CONTROL SYSTEM MCQS SET 33

CONTROL SYSTEM MCQS SET 33

1. The constant M circle for M=1 is the
a) straight line x=-1/2              b) critical point (-1j0)
c) circle with r= 0.33                d) circle with r=0.67
Answer: a

2. The polar plot of a transfer function passes through the critical point (-1,0). Gain margin is
a) Zero       b) -1dB         c) 1dB              d) Infinity
Answer: a

3. Consider the following statements:
1. The effect of feedback is to reduce the system error
2. Feedback increases the gain of the system in one frequency range but decreases in another
3. Feedback can cause a system that is originally stable to become unstable
Which of these statements are correct.
a) 1,2 and 3
b) 1 and 2
c) 2 and 3
d) 1 and 3
Answer: c

4. The open loop transfer function of a system is G(s) H(s)= K / (1+s)(1+2s)(1+3s)
The phase cross over frequency ωc is
a) V2
b) 1
c) Zero
d) V3
Answer: b

5. If the gain of the open-loop system is doubled, the gain margin
a) Is not affected
b) Gets doubled
c) Becomes half
d) Becomes one-fourth
Answer: a

6. The unit circle of the Nyquist plot transforms into 0dB line of the amplitude plot of the Bode diagram at
a) 0 frequency
b) Low frequency
c) High frequency
d) Any frequency
Answer: d

7. Consider the following statements:
The gain margin and phase margin of an unstable system may respectively be
1. Positive, positive
2. Positive, negative
3. Negative, positive
4. Negative, negative
Of these statements
a) 1 and 4 are correct
b) 1 and 2 are correct
c) 1, 2 and 3 are correct
d) 2,3 and 4 are correct
Answer: d

8. If a system has an open loop transfer function
1-s / 1+s, then the gain of the system at frequency of 1 rad/s will be
a) 1            b) ½          c) Zero               d) -1
Answer: d

9. The polar plot of the open loop transfer function of a feedback control system intersects the real axis at -2. The gain margin of the system is
a) -5dB              b) 0dB            c) -6dB               d) 40dB
Answer: c

10. The corner frequencies are
a) 0 and 1         b) 0 and 2         c) 0 and 1              d) 1 and 2
Answer: d