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第1行： − 此词条暂由彩云小译翻译，翻译字数共1060，未经人工整理和审校，带来阅读不便，请见谅。+ 第15行：
第15行： − + − + − 当系统的输出作为输入路由回来，作为形成电路或回路的因果链的一部分时，反馈就发生了。+ 第25行：
第25行： − Centrifugal governors were used to regulate the distance and pressure between millstones in windmills since the 17th century. In 1788, James Watt designed his first centrifugal governor following a suggestion from his business partner Matthew Boulton, for use in the steam engines of their production. Early steam engines employed a purely reciprocating motion, and were used for pumping water – an application that could tolerate variations in the working speed, but the use of steam engines for other applications called for more precise control of the speed.+ − 自17世纪以来，离心调速器就被用来调节风车磨盘之间的距离和压力。1788年，James Watt 根据他的商业伙伴 Matthew Boulton 的建议设计了他的第一台离心式调速器，用于他们生产的蒸汽机。早期的蒸汽机采用纯往复运动，用于抽水——这种应用可以容忍工作速度的变化，但是蒸汽机用于其他应用需要更精确的速度控制。+ + + + + − In 1868, James Clerk Maxwell wrote a famous paper, "On governors", that is widely considered a classic in feedback control theory.+ − 1868年，詹姆斯·克拉克·麦克斯韦写了一篇著名的论文，《论州长》 ，这被广泛认为是反馈控制理论的经典之作。+ − + − </ref>}}+ − Over the years there has been some dispute as to the best definition of feedback. According to Ashby (1956), mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of "circularity of action", which keeps the theory simple and consistent. For those with more practical aims, feedback should be a deliberate effect via some more tangible connection.+ − 多年来，关于反馈的最佳定义一直存在一些争议。按照阿什比(1956)的说法，对反馈机制原理感兴趣的数学家和理论家更喜欢“循环行动”的定义，这使得理论简单和一致。对于那些有更实际目标的人来说，反馈应该是通过一些更切实的联系而产生的有意的效果。+ 第49行：
第53行： − + − Even prior to the terms being applied, James Clerk Maxwell had described several kinds of "component motions" associated with the centrifugal governors used in steam engines, distinguishing between those that lead to a continual increase in a disturbance or the amplitude of an oscillation, and those that lead to a decrease of the same.+ − 甚至在这些术语被使用之前，詹姆斯·克拉克·麦克斯韦就已经描述了几种与蒸汽发动机中使用的离心调速器相关的“组件运动” ，区分那些导致扰动持续增加或振幅振荡的组件运动，以及那些导致扰动减少的组件运动。+ − the valence of the action or effect that alters the gap, based on whether it has a happy (positive) or unhappy (negative) emotional connotation to the recipient or observer.}}+ − 改变差距的行为或效果的效价，基于它是否对接受者或观察者有快乐(积极)或不快乐(消极)的情感内涵。}+ 第65行：
第69行： + + − In general, feedback systems can have many signals fed back and the feedback loop frequently contain mixtures of positive and negative feedback where positive and negative feedback can dominate at different frequencies or different points in the state space of a system. − 一般来说，反馈系统可以有多个信号反馈，反馈回路常常包含正反馈和负反馈的混合，其中正反馈和负反馈可以在系统的不同频率或状态空间的不同点占主导地位。 + + − The term bipolar feedback has been coined to refer to biological systems where positive and negative feedback systems can interact, the output of one affecting the input of another, and vice versa. − 双极反馈一词被创造出来，指的是生物系统中正反馈系统可以相互作用，一个系统的输出影响另一个系统的输入，反之亦然。 + + − The Great Eastern was one of the largest steamships of its time and employed a steam powered rudder with feedback mechanism designed in 1866 by John McFarlane Gray. Joseph Farcot coined the word servo in 1873 to describe steam-powered steering systems. Hydraulic servos were later used to position guns. Elmer Ambrose Sperry of the Sperry Corporation designed the first autopilot in 1912. Nicolas Minorsky published a theoretical analysis of automatic ship steering in 1922 and described the PID controller. − 大东方号是当时最大的轮船之一，它使用了一个带有反馈机制的蒸汽动力舵，由约翰 · 麦克法兰 · 格雷在1866年设计。约瑟夫 · 法科特在1873年创造了“伺服”这个词来描述蒸汽动力转向系统。液压伺服系统后来被用来定位枪支。史派里公司的 Elmer Ambrose Sperry 在1912年设计了第一个自动驾驶仪。尼古拉斯·米诺尔斯基在1922年发表了一篇关于船舶自动操舵的理论分析，并描述了 PID 控制器。 − − Oscillators are often characterized by the frequency of their output signal: − − 振荡器的频率通常与其输出信号的频率成拥有属性: 第100行：
第100行： + + + + + + + + + + + + − Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.+ − 为从直流电源产生大功率交流输出而设计的振荡器通常称为逆变器。+ 第115行：
第127行： − There are two main types of electronic oscillator: the linear or harmonic oscillator and the nonlinear or relaxation oscillator.+ − 振盪器有两种主要类型: 线性的或谐振子的和非线性的或张弛振荡器的。+ 第123行：
第135行： + + − A 4-bit [[ring counter using D-type flip flops]] − 4位[使用 d 型触发器的环形计数器] − {{Quote|[Practical experimenters] object to the mathematician's definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum ... between its position and its momentum—a "feedback" that, from the practical point of view, is somewhat mystical. To this the mathematician retorts that if feedback is to be considered present only when there is an actual wire or nerve to represent it, then the theory becomes chaotic and riddled with irrelevancies.<ref name=Ashby>+ − A latch or a flip-flop is a circuit that has two stable states and can be used to store state information. They typically constructed using feedback that crosses over between two arms of the circuit, to provide the circuit with a state. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Latches and flip-flops are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems.+ − 锁存器或触发器是具有两个稳定状态的电路，可用于存储状态信息。它们通常利用电路的两个臂之间交叉的反馈来构造，以便为电路提供一个状态。该电路可以通过施加到一个或多个控制输入的信号来改变状态，并且具有一个或两个输出。它是时序逻辑电路的基本存储元素。锁存器和触发器是用于计算机、通信和许多其他类型系统的数字电子系统的基本构件。+ 第141行：
第153行： − Latches and flip-flops are used as data storage elements. Such data storage can be used for storage of state, and such a circuit is described as sequential logic. When used in a finite-state machine, the output and next state depend not only on its current input, but also on its current state (and hence, previous inputs). It can also be used for counting of pulses, and for synchronizing variably-timed input signals to some reference timing signal.+ − 锁存器和触发器用作数据存储元件。这样的数据存储可以用来存储状态，这样的电路被描述为时序逻辑电路。当用于有限状态机时，输出和下一状态不仅取决于其当前输入，还取决于其当前状态(因此，以前的输入)。它也可以用于计数脉冲，并用于同步一些参考定时信号的变时输入信号。+ + + − Flip-flops can be either simple (transparent or opaque) or clocked (synchronous or edge-triggered). Although the term flip-flop has historically referred generically to both simple and clocked circuits, in modern usage it is common to reserve the term flip-flop exclusively for discussing clocked circuits; the simple ones are commonly called latches. − 触发器可以是简单的(透明的或者不透明的)或者是计时的(同步的或者边缘触发的)。虽然触发器这个术语在历史上一直泛指简单电路和时钟电路，但在现代用法中，通常将触发器这个术语专门用于讨论时钟电路，简单的电路通常称为锁存电路。 第157行：
第169行： − Using this terminology, a latch is level-sensitive, whereas a flip-flop is edge-sensitive. That is, when a latch is enabled it becomes transparent, while a flip flop's output only changes on a single type (positive going or negative going) of clock edge.+ − 使用这个术语，锁存器是电平敏感的，而触发器是边缘敏感的。也就是说，当锁存器启用时，它变得透明，而触发器的输出只在时钟边缘的单一类型(正向或负向)上发生变化。+ + + + + − + − 反馈回路为控制软件和计算系统的运行、维护和进化提供了通用机制。反馈回路是自适应软件工程中的重要模型，它定义了自适应过程中控制元件之间相互作用的行为，以保证系统在运行时的性能。反馈环路和控制理论的基础已成功地应用于计算系统。特别是，它们已经应用于产品的开发，如 IBM 的 Universal Database server 和 IBM Tivoli。从软件的角度来看，IBM 研究人员提出的自主(MAPE，monitor analyze plan execute)回路是对反馈回路应用于动态特性控制和自主软件系统设计与演化的另一个有价值的贡献。+ − [[File:Outcome Feedback Negative Feedback Loop.png|thumb|An example of a negative feedback loop with goals]]+ + + + + + + + + 第187行：
第211行： − Feedback is also a useful design principle for designing user interfaces.+ − 反馈也是设计用户界面的一个有用的设计原则。+ + + + + − Video feedback is the video equivalent of acoustic feedback. It involves a loop between a video camera input and a video output, e.g., a television screen or monitor. Aiming the camera at the display produces a complex video image based on the feedback.+ − 视频反馈是视频等效的声学反馈。它涉及一个循环之间的视频摄像机输入和视频输出，例如，一个电视屏幕或显示器。将摄像机对准显示器，根据反馈信息生成复杂的视频图像。+ − |title=Between Human and Machine : Feedback, Control, and Computing before Cybernetics.+ + + + + 第215行：
第247行： − + − 股票市场就是这样一个系统的例子，它倾向于振荡性的”捕猎” ，由市场参与者的认知和情感因素所产生的正反馈和负反馈来控制。例如:+ + + + + 第229行：
