Question

The closed loop transfer function of a unity negative feedback system is 100/(s^2+8s+100). Its open loop transfer function is:

(a) 100/s+8

(b) 1/s^2+8s

(c) 100/s^2-8s

(d) 100/s^2+8s

This question was posed to me in unit test.

My question is based upon State Variables and Linear Discrete-Time Systems in chapter State Variable Analysis and Design of Control Systems

Answer 1

Right option is (d) 100/s^2+8s

To explain I would say: For unity feedback system the closed loop transfer function is: G/1+GH and the open loop transfer function can be calculated by balancing the value of G.