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# Feedback control

(Redirected from Control loop)

Synonyms: control circuit, control loop, closed-loop control, feedback interaction
German: Regelkreis

## 1 Definition

Information processing structures consisting in a control process with inclosed degenerative feedback are referred to as feedback control system. Feedback control thus permits that vitally important parameters of body function like osmolality, pH and Oxygen-tension as well as plasma level of hormones and body temperature remain constant or in a compliant range.

## 2 Example

Example of a 0th order linear feedback control system with load: e(t) = x(t) - yR(t)

yS(t) = V1 e(t) = V1 [x(t) - yR(t)]

y(t) = yS(t) + z(t) = V1 [x(t) - yR(t)] + z(t)

yR(t) = V2 y(t)

y(t) = V1 x(t) - V1 V2 y(t) + z(t)

y = [V1 x + z] / [1 + V1 V2]

x: set point, e: error, y: controlled variable, yS: manipulated variable, yR: measured variable, z: load, disturbance variable, V1: amplification factor of direct branch, V2: amplification factor of feedback path.

## 3 Physiology

The physiological principle of feed-back control is that a controlled variable (f.e. pH, temprature, etc) is monitored by a sensor all the time. The sensor which is manly represented by an enzyme send the input to a comparator. The comparator compares the value to a set point. In the case of differences between the set point and the value sended by the sensor the comparator will send a signal to an effector which will in turn bring the value back to normality.

Feedback control systems play essential roles in the organism. Examples are:

## 4 Background

Physiological systems theory, a subsection of medical cybernetics deals with mathematical description and analysis of feedback control systems and other information processing structures.

## 5 External Link

Specialties: Molecular genetics