第265行： − George Soros used the word reflexivity, to describe feedback in the financial markets and developed an investment theory based on this principle.+ − 乔治•索罗斯(George Soros)用“反身性”(reflexivity)一词来描述金融市场的反馈，并根据这一原则发展了一套投资理论。+ − {{Quote|...Friis and Jensen had made the same distinction Black used between "positive feed-back" and "negative feed-back", based not on the sign of the feedback itself but rather on its effect on the amplifier's gain. In contrast, Nyquist and Bode, when they built on Black's work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition.<ref name=mindell/>{{rp|page=121}}}}+ − The conventional economic equilibrium model of supply and demand supports only ideal linear negative feedback and was heavily criticized by Paul Ormerod in his book The Death of Economics, which, in turn, was criticized by traditional economists. This book was part of a change of perspective as economists started to recognise that chaos theory applied to nonlinear feedback systems including financial markets.+ − 传统的经济均衡/需求模型只支持理想的线性负反馈，Paul Ormerod 在他的《经济学之死》一书中对此进行了严厉的批评，而这本书反过来又遭到了传统经济学家的批评。随着经济学家开始认识到混沌理论适用于包括金融市场在内的非线性反馈系统，这本书是观点转变的一部分。+ − Even prior to the terms being applied, [[James Clerk Maxwell]] had described several kinds of "component motions" associated with the [[centrifugal governor]]s used in steam engines, distinguishing between those that lead to a continual ''increase'' in a disturbance or the amplitude of an oscillation, and those that lead to a ''decrease'' of the same.<ref name=maxwell>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|url=http://en.wikipedia.org/wiki/File:On_Governors.pdf|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283|doi=10.1098/rspl.1867.0055}}</ref>+ 第247行：
第283行： − {{cmn|+ − {{ cmn | + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 第283行：
第347行： − }}+ − }}+ − </ref> ''reinforcing/balancing'',<ref name="sterman">+ 第296行：
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第725行： − +
Moved page from wikipedia:en:Feedback (history)
此词条暂由彩云小译翻译，翻译字数共3364，未经人工整理和审校，带来阅读不便，请见谅。
{{Other uses}}
{{Other uses}}
'''Feedback''' occurs when outputs of a system are routed back as inputs as part of a [[Signal chain (signal processing chain)|chain]] of [[Causality|cause-and-effect]] that forms a circuit or loop.<ref name=Ford>{{cite book |title=Modeling the Environment |author=Andrew Ford |chapter=Chapter 9: Information feedback and causal loop diagrams |pages=99 ''ff'' |publisher=Island Press |year=2010 |isbn=9781610914253 |chapter-url=https://books.google.com/books?id=38PJahZTzC0C&pg=PA99lpg=PA99 |quote=This chapter describes [[causal loop diagram]]s to portray the information feedback at work in a system. The word ''causal'' refers to cause-and-effect relationships. The word''loop'' refers to a closed chain of cause and effect that creates the feedback.}}</ref> The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems:
'''Feedback''' occurs when outputs of a system are routed back as inputs as part of a [[Signal chain (signal processing chain)|chain]] of [[Causality|cause-and-effect]] that forms a circuit or loop.<ref name=Ford>{{cite book |title=Modeling the Environment |author=Andrew Ford |chapter=Chapter 9: Information feedback and causal loop diagrams |pages=99 ''ff'' |publisher=Island Press |year=2010 |isbn=9781610914253 |chapter-url=https://books.google.com/books?id=38PJahZTzC0C&pg=PA99lpg |quote=This chapter describes [[causal loop diagram]]s to portray the information feedback at work in a system. The word ''causal'' refers to cause-and-effect relationships. The word''loop'' refers to a closed chain of cause and effect that creates the feedback.}}</ref> The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems:
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop.
