From Computer Science Wiki

Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself [2].

The output value is (continuously) compared to the desired value, to produce an error value/difference between observed and measured, the controller uses the error value/difference between observed and measured to determine the new input to the system.

If we were to use a heating system, we could deduce how feedback is used. A sensor detects the temperature. When the temperature reaches a certain threshold, a signal will be sent to an actuator which will trigger the heating to turn on and start heating the area where the temperature sensor is located.

Feedback loops[edit]

Control systems can be open loop or closed loop.

Open loop systems will just consider the input and then keep repeating the same task given the input, e.g. a microwave heats for a given time period without actually checking the temperature of the food.

Closed loop systems on the other hand will also take into account other factors, including the output itself. For example a water tank control system that keeps water levels constant will constantly adjust its output (opening or closing a valve) depending on the input it gets from water level sensors.[3]

Negative feedback[edit]

Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances.[4]

Positive feedback[edit]

Positive feedback is a process that occurs in a feedback loop in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation[5]


  • Describe the role of feedback in a control system