Chemical Engineering Objective Type Questions Instrumentation and Process Control

CHEMICAL ENGINEERING OBJECTIVE TYPE QUESTIONS: A COMPILATION

DR. LEONARDO C. MEDINA, JR. DEAN, COLLEGE OF ENGINEERING LYCEUM OF THE PHILIPPINES UNIVERSITY

INSTRUMENTATION AND PROCESS CONTROL

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1. What is the Laplace transform of sin t ? (a) __1__ (b) __s_____ s² + 1 1 + s² (c) __1 (d) __s_____ s² - 1 s² - 1 2. The transfer function of the first order system is (a) __1 (b) _1_ Ts + 1 Ts (c) ___s__ (d) 1/s Ts + 1 3. 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 4. Response of a system to a sinusoidal input called (a) impulse response (b) unit step response (c) frequency response (d) step response 5. What is the ratio of output amplitude to input amplitude for a sinusoidal forcing function in a first order system ? (a) 1 (b) > 1 (c) < 1 (d) none of these 6. Phase lag of the sinusoidal response of a first order system is (a) 120º (b) 30º (c) 180º (d) 90º 7. Conversion formula for converting amplitude ratio ( AR) into decibels is (a) Decibel=20 log10 (AR) (b) Decibel=20 log e(AR) (c) Decibel=20 log10 (AR)0.5 (d) Decibel = log10 (AR) 8. “A control system is unstable if the open loop frequency response exhibits an amplitude ratio exceeding unity at the cross-over frequency.” This is (a) Bode stability criterion (b) Nyquist criterion (c) Routh stability criterion (d) both b and c Page 2

9. Typical specifications for design stipulates the gain margin and phase margin to be respectively (a) > 1.7 and > 30º (b) < 1.7 and > 30º (c) < 1.7 and < 30º (d) >1.7 and < 30º 10. The frequency at which maximum amplitude ratio is attained is called (a) corner frequency (b) resonant frequency (c) cross-over frequency (d) natural frequency 11. A negative gain margin expressed in decibels means (a) a stable system (b) unstable system (c) critically damped system (d) both a and c 12. Bode diagram is a plot of (a) log (AR) vs. log (f) and Ø vs. log (f) (b) log (AR) vs. f and log Ø vs. f (c)AR vs.log (f) and Ø vs. log (f) (d) log (AR) vs. log f 13. For measuring the temperature of a furnace, which is the most suitable instrument? (a) Platinum resistance thermometer (b) Thermocouple (c) Optical pyrometer (d) Bimetallic thermometer 14. Degree to which an instrument indicates the changes in measured variable without dynamic error is called (a) speed of response (b) reproducibility of instrument (c) fidelity (d) its static characteristics 15. Which of the following is a desirable characteristic of an instrument? (a) high drift (b) high fidelity (c) high temperature lag (d) poor reproducibility 16. Which of the following shows maximum dip affect (indicating reverse direction of temperature change)? (a) mercury thermometer (b) radiation pyrometer (c) bimetallic thermometer (d) thermocouple

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17. Pick out the most suitable instrument for measuring temperature in the range of 40 to 800ºF. (a) mercury thermometer (b) bimetallic thermometer (c) radiation pyrometer (d) radiation pyrometer 18. Thermocouple is suitable for measuring (a) liquid temperatures only (b) very high temperatures only (c) very low temperatures only (d) both high and low temperatures 19. Which of the following relates the absorption and 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 20. Thermal wells are used in temperature measurement to (a) guard against corrosive and oxidizing action on thermocouple materials (b) reduce measuring lag (c) increase the fidelity (d) increase the sensitivity 21. Gas analysis is commonly done using (a) thermal conductivity cell (c) mass spectrometer

(b) X-ray diffraction (d) emission spectrometer

22. Psychrometer determines (a) humidity of gases (c) water of crystallization

(b) moisture content of solids (d) hygroscopic nature of solids

23. Continuous measurement of moisture content of paper in paper industry is done by measuring (a) thermal conductivity through the paper (b) electrical resistance through the paper (c) magnetic susceptibility (d) both b and c 24. Optimal activity of a solution can be determined using a (a) polarimeter (b) polarograph (c) dilatometer (d) refractometer Page 4

