P, PI, PD, PID Controller MCQ

1. The effect of an integral controller on the steady-state error ess and that on the relative stability Rs of the system is

  1. both are reduced
  2. ess is reduced but Rs in increased
  3. ess is increased but Rs is reduced
  4. both are increased

Answer. a

2. The correct sequence of steps needed to improve system stability is

  1. use negative feedback, reduce gain and insert derivation action
  2. reduce gain, insert derivation action and use negative feedback
  3. reduce gain, use negative feedback and insert derivation action
  4. insert derivation action, use negative feedback and reduce gain

Answer. a

3. In a closed-loop system for which the output is the speed of a motor, the output rate control can be used to

  1. limit the acceleration of the motor
  2. limit the speed of the motor
  3. limit the torque output of the motor
  4. reduce the damping of the system

Answer. b

4. Consider the following statements in connection with two-position controller:

  1. If the controller has a 4% neutral zone, its positive error band will be 2% and negative error band will be 8%.
  2. The neutral zone is also known as dead.
  3. The controller action of a two-position controller is very similar to that of a pure on-off controller.
  4. Air-conditioning system works essentially on a two-position control basis.

Which of the above statements are correct?

  1. i, ii and iii only
  2. ii, iii and iv only
  3. ii and iv only
  4. i, ii, iii and iv

Answer. b

5. Consider the following statements:

A first-order system with a proportional controller exhibits an offset to a step input. In order to reduce the offset, it is necessary to

  1. increase the gain of proportional controller
  2. add a derivative mode
  3. add an integral mode

Select the correct answer using the code given below:

  1. i and iii only
  2. ii and iii only
  3. i and ii only
  4. i, ii, iii

Answer. a

6. The transfer function of a P-I controller is

  1. Kp + Kis
  2. Kp + (Ki/s)
  3. (Kp/s) + Kis
  4. Kps + (Ki/s)

Answer. b

7. The characteristics of a mode of the controller are summarized:

  1. If error is zero, the output from the controller is zero.
  2. If error is constant in time, the output from the controller is zero.
  3. For changing error in time, the output from the controller is |K|% for every 1% sec-1 rate of change of error.
  4. For positive rate of change of error, the output is also positive.

The mode of controller is

  1. Integral controller
  2. Derivative controller
  3. Proportional derivative
  4. Proportional integral

Answer. b

8. What is the effect on the natural frequency (ωn) and damping factor (δ) in the control systems when derivative controller is used?

  1. ωn increases and δ decreases
  2. ωn remains unchanged and δ increases
  3. ωn remains unchanged and δ decreases
  4. ωn decreases and δ increases

Answer. b

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