Feedback

 
 Editor
Al-Hadithi, Basil. Mohammed. basil61@gmail.com
 Incorporated contributions
J.M. Díaz Nafria, Basil Mohammed Al-Hadithi
 Usage domain
Transdisciplinary, System theory, Control theory, Cybernetics
 Type
concept
 French
rétroaction
 German Rückkopplung

It consists of feeding back the output of a circuit or system to its own input. Usually used in controlling the behaviour of systems, it can be found in the most complex systems such as: technical, economical, thermodynamical, biological or social ones. In the field of social groups or human organizations of functional type, "feedback" is used in the sense of sharing observations, concerns, proposals (especially in the opposite sense of normal circulation of the operating instructions or orders) to regulate the operation of the system toward its goals. Feedback systems are also called closed-loop systems.

This is one of the fundamental means considered by cybernetics for the regulation, control, and evolution (specially in second-order cybernetics) of complex systems. Feedback can be divided into positive and negative depending on whether the feedback path of the system -from output to input- reinforces or counteracts the causes that creates a change in the system output. In the study of stability of feedback electronic systems, Nyquist found the general conditions that such feedback should be met to ensure the stability of the system (based on mathematical models of the behaviour of both the open-loop system -without feedback- and the feedback subsystem).

Positive feedback refers to the situation in which the system output -in response to a change in its input- tends to increase the variation in the same direction. Obviously, this does not lead to stability; nevertheless, it serves to explain the evolution of a system towards a new equilibrium state in which it can be stabilized. This type of feedback plays a key role in morphogenesis, growth and organic development and, in general, in processes which are characterized by quick changes in their behaviour with respect to their initial conditions.

Negative feedback refers to the situation in which the system output -in response to a change in its input- aims at reducing the variation; therefore, operating in an opposite direction to the change of input. In this case the feedback is applied to prevent the instability of the system due to external changes -which is referred as homeostasis, or maintenance of the equilibrium- accounting for control of organic behaviour and the possibility of a linear operation of the system. Such stability with regard to the external changes enables a teleological behaviour of the system (Rosenblueth 1943).

Bipolar feedback refers to the situation in which the system output -in response to a change in its input- can either increase or decrease such variation (depending on both: the system state, and the variation of the input).

References
  • Ashby, W. R. (1957). An Introduction to Cybernetics, London: Chapman & Hall Ltd.
  • Ogata, K. (1998). Ingeniería de control Moderna, México D.F.: Prentice-Hall Hispanoamericana.
  • Rosenblueth, Arturo; Norbert Wiener & Julian Bigelow (1943). Behavior, Purpose and Teleology. Philosophy of Science, Vol. 10, No. 1 (Jan., 1943), pp. 18-24.
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Incorporated entries
J.M. Díaz Nafria, B.M. Al-Hadithi (07/03/2010)

It consists of feeding part of the output of a circuit or system to its own input. It usually used in controlling the behaviour of systems. It can be found in various types of systems such as; technical, economic, thermodynamic, biological or social ones. In the field of social groups or human organizations, feedback is used in the sense of sharing observations, concerns, proposals (especially in the opposite sense of normal circulation of the operating instructions or orders) to regulate the operation of the system toward its goals. Feedback systems are also called closed loop ones.
 
This is one of the fundamental ways that considers the cybernetics to the regulation, control and evolution (in the second-order cybernetics) of complex systems. Feedback can be divided into positive and negative one depending on whether the feedback path of the system output to input reinforces or counteracts the causes that create a change in the system output. In the study of stability of feedback electronic systems, Nyquist found the general conditions that such feedback should meet to ensure the stability of the system (based on mathematical models of behaviour of open-loop system without feedback).
 
Positive feedback, is used when the system output due to a change in its input tends to increase the variation in the same direction. Obviously, this does not lead to stability; nevertheless, it serves to explain the evolution of a system towards a new equilibrium state in which it can be stabilized. This type of feedback plays a key role in morphogenesis, growth and organic development and, in general, in processes which are characterized by quick changes in their behaviour with respect to their initial conditions.

Negative feedback, is applied when the system output due to a change in its input aims at reducing the variation (therefore, operating in an opposite direction to the change of input). In this case the feedback is applied to prevent the instability of the system due to external changes.

Bipolar feedback, is used when the system output due to a change in its input can either increase or decrease such variation (depending on the case under study, which depends on both; the system state, and the variation in the input).

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