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PROCESS CONTROL
1. Gain and time constant of a First order system with transfer function ( )( ) 12
1+
=ssx
sy
are
2. Poles and zeros of the transfer function ( )( ) 15.0
12
+−
=s
ssxsy
are
3. Degree of freedom is a. Total No. of dependent variables in the system b. Total No. of independent variables in the system c. Total No. of independent variables to be specified in the system d. No of equations – No of variables
4. Roots of the open loop characteristic equation having 12
1+
=s
Gp , Gc=2, Gf=1 and
Gm=2 are
5. Repeat Question (4) for closed loop.
6. Gain and time constant of a First order system with transfer function ( )( ) 5.01
1+
=ssx
sy are
7. The system with transfer function ⎟⎠⎞
⎜⎝⎛
++ 21
11
ssis
a. Oscillating b. Non‐ Oscillating c. Critically Oscillating
8. Second order transfer function is given by ⎟⎠⎞
⎜⎝⎛
++ 11
2 ss . What is the percentage of
damping away from criticality?
a. 20% b. 40% c. 50% d. 82%
9. In a distillation operation, what are the controlled variables, manipulated variables and set points?
10. Repeat the Question (9) for extraction.
11. If area of the tank is doubled, time constant will become a. Double b. half c. four times d. constant
12. Time constant is independent of a. mass b. capacitance to store mass c. resistance to flow d. distance velocity lag
13. Pτ is
a. Pure delay b. Processing time c. Process time constant d. Response time
14. dτ is
a. Distance velocity lag b. Derivative time constant c. Deviation time constant d. Disturbance time constant
15. Rt is a. Residence time b. Time required to respond system c. Rise time d. Response time
16. RT is
a. Reference temperature b. Reference time c. Rise time d. Response time
17. Transfer function of P controller is given by 10)()(=
ssc
ε. The proportionality band of
the P controller is
18. 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
19. Response of a system to a sinusoidal input is called 20. For two non‐interacting first order systems connected in series, the overall transfer
function is a. Product of the individual transfer functions b. Addition of the individual transfer functions c. Difference of the individual transfer functions d. Cant not be determined
21. For two non‐interacting first order systems connected in series, the overall transfer
function is a. Product of the individual transfer functions b. Addition of the individual transfer functions c. Difference of the individual transfer functions d. Ratio of the individual transfer functions
22. Response of a linear control system for a change in set point is called
a. Servo problem b. Regulatory problem c. Transient Problem d. Frequency response
23. As damping co‐efficient increases, overshoot
a. Increases b. Decreases c. Remains constant
24. As damping co‐efficient increases, decay ratio a. Increases b. Decreases c. Remains constant
25. Draw a block diagram for a transfer function given byGHG+1
, where 321 GGGG =
and 321 HHHH = .
26. Bode diagram is a plot of
27. Gain margin is
a. Difference between AR b. Addition of AR c. Reciprocal of AR d. Multiplication of AR
28. Servo problem means
a. Set point constant b. Load constant c. Set point change d. both (b) and (c)
29. Regulatory problem means a. Set point constant b. Load constant c. Set point change d. both (b) and (c)
30. In feedback loop, control action is taken on
31. In feed forward loop, control action is taken on
32. Nyquist plot is used to represent
a. Frequency response b. Bode diagram c. Sinusoidal response d. None of these
33. Routh Harwitz stability criteria is applied to
a. Open loop b. Closed loop c. Both (a) and (b) d. None of these
34. Amplitude ratio is
a. Ratio of input amplitude to output amplitude b. Ratio of output amplitude to input amplitude c. Independent of gain d. Both (a) and (c)
35. Phase lag is
a. Transportation lag b. Distance‐velocity lag c. Phase Difference between input and output response of frequency response d. Phase difference at amplitude change
36. What is the phase lag of sinusoidal response of first order system?
a. 90 b. 45 c. 180 d. 60
37. A system has transfer function46.1
102 ++ ss
. A step change of 4 unit magnitude is
introduced in the system. The percent overshoot is a. 20 b. 30 c. 25 d. 35
38. A thermometer follows a first order system with time constant 0.2 min. It is placed in
a temperature bath at 100◦C and allowed to reach steady state. It is suddenly transferred to another bath at 150◦C at t=0 and is left there for 2min. Its temperature reading at t=0.1 min is
a. 119◦C b. 130◦C c. 127◦C d. 145◦C
39. For following Given block diagram: a. Determine the maximum gain for the stable operation. b. Determine the corresponding frequency of oscillations.
40. A closed loop feedback control system consists of a second order process,
( )( )⎟⎟⎠⎞
⎜⎜⎝
⎛++ 11 21 ss
KP
ττ, and a proportional controller (Kc). The roots of the
characteristics equation of the closed loop system are ‐2 and ‐1 in the absence of controller and roots are i5.05.1 ±− when controller Kc =4. Determine 21,, ττPK .
41. The characteristics equation for a closed loop system is given by 03264 234 =++++ ssss . Check whether the system is stable or not.
42. Find the minimum value of K such that the following closed loop characteristic
equation is stable: 04)1(23 =++++ sKKss [Ans.: K > 2]
43. Transfer function of pure dead time with dead time constant Dτ is
a. 1
1+sDτ
b. 1+sDτ c. sDe τ− d. sDeτ
44. The offset introduced by the proportional controller, having gain Kc, to the first order
system can be reduced by a. Increasing gain b. Reducing gain c. Introducing derivative controller d. None of these
45. When a thermometer at 300°C is placed in a water bath at 900°C, the initial rate of
rise in thermometer temperature is found to be 20°C/sec. What is the time constant of the thermometer, assuming it is a first order device with unity steady state gain? What will thermometer read after one minute?
46. Amplitude ratio corresponding to crossover frequency of 10 rad/sec is found to be 1.
a. What is ultimate gain? b. What is the period of sustained oscillations corresponding to ultimate gain? c. If proportional controller is used, what value of the Kc will u recommend?
47. The transfer functions of process, measuring element, controller and control valve
have been given as
( )( )42 ++=
ssKG P
P , Gm=1, Gc=Kc and Gv=1. The root locus diagram of the system is
given below. a. What are points A and B? b. At Kc=1, the roots of the system are located at point C. What is point C? c. Determine the value of Kp.
48. Reset time is a. Time required to settle down the system b. Time required to set a system to new steady state c. Time required to make system stable d. None of these
49. A integral controller repeats the action of proportional controller in 2 min. What is
the reset rate?
50.