Cascade and Feedforward Control — MCQs – EE

1. The main objective of cascade control is to:
(A) Reduce steady-state error
(B) Improve disturbance rejection and dynamic response
(C) Increase system gain
(D) Simplify the control system

2. A cascade control system consists of:
(A) A single controller and single feedback loop
(B) Two or more controllers in series
(C) One controller and one sensor
(D) A feedforward loop only

3. In cascade control, the output of the primary (master) controller:
(A) Acts as the setpoint for the secondary (slave) controller
(B) Directly drives the final control element
(C) Measures process variable
(D) Controls actuator position

4. The secondary loop in cascade control:
(A) Responds faster than the primary loop
(B) Responds slower than the primary loop
(C) Is used for manual control
(D) Controls setpoint directly

5. The main advantage of cascade control is:
(A) Improved disturbance rejection before it affects the main variable
(B) Simpler tuning
(C) Elimination of sensors
(D) Reduced control cost

6. Feedforward control acts:
(A) Before the disturbance affects the process
(B) After the process variable changes
(C) Independently of disturbances
(D) As a feedback correction

7. The basic idea of feedforward control is to:
(A) Measure disturbances and compensate for them directly
(B) Eliminate the need for feedback
(C) Increase actuator speed
(D) Reduce steady-state gain

8. A feedback control system corrects errors:
(A) After they occur
(B) Before they occur
(C) Simultaneously with disturbances
(D) Without sensors

9. A feedforward control system corrects:
(A) Before the disturbance affects the process output
(B) After measuring the error
(C) Only when error exists
(D) Randomly

10. The primary disadvantage of feedforward control is:
(A) It requires accurate disturbance and process models
(B) It introduces steady-state error
(C) It increases process lag
(D) It reduces response speed

11. A cascade control system is most effective when:
(A) The secondary variable responds much faster than the primary variable
(B) Both loops respond equally fast
(C) The primary loop is slower
(D) The secondary loop is unstable

12. In cascade control, if the secondary loop is too slow:
(A) The system performance deteriorates
(B) Stability improves
(C) The response is faster
(D) It reduces overshoot

13. The inner loop in cascade control:
(A) Handles fast disturbances
(B) Controls the main process variable
(C) Is used for manual operation
(D) Acts as the setpoint generator

14. The outer loop in cascade control:
(A) Maintains the primary process variable
(B) Measures secondary disturbances
(C) Controls valve position
(D) Provides feedback to the actuator

15. In a temperature control system using cascade control, the inner loop often controls:
(A) Flow rate
(B) Temperature
(C) Pressure
(D) Level

16. A feedforward controller must know:
(A) The effect of disturbance on the process
(B) The feedback gain only
(C) The actuator size
(D) The setpoint change

17. A combination of feedforward and feedback control provides:
(A) Fast response and correction of unmeasured disturbances
(B) Only slow response
(C) No error correction
(D) Simple control design

18. The feedforward signal is usually:
(A) Added to the controller output
(B) Subtracted from the error signal
(C) Used as a feedback input
(D) Ignored during tuning

19. The feedforward control system cannot correct for:
(A) Unmeasured disturbances
(B) Known process variations
(C) Measured input changes
(D) Linear process gains

20. Cascade control improves performance mainly by:
(A) Reducing the effect of secondary disturbances
(B) Simplifying control logic
(C) Eliminating feedback
(D) Reducing setpoint variation

21. The feedforward control is called “anticipatory” because it:
(A) Reacts before the process variable changes
(B) Waits for feedback error
(C) Reduces gain
(D) Increases delay

22. Cascade control can be viewed as:
(A) Two nested feedback loops
(B) Two independent controllers
(C) A feedforward-only system
(D) An open-loop process

23. Feedforward control cannot function properly without:
(A) A measurable disturbance
(B) A large time constant
(C) A secondary loop
(D) Manual calibration

24. Cascade control is preferred when:
(A) A secondary measurable variable affects the primary variable
(B) The process is very slow
(C) No measurable disturbances exist
(D) Only one sensor is available

25. Feedforward control is preferred when:
(A) Disturbances can be measured accurately
(B) Disturbances cannot be measured
(C) No process model exists
(D) Feedback loop is unstable

26. A feedforward controller typically works in:
(A) Parallel with the feedback controller
(B) Series with the actuator
(C) Feedback path
(D) Sensor circuit

27. The feedforward signal is designed based on:
(A) Process and disturbance transfer functions
(B) Only process gain
(C) Random noise
(D) Steady-state data

28. In cascade control, the secondary controller should be tuned to be:
(A) Faster than the primary controller
(B) Slower than the primary controller
(C) Equal to the primary controller
(D) Unaffected by disturbances

29. The master controller in a cascade loop is responsible for:
(A) Maintaining the main process variable
(B) Controlling the actuator directly
(C) Adjusting inner loop dynamics
(D) Measuring disturbances

30. The slave controller in a cascade loop:
(A) Receives its setpoint from the master controller
(B) Operates independently
(C) Directly measures the main variable
(D) Controls the process without feedback

31. Cascade control is not suitable when:
(A) The secondary variable responds slower than the primary variable
(B) The process has measurable disturbances
(C) The secondary variable is faster
(D) The sensors are accurate

32. Feedforward plus feedback control is commonly used to:
(A) Compensate both measurable and unmeasurable disturbances
(B) Reduce process gain
(C) Increase dead time
(D) Eliminate noise

33. The primary loop in cascade control measures the:
(A) Final controlled variable
(B) Actuator signal
(C) Disturbance
(D) Valve position

34. A feedforward control system needs:
(A) A model of how disturbances affect output
(B) Only a proportional gain
(C) No feedback loop
(D) No sensors

35. The major benefit of feedforward control over feedback control is:
(A) Faster disturbance rejection
(B) Easier tuning
(C) Lower cost
(D) Simpler design