PID regulator

Desired values: The value of the controlled condition that the operator desires to obtain.

Set values: The value of the controlled condition to which the comparing element is set . It si usually the desired value.

Deviation: It is the difference between measured and desired values.

Offset: It is sustained deviation (or error).

Two step (ON-OFF) controller action is the action of a contraller whose output signal changes from one predetermined value to another when teh deviation parameter changes. (such as boiler water level control) This controller action is mainly on/off control.