SOLUTION

Disturbance:- Disturbance is the unwanted signal (e.g, gust) in a control system that tends to affect the controlled variable. The disturbance may be introduced into the system at many places.

Noise:- Noise is the unwanted signal (eg., engine vibration) that tends to affect the measured variable. A filter may be utilized to get rid of noise in the measurement device.

Reference (command) input is a signal supplied to the control system which represents the desired value (or variation) of the controlled output.

Control signal is the output of the controller that will be used to bring the output of the system as close to the desired value as possible.