Multiple Choice Questions and Answers on Process Control and Instrumentation

1. The temperature of tempering oil baths maintained at 400°C during heat treatment of steel is measured by a/an __________ thermocouple.

a) chromel-alumel

b) iron-constantan

c) platinum-platinum/rhodium

d) none of these.

Answer: iron-constantan

2. Flapper nozzle is used in a/an __________ controller.

a) electronic

b) hydraulic

c) pneumatic

d) none of these

Answer: pneumatic

3. The __________ of a vapor pressure thermometer is a functioning element.

a) pointer

b) bourdon tube

c) bulb

d) none of these

Answer: pointer

4. A negative gain margin expressed in decibels means a/an __________ system.

a) stable

b) unstable

c) critically damped

d) none of these

Answer: unstable

5. Temperature measuring instruments are standardised mostly with __________ points of pure substances.

a) melting

b) boiling

c) both (a) & (b)

c) neither (a) nor (b)

Answer: both (a) & (b)

6. Response of a system to a sinusoidal input is called __________ response.

a) impluse

b) unit step

c) frequency

d) none of these

Answer: frequency

7. Dilute wine was used as a thermometric liquid initially to develop temperature scale. First emperical temperature scale developed was the __________ scale.

a) Kelvin

b) Centigrade

c) Fahrenheit

d) Reaumer

Answer: Fahrenheit

8. The maximum service temperature for fibre glass used as thermocouple wire insulation material is __________ °C.

a) 250

b) 500

c) 750

d) 1000

Answer: 500

9. In a shell and tube heat exchanger, the flow rate of heating/cooling fluid is the __________ variable.

a) load

b) controlled

c) manipulated

d) none of these

Answer: manipulated

10. Volumetric expansion is the working principle of the __________ thermometers.

a) mercury in glass

b) constant volume gas

c) vapor pressure

d) bimetallic

Answer: mercury in glass

11. Zirconia probe is used for the continuous measurment of __________ flue gases going out of the furnace.

a) oxygen in

b) carbon dioxide in

c) carbon monoxide in

d) temperature of

Answer: oxygen in

12. Strain gage pressure transducers are used to measure __________ pressures.

a) gage as well as vacuum

b) absolute as well as differential

c) both (a) and (b)

d) neither (a) nor (b)

Answer: both (a) and (b)

13. Compositional analysis of __________ is done using mass spectrometer.

a) an isotope

b) natural gas

c) a solid

d) an alloy

Answer: an isotope

14. The __________ of a vapor pressure thermometer is a secondary element.

a) pointer

b) Bourdon tube

c) bulb

d) none ofthese

Answer: Bourdon tube

15. __________ is undesirable in thermocouples used in industries,

a) Linear relation of emf to temperature

b) Corrosion resistance

c) Oxidation resistance

d) Non-linear relation of emf to temperature

Answer: Non-linear relation of emf to temperature

16. For an input forcing function, X(t) = 2t^2, the Laplace transform of this function is

a) 2/s2

b) 4/s2

c) 2/s3

d) 4/s3

Answer: 4/s3

17. In a single tank system, the transfer function of level to inlet flow rate is

a) R/TS

b) R/(TS + 1)

c) l(TS + l)

d) 1/TS

Answer: R/(TS + 1)

18. Typical specifications for design stipulates the gain margin and phase margin to be respectively

a) > 1.7 and > 30°

b) < 1.7 and > 30°

c) < 1.7 and < 30°

d) > 1.7 and < 30°

Answer: > 1.7 and > 30°

19. Which of the following is not the triple point of water ?

a) 32°R

b) 273°K

c) 492°R

d) 32°F

Answer: 32°R

 

20. Pick out the one which is a first order instrument.

a) Mercury in glass thermometer (without any covering or air gap).

b) Bare metallic thermometer.

c) Bare vapor pressure thermometer.

d) All of the above 

Answer: All of the above 

21. Load cells are used for the measurement of

a) stress

b) weight

c) strain

d) velocity

Answer: weight

22. Pick out the wrong statement.

a) O2, NO and NO2 exhibit paramagnetic properties as a result of unpaired electrons.

b) CO2 is the strongest paramagnetic gas.

c) Paramagnetic susceptibility of gases decreases with temperature.

d) Paramagnetic susceptibility of gases permits the measurement of their concentration.

Answer: CO2 is the strongest paramagnetic gas.

23. Which of the following is the dynamic characteristics of an instrument ?

a) Reproducibility

b) Sensitivity

c) Dead zone

d) Fidelity

Answer: Fidelity

24. Which of the following is an undesirable dynamic characteristic of an instrument ?

a) Reproducibility

b) Dead zone

c) Time lag

d) Static error

Answer: Time lag

25. Thermistor, which has high temperature co-efficient of resistivity, is used as the sensing element in resistance thermometer. It is a/an

a) insulator

b) conductor

c) solid semi-conductor

d) liquid semi-conductor

Answer: solid semi-conductor

26. Which of the following is a desirable characteristic of an instrument ?

a) High drift

b) High fidelity

c) High measuring lag

d) Poor reproducibility

Answer: High fidelity

27. The operation of a rotameter is based on

a) variable flow area.

b) rotation of a turbine.

c) pressure drop across a nozzle.

d) pressure at a stagnation point.

