Compensator MCQ

1. A transfer function of a compensator is

$\frac{1+3sT}{1+sT}$

The maximum possible phase shift is

  1. 30°
  2. 45°
  3. 60°
  4. 90°
Answer
Answer. a

2. The bandwidth of a control system can be increased by using

  1. Phase-lead network
  2. Phase-lag network
  3. Both phase-lead network and phase-lag network
  4. Cascaded amplifier in the system
Answer
Answer. a

3. A phase-lead network has its transfer function

$G_c(s)=\frac{1+0.04s}{1+0.01s}$

What is the frequency at which the maximum phase-lead occurs?

  1. 25 rad/sec
  2. 50 rad/sec
  3. 100 rad/sec
  4. 75 rad/sec
Answer
Answer. b

4. A linear time-invariant control system with unsatisfactory steady state error is to be compensated. Which is/are the correct type of cascade compensation to be provided ?

  1. Lead
  2. Lag
  3. Lag-lead

Select the correct answer using the codes given below:

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

5. An R-C network has the transfer function

$G_c(s)=\frac{s^2+10s+24}{s^2+10s+16}$

The network could be used as

  1. lead compensator
  2. lag compensator
  3. lag-lead compensator

Which of the above is/are, correct?

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

6. An effect of phase-lag compensation on servo-system performance is that

  1. for a given relative stability the velocity constant is increased.
  2. for a given relative stability, the velocity constant is decreased.
  3. the bandwidth of the system is increased.
  4. the time response of the system is made faster.
Answer
Answer. a

7. The following transfer function represents a phase-lead compensator:

  1. $\frac{1}{s}$
  2. $\frac{s+4}{3s+6}$
  3. $\frac{4s+2}{6s+1}$
  4. $\frac{s+4}{s+6}$
Answer
Answer. d

8. Given a badly underdamped control system, the type of cascade compensator to be used to improve its damping is

  1. phase-lag
  2. phase-lead
  3. notch filter
  4. phase-lag-lead
Answer
Answer. b

9. The phase-lead compensation is used to

  1. increase rise time and decrease overshoot.
  2. decrease both rise time and overshoot.
  3. increase both rise time and overshoot.
  4. decrease rise time and increase overshoot.
Answer
Answer. b

10. What is the effect of lag compensator on the system bandwidth and the signal-to-noise ratio?

  1. Bandwidth is increased and signal-to-noise ratio is improved.
  2. Bandwidth is increased and signal-to-noise ratio is deteriorated.
  3. Bandwidth is reduced and signal-to-noise ratio is deteriorated.
  4. Bandwidth is reduced and signal-to-noise ratio is improved.
Answer
Answer. d

11. The transfer function of a phase-lead compensator is given by

$G(s)=\frac{1+3sT}{1+sT}$, T > 0.

The maximum phase shift provided by such a compensator is

  1. 30°
  2. 45°
  3. 60°
  4. 90°
Answer
Answer. a

12. The poles and zeroes of an all-pass network are located in which part of the s-plane?

  1. Poles and zeroes are in the right half of s-plane
  2. Poles and zeroes are in the left half of s-plane
  3. Poles in the right half and zeroes in the left half of s-plane
  4. Poles in the left half and zeroes in the right half of s-plane
Answer
Answer. d

13. Consider the following statements:

  1. A phase lead network provides a positive phase angle over the frequency range of interest.
  2. Armature controlled d.c. servo motor is inherently a closed-loop system.
  3. Phase lag network provides significant amplification over the frequency range of interest.
  4. Transfer functions with zeros in the right half of a s-plane is a non-minimum phase system.

Which of these statements is/are correct?

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

14. Consider the following statements:

  1. Bandwidth is increased.
  2. Peak overshoot in the step response is increased.

Which of these are the effects of using lead compensation in a feedback system?

  1. i only
  2. ii only
  3. Both i and ii
  4. Neither i nor ii
Answer
Answer. a

15. Which of the following are the characteristics of a phase-lead controller?

  1. When used properly it can increase the damping of the system.
  2. It improves rise time.
  3. It improves settling time.
  4. It affects the steady-state error

Select the correct answer using the code given below

  1. i, iii and iv
  2. i, ii and iv
  3. i, ii and iii
  4. ii, iii and iv
Answer
Answer. c

16. The phase lead compensation is used for which one of the following?

  1. To increase rise time and decrease overshoot
  2. To decrease both rise time and overshoot
  3. To increase both rise time and overshoot
  4. To decrease rise time and increase overshoot
Answer
Answer. b

17. What is the effect of lag compensator on the system bandwidth (BW) and the signal to noise ratio (SNR)?

  1. BW is reduced and SNR is improved
  2. BW is reduced and SNR is deteriorated
  3. BW is increased and SNR is improved
  4. BW is increased and SNR is deteriorated
Answer
Answer. a

18. What is the effect of providing distance-velocity lag/transportation lag?

  1. To increase the phase margin
  2. To reduce the phase margin
  3. To alter the gain at a given ω
  4. To improve the transient response of the system
Answer
Answer. b

19. The transfer function of a phase lead compensator is found to be of the form $\frac{s+z_1}{s+p_1}$ and that of a lag compensator to be of the form $\frac{s+z_2}{s+p_2}$.

Then which of the following conditions must be satisfied?

  1. z1 > p1, and z2 > p2
  2. z1 > p1, and z2 < p2
  3. z1 < p1, and z2 < p2
  4. z1 < p1, and z2 > p2
Answer
Answer. d

20. What is the effect of phase lead compensator on gain cross-over frequency (ωgc) and on the bandwidth (ωb)?

  1. Both are increased.
  2. ωgc increased but ωb is decreased.
  3. ωgc decreased but ωb is increased.
  4. Both are decreased.
Answer
Answer. a
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