Review Che

PROCESS CONTROL 1.

The symbol for “capillary line” in instrumentation diagram is a)

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13. 14.

15.

c)

b) d) Pick out the symbol for “locally mounted instrument” in instrumentation diagram a) b) c) d) Which is the symbol for “pneumatic control valve”

a) b) c) d) no answer Arrangement of physical components connected or related in such a manner as to command, direct or regulate itself or another system is a a) stimulus c) control system b) unit process d) process control Ratio of the maximum controllable flow to the minimum controllable flow a) rangeability c) zero-span ratio b) hysteresis d) installed flow characteristics Type of control mode which does not influence the final steady state value of the error, provides rapid correction based on the rate of change of the error. a) proportional c) proportional-integral b) derivative d) integral Type of control mode which achieves zero offset and adjusts the manipulated variable in a slower manner, thus giving poor dynamic performance and can cause instability if tuned improperly a) proportional c) proportional-integral b) derivative d) integral Type of control mode which does not provide zero offset but reduces the error and speeds the dynamic response of the system, it may cause instability if tuned improperly. a) proportional c) proportional-integral b) derivative d) integral The most commonly used control mode in the industry a) proportional c) proportional-integral b) derivative d) integral The simplest mode of control which is characteristic of a two position control commonly utilized in a thermostat for controlling the temperature of heaters, air-conditioners, refrigerators and etc. a) proportional c) programmable logic control b) derivative d) on-off control It is a control system in which the control action is independent of the output. a) closed loop system c) feedback control system b) open loop system d) feedforward control system Actual response obtained from the control system. It may or may not be equal to the specified response. a) input b) output c) answer d) result It is used to convert one signal or energy form into another. a) transducer b) amplifier c) detector d) resistor It establishes the functional relationship between the controlled output and the primary feedback signal a) control signal c) measurement b) reference input d) controlled output Not a flow measuring device a) orifice meter c) magnetic flowmeter b) turbine meter d) diaphragm meter

16. A frequency response measure on how well the system response to variations in the output signal. a) feedback c) control system b) continuous time d) bandwidth 17. The stimulus, excitation or command applied to control a system, typically from an external energy source, usually to produce a specified response from the control system. a) process control c) input b) set d) control system 18. A sensor usually made of a semiconductor that utilizes the effect of temperature on the resistance to current is a a) thermocouple b) thermistor c) resistor d) capacitor 19. The proportional action repeat rate is known from this control parameter. a) derivative time c) integral time b) controller bias d) controller gain 20. It is an external signal applied to the feedback control system usually at the first summing point, in order to command a specified action of the plant. It usually represents the desired plant output behavior. a) control signal c) feedback element b) reference input d) controlled output 21. A control structure with two feedback controllers with the output of the primary controller changing the set point of the secondary controller whose output goes to the final controller. a) feedforward control c) cascade control b) ratio control d) override control 22. Closed loop poles of a stable second order system could be a) both real and positive b) complex conjugate with positive real part c) both real and negative d) one real positive and the other real negative 23. The term analogous to the electrical current in a thermal system is the a) temperature difference c) heat flow rate b) heat content in the system d) no answer 24. The response of two tanks of same size and resistance in series is a) over damped c) under damped b) critically damped d) no answer 25. A simple pitot tube measures a) average velocity c) maximum velocity b) point velocity d) static pressure 26. Which of the following is a contact pyrometer? a) optical pyrometer c) radiation pyrometer b) infrared pyrometer d) resistance pyrometer 27. The amplitude ratio for the sinusoidal response of _________ is less than 1 a) first order system c) transportation lag b) second order system d) no answer 28. Pressure of 0.0001 absolute psi can be measured by a) Mcleod gauge c) Pirani gauge b) Thermocouple gauge d) Bourdon gauge 29. The Bode stability criterion is applicable when a) Gain and phase curves decrease continuously with frequency b) Gain curve increases and the phase curve decreases with frequency c) Gain curve and phase curve both increase with frequency d) Gain curve decreases and the phase curve increase with frequency

PROCESS CONTROL 30. 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 31. A barometer measures a) atmospheric pressure c) dynamic pressure b) gauge pressure d) absolute pressure 32. Routh stability method uses a) open loop transfer function c) either a or b b) closed loop transfer function d) neither a nor b 33. Bode stability method uses a) open loop transfer function c) either a or b b) closed loop transfer function d) neither a nor b 34. An unwanted signal that affects the system’s output signal a) disturbance signal c) controlled variable signal b) error signal d) sensor signal 35. The device that causes the process to provide the output a) sensor b) transmitter c) adaptor d) actuator 36. The time for the system to respond to a step input and attain a response equal to the magnitude of the input. a) response time c) rise time b) equalization time d) equilibrium time 37. The system that uses a measurement of the output and compares it with the desired output is control system a) feed-forward c) closed-loop feedback b) adaptive d) inferential 38. The amount the system output response proceeds beyond the desired response a) offset b) offshoot c) gain d) overshoot 39. Output signal is fed back so that it adds to the input signal a) positive feedback c) comparator gain b) negative feedback d) forward feedback 40. A system that exhibits the desired performance in the presence of significant plant uncertainty. a) stable control c) automatic control b) reliable control d) robust control 41. 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 42. A temperature sensor with the following advantages: no physical contact, wide range and fast response and measures small target or average value over large size a) thermocouple c) pyrometer b) thermistor d) RTDs 43. Which of the following controllers has the least maximum deviation? a) P-controller c) P-I controller b) P-D controller d) P-I-D controller