Answer: variable flow area.

28. Which of the following temperature measuring instruments need not touch the object whose temperature is being measured ?

a) Radiation/infrared pyrometer

b) Filled system thermometer

c) Mercury in glass thermometer

d) Thermo electric pyrometer

Answer: Radiation/infrared pyrometer

29. Thermal conductivity measurement com-prises the working principle of a

a) CO2 analyser

b) polarimeter

c) spectrometer

d) chromatograph

Answer: CO2 analyser

30. Working principle of radiation pyrometer is based on the

a) Wien's law

b) Kirchoffs law

c) Stafan-Boltzman law

d) Seebeck effect

Answer: Stafan-Boltzman law

31. Which of the following relates the emf. generated in a single homogeneous wire to the temperature difference ?

a) Peltier effect

b) Thomson effect

c) Seebeck effect

d) none of these

Answer: Thomson effect

32. Instrumentation in a plant offers the advantage of

a) greater safety of operation

b) better quality of product

c) greater operation economy

d) All of the above 

Answer: All of the above 

33. The closed loop pole of a stable second order system could be

a) both real and positive.

b) complex conjugate with positive real parts.

c) both real and negative.

d) one real positive and the other real negative.

Answer: both real and negative.

 

34. moke density of the flue gas going out of the chimney is measured by a

a) polarograph

b) thermal conductivity meter

c) photo electric cell

d) chromatograph

Answer: photo electric cell

 

35. Transfer function of transportation lag is

a) eTS

b) e-TS

c) e

d) none of these

Answer: e-TS

36. Pick out the first order system from among the following.

a) Damped vibrator.

b) Mercury in glass thermometer kept in boiling water.

c) Interacting system of two tanks in series.

d) Non-interacting system of two tanks in series.

Answer: Mercury in glass thermometer kept in boiling water.

37. Which of the following controllers has the least maximum deviation ?

a) P-controller

b) P-I controller

c) P-I-D controller

d) P-D controller

Answer: P-D controller

38. The function of a transducer is to

a) modify the input signal.

b) amplify the input signal.

c) convert the primary signal into a more useful quantity, usually an electric impulse.

d) codify/decodify the input signal.

Answer: convert the primary signal into a more useful quantity, usually an electric impulse.

 

39. Nichol's chart deals with

a) A.R. vs. phase lag of first order.

b) A.R. vs. phase lag of second order.

c) closed loop values vs. open loop values.

d) frequency response values of controllers.

Answer: closed loop values vs. open loop values.

40. Which of the following thermocouples will give the highest output for the same value of hot and cold junction temperature ?

a) Platinum-platinum + rhodium.

b) Iron-constantan.

c) Chromel-constantan.

d) All will give the same output.

Answer: Chromel-constantan.

41. A proportional controller with a gain of Kc is used to control a first order process. The offset will increase, if

a) Kc is reduced.

b) Kc is increased.

c) integral control action is introduced.

d) derivative control action is introduced.

Answer: Kc is reduced.

42. Select the correct statement from the following.

a) The frequency response of a pure capacity process is unbounded.

b) The phase lag of a pure time delay system decreases with increasing frequency.

c) The amplitude ratio of a pure capacity process is inversely proportional to frequency.

d) The amplitude ratio of a pure time delay system increases with frequency.

Answer: The amplitude ratio of a pure capacity process is inversely proportional to frequency.

43. Which of the following measurements can be made by the measurement of emf ?

a) pH value

b) Degree of hydrolysis

c) Composition of complex ions

d) All of the above 

Answer: All of the above

44. Emf developed by a thermocouple, while measuring a temperature of 600°C is about 5.5 mV. The type of thermocouple used is

a) chromel-alumel

b) iron-constantan

c) platinum-platinum+rhodium

d) All of the above

Answer: platinum-platinum+rhodium

45. Which of the following relates the absorption & evolution of heat at the junctions of a thermocouple to the current flow in the circuit?

a) Seebeck effect

b) Peltier effect

c) Joule heating effect

d) Thomson effect

Answer: Peltier effect

46. A magnetic flowmeter is

a) based on the principle of Faraday's law.

b) capable of measuring the flow rate of slurries and electrolytes.

c) based on the linear relationship between the fluid flow rate and the induced voltage.

d) All of the above

Answer: All of the above

47. Continuous shell temperature measurement in a liquid-liquid heat exchanger is done by a

a) thermocouple

b) reistance thermometer

c) mercury in glass thermometer

d) vapor pressure thermometer

Answer: thermocouple

48. A non-linear chemical system is exemplified by a/an

a) isothermal CSTR

b) mixer

c) non-isothermal CSTR

d) none of these

Answer: non-isothermal CSTR

49. Gas chromatography is used for the measurement of

a) temperature

b) pressure

c) concentration

d) flow rate

Answer: concentration

50. Which of the following thermocouples can measure the maximum temperature ?

a) Platinum-rhodium

b) Tungsten-molybdenum

c) Chromel-alumel

d) Iron-constantan

Answer: Tungsten-molybdenum