Feedback: Difference between revisions
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'''Feedback''' is an alteration of the input to a system based upon a monitored internal state that changes the input either to modify that state (positive feedback), or to maintain it (negative or degenerative feedback). | '''Feedback''' is an alteration of the input to a system based upon a monitored internal state that changes the input either to modify that state (positive feedback), or to maintain it (negative or degenerative feedback). Unlike ''feedforward'' control, which anticipates a need for change, ''feedback'' introduces change only as a response to a disturbance.<ref name=Seborg/> | ||
==Example== | ==Example== | ||
{{Image|Thermostat system.png|right|350px|Thermostatic control of house temperature using a negative feedback system.}} | {{Image|Thermostat system.png|right|350px|Thermostatic control of house temperature using a negative feedback system.}} | ||
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<ref name= Ganesh> | <ref name= Ganesh> | ||
{{cite book |title=Control engineering |author=Rao Ganesh |chapter=Feedback control |pages=pp. 29 ''ff'' |url=http://books.google.com/books?id=L0ne8OjCd1IC&pg=PA29 |isbn=9788131732335 |publisher=Pearson Education India |year=2010}} | {{cite book |title=Control engineering |author=Rao Ganesh |chapter=Feedback control |pages=pp. 29 ''ff'' |url=http://books.google.com/books?id=L0ne8OjCd1IC&pg=PA29 |isbn=9788131732335 |publisher=Pearson Education India |year=2010}} | ||
</ref> | |||
<ref name=Seborg> | |||
{{cite book |title=Process Dynamics and Control |chapter=§15.1 Introduction to feedforward control |author= Dale E. Seborg, Duncan A. Mellichamp, Thomas F. Edgar, Francis J. Doyle, III |url=http://books.google.com/books?id=_PQ42kOvtfwC&pg=PA274 |pages=pp. 274 ''ff'' |isbn=9780470128671 |year=2010 |publisher=John Wiley & Sons}} | |||
</ref> | </ref> | ||
Revision as of 12:36, 4 June 2014
Feedback is an alteration of the input to a system based upon a monitored internal state that changes the input either to modify that state (positive feedback), or to maintain it (negative or degenerative feedback). Unlike feedforward control, which anticipates a need for change, feedback introduces change only as a response to a disturbance.[1]
Example
The thermostatic control of house temperature is a commonly used example of a negative feedback system.[2] In the figure, the house temperature is a response to the combined heat input from the world and from the furnace. Suppose a change occurs in the heat supplied to the house by the outside world. The resultant house temperature is sensed by a thermometer and converted to an electrical signal. This signal is compared by the thermostat to a set-point signal that corresponds to the desired temperature value. The discrepancy between the set point and the signal is calculated as an error signal by the thermostat, triggering (activating) action by the furnace. Depending upon the sign of the error the furnace produces more or less heat, regulating the combined heat input to the house so the temperature stays constant. In other words, the information on system temperature is used to generate feedback that keeps the temperature at value.
The same principle is found in biology as homeostasis.[3]
References
- ↑ Dale E. Seborg, Duncan A. Mellichamp, Thomas F. Edgar, Francis J. Doyle, III (2010). “§15.1 Introduction to feedforward control”, Process Dynamics and Control. John Wiley & Sons, pp. 274 ff. ISBN 9780470128671.
- ↑ Rao Ganesh (2010). “Feedback control”, Control engineering. Pearson Education India, pp. 29 ff. ISBN 9788131732335.
- ↑ See, for example, Lauralee Sherwood (2005). Fundamentals of Physiology: A Human Perspective, 3rd ed. Cengage Learning, p. 14. ISBN 9780534466978.