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself. The notion of cause-and-effect has to be handled carefully when applied to feedback systems:
当系统的输出作为输入路由回来，作为形成电路或回路的因果链的一部分时，反馈就发生了。这个系统可以说是自我反馈。因果关系的概念在应用于反馈系统时必须谨慎处理:
{{quote
{{quote
{{quote
{引用
|text=Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole.
|text=Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole.
|text=Simple causal reasoning about a feedback system is difficult because the first system influences the second and second system influences the first, leading to a circular argument. This makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole.
关于反馈系统的简单因果推理是困难的，因为第一个系统影响第二个系统，第二个系统影响第一个系统，导致循环论证。这使得基于因果的推理变得棘手，因此有必要将系统作为一个整体进行分析。
|author=Karl Johan Åström and Richard M.Murray
|author=Karl Johan Åström and Richard M.Murray
|author=Karl Johan Åström and Richard M.Murray
2012年10月15日 | 作者: 卡尔·约翰·阿斯特洛姆 · 马丁和理查德 · m · 默里
|title=''Feedback Systems: An Introduction for Scientists and Engineers''<ref>{{cite book |title=Feedback Systems: An Introduction for Scientists and Engineers |author1=Karl Johan Åström |author2=Richard M. Murray |chapter=§1.1: What is feedback? |chapter-url=https://books.google.com/books?id=cdG9fNqTDS8C&pg=PA1&dq=%22This+makes+reasoning+based+on+cause+and+effect+tricky%22 |isbn= 9781400828739 |year=2008 |page=1 |publisher=Princeton University Press}} Online version found [http://authors.library.caltech.edu/25062/1/Feedback08.pdf here].
|title=''Feedback Systems: An Introduction for Scientists and Engineers''<ref>{{cite book |title=Feedback Systems: An Introduction for Scientists and Engineers |author1=Karl Johan Åström |author2=Richard M. Murray |chapter=§1.1: What is feedback? |chapter-url=https://books.google.com/books?id=cdG9fNqTDS8C&q=%22This+makes+reasoning+based+on+cause+and+effect+tricky%22&pg=PA1 |isbn= 9781400828739 |year=2008 |page=1 |publisher=Princeton University Press}} Online version found [http://authors.library.caltech.edu/25062/1/Feedback08.pdf here].
|title=Feedback Systems: An Introduction for Scientists and Engineers}}
| title = 反馈系统: 科学家和工程师介绍}
</ref>}}
==History==
==History==
Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter [[Economics|economic theory]] in Britain by the 18th century, but it was not at that time recognized as a universal abstraction and so did not have a name.<ref name=mayr>
Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter economic theory in Britain by the 18th century, but it was not at that time recognized as a universal abstraction and so did not have a name.
自我调节机制自古以来就存在，到18世纪，反馈的概念开始进入英国的经济理论，但当时它还没有被认为是一个普遍的抽象概念，因此没有名称。
Self-regulating mechanisms have existed since antiquity, and the idea of feedback had started to enter [[Economics|economic theory]] in Britain by the 18th century, but it was not at that time recognized as a universal abstraction and so did not have a name.<ref name=mayr>
{{Cite book |author= Otto Mayr|title=Authority, liberty, & automatic machinery in early modern Europe |year=1989 |isbn=978-0-8018-3939-9 | publisher=Johns Hopkins University Press |author-link=Otto Mayr }}</ref>
{{Cite book |author= Otto Mayr|title=Authority, liberty, & automatic machinery in early modern Europe |year=1989 |isbn=978-0-8018-3939-9 | publisher=Johns Hopkins University Press |author-link=Otto Mayr }}</ref>
The first ever known artificial feedback device was a float valve, for maintaining water at a constant level, invented in 270 BC in Alexandria, Egypt. This device illustrated the principle of feedback: a low water level opens the valve, the rising water then provides feedback into the system, closing the valve when the required level is reached. This then reoccurs in a circular fashion as the water level fluctuates. This was a landmark paper on control theory and the mathematics of feedback.
