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A unity feedback system has the open-loop transfer function
G(s) = 1 (s – 1)(s + 2)(s + 3)
The Nyquist plot of G(s) encircles the origin—
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- never
- once
- twice
- thrice
- never
Correct Option: B
No. of encirclement, N = P+ – Z+
where P+ = no. of poles on RHS on the open loop T.F.
Z+ = no. of zeros on RHS on the closed loop
T.F. The given open loop T.F.
G(s) = 1/(s – 1)(s + 2)(s + 3)
Here
P+ = 1
Z+ = 0
So, N = 1 – 0 = 1 Hence alternative (B) is the correct choice.
