Electronics and Communication Engineering - Automatic Control Systems

6. 

The primary function of lag compensator is to provide sufficient

A. gain margin
B. phase margin
C. both gain margin and phase margin
D. either (a) or (b)

Answer: Option B

Explanation:

It changes phase.


7. 

In the given figure, C(s) =

A.
B.
C.
D.

Answer: Option B

Explanation:

Use principle of superposition. Initially assume R(s) = 0 and find C(s).

Then assume U(s) = 0 and find C(s). Add the two responses.


8. 

For G(jω) =

A. magnitude is 1 at all frequencies and phase angle varies from 0 to - 180° as ω varies from 0 to ∞
B. magnitude is T at all frequencies and phase angle 0
C. magnitude is (1 + ω2T2)0.5 and phase angle varies from0 to 0 - 180° as ω varies from 0 to ∞
D. none of the above

Answer: Option A

Explanation:

When ω = 0, phase angle is 0.

For high values of phase angle = - 90° - 90° = 180°.


9. 

The transient response of a second order system is given by for 5% criterion the settling time is

A. 0.25 sec
B. 0.75 sec
C. 1.25 sec
D. 4 sec

Answer: Option B

Explanation:

For 5% criterion settling time = 3T = .

Since ξωn = 4, and 3T = 0.75 secs.


10. 

The polar plot of a transfer function passes through (-1, 0) point. The gain margin is

A. zero
B. - 1 dB
C. 1 dB
D. infinity

Answer: Option A

Explanation:

When polar plot passes through (-1, 0) the system is on limit of stability and gain margin is zero.