第一个已知的人工反馈装置是一个浮子阀门，用来维持水的恒定水平，发明于公元前270年在埃及的亚历山大。这个装置说明了反馈原理: 低水位打开阀门，上升的水向系统提供反馈，当达到要求的水位时关闭阀门。随着水位的波动，这种情况会以循环的方式再次发生。这是一个具有里程碑意义的论文控制理论和数学的反馈。
The first ever known artificial feedback device was a [[Ballcock|float valve]], for maintaining water at a constant level, invented in 270 BC in [[Alexandria]], [[Ancient Egypt|Egypt]].<ref name=":0">{{Cite book|title=Designing Kinetics for Architectural Facades|last=Moloney|first=Jules|publisher=Routledge|year=2011|isbn=978-0415610346}}</ref> This device illustrated the principle of feedback: a low water level opens the valve, the rising water then provides feedback into the system, closing the valve when the required level is reached. This then reoccurs in a circular fashion as the water level fluctuates.<ref name=":0" />
The first ever known artificial feedback device was a [[Ballcock|float valve]], for maintaining water at a constant level, invented in 270 BC in [[Alexandria]], [[Ancient Egypt|Egypt]].<ref name=":0">{{Cite book|title=Designing Kinetics for Architectural Facades|last=Moloney|first=Jules|publisher=Routledge|year=2011|isbn=978-0415610346}}</ref> This device illustrated the principle of feedback: a low water level opens the valve, the rising water then provides feedback into the system, closing the valve when the required level is reached. This then reoccurs in a circular fashion as the water level fluctuates.<ref name=":0" />
The verb phrase to feed back, in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s, and in 1909, Nobel laureate Karl Ferdinand Braun used the term "feed-back" as a noun to refer to (undesired) coupling between components of an electronic circuit.
19世纪60年代，美国开始使用动词短语反馈，意思是在机械过程中回到原来的位置。1909年，诺贝尔奖获得者卡尔·费迪南德·布劳恩用名词“反馈”来指电子电路元件之间的(不希望的)耦合。
[[Centrifugal governor]]s were used to regulate the distance and pressure between [[millstone]]s in [[windmill]]s since the 17th century. In 1788, [[James Watt]] designed his first centrifugal governor following a suggestion from his business partner [[Matthew Boulton]], for use in the [[steam engine]]s of their production. Early steam engines employed a purely [[reciprocating motion]], and were used for pumping water – an application that could tolerate variations in the working speed, but the use of steam engines for other applications called for more precise control of the speed.
[[Centrifugal governor]]s were used to regulate the distance and pressure between [[millstone]]s in [[windmill]]s since the 17th century. In 1788, [[James Watt]] designed his first centrifugal governor following a suggestion from his business partner [[Matthew Boulton]], for use in the [[steam engine]]s of their production. Early steam engines employed a purely [[reciprocating motion]], and were used for pumping water – an application that could tolerate variations in the working speed, but the use of steam engines for other applications called for more precise control of the speed.
By the end of 1912, researchers using early electronic amplifiers (audions) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through regeneration), but would also cause the audion to howl or sing. This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920.}}
到1912年底，研究人员利用早期电子放大器(音频)发现，故意将输出信号的一部分耦合回输入电路，可以增强放大(通过再生) ，但也会导致音频发出嚎叫或唱歌。这种将信号从输出反馈到输入的行为导致了术语“反馈”在1920年被用作一个不同的词。}
In [[1868]], [[James Clerk Maxwell]] wrote a famous paper, "On governors", that is widely considered a classic in feedback control theory.<ref>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283 | doi = 10.1098/rspl.1867.0055 | jstor=112510|doi-access=free}}</ref> This was a landmark paper on [[control theory]] and the mathematics of feedback.
In [[1868]], [[James Clerk Maxwell]] wrote a famous paper, "On governors", that is widely considered a classic in feedback control theory.<ref>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283 | doi = 10.1098/rspl.1867.0055 | jstor=112510|doi-access=free}}</ref> This was a landmark paper on [[control theory]] and the mathematics of feedback.
