Question

The transfer function of the system is G(s) =100/(s+1) (s+100). For a unit step input to the system the approximate settling time for 2% criterion is:

(a) 100 sec

(b) 4 sec

(c) 1 sec

(d) 0.01 sec

This question was addressed to me in examination.

Question is taken from Time Response of First Order Systems topic in division Time Response Analysis, Design Specifications and Performance Indices of Control Systems

Answer 1

Correct option is (b) 4 sec

The best I can explain: G(s) =100/(s+1) (s+100)

  Taking the dominant pole consideration,

  S=-100 pole is not taken.

  G(s)= 100/s+1

  Now it is first order system, ts=4T=4 sec.