# Multiple Choice Questions and Answers on Control System

## Multiple Choice Questions and Answers on Control System

1. What is the primary objective of a control system?

A) To maximize system efficiency
B) To minimize system complexity
C) To maintain desired system performance
D) To eliminate the need for human intervention

Answer: C) To maintain desired system performance

2. Which of the following is NOT a type of control system?

A) Open-loop control system
B) Closed-loop control system
D) Static control system

3. In a feedback control system, what is the purpose of the feedback loop?

A) To measure the system’s output
B) To provide the control input
C) To amplify the error signal
D) To eliminate the reference signal

Answer: A) To measure the system’s output

4. What is the transfer function of a linear time-invariant system?

A) A function that relates the input to the output
B) A function that describes the system’s internal state
C) A function that depends on time and varies with system parameters
D) A constant value

Answer: A) A function that relates the input to the output

5. Proportional-Integral-Derivative (PID) control is commonly used in control systems. What does the “I” in PID stand for?

A) Immediate
B) Integral
C) Input
D) Inverse

6. In a control system, what is the purpose of a compensator?

A) To amplify the error signal
B) To filter the control input
C) To modify the system transfer function
D) To provide feedback

Answer: C) To modify the system transfer function

7. What is the steady-state error of a control system?

A) The error that occurs when the system is initially started
B) The error that remains when the system has reached a stable condition
C) The error due to disturbances in the system
D) The error caused by measurement inaccuracies

Answer: B) The error that remains when the system has reached a stable condition

8. Which of the following control system responses indicates an overdamped system?

A) Oscillatory response
B) Exponential decay without oscillations
C) Slow convergence to zero error
D) Fast rise time with overshoot

Answer: B) Exponential decay without oscillations

9. What is the Laplace transform used for in control system analysis?

A) To convert time-domain signals to frequency-domain signals
B) To convert analog signals to digital signals
C) To filter noise from control signals
D) To amplify control signals

Answer: A) To convert time-domain signals to frequency-domain signals

10. Which of the following is a characteristic of an unstable control system?

A) Rapid convergence to the setpoint
B) Oscillations that grow over time
D) High noise resistance

Answer: B) Oscillations that grow over time

11. Which of the following is an example of an open-loop control system?

A. Thermostat
B. Cruise control in a car
C. Elevator control with position feedback
D. None of the above

12. In a closed-loop control system, feedback is used to:

A. Open the control loop
B. Determine the reference signal
C. Correct errors and regulate the system
D. Calculate the control input directly

Answer: C) Correct errors and regulate the system

13.The transfer function of a system is a mathematical representation of:

A. Input signals
B. Output signals
C. System dynamics
D. Controller parameters

14.Which type of control system has both a forward path and a feedback path?

A. Open-loop control
B. Closed-loop control
C. Proportional control
D. Integral control

15. Proportional-Integral-Derivative (PID) controllers are commonly used in control systems. What does the “D” in PID stand for?

A. Dynamic
B. Derivative
C. Differential
D. Direct

16. In an open loop control system

A. Output is independent of control input
B. Output is dependent on control input
C. Only system parameters have effect on the control output
D. None of the above

Answer: A) Output is independent of control input

17. For open control system which of the following statements is incorrect ?

A. Less expensive
B. Recalibration is not required for maintaining the required quality of the output
C. Construction is simple and maintenance easy
D. Errors are caused by disturbances

Answer: B) Recalibration is not required for maintaining the required quality of the output

18. A control system in which the control action is somehow dependent on the output is known as

A. Closed loop system
B. Semiclosed loop system
C. Open system
D. None of the above

Ans: A) Closed loop system

19. In closed loop control system, with positive value of feedback gain the overall gain of the system will

A. decrease
B. increase
C. be unaffected
D. any of the above

Ans: A) decrease

20. Which of the following is an open loop control system ?

A. Field controlled D.C. motor
B. Ward leonard control
D. Stroboscope

Ans: A) Field controlled D.C. motor

21. Which of the following statements is not necessarily correct for open control system ?

A. Input command is the sole factor responsible for providing the control action
B. Presence of non-linearities causes malfunctioning
C. Less expensive
D. Generally free from problems of non-linearities

Ans: B) Presence of non-linearities causes malfunctioning

22. In open loop system

A. the control action depends on the size of the system
B. the control action depends on system variables
C. the control action depends on the input signal
D. the control action is independent of the output

Ans: D) the control action is independent of the output

23. ___has tendency to oscillate.

