Question

A signal other than the reference input that tends to affect the value of controlled variable is known as

(a) Disturbance

(b) Command

(c) Control element

(d) Reference input

I got this question by my college director while I was bunking the class.

This is a very interesting question from Constructing  Phase-Trajectories topic in division Nonlinear Systems of Control Systems

Answer 1

The correct choice is (a) Disturbance

To explain: Disturbance signal is also the reference signal only there can be multiple inputs in a control system or the other input is called the disturbance signal.