Editing Negative feedback (section)

== History ==
Negative feedback as a control technique may be seen in the refinements of the [[water clock]] introduced by [[Ctesibius|Ktesibios]] of Alexandria in the 3rd century BCE. Self-regulating mechanisms have existed since antiquity, and were used to maintain a constant level in the reservoirs of water clocks as early as 200 BCE.<ref>{{cite journal | last1 = Breedveld | first1 = Peter C | year = 2004 | title = Port-based modeling of mechatronic systems | journal = Mathematics and Computers in Simulation | volume = 66 | issue = 2| pages = 99–128 | doi=10.1016/j.matcom.2003.11.002| citeseerx = 10.1.1.108.9830 }}</ref>

[[File:Centrifugal governor.png|thumb|The [[Centrifugal governor|fly-ball governor]], an early example of negative feedback]]
Negative feedback was implemented in the 17th century. [[Cornelius Drebbel]] had built [[Thermostat#History|thermostatically controlled]] incubators and ovens in the early 1600s,<ref>{{cite web|url=http://www.drebbel.net/Tierie.pdf|title=Tierie, Gerrit. Cornelis Drebbel. Amsterdam: HJ Paris, 1932.|access-date=2013-05-03}}</ref> and [[centrifugal governor]]s were used to regulate the distance and pressure between [[millstone]]s in [[windmill]]s.<ref>{{cite book|last=Hills|first=Richard L|authorlink=Richard L. Hills|title=Power From the Wind |url=https://books.google.com/books?id=FoVkfkBV1_8C |publisher=Cambridge University Press|year=1996|isbn=9780521566865}}</ref> [[James Watt]] patented a form of governor in 1788 to control the speed of his [[steam engine]], and [[James Clerk Maxwell]] in 1868 described "component motions" associated with these governors that lead to a decrease in a disturbance or the amplitude of an oscillation.<ref name=maxwell>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|url=https://commons.wikimedia.org/wiki/File:On_Governors.pdf|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283|via=Wikimedia|doi=10.1098/rspl.1867.0055|s2cid=51751195|doi-access=free}}</ref>

The term "[[feedback]]" was well established by the 1920s, in reference to a means of [[Regenerative circuit|boosting the gain]] of an electronic amplifier.<ref name=mindell>{{Cite book
|author=David A. Mindell
|title=Between Human and Machine : Feedback, Control, and Computing before Cybernetics
|year= 2002
|publisher=Johns Hopkins University Press
|location=Baltimore, MD, USA
|url=https://books.google.com/books?id=sExvSbe9MSsC|isbn=9780801868955
}}</ref> Friis and Jensen described this action as "positive feedback" and made passing mention of a contrasting "negative feed-back action" in 1924.<ref name=friis>{{Cite journal | doi=10.1002/j.1538-7305.1924.tb01354.x|title = High Frequency Amplifiers| journal=Bell System Technical Journal| volume=3| issue=2| pages=181–205|year = 1924|last1 = Friis|first1 = H. T.| last2=Jensen| first2=A. G.}}</ref> [[Harold Stephen Black]] came up with the idea of using negative feedback in electronic amplifiers in 1927, submitted a patent application in 1928,<ref name=Brittain/> and detailed its use in his paper of 1934, where he defined negative feedback as a type of coupling that ''reduced'' the gain of the amplifier, in the process greatly increasing its stability and bandwidth.<ref name="Black">{{cite journal
  | last = Black
  | first = H.S.
  | title = Stabilized Feedback Amplifiers
  | journal = Bell System Tech. J.
  | volume = 13
  | issue = 1
  | pages = 1–18
  | date = January 1934
  | url = http://www3.alcatel-lucent.com/bstj/vol13-1934/articles/bstj13-1-1.pdf
  | doi = 10.1002/j.1538-7305.1934.tb00652.x
  | access-date = January 2, 2013}}
</ref><ref name=BennettS>{{cite book | title=A history of control engineering 1930-1955 |chapter=Chapter 3: The electronic negative feedback amplifier |pages=70 ''ff'' |author=Stuart Bennett |isbn=9780863412806 |year=1993 |publisher=Institution of Electrical Engineers |chapter-url=https://books.google.com/books?id=JMUPAjK490gC&pg=PA70}}</ref>