A. Open loop system
B. Closed loop system
C. Both (a) and (b)
D. Neither (a) nor (b)

Ans: B) Closed loop system

24. A good control system has all the following features except

A. good stability
B. slow response
C. good accuracy
D. sufficient power handling capacity

Ans: B) slow response

25. A car is moving at a constant speed of 50 km/h, which of the following is the feedback element for the driver ?

A. Clutch
B. Eyes
C. Needle of the speedometer
D. Steering wheel

Ans: C) Needle of the speedometer

26. The initial response when tune output is not equal to input is called

A. Transient response
B. Error response
C. Dynamic response
D.  Either of the above

Ans: A) Transient response

27. A control system working under unknown random actions is called

A. computer control system
B. digital data system
C. stochastic control system

Ans: C) stochastic control system

28. An automatic toaster is a ______ loop control system.

A.  open
B. closed
C.  partially closed
D. any of the above

Ans: A) open

29. Any externally introduced signal affecting the controlled output is called a

A. feedback
B. stimulus
C. signal
D. gain control

Ans: B) stimulus

30. A closed loop system is distinguished from open loop system by which of the following ?

A. Servomechanism
B. Feedback
C. Output pattern
D.  Input pattern

Ans: B) Feedback

31. ___ is a closed loop system.

A. Auto-pilot for an aircraft
B. Direct current generator
C. Electric switch
D. None of the above

Ans: A) Auto-pilot for an aircraft

32. Which of the following should be done to make an unstable system stable ?

A. The gain of the system should be decreased
B. The gain of the system should be increased
C. The number of poles to the loop transfer function should be increased
D. The number of zeros to the loop transfer function should be increased

Ans: B) The gain of the system should be increased

33. As a result of introduction of negative feedback which of the following will not decrease ?

A. Band width
B.  Overall gain
C. Distortion
D. Instability

Ans: A) Band width

34. Regenerative feedback implies feedback with

A. oscillations
B. step input
C. negative sign
D. positive sign

Ans: D) positive sign

35. The band width, in a feedback amplifier.

A. remains unaffected
B. decreases by the same amount as the gain increase
C. increases by the same amount as the gain decrease
D. decreases by the same amount as the gain decrease

Ans: C) increases by the same amount as the gain decrease

36. The output of a feedback control system must be a function of

A. reference and output
B. reference and input
C. input and feedback signal
D. output and feedback signal

Ans: A) reference and output

37. ___ is an open loop control system.

A. Ward Leonard control
B. Field controlled D.C. motor
C. Stroboscope

Ans: B) Field controlled D.C. motor

38. A control system with excessive noise, is likely to suffer from

A. saturation in amplifying stages
B. loss of gain
C. vibrations
D. oscillations

Ans: A) saturation in amplifying stages

39. Zero initial condition for a system means

A. input reference signal is zero
B. zero stored energy
C. no initial movement of moving parts
D. system is at rest and no energy is stored in any of its components

Ans: D) system is at rest and no energy is stored in any of its components

40. Transfer function of a system is used to calculate which of the following ?

A. The order of the system
B. The time constant
C. The output for any given input

Ans: C) The output for any given input

41.  A controller, essentially, is a

A. sensor
B. clipper
C. comparator
D. amplifier

Ans: C) comparator

42. In an automatic control system which of the following elements is not used ?

A. Error detector
B. Final control element
C. Sensor
D. Oscillator

Ans: D) Oscillator

43. In a control system the output of the controller is given to

A. final control element
B. amplifier
C. comparator
D. Sensor

Ans: A) final control element

44. In a stable control system backlash can cause which of the following ?

A. Underdamping
B. Overdamping
C. Poor stability at reduced values of open loop gain
D. Low-level oscillations

Ans: D) Low-level oscillations

45. Which of the following is the input to a controller?

A. Servo signal
B. Desired variable value
C. Error signal
D. Sensed Signal

46. The output of a feedback control system must be a function of

A. reference and output
B. reference and input
C. input and feedback signal
D. output and feedback signal

47. Which of the following is the non-linearity caused by servomotor?

A. static friction
B. backlash
C. saturation
D. none of the above

48. A conditionally stable system exhibits poor stability at

A. low frequencies
B. reduced values of loop gain
C. increased values of loop gain
D. none of the above

Answer: B) reduced values of loop gain

49. Which of the following is the best method for determining the stability and transient response ?

A. Root locus
B. Bode plot
C. Nyquist plot
D. None of the above

50. The transient response of a system is mainly due to

A. inertia forces
B. internal forces
C. stored energy
D. friction

51. In case of type-1 system steady state acceleration is

A. unity
B. infinity
C. zero
D. ten