Free Process Control and Instrumentation MCQs with Answers

• A. Low loads
• B. High loads
• C. Temperature changes
• D. Flow rate changes

Explanation: A positioning controller gives an essentially on-off output, making it suitable for switching large or high-capacity loads where fine…

• A. Load
• B. Controlled
• C. Manipulated
• D. None of these

Explanation: The heating or cooling-fluid flow rate is adjusted by the controller to influence shell temperature, so it is the manipulated variable.

• A. d
• B. d2
• C. d3
• D. d4

Explanation: For a diaphragm of fixed material and thickness, deflection strongly depends on diameter and varies approximately with the fourth power of…

• A. Closed loop values vs. open loop values
• B. A.R. vs. phase lag of second order
• C. A.R. vs. phase lag of first order
• D. Frequency response values of controllers

Explanation: A Nichols chart relates open-loop gain and phase to the resulting closed-loop performance, with closed-loop magnitude contours…

• A. Helical
• B. Semi-circular
• C. Circular
• D. Spiral

Explanation: Bourdon tubes are commonly formed as C-shaped, helical, or spiral tubes, while a circular form is not a standard configuration.

• A. Piston type meter
• B. Rotameter
• C. Orifice and tapered plug meter
• D. Magnetic flow meter

Explanation: A magnetic flow meter determines flow from the voltage induced in a conductive fluid, so it does not use a changing flow area.

• A. Introducing integral control
• B. Reducing value of Kc
• C. Introducing derivative control
• D. None of the above

Explanation: Proportional-only control leaves a steady-state offset when a sustained error is needed to produce the required output.

• A. Velocity
• B. Time
• C. (Time)-1
• D. None of these

Explanation: A time constant characterizes how quickly a system responds, and its dimension is time.

• A. Ruth
• B. Mikhailov
• C. Nyquist
• D. None of these

Explanation: The Nyquist stability method assesses closed-loop stability from the frequency response of the open-loop transfer function.

• A. Speed of response
• B. Reproducibility
• C. Fidelity
• D. Static characteristics

Explanation: Fidelity is the ability of an instrument to reproduce changes in the measured variable without dynamic error.

• A. Gold
• B. Antimony
• C. Silver
• D. Nickel

Explanation: An optical pyrometer is generally used above the gold point, approximately 1063°C, where contact thermometers become unsuitable.

• A. Iron-constantan
• B. Platinum-platinum + rhodium
• C. Copper-constantan
• D. Chromel-alumel

Explanation: A platinum-rhodium thermocouple withstands very high temperatures and oxidizing atmospheres, making it suitable near 1600°C.

• A. Product
• B. Reactants
• C. Coolant
• D. None of these

Explanation: For temperature control in an exothermic reactor, coolant flow is commonly manipulated to remove more or less heat and maintain the…

• A. -10 to 20
• B. 400 - 1000
• C. 100 - 500
• D. 0 to 100

Explanation: A hydrogen constant-volume thermometer is commonly used over approximately 0 to 100°C, where hydrogen provides a useful reference gas.

• A. 1/(T2s2 + 2ξTs + 1)
• B. 1/(T2s2 + 2Ts + 1)
• C. 1/(T2s2 + 2ξT + 1)
• D. None of these

Explanation: The standard normalized second-order transfer function is 1/(T²s² + 2ξTs + 1), where T is the time constant and ξ is the damping ratio.

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

Explanation: A mercury-in-glass thermometer gives a local visual reading and cannot conveniently transmit that reading over 60 metres.

• A. < 100
• B. > 0
• C. < 0
• D. > 800

Explanation: Helium gas thermometers are particularly suitable for low-temperature measurements below 0°C because helium remains useful in the…

• A. Bulb
• B. Bourdon tube
• C. Pointer
• D. None of these

Explanation: The bulb is the primary element because it senses temperature directly through the vapor-pressure change.

• A. A metal powder or graphite
• B. Air
• C. Oil
• D. Mercury

Explanation: Air is a poor heat-transfer medium and creates a large thermal resistance between the bulb and thermal well, slowing response.

• A. Alumel
• B. Chromel
• C. None of these
• D. Constantan

Explanation: Alumel and Chromel are nickel-containing alloys, while Constantan is a copper-nickel alloy and also contains nickel.