PROCESS CONTROL

Question 1

1. A Direct Acting controller defines the error as e = SP – PV?
   a. True
   b. False

Answer 1

b. False

Question 2

2. A controller is in AUTO which statement is true?
   a. The loop is closed
   b. The SP is 50%
   c. The manipulated variable is changing in response to the controlled variable
   d. The loop is open

Answer 2

a. The loop is closed

Question 3

3. In order to achieve negative feedback:
   a. The controller output must match the process and measurement variable
   b. The process variable must subtract from the measurement variable
   c. The controller output must increase with an increase in process variable
   d. The controller output must be such as to oppose the change in the process variable

Answer 3

D. The controller output must be such as to oppose the change in the process variable

Question 4

4. The type of response which is as fast as possible without overshoot?
   a. Marginally damped
   b. Under damped
   c. Critically damped
   d. ¼ Amplitude decay

Answer 4

c. Critically damped

Question 5

5. Controller Bias is :
   a. Controller setpoint with no error
   b. Controller feedback trim
   c. Controller error
   d. Controller output with no error

Answer 5

d. Controller output with no error

Question 6

6. Which of the following controllers have Manual Bias:
   a. P-only
   b. PI
   c. PD
   d. PID

Answer 6

a. P-only

Question 7

7. The output of a controller decreases from 12 psi to 6 psi due to a measurement signal (PV) increase from 8 psi to 10 psi. Which of the following is true?
   a. RA with Kc = 0.3
   b. RA with Kc = 3.0
   c. DA with Kc = 0.3
   d. DA with Kc = 3.0

Answer 7

A. RA with Kc = 3.0

Question 8

8. On what does the output of a P-only controller depend?
   a. The magnitude, sign and duration of the error
   b. The magnitude and sign of the error
   c. The rate of change of the error
   d. The duration and rate of change of the error

Answer 8

b. The magnitude and sign of the error

Question 8

9. The output of a PI controller depends upon on what?
   a. The magnitude , sign and duration of the error
   b. The magnitude and sign of the error
   c. The rate of change of error
   d. All of the above

Answer 8

a. The magnitude , sign and duration of the error

Question 9

10. What is the controller output change if a 5% error is on a reverse acting proportional controller with a 50% PB?
    a. 10%
    b. 40%
    c. 25%
    d. 2.5%

Answer 9

a. 10%

Question 9

11. A PI controller has an integral time of 0.25 min/repeat. What is the integral rate?
    a. 4 repeats/minute
    b. 4 minutes/repeat
    c. 0.25 repeats/minute
    d. 0.25 minutes/repeat

Answer 9

a. 4 repeats/minute

Question 10

12. What is the gain (Kc) of a controller which has a proportional band of 20%?
    a. 2.0
    b. 0.5
    c. 1.0
    d. 5.0

Answer 10

d. 5.0

Question 11

13. What is the effect of adding Integral action on a process:
    a. stability increases
    b. offset increases
    c. deadtime decreases
    d. offset is eliminated

Answer 11

d. offset is eliminated

Question 12

14. Reset Windup can be prevented in a pneumatic PI controller by:
    a. Detuning the control loop
    b. Adjusting the manual output regulator
    c. Adding a derivative filter
    d. Restricting the magnitude the controllers bias can accumulate to

Answer 12

d. Restricting the magnitude the controllers bias can accumulate to

Question 13

15. Determine the Correct Controller Action for the following P&ID diagram if the FCE = Fail Closed :

a. Direct Acting
b. Reverse Acting

Answer 13

a. Direct Acting

Question 14

16. Which of the following can cause non-linearity in a control loop?
    a. Final Control Element
    b. Process
    c. Transmitter
    d. All of the above

Answer 14

d. All of the above

Question 15

17. A non linear control loop
    a. Provides the same control at any operating point
    b. PID Controller gives good control at all operating points
    c. Process Gain changes at different operating points
    d. Proportional gain changes at different operating points

Answer 15

c. Process Gain changes at different operating points

Question 16

18. To negate the effects of non-linearity:
    a. Use a multipoint characterizer to linearize the loop
    b. Tune the control loop at the normal operating point
    c. Use a cascade controller
    d. Use a linear control valve

Answer 16

a. Use a multipoint characterizer to linearize the loop

Question 17

19. A load disturbance:
    a. Can change the inherent valve characteristics
    b. Should be tuned for PID Control
    c. Can change the Process Transfer function
    d. Results in offset

