Question

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

I had been asked this question during an interview.

The above asked question is from Polar Plots in division Frequency Response Analysis of Control Systems

Answer 1

Correct option is (c) -6dB

Explanation: Gain margin of the system is inverse of the intersect on the real axis and calculated in decibels.

G(s) = 1+s / s(1+0.5s).