Free Process Control and Instrumentation MCQs with Answers

• A. Polarimeter
• B. CO2 analyser
• C. Spectrometer
• D. Chromatograph

Explanation: A thermal-conductivity gas analyser infers composition from the change in heat conduction of the gas mixture, and it is commonly used for…

• A. Radiation pyrometer
• B. Optical pyrometer
• C. Resistance pyrometer
• D. Infra red pyrometer

Explanation: A resistance pyrometer is a contact instrument because its sensing element must be placed in contact with the body whose temperature is…

• A. Mercury in glass thermometer with covering
• B. None of these
• C. Pressure gauge with one bellow, two tubes and a tank
• D. Bare mercury in glass thermometer

Explanation: A bare mercury-in-glass thermometer is normally treated as a first-order instrument, since its bulb temperature follows the surroundings…

• A. Very high pressure
• B. High vacuum
• C. Liquid level under pressure
• D. Liquid level at atmospheric pressure

Explanation: A Pirani gauge measures very low pressures by relating the heat loss from a heated filament to the gas pressure, so it is used for…

• A. Humidity of air
• B. % CO2 in flue gas
• C. % O2 in flue gas
• D. Speed of a submarine

Explanation: A zirconia probe develops an electrochemical voltage related to the difference in oxygen partial pressure, so it is used to determine…

• A. Vapor pressure
• B. Constant volume gas
• C. Mercury in glass
• D. Bimetallic

Explanation: A mercury-in-glass thermometer works because mercury expands in volume when heated and rises through a calibrated capillary.

• A. Transportation lag
• B. None of these
• C. Second order system
• D. First order system

Explanation: For a first-order system, the sinusoidal amplitude ratio is 1 divided by the square root of 1 plus the squared frequency time constant, so…

• A. Mcleod
• B. Pirani
• C. Ionisation
• D. None of these

Explanation: A pressure of 0.01 psi absolute is about 0.52 mmHg, which lies in the low-pressure range commonly measured by a McLeod gauge.

• A. Melting
• B. Both A. & B.
• C. Boiling
• D. Neither A. nor B.

Explanation: Temperature instruments are commonly calibrated against reproducible fixed points such as the melting or freezing point and the boiling…

• A. Sling psychrometer
• B. Hair-hygrometer
• C. Weighing
• D. High resistance Wheatstone bridge circuit

Explanation: In continuous paper-moisture measurement, water changes the electrical resistance of the paper, and a high-resistance Wheatstone bridge…

• A. CO2 percentage in the flue gas
• B. Specific gravity of petrofuels
• C. Composition of an alloy
• D. O2 percentage in the flue gas

Explanation: Carbon dioxide has a thermal conductivity sufficiently different from the major gases in flue gas for a thermal-conductivity analyser to…

• A. Electronic
• B. Pneumatic
• C. Hydraulic
• D. None of these

Explanation: A flapper-nozzle arrangement converts a mechanical displacement into a pneumatic pressure signal, forming the basic transmitter or…

• A. Dead zone
• B. Drift
• C. Static error
• D. None of these

Explanation: Static error is the difference between the true value and the value indicated by an instrument under steady conditions, so it directly…

• A. P
• B. PD
• C. PID
• D. PI

Explanation: A PI controller generally has the longest settling or stabilising time because integral action removes offset but can make the response…

• A. Optical pyrometer
• B. Mercury in glass thermometer
• C. Iron-constantan thermocouple
• D. Alcohol filled thermometer

Explanation: An optical pyrometer estimates temperature from thermal radiation and is generally less accurate than direct-contact thermometers over…

• A. High drift
• B. High fidelity
• C. High measuring lag
• D. Poor reproducibility

Explanation: High fidelity means an instrument reproduces the input signal accurately in magnitude and form, making it a desirable characteristic.

• A. Under damped
• B. None of the above
• C. Over damped
• D. Critically damped

Explanation: Two identical non-interacting tanks in series give a denominator proportional to (τs + 1)², which has two equal real poles.

• A. 1/(s2 + 2)
• B. 1/(s2 - 2s + 3)
• C. 1/(s2 + 2s + 2)
• D. exp (-20s)/(s2 + 2s - 1)

Explanation: A system is stable when all poles lie in the left half of the s-plane. For option c, s² + 2s + 2 = 0 gives poles -1 ± j, whereas the other…

• A. Determining water purity
• B. Solids and metal analysis
• C. Determination of CO2 in gases
• D. NOx determination

Explanation: Emission spectroscopy identifies elements from the characteristic wavelengths emitted by excited atoms, so it is widely used for elemental…

• A. 800
• B. 400
• C. 1200
• D. 1500

Explanation: Optical radiation pyrometers are used for high-temperature measurement and typically begin operating at about 800°C.