Answer 17

c. Can change the Process Transfer function

Question 18

20. FT-1 is a 4 -20 ma Flow transmitter with a range of 0 – 50 m3/hr.
    A Flow Rate decrease of 10 m3/hr causes an output change of + 4 ma in Flow Transmitter FT-1. What is the static gain, KT, of FT-1?
    a. - 0.4
    b. - 1.25
    c. 0.32
    d. 2.5

Answer 18

b. - 1.25

Question 19

21. What is the gain of the following process if when the steam flow is reduced by 50 kg/min the temperature drops by 25C?
    0-1000KG/MIN
    0-300 DEG C

Figure 1
a. 2.0
b. 0.6
c. 1.66
d. 3.33

Answer 19

c. 1.66

Question 20

22. The transfer function of a first order system is described as follows:
    a. It has a static and dynamic gains and the output returns to equilibrium after a change in input
    b. It has a static and dynamic gain, but is non self-regulating
    c. It has a dynamic gain only and is self-regulating
    d. It has dynamic and static gains and has an output represented by a straight line

Answer 20

a. It has a static and dynamic gains and the output returns to equilibrium after a change in input

Question 21

23. What is the value of the change in output for the following first order process, after 1 time constant, if a +20% input is applied? Assume time is in minutes and the output in %.
    G(s) = 1.5/0.1s + 1

a. 20%
b. 33.3%
c. 18.96%
d. 40%

Answer 21

c. 18.96%

Question 22

24. When would the above process reach a new steady state?
    a. 0.1 min
    b. 0.5 min
    c. 1.5 min
    d. 2.0 min

Answer 22

b. 0.5 min

Question 23

25. For an Integrating Process, time constant τ is defined as: a. The amount of time it takes for the output to reach 63.2% of the final steady state value b. The amount of time it takes for the process variable to change by the same amount as the step input c. The equilibrium process value at 63.2 % of the initial process d. The slope of the integrating line

Answer 23

b. The amount of time it takes for the process variable to change by the same amount as the step input

Question 24

26. For a First Order Process, time constant τ is defined as: a. The amount of time it takes for the output to reach 63.2% of the final steady state value b. The amount of time it takes for the process variable to change by the same amount as the step input c. The equilibrium process value at 63.2 % of the initial process d. The slope of the integrating line

Question 25

What is the output @ τ = 11 min if a -5% step input is applied to the above transfer function and the original output was 50%? a. 40% b. 50% c. 45% d. 55%

Question 26

28. Process with the a type of response in which the PV begins to change slowly, then faster, then slowly again, gradually re-balancing at a new steady state : a. Integrating Process b. Multi Capacity c. First Order Process d. Steady State Process

Answer 26

b. Multi Capacity

Question 27

29. A 10% increase in the input to a pure integrating process, results in a 2% decrease in the output after 1 minute. The time constant is: a. 1 minute b. 0.5 minutes c. 5 minutes d. 10 minutes

Answer 27

c. 5 minutes

Question 28

30. How can a multi-capacity process be represented with a transfer function model? a. first-order plus deadtime b. deadtime c. first-order lag d. pure gain

Answer 28

a. first-order plus deadtime

Question 29

31. What happens if the dynamic loop gain is greater than 1? a. Oscillations get smaller and eventually reach steady state b. Sustained Oscillations c. ¼ Amplitude decay d. Oscillations get larger and eventually reach system limits

Answer 29

d. Oscillations get larger and eventually reach system limits

Question 30

32. What happens if the dynamic loop gain is 1? a. Oscillations get smaller and eventually reach steady state b. Sustained Oscillations c. ¼ Amplitude decay d. Oscillations get larger and eventually reach system limits

Answer 30

b. Sustained Oscillations

Question 31

33. What happens if the dynamic loop gain is less than 1? a. Oscillations get smaller and eventually reach steady state b. Sustained Oscillations c. ¼ Amplitude decay d. Oscillations get larger and eventually reach system limits

Answer 31

a. Oscillations get smaller and eventually reach steady state

Question 32

35. What is the effect of increasing the gain of a proportional controller on a closed loop multicapacity process to a setpoint change a. stability increases b. the speed of response increases c. offset increases d. deadtime increases