Focusing on uses in management theory, Ramaprasad (1983) defines feedback generally as "...information about the gap between the actual level and the reference level of a system parameter" that is used to "alter the gap in some way". He emphasizes that the information by itself is not feedback unless translated into action.
关注管理理论中的应用，Ramaprasad (1983)将反馈一般定义为“ ... 关于实际水平和系统参数参考水平之间的差距的信息” ，用于“以某种方式改变差距”。他强调，信息本身不是反馈，除非转化为行动。
The verb phrase ''to feed back'', in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s,<ref>
The verb phrase ''to feed back'', in the sense of returning to an earlier position in a mechanical process, was in use in the US by the 1860s,<ref>
''"Heretofore ... it has been necessary to reverse the motion of the rollers, thus causing the material to travel or feed back, ..."''
''"Heretofore ... it has been necessary to reverse the motion of the rollers, thus causing the material to travel or feed back, ..."''
HH Cole, "Improvement in Fluting-Machines", [http://www.google.co.nz/patents/US55469 US Patent 55,469 (1866)] accessed 23 March 2012.
HH Cole, "Improvement in Fluting-Machines", [http://www.google.co.nz/patents/US55469 US Patent 55,469 (1866)] accessed 23 March 2012.
''"When the journal or spindle is cut ... and the carriage is about to feed back by a change of the sectional nut or burr upon the screw-shafts, the operator seizes the handle..."'' JM Jay, "Improvement in Machines for Making the Spindles of Wagon-Axles", [http://www.google.co.nz/patents/US47769 US Patent 47,769 (1865)] accessed 23 March 2012.
''"When the journal or spindle is cut ... and the carriage is about to feed back by a change of the sectional nut or burr upon the screw-shafts, the operator seizes the handle..."'' JM Jay, "Improvement in Machines for Making the Spindles of Wagon-Axles", [http://www.google.co.nz/patents/US47769 US Patent 47,769 (1865)] accessed 23 March 2012.
Maintaining a desired system performance despite disturbance using negative feedback to reduce system error
保持一个理想的系统性能，尽管干扰使用负反馈，以减少系统误差
</ref> and in 1909, Nobel laureate [[Karl Ferdinand Braun]] used the term "feed-back" as a noun to refer to (undesired) [[Coupling (electronics)|coupling]] between components of an [[electronic circuit]].<ref>''"...as far as possible the circuit has no feed-back into the system being investigated."''
</ref> and in 1909, Nobel laureate [[Karl Ferdinand Braun]] used the term "feed-back" as a noun to refer to (undesired) [[Coupling (electronics)|coupling]] between components of an [[electronic circuit]].<ref>''"...as far as possible the circuit has no feed-back into the system being investigated."''
An example of a negative feedback loop with goals
有目标的负反馈循环的一个例子
[http://www.cdvandtext2.org/Braun-Nobel-lecture%201909.pdf]
[http://www.cdvandtext2.org/Braun-Nobel-lecture%201909.pdf]
A positive feedback loop example
一个正反馈循环的例子
Karl Ferdinand Braun, [https://www.nobelprize.org/nobel_prizes/physics/laureates/1909/braun-lecture.html "Electrical oscillations and wireless telegraphy"], Nobel Lecture, 11 December 1909. Retrieved 19 March 2012.</ref>
Karl Ferdinand Braun, [https://www.nobelprize.org/nobel_prizes/physics/laureates/1909/braun-lecture.html "Electrical oscillations and wireless telegraphy"], Nobel Lecture, 11 December 1909. Retrieved 19 March 2012.</ref>
Positive feedback: If the signal fed back from output is in phase with the input signal, the feedback is called positive feedback.
