# Feedback control

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**Synonyms**: control circuit, control loop, closed-loop control, feedback interaction

**German**: Regelkreis

## DefinitionEdit

Information processing structures consisting of a control process with degenerative feedback are referred to as **feedback control systems**. In living systems, feedback control systems permit that vitally important parameters of body function like body core temperature, pH and Oxygen-tension as well as plasma level of hormones and osmolality remain constant or in a compliant range. Today, feedback control systems find wide application in technology, e.g. in power plants, automotive systems, space flight, air conditioning or chemical industry.

## ExampleEdit

Example of a 0th order linear feedback control system with load:

e(t) = x(t) - y_{R}(t)

y_{S}(t) = G_{1} e(t) = G_{1} [x(t) - y_{R}(t)]

y(t) = y_{S}(t) + z(t) = G_{1} [x(t) - y_{R}(t)] + z(t)

y_{R}(t) = G_{2} y(t)

y(t) = G_{1} x(t) - G_{1} G_{2} y(t) + z(t)

y = [G_{1} x + z] / [1 + G_{1} G_{2}]

x: set point, e: error, y: controlled variable, y_{S}: manipulated variable, y_{R}: measured variable, z: load, disturbance variable, G_{1}: amplification factor of direct branch, G_{2}: amplification factor of feedback path.