Question

A system has poles at 0.01 Hz, 1 Hz and 80Hz, zeroes at 5Hz, 100Hz and 200Hz. The approximate phase of the system response at 20 Hz is :

(a) -90°

(b) 0°

(c) 90°

(d) -180°

This question was posed to me during an interview for a job.

The question is from Bode Plots in portion Frequency Response Analysis of Control Systems

Answer 1

Correct choice is (a) -90°

The best explanation: Pole at 0.01 Hz gives -180° phase. Zero at 5Hz gives 90° phase therefore at 20Hz -90° phase shift is provided.