25. A simple pitot tube measures (a) average velocity (c) point velocity

(b) maximum velocity (d) static pressure

26. Pirani gauge is used for (a) measurement of very high pressure (c) liquid level under pressure

(b) measurement of high vacuum (d) liquid level at atmospheric pressure

27. A barometer measures (a) absolute pressure (c) both absolute and gauge pressure

(b) gauge pressure (d) dynamic pressure

28. The level of a liquid under pressure can be determined using (a) bubbler system (b) differential pressure manometer (c) diaphragm box system (d) air-trap system 29. Continuous measurement of specific gravity of a liquid is done by (a) hydrometer (b) contact-type electric indicators (c) displacement meter (d) both a and c 30. Hot wire anemometer is used for the measurement of (a) flow rates of fluid (b) flow rates of granular solids (c) very high temperature (d) thermal conductivity of gases 31. Flow rate through an orifice is (a) proportional to the pressure differential (b) inversely proportional to the square root of pressure differential (c) proportional to the square root of pressure differential (d) inversely proportional to the square root of pressure differential 32. Which of the following flow-metering instruments is an area meter? (a) venturi meter (b) rotameter (c) pitot tube (d) hot wire anemometer 33. Continuous measurement of flow rates of dry granular fertilizer is done using (a) velocity meters (b) area-meters (c) weighing meters (d) anemometer

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34. Pick out the symbol for “locally mounted instrument” in instrumentation diagram (a) (b) _ (c) (d) _ _ 35. Which is the symbol _for “pneumatic control valve” (a) (b) _ (c) (d) none of these _ 36. The symbol for “capillary line” in instrumentation diagram is (a) ___ ___ _ ___ _ ___ (b) (c) _________________

(d)

Χ

Χ

Χ

37. Instrumentation in a plant offers the advantage of (a) greater safety of operation (b) better quality of product (c) greater operation economy (d) all a, b and c 38. Dilatometer is used to measure (a) stress (c) deflection

(b) strain (d)contraction/expansion due to changes in temperature

39. Stalagmometer is used for the measurement of (a) kinematic viscosity (b) surface tension (c) refractive index (d) optical activity 40. Stroboscope is used for the measurement of (a) rpm of a flywheel (b) frequency of light (c) depression of freezing point (d) liquid level under pressure 41. Minute depression of freezing point of a liquid solvent or addition of a solid solute can be best measured by (a) Beckman thermometer (b) dilatometer (c) mercury thermometer (d) bimetallic thermometer 42. Gain margin is equal to the (a) amplitude ratio (c) gain in P controller

(b) reciprocal of amplitude ratio (d) gain in P-I controller Page 6

43. Phase margin is equal to (a) 180º - phase lag (c) phase lag + 180º

(b) phase lag - 180º (d) phase lag - 90º

44. A system with a transfer function __2s _ is of 4s + 1 (a) zero order (b) 1st order (c) 2nd order (d) 3rd order 45. Bode stability method uses (a) open loop transfer function (c) either a or b 46. Routh stability method uses (a) open loop transfer function (c) either a or b

(b) closed loop transfer function (d) neither a nor b

(b) closed loop transfer function (d) neither a nor b

47. Nichel’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 value (d) frequency response values of controllers 48. The fluid used in hydraulic controller is (a) water (b) steam (c) air (d) oil 49. Number of poles in a system with transfer function ________1______ s² + 2s² + 1 (a) 2 (b) 5 (c) 3 (d) 1

is

50. Which of the following controllers has maximum offset? (a) P-controller (b) P-I controller (c) P-D controller (d) P-I-D controller

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51. Process degrees of freedom (a) indicates the maximum number of controller to be used (b) indicates the minimum number of controller to be used (c) determines both maximum and minimum number of controllers to be used (d) gives no idea of controllers 52. Resistance of a gas in a vessel is (a) __V__

nRT (c) nRT P

(b) nRT

V (d) __P_

nRT

Where: P =pressure V= volume of the vessel n= number of moles of the gas R= gas constant 52. In an exothermic chemical reactor, the manipulated variable is the flow rate of (a) coolant (b) reactant (c) product (d) hot fluid 53. Use of I-control along with P-control facilitates (a) elimination of offset (c) reduction of stability time

(b) reduction of offset (d) both b and c

54. Which of the following error integral is considered as the best criterion in controller settings? (a) ∫∞ | e | dt (b) ∫∞ | e | dt 0

