Question

The For a unity feedback system the open loop transfer function is G(s) = K(s+2)/s^2 (s^2+7s+12). What is the value of Ka?

(a) 12/k

(b) k/12

(c) k/6

(d) 6/k

The question was posed to me in exam.

This interesting question is from Steady State Error topic in chapter Error Analysis of Control Systems

Answer 1

Correct answer is (c) k/6

For explanation: As limit s tends to zero :  s^2G(s) = K(s+2)/ (s^2+7s+12) = k/6.  Ka is the acceleration error constant which is calculated by the above method.