This set of Process Control Multiple Choice Questions & Answers (MCQs) focuses on “Use and Working Principles of Instruments – 2”.
1. Which of the following instrument is used to measure the amount of water vapour in air?
a) Strain gauge
b) Manometer
c) Thermocouple
d) Hygrometer
View Answer
Explanation: Strain gauge and manometer are used to measure the pressure. Thermocouple is also used to measure temperature. Hygrometer is used to measure the amount of water vapour in air.
2. Which of the following instrument is used to measure the composition of miscible liquid?
a) Interferometer
b) Manometer
c) Conductivity cells
d) Hygrometer
View Answer
Explanation: Manometer is used to measure the pressure. Conductivity cells is also used to measure conductivity. Hygrometer is used to measure the amount of water vapour in air. Interferometer is used to measure the composition of miscible liquid.
3. Which of the following instrument is used to measure viscosity of a liquid?
a) Interferometer
b) Rheometer
c) Conductivity cells
d) Hygrometer
View Answer
Explanation: Rheometer is used to measure the viscosity of a liquid. Conductivity cells is also used to measure conductivity. Hygrometer is used to measure the amount of water vapour in air. Interferometer is used to measure the composition of miscible liquid.
4. Which of the following process variable is measured by differential pressure sensor?
a) Liquid level
b) Weight
c) Conductivity
d) Flow
View Answer
Explanation: Load cells effectively measure weight. Conductivity is measure by conductivity probe. Flow is measured by venturi meter/orifice meter. Liquid level is measured by differential pressure sensor.
5. Which of the following principle is used by thermocouple to measure temperature?
a) Maxwell effect
b) Peltier effect
c) Seeback effect
d) Holick effect
View Answer
Explanation: Seeback effect i.e., thermoelectric effect is the conversion of temperature differences to electric voltage and vice versa via a thermocouple. That means the temperature difference causes a voltage difference which is measured.
6. Which of the following instrument is used to convert displacement to voltage?
a) Mcleod gauge
b) Linear variable differential transformer
c) Thermocouple
d) RTD
View Answer
Explanation: Mcleod gauge measures vacuum pressure. RTD and thermocouple are used to measure temperature. Linear variable differential transformer or LVDT is used to convert displacement to voltage.
7. Which of the following instrument is used to measure flow?
a) Manometer
b) Linear variable differential transformer (LVDT)
c) Turbine meter
d) RTD
View Answer
Explanation: Manometer is used to measure pressure. LVDT is used to convert displacement to voltage. RTD is used to measure temperature. Turbine meter is used to measure flow.
8. What is the unit of conductivity used in fermenters or bioreactor?
a) Psi
b) μS
c) gram/Litre
d) m/s
View Answer
Explanation: Psi i.e., pound per square inch is the unit of pressure. g/L is the unit of density. m/s is the unit of velocity of fluid. μS or micro siemens is the unit of conductivity.
9. Which of the following statement is true for equal percentage valve?
a) If the valve position is opened from 10% to 20% and then 20% to 30%, the flowrate will also increase from 10LPM to 15LPM and then from 15LPM to 22.5 LPM
b) If the valve position is opened from 10% to 20% and then 20% to 30%, the flowrate will also increase from 10LPM to 20LPM and then from 20LPM to 30LPM
c) If the valve position is opened from 10% to 20% and then 20% to 30%, the flowrate will also increase from 10LPM to 15LPM and then from 15LPM to 20LPM
d) If the valve position is opened from 10% to 20% and then 20% to 30%, the flowrate will also increase from 10LPM to 25LPM and then from 25LPM to 50LPM
View Answer
Explanation: For an equal percentage valve, the percentage opening has increases from 10% to 20% i.e., the opening has increased by 10%, so has the flowrate changed from 10LPM to 15LPM i.e., 50%. Hence, if the opening now is increased from 20% to 30% i.e., extra 10%, the flow rate will get increased by 50% of 15LPM i.e., 22.5LPM.
10. What type of valve is preferred in an exothermic reactor for the coolant supply?
a) Pneumatic, air to open
b) Pneumatic, air to close
c) Globe control valve
d) Manual diaphragm angle seat valve
View Answer
Explanation: In case of any problem of a valve, we would like to fail the valve in safe position. In case of exothermic reaction with jacket cooling supply if the valve fails in close condition, then the reactor temperature will go on increases resulting in runaway reaction. Hence if it is air to close valve, even if the valve fails in event of loss of air pressure, the coolant supply will be maintained and the safety of the reactor can be ensured.
11. What is the normal air pressure required for pneumatic control valve?
a) 6-7 bar(g)
b) 100-200 bar(g)
c) Vacuum
d) Atmospheric pressure i.e., 0 bar(g)
View Answer
Explanation: For pneumatic valves to operate, a minimum of 6-7 bar(g) pressure is required. It is not possible to run the valve in vacuum or even in atmospheric pressure.
12. What type of valve is shown in the graph marked by ‘X’?
a) Cube root
b) Linear
c) Equal percentage
d) Quick opening
View Answer
Explanation: It is clear from the graph that with the percentage opening increasing slightly, the flow rate is increasing quickly. Hence the valve marked by ‘X’ will be quick opening.
13. What type of energy is converted in a thermocouple?
a) Electric to thermal
b) Thermal to electric
c) Thermal to pressure
d) Pressure o electric
View Answer
Explanation: In case of thermocouple, the temperature is sensed and the difference in temperature creates an electric signal. This electric signal is then sent to SCADA in form of 4-20 mA when is it then converted to the reading of the corresponding temperature. Thus, in a thermocouple thermal energy is converted to electric energy.
Sanfoundry Global Education & Learning Series – Process Control.
To practice all areas of Process Control, here is complete set of Multiple Choice Questions and Answers.
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