Feedback in a Closed-Loop Control System:

Feedback is information in a closed-loop control system about the condition of a procedure variable. This variable is compared along with a desired condition to generate the proper control action on the procedure. Information is continually "fed back" to the control circuit in response to control action. Within the previous instance, the fact storage tank water level, sensed through the level transmitter, is feedback to the level controller. This feedback is compared along with a desired level to generate the needed control action which will position the level control as required to maintain the desired level. Below figure displays this relationship.

Figure: Feedback in a Closed-Loop Control System