Answer 32

b. the speed of response increases

Question 33

36. What does phase lag do when gain decreases in a first order process? a. Phase lag increases with a decrease in gain b. Phase lag decreases with a decrease in gain Notes: Page 16 of Process Loop Dynamics: For a First Order Process : As Input frequency increases , dynamic gain decreases As Dynamic Gain decreases : Phase shift increases and Output amplitude decreases. Phase lag and gain are inversely proportional if gain goes up, phase lag goes down

Answer 33

a. Phase lag increases with a decrease in gain

Question 34

37. What is the closed loop gain? a. 1 b. Kc * Kp c. (Kc * Kp) / (1+Kc * Kp) d. 0

Answer 34

c. (Kc * Kp) / (1+Kc * Kp)

Question 35

38. In the Ziegler Nichols open loop tuning method: a. The proportional gain is adjusted until sustained oscillations occur b. Adjusting the manual output regulator c. Adding a derivative filter d. Deadtime and ΔPV/Δt are determined from the reaction curve

Answer 35

d. Deadtime and ΔPV/Δt are determined from the reaction curve

Question 36

39. The Ziegler Nichols Ultimate gain and the Reaction curve tuning method provides tuning parameters for what type of response? a. Under damped b. Critically damped c. Linear d. Quarter Amplitude decay

Answer 36

d. Quarter Amplitude decay

Question 37

45. A Cascade Control setup consists of: a) 2 controllers and 2 manipulated variables b) 2 controllers and 1 manipulated variable c) 1 controller and 1 manipulated variable d) 1 controllers and 2 manipulated variables

Answer 37

b) 2 controllers and 1 manipulated variable

Question 38

46. Which controller is the Primary (Master)? a. FIC-101 b. TIC-101

Answer 38

b. TIC-101 (slower loop is the master)

Question 39

47. What mode should the controllers be in for normal operation? a. FIC-101 in Auto, TIC-101 in Manual b. FIC-101 in Cascade, TIC-101 in Auto c. FIC-101 in Auto, TIC-101 in Cascade d. FIC-101 in Auto, TIC-101 in Cascade

Answer 39

b. FIC-101 in Cascade, TIC-101 in Auto

Question 40

48. In which of the controllers in the above cascade setup can reset windup occur? a. Primary b. Secondary c. Neither primary or secondary d. Both primary and secondary

Answer 40

d. Both primary and secondary

Question 41

49. Which of the following cascaded controllers could wind up? a) Primary b) Secondary c) Both d) none (illustration shows that Primary controller is in manual thus RSP wont get any signal at all)

Answer 41

b) Secondary

Question 42

50. A disadvantage of cascade control is: a. Instability of the inner control loop b. Additional measurement cost and installation c. Decreased Response time of Primary Loop d. Overshoot with Quarter Amplitude decay response

Answer 42

50. A disadvantage of cascade control is: a. Instability of the inner control loop b. Additional measurement cost and installation c. Decreased Response time of Primary Loop d. Overshoot with Quarter Amplitude decay response

Question 43

51. For Cascade control to be effective, the secondary loop should be: a. At least 3 times faster than the primary loop b. At least 3 times slower than the primary loop c. At least 10 times slower than the primary loop d. At least 10 times faster than the primary loop

Answer 43

a. At least 3 times faster than the primary loop

Question 44

52. What is the most common Cascade loop found in Industry? e. 3 element control loop f. Valve positioner g. Variable frequency drive h. Flow control with pressure override

Answer 44

f. Valve positioner

Question 45

53. What is the Normal Operation for PC-100 and FC-100? (Illustration show a Low select override control scheme) a. PC-100 in Cascade and FC-100 in Automatic b. PC-100 in Automatic and FC-100 in Automatic c. PC-100 in Automatic and FC-100 in Manual d. PC-100 in Automatic and FC-100 in Cascade

Answer 45

b. PC-100 in Automatic and FC-100 in Automatic

Question 46

54. Under normal operation, if the output of PC-100 is 90% and the output of FC-100 is 55%, the output to the control valve is : a. 90% b. 55%

Answer 46

b. 55% (low select)

Question 47

55. The connection of the External Feedback signal from the output to the EF point on each controller is used to : a. Boost the output to prevent valve stiction. b. Prevent anti reset windup in the currently selected controller. c. Prevent reset windup in the non-selected controller d. Allow different setpoints from each controller for maximum efficiency.

Answer 47

c. Prevent reset windup in the non-selected controller