44. Which of the following controllers has maximum offset? a) P-controller c) P-I controller b) P-D controller d) P-I-D controller 45. The roots of the characteristic equation of an under damped second order system are a) real, negative and equal c) real, negative & unequal b) real, positive and unequal d) complex conjugates 46. An inherent disadvantage of this control system is that it results in continuous cycling of the controlled variable and thus produces excessive wear in the final control element. a) on-off control c) P-only control b) PI-only control d) PID control 47. Which of the following flow-metering instruments is an area meter? a) venturi meter c) rotameter b) pitot tube d) hot wire anemometer 48. Conversion formula for converting amplitude ratio ( AR) into decibels is a) Decibel = log10 (AR) c) Decibel=20 log10 (AR) b) Decibel=20 log e(AR) d) Decibel=20 log10 (AR)0.5 49. 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 50. Process degrees of freedom a) indicates the minimum number of controller to be used b) indicates the maximum number of controller to be used c) determines both maximum and minimum number of controllers to be used d) gives no idea of controllers 51. Steady state deviation resulting from a change in the value of the load variable is called a) error ratio b) static ratio c) deviation d) offset 52. Which of the following is an undesirable dynamic characteristic of an instrument? a) reproducibility c) time lag b) dead zone d) static error 53. Load cells are used for the measurement of a) stress b) strain c) velocity d) weight 54. Which of the following is the dynamic characteristics of an instrument? a) reproducibility c) sensitivity b) dead zone d) fidelity 55. In a single tank system, the transfer function of level to inlet flow rate a) R/TS b) R/(TS + 1) c) 1/(TS + 1) d) 1/TS 56. 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

PROCESS CONTROL c) integral control action is introduced d) derivative control action is introduced 57. Response of a system to a sinusoidal input called a) impulse response c) unit step response b) frequency response d) step response 58. Flow measuring instruments with different specifications (zero and span) are available for an application that flow rate measurements in the range of 300 L/h to 400 L/h. The appropriate instrument for this application is one whose specifications are a) zero=175 L/h, span=150 L/h b) zero=175 L/h, span=200 L/h c) zero=275 L/h, span=100 L/h d) zero=275 L/h, span=150 L/h

 is subjected to a sinusoidal input of frequency  = 1/.

59. A first order system with unity gain and time constant The amplitude ratio for this system is a) 0.25

b) 0.5

c) 1

1 √2

d)

respectively at these two temperatures. If the cold junction temperature is shifted from 00C and 300C, then the emf correction in mV is a) 3.13 b) 2.92 c) 2.61 d) 2.02 68. The characteristic equation for a system is s3 + 9s2 + 26s + 12 (2+ KC) = 0. Using the Routh test, the value of KC that will keep the system on the verge of instability is a) 20.9 b) 18.4 c) 17.5 d) 15.3

69. The inverse Laplace transform of a)

is

c)

b) d) 70. A block diagram for a control system is shown below. The steady state gain of the closed loop system, between output Y(s) and set point R(s) is

60. An amplitude ratio of 0.1 corresponds to ______ decibels a) -10 b) -20 c) 10 d) 20 61. The transfer function of the first order system is

a)

1 τ s+ 1 s d) τs

1 τs

b)

s τ s+ 1

c)

62. What is the Laplace transform of sin t ?

1 a) 2 s +1 1 d) 2 s −1

s 2 s +1

b)

s s −1

a) 5/9 b) 4/9 c) 1/3 d) 2/9 71. The characteristic equation of a closed loop system using a proportional controller with gain KC is 12s3 + 19s2 + 8s + 1+ KC=0 At the onset of instability, the value of KC is a) 35/3 b) 10 c) 25/3 d) 20/3 72. The block diagram of a system with a proportional controller is shown below. A unit step input is introduced in the set point. The value of KC to provide a critically damped response for U=0, P=8 and m=1 is a) 3.34 b) 2.58 c) 1.53 d) 1.12

c)

2

63. A system with a transfer function

2s 4 s+1

is

a) zero order c) 2nd order st b) 1 order d) 3rd order 64. Number of poles in a system with transfer function

1 s ²+ 2 s ²+1

a) 1 b) 2 c) 3 d) 5 65. The frequency response of a first order system has a phase shift with lower and upper bounds given by

a)

[

[

−∞ ,

−π π , 2 2

]

π 2

]

d)

b)

[

−π ,0 2

]

c)

[ ] 0,

π 2

66. A thermometer initially at 100 0C is dipped at t = 0 into an oil bath, maintained at 150 0C. If the recorded temperature is 1300C after 1 minute, then the time constant of the thermometer in minutes is a) 1.98 b) 1.35 c) 1.26 d) 1.09 67. A thermocouple having a linear relationship between 0 0C and 3500C shows an emf of zero and 30.5 mV

73. The transfer function, G(s), whose asymptotic Bode diagram is shown below is

PROCESS CONTROL

a) 10s + 1 b) 10s – 1 c) s – 10 d) s + 10 74. Consider the process as shown below. A constant head pump transfers a liquid from a tank maintained at 20 psi to a reactor operating at 100 psi, through a heat exchanger and a control valve. At the design conditions, the liquid flow rate is 1000 L/min, while the pressure drop across the heat exchanger is 40 psi, and that across the control valve is 20 psi. Assume that the pressure drop across the heat exchanger varies as the square of the flow rate. If the flow is reduced to 500 L/min, then the pressure drop across the control valve is a) 30 psi b) 50 psi c) 80 psi d) 150 psi

75. The Laplace transform of the function shown below is

a)

c)

b)

d)