[[Karl Küpfmüller]] published papers on a negative-feedback-based [[automatic gain control]] system and a feedback system stability criterion in 1928.<ref>{{cite journal 
 | author = C. Bissell
 | title = Karl Kupfmuller, 1928: an early time-domain, closed-loop, stability criterion
 | journal = IEEE Control Systems Magazine
 | year = 2006
 | pages = 115–116, 126
 | url = http://oro.open.ac.uk/5575/1/01636314.pdf }}</ref>

Nyquist and Bode built on Black's work to develop a theory of amplifier stability.<ref name=BennettS/>

Early researchers in the area of [[cybernetics]] subsequently generalized the idea of negative feedback to cover any goal-seeking or purposeful behavior.<ref name=Rosenblueth>Rosenblueth, Arturo, Norbert Wiener, and Julian Bigelow. "[http://courses.media.mit.edu/2004spring/mas966/rosenblueth_1943.pdf Behavior, purpose and teleology]." Philosophy of science 10.1 (1943): 18-24.</ref>
{{quote|text=All purposeful behavior may be considered to require negative feed-back. If a goal is to be attained, some signals from the goal are necessary at some time to direct the behavior.}}
Cybernetics pioneer [[Norbert Wiener]] helped to formalize the concepts of feedback control, defining feedback in general as "the chain of the transmission and return of information",<ref name=wiener>Norbert Wiener ''[[Cybernetics: Or Control and Communication in the Animal and the Machine]]''. Cambridge, Massachusetts: The Technology Press; New York: John Wiley & Sons, Inc., 1948.</ref> and negative feedback as the case when:
{{quote|text=The information fed back to the control center tends to oppose the departure of the controlled from the controlling quantity...{{rp|page=97}}}}
While the view of feedback as any "circularity of action" helped to keep the theory simple and consistent, [[William Ross Ashby|Ashby]] pointed out that, while it may clash with definitions that require a "materially evident" connection, "the exact definition of feedback is nowhere important".<ref name=Ashby/> Ashby pointed out the limitations of the concept of "feedback":
{{quote|text=The concept of 'feedback', so simple and natural in certain elementary cases, becomes artificial and of little use when the interconnections between the parts become more complex...Such complex systems cannot be treated as an interlaced set of more or less independent feedback circuits, but only as a whole. For understanding the general principles of dynamic systems, therefore, the concept of feedback is inadequate in itself. What is important is that complex systems, richly cross-connected internally, have complex behaviors, and that these behaviors can be goal-seeking in complex patterns.{{rp|page=54}} }}

To reduce confusion, later authors have suggested alternative terms such as ''degenerative'',<ref>
Hermann A Haus and Richard B. Adler, ''Circuit Theory of Linear Noisy Networks'', MIT Press, 1959
</ref> ''self-correcting'',<ref name="senge">{{Cite book
|author=Peter M. Senge
|title=The Fifth Discipline: The Art and Practice of the Learning Organization
|year=1990
|publisher=Doubleday
|location=New York
|isbn=978-0-385-26094-7
|pages=424
|url-access=registration
|url=https://archive.org/details/fifthdisciplineasen00seng
}}
</ref> ''balancing'',<ref name=Hobbs>{{cite book |title=Science and Policy in Natural Resource Management: Understanding System Complexity |isbn= 9781139458603 |year=2006 |author1=Helen E. Allison |author2=Richard J. Hobbs |url=https://books.google.com/books?id=bgHVGj_DOxAC |publisher=Cambridge University Press|quote=Balancing or negative feedback counteracts and opposes change |page=205}}
</ref> or ''discrepancy-reducing''<ref name="carver">{{cite book |url=https://books.google.com/books?id=U9xi8wlfWccC |title = On the Self-Regulation of Behavior|isbn = 9780521000994|last1 = Carver|first1 = Charles S.|last2 = Scheier|first2 = Michael F.|date = 2001-05-07| publisher=Cambridge University Press }}</ref> in place of "negative".