(c) ∫

∞

0

2

e dt

(d) both a and b

0

55. Cascade control means (a) feed forward control (c) on-off control

(b) more than one feed-back loop (d) one feed-back loop

56. 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

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57. Measurement of pressure in ammonia reactor is done by (a) Bourdon gauge (b) U-tube manometer (c) Inclined tube manometer (d) Pirani gauge 58. Pressure of 0.01 psi (absolute) can be measured by (a) Ionization gauge (b) Pirani gauge (c) Mcleoid gauge (d) Bourdon gauge 59. Continuous measurement of moisture in paper is done by (a) sling psychrometer (b) hair-hygrometer (c) weighing (d) high resistance, Wheatstone’s bridge circuit 60. Pressure of 0.0001 absolute psi can be measured by (a) Meloid gauge (b) Pirani gauge (c) Thermocouple gauge (d) Bourdon gauge 61. E.m.f. generated by thermocouples is of the order of (a) millivolts (b) microvolts (c) volts (d) bi-metallic thermometer 62. Measurement of sub-zero Celsius temperature in industry is done by (a) thermocouples (b) resistance thermometers (c) gas thermometer (d) bi-metallic thermometer 63. Starting temperature of optical radiation pyrometer is (a) 800ºC (b) 400ºC (c) 1200ºC (d) 1500ºC 64. Which thermocouple can be used to measure temperature around 1400ºC? (a) copper-constantan (b) aluminum-chromel (c) platinum-platinum+rhodium (d) copper-aluminum 65. pH meter has (a) one cell (c) three cells

(b) two cells (d) no cell

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66. Maximum differential pressure in liquid manometer is (a) 20 psi (b) 30 psi (c) 40 psi (d) 50 psi 67. Interfacial level in pressure vessel is measured by (a) float (b) manometers of float type (c) U-tube manometer (d) Bourdon gauge 68. Flow rate of sludge is measured by (a) V-notch (c) circular pipe

(b) rectangular notch (d) Kennison nozzle

69. Composition of natural gas can be determined by (a) chromatograph (b) orsat apparatus (c) spectrometer (d) photometer 70. Bellows are made of (a) leather (c) plastic

(b) paper (d) thin copper

71. Flapper nozzle is a (a) pneumatic controller (c) electronic controller

(b) hydraulic controller (d) both a and b

72. Weir valve is used for (a) slurries (c) neutral solutions

(b) acids (d) bases

73. Valve used to supply oil to burner is (a) gate valve (c) rotary plug valve

(b) butterfly valve (d) both a and b

74. Mode used for transmitting signal for one kilometer distance is (a) hydraulic (b) pneumatic (c) electronic (d) all a, b and c 75. Use of pilot in transmission (pneumatic) is to (a) speed up signal (b) change the flow of air (c) adjust the signal (d) all a, b and c Page 10

76. Final control element is a (a) valve (c) signal

(b) switch (d) both a and b

77. Example of a second order instrument is a (a) mercury-glass thermometer with covering (b) bare mercury-glass thermometer (c) pressure gauge (d) Bourdon gauge 78. Offset (a) varies with time (c) does not vary with time

(b) varies exponentially with time (d) varies as square of the time

79. Regulator problem means that (a) set point is constant (b) load is constant (c) both set point and load are constant (d) neither set point nor load is constant 80. Servo problem means that (a) set point is constant (c) both a and b

(b) load is constant (d) neither a nor b

81. Critically damped system means that the damping coefficient is (a) 1 (b) < 1 (c) > 1 (d) 0 82. In Bode stability criterion, amplitude ratio at 180º should be (a) 1 (b) < 1 (c) > 1 (d) 0 83. Phase plane method is used for (a) linear-behavior (c) both a and b