正反馈: 如果输出反馈的信号与输入信号同相，这种反馈称为正反馈。
By the end of 1912, researchers using early electronic amplifiers ([[audion tube|audions]]) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through [[Regenerative circuit|regeneration]]), but would also cause the audion to howl or sing.<ref name="bennett">{{Cite book|url=http://worldcat.org/isbn/0-906-04807-9|title=A history of control engineering, 1800–1930|author=Stuart Bennett|publisher=Peregrinus for the Institution of Electrical Engineers|year=1979|isbn=978-0-906048-07-8|location=Stevenage; New York}}
By the end of 1912, researchers using early electronic amplifiers ([[audion tube|audions]]) had discovered that deliberately coupling part of the output signal back to the input circuit would boost the amplification (through [[Regenerative circuit|regeneration]]), but would also cause the audion to howl or sing.<ref name="bennett">{{Cite book|url=http://worldcat.org/isbn/0-906-04807-9|title=A history of control engineering, 1800–1930|author=Stuart Bennett|publisher=Peregrinus for the Institution of Electrical Engineers|year=1979|isbn=978-0-906048-07-8|location=Stevenage; New York}}
Negative feedback: If the signal fed back is of opposite polarity or out of phase by 180° with respect to input signal, the feedback is called as negative feedback.
负反馈: 如果反馈信号相对于输入信号的极性相反或相位相差180 ° ，这种反馈称为负反馈。
[https://books.google.com/books?id=1gfKkqB_fTcC]
[https://books.google.com/books?id=1gfKkqB_fTcC]
</ref> This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920.<ref name=bennett/>
</ref> This action of feeding back of the signal from output to input gave rise to the use of the term "feedback" as a distinct word by 1920.<ref name=bennett/>
As an example of negative feedback, the diagram might represent a cruise control system in a car, for example, that matches a target speed such as the speed limit. The controlled system is the car; its input includes the combined torque from the engine and from the changing slope of the road (the disturbance). The car's speed (status) is measured by a speedometer. The error signal is the departure of the speed as measured by the speedometer from the target speed (set point). This measured error is interpreted by the controller to adjust the accelerator, commanding the fuel flow to the engine (the effector). The resulting change in engine torque, the feedback, combines with the torque exerted by the changing road grade to reduce the error in speed, minimizing the road disturbance.
作为负反馈的一个例子，该图可以表示汽车中的巡航控制系统，例如，它与目标速度(如车速限制)匹配。受控系统是汽车，其输入包括来自发动机和来自道路坡度变化(扰动)的组合扭矩。汽车的速度(状态)是用速度计测量的。误差信号是速度计测量的速度偏离目标速度(设定点)。这个测量的误差由控制器来解释，以调整加速器，指挥燃料流到发动机(效应器)。由此产生的发动机扭矩的变化，即反馈，与改变路面坡度所施加的扭矩相结合，以减少速度误差，最大限度地减少道路干扰。
Over the years there has been some dispute as to the best definition of feedback. According to [[William Ross Ashby|Ashby]] (1956), mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of "circularity of action", which keeps the theory simple and consistent. For those with more practical aims, feedback should be a deliberate effect via some more tangible connection.
Over the years there has been some dispute as to the best definition of feedback. According to [[William Ross Ashby|Ashby]] (1956), mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of "circularity of action", which keeps the theory simple and consistent. For those with more practical aims, feedback should be a deliberate effect via some more tangible connection.
The terms "positive" and "negative" were first applied to feedback prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit. Friis and Jensen (1924) described regeneration in a set of electronic amplifiers as a case where the "feed-back" action is positive in contrast to negative feed-back action, which they mention only in passing. Harold Stephen Black's classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:
“正面”和“负面”这两个词在第二次世界大战之前首次用于反馈。正反馈的想法在20世纪20年代随着再生回路的引入已经很流行了。Friis 和 Jensen (1924)描述了在一套电子放大器的再生情况下，“反馈”行动是积极的，而不是消极反馈行动，他们只是顺便提到。哈罗德·史蒂芬·布莱克1934年的经典论文首次详细阐述了负反馈在电子放大器中的应用。布莱克说:
{{Quote|[Practical experimenters] object to the mathematician's definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum ... between its position and its momentum—a "feedback" that, from the practical point of view, is somewhat mystical. To this the mathematician retorts that if feedback is to be considered present only when there is an actual wire or nerve to represent it, then the theory becomes chaotic and riddled with irrelevancies.<ref name=Ashby>
