of granular solids
- B. Flow rates of fluids
- C. Very high temperature
- D. Thermal conductivity of gases
Explanation: A hot-wire anemometer measures fluid velocity by detecting the cooling of a heated wire, and the velocity can be converted into flow rate.
Correct answer: Flow rates of fluids- A. Platinum-platinum + rhodium
- B. Iron-constantan
- C. Chromel-alumel
- D. None of these
Explanation: A chromel-alumel thermocouple, also called Type K, develops roughly 31 to 33 mV at 800°C when referenced to 0°C.
Correct answer: Chromel-alumel- A. Lead
- B. Nickel
- C. Copper
- D. 30% iron + 70% nickel
Explanation: Lead is not normally used as the sensing element of an industrial resistance thermometer because its resistance-temperature…
Correct answer: Lead- A. Chromel-alumel thermocouple
- B. Optical pyrometer
- C. Radiation pyrometer
- D. Either B. or C.
Explanation: Molten iron and slag are too hot for ordinary contact thermometers, so non-contact optical or radiation pyrometers are used.
Correct answer: Either B. or C.- A. Decibel = 20 loge (AR)
- B. Decibel = 20 log10 (AR)
- C. Decibel = 20 log10 (AR)0.5
- D. Decibel = 20 loge (AR)0.5
Explanation: For an amplitude ratio, the decibel value is defined as 20 times the base-10 logarithm of the ratio: dB = 20 log10(AR).
Correct answer: Decibel = 20 log10 (AR)- A. 12
- B. 36
- C. 54
- D. 68
Explanation: Invar is an iron-nickel alloy containing approximately 36% nickel, which gives it an exceptionally low coefficient of thermal expansion.
Correct answer: 36- A. Liquid level under pressure
- B. Frequency of light
- C. Depression of freezing point
- D. Rpm of a flywheel
Explanation: A stroboscope makes a rotating object appear stationary when the flashing frequency matches its rotational frequency, allowing its rpm to…
Correct answer: Rpm of a flywheel- A. Servo problem
- B. Transient response
- C. Frequency response
- D. Regulator problem
Explanation: A control response caused by a change in set point is called a servo problem or servo response.
Correct answer: Servo problem- A. Thermal conductivity cell
- B. Hot wire anemometer
- C. Polarograph
- D. Mass spectrometer
Explanation: A hot-wire anemometer measures fluid velocity or flow, not composition.
Correct answer: Hot wire anemometer- A. No change
- B. Decrease
- C. Exponential decrease
- D. Increase
Explanation: Resistance follows R = ρL/A, so stretching increases the wire length while reducing its cross-sectional area.
Correct answer: Increase- A. Polarimeter
- B. Polarograph
- C. Dilatometer
- D. Refractometer
Explanation: A polarimeter measures the rotation of plane-polarised light caused by an optically active solution.
Correct answer: Polarimeter- A. Platinum-rhodium
- B. Tungsten-molybdenum
- C. Chromel-alumel
- D. Iron-constantan
Explanation: Tungsten-molybdenum thermocouples withstand higher temperatures than platinum-rhodium, chromel-alumel, and iron-constantan types.
Correct answer: Tungsten-molybdenum- A. Of cold junction only
- B. Of hot junction only
- C. Difference between hot and cold junctions
- D. Difference between cold junction and atmospheric temperature
Explanation: Thermocouple emf is produced by the temperature difference between its hot and cold junctions, with the exact relation being nonlinear.
Correct answer: Difference between hot and cold junctions- A. Mercury in glass thermometer
- B. Mercury in steel thermometer
- C. Fused metal (Na or K) in steel thermometer
- D. Alcohol in glass thermometer
Explanation: Alcohol remains liquid at much lower temperatures than mercury, so an alcohol-in-glass thermometer is used for low-temperature…
Correct answer: Alcohol in glass thermometer- A. Mercury
- B. Water
- C. Methyl alcohol
- D. Carbon-tetrachloride
Explanation: Among the listed liquids, mercury has the smallest volumetric expansion coefficient under ordinary thermometer conditions.
Correct answer: Mercury- A. Pitot tube
- B. Magnetic flowmeter
- C. Flow nozzle type flowmeter
- D. Turbine flowmeter
Explanation: A magnetic flowmeter measures conductive-fluid velocity through the voltage induced in the fluid by a magnetic field, so density…
Correct answer: Magnetic flowmeter- A. One cell
- B. No cell
- C. Three cells
- D. Two cells
Explanation: A pH meter uses two electrode systems: a glass measuring electrode and a reference electrode, often assembled as a combined electrode.
Correct answer: Two cells- A. Peltier
- B. Thomson
- C. Seebeck
- D. None of these
Explanation: The Peltier effect is the absorption or release of heat at the junction of two dissimilar conductors when current passes through it.
Correct answer: Peltier