(b) non-linear behavior (d) neither a nor b

84. Laplace transform method is used for (a) linear behavior (c) both a and b

(b) non-linear behavior (d) neither a nor b Page 11

85. Phase lag of first order system is (a) tan-1 (ωT) (c) /2

(b) tan-1 (ωT) (d) 0

86. P-I controller as compared to P-controller has a (a) higher maximum deviation (b) longer response time (c) longer period of oscillation (d) all a, b and c 87. Difference at any instant between the value of controlled variable and the set point is called (a) deviation (b) derivative time (c) error ratio (d) differential gap 88. The time difference by which the output of a P-D controller leads the input when the input changes linearly with time is called (a) error ratio (b) derivative time (c) proportional sensitivity (d) gain 89. Steady state deviation resulting from a change in the value of the load variable is called (a) offset (b) error ratio (c) deviation (d) static ratio 90. Time required for the output of a first order system to change from a given value to within 36.8% of the final value when a step change of input is made is called (a) time constant (b) settling time (c) rise time (d) derivative time 91. A controller action in which there is a continuous linear relation between value of the controlled variable and rate of change of controlled output signal is called (a) proportional action (b) integral action (c) derivative action (d) proportional-integral action 92. A controller action in which there is a continuous relation between value of the controlled variable and the value of the output signal of the controller is called (a) proportional action (b) derivative action (c) integral action (d) proportional-derivative action

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93. Steady state ratio of the change of proportional controller output variable and the change in actuating signal is called (a) proportional sensitivity (b) reset rate (c) rangeability (d) integral action 94. In case of flow measurement by an orifice, the pressure difference signal is proportional to (a) Q² (b) Q 3 (c) Q (d) 1 /√Q where Q= volumetric flow rate 95. Thermistor is a (a) semiconductor whose resistance decreases with temperature rise (b) metal whose resistance increases linearly with temperature rise (c) metal whose resistance does not vary with temperature (d) device for measuring nuclear radiation 96. Which of the following factors does not influence measurement accuracy? (a) static and dynamic error (b) reproducibility (c) dead zone (d) none of these 97. Which of the following is suitable for measuring the temperature of a red hot moving object (e.g. steel ingots on roller table) ? (a) thermocouple (b) radiation pyrometer (c) thermistor (d) radiograph 98. Thermocouples (a) have very slow speed of response (b) can’t be connected to the measuring instrument remotely located (c) need cold junction compensation (d) are much less accurate compared to bimetallic or vapor pressure thermometer 99. Selection of material for thermocouple depends on the (a) depth of immersion in the hot fluid (b) minimum and maximum temperature (c) pressure and velocity condition of the fluid whose temperature is to be measured (d) both a and b Page 13

100. Radiation pyrometers (a) have very low speed of response (b) need not “see” the temperature source; it is measuring (c) can’t measure temperature of objects without making physical contact (d) none of these 101. V-notch is used to measure flow rate of a liquid in (a) an open channel (b) a non-circular cross-section closed channel (c) vertical pipeline (d) horizontal pipeline 102. Which of the following is not a head flowmeter? (a) segmental orifice plate (b) pitot tube (c) rotameter (d) flow nozzle 103. Flow rate of a liquid containing heavy solids ( e.g. sand) can be best measured by (a) pitot tube (b) concentric orifice (c) eccentric orifice (d) rotameter 104. Orifice plates for flow measurement (a) incurs very low permanent pressure loss (b) has poor accuracy on high orifice ratios (c) can’t be easily interchanged (d) is best for very large liquid flows and big pipelines

(above

0.75)

105. Pitot tube is used (a) for highly accurate flow measurement (b) when the fluid contains lot of suspended material (c) when the line is large and the velocity is high (d) both a and c 106. In an area meter (e.g. rotameter), the flow rate is (a) proportional to the square root of the differential pressure (b) inferred from the change in area of an orifice in the flow line across which the pressure differential is constant zero (c) inferred from change in flow cross-section across which the pressure differential is zero (d) all a, b and c

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107. A rotameter (a) incurs constant and small permanent pressure drop (b) incurs constant but very large permanent pressure drop (c) is inaccurate for low flow rates (d) need not be mounted always vertically 108. On-off control (a) fully opens the final control element when the measured variable is below the set point (b) fully closes the final control element when the measured variable is above the set point (c) is a two position (fully open or fully closed) control adequate to control a process with slow reaction rate and minimum dead time or transfer lag (d) all a, b, and c 109. Floating control action (a) moves the final control element at constant speed in either direction in response to an error signal (b) changes the position of the final control element from on to off (c) is used to counteract rapid load changes (d) both b and c 110. Cascade control is (a) the continuous adjustment of the set point index of an automatic control loop by a primary (master) controller (b) used when changes in process conditions cause serious upsets in controlled variable (c) useful to control flow from temperature (d) all a, b and c

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