{{cite book |author=W. Ross Ashby |title=An introduction to cybernetics |publisher=Chapman & Hall |year=1957 |url=http://pcp.vub.ac.be/books/IntroCyb.pdf}}</ref>{{rp|page=54}}}}
{{cite book |author=W. Ross Ashby |title=An introduction to cybernetics |publisher=Chapman & Hall |year=1957 |url=http://pcp.vub.ac.be/books/IntroCyb.pdf}}</ref>{{rp|page=54}}}}
According to Mindell (2002) confusion in the terms arose shortly after this:
据 Mindell (2002)说，术语上的混乱是在这之后不久产生的:
Focusing on uses in management theory, Ramaprasad (1983) defines feedback generally as "...information about the gap between the actual level and the reference level of a system parameter" that is used to "alter the gap in some way". He emphasizes that the information by itself is not feedback unless translated into action.<ref name="Ramaprasad">{{Cite journal | doi=10.1002/bs.3830280103|title = On the definition of feedback| journal=Behavioral Science| volume=28| pages=4–13|year = 1983|last1 = Ramaprasad|first1 = Arkalgud}}</ref>
Focusing on uses in management theory, Ramaprasad (1983) defines feedback generally as "...information about the gap between the actual level and the reference level of a system parameter" that is used to "alter the gap in some way". He emphasizes that the information by itself is not feedback unless translated into action.<ref name="Ramaprasad">{{Cite journal | doi=10.1002/bs.3830280103|title = On the definition of feedback| journal=Behavioral Science| volume=28| pages=4–13|year = 1983|last1 = Ramaprasad|first1 = Arkalgud}}</ref>
{{Quote|...Friis and Jensen had made the same distinction Black used between "positive feed-back" and "negative feed-back", based not on the sign of the feedback itself but rather on its effect on the amplifier's gain. In contrast, Nyquist and Bode, when they built on Black's work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition.
{{ Quote | ... Friis 和 Jensen 对 Black 所用的“正反馈”和“负反馈”作了同样的区分，不是基于反馈本身的符号，而是基于它对放大器增益的影响。相比之下，当 Nyquist 和 Bode 基于 Black 的研究成果时，他们将负面反馈称为符号相反的负面反馈。布莱克很难说服其他人相信他的发明是有用的，部分原因是在基本的定义问题上存在混淆。
==Types==
==Types==
The terms positive and negative feedback are defined in different ways within different disciplines.
正反馈和负反馈在不同的学科中有不同的定义。
===Positive and negative feedback===
===Positive and negative feedback===
{{Main|Negative feedback|Positive feedback}}
{{Main|Negative feedback|Positive feedback}}
the altering of the gap between reference and actual values of a parameter, based on whether the gap is widening (positive) or narrowing (negative).
一个参数的参考值和实际值之间的差距的改变，根据差距是扩大(正面)还是缩小(负面)。
[[File:Set-point control.png|thumb|350px|Maintaining a desired system performance despite disturbance using negative feedback to reduce system error]]
[[File:Set-point control.png|thumb|350px|Maintaining a desired system performance despite disturbance using negative feedback to reduce system error]]
Feedback loops provide generic mechanisms for controlling the running, maintenance, and evolution of software and computing systems. Feedback-loops are important models in the engineering of adaptive software, as they define the behaviour of the interactions among the control elements over the adaptation process, to guarantee system properties at run-time. Feedback loops and foundations of control theory have been successfully applied to computing systems. In particular, they have been applied to the development of products such as IBM's Universal Database server and IBM Tivoli. From a software perspective, the autonomic (MAPE, monitor analyze plan execute) loop proposed by researchers of IBM is another valuable contribution to the application of feedback loops to the control of dynamic properties and the design and evolution of autonomic software systems.
[[File:Outcome Feedback Negative Feedback Loop.png|thumb|An example of a negative feedback loop with goals]]
The two definitions may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to definition 1, some authors use alternative terms, replacing positive/negative with self-reinforcing/self-correcting, reinforcing/balancing, discrepancy-enhancing/discrepancy-reducing or regenerative/degenerative respectively. And for definition 2, some authors advocate describing the action or effect as positive/negative reinforcement or punishment rather than feedback.
这两个定义可能会引起混淆，例如当一个激励(奖励)被用来提高不良业绩(缩小差距)。参照定义1，一些作者使用替代术语，分别用自我强化/自我纠正、强化/平衡、差异增强/差异减少或再生/退化代替正/负。对于定义2，一些作者主张将行为或效果描述为正/负强化或惩罚，而不是反馈。
[[File:Process Feedback Loop.png|thumb|A positive feedback loop example]]
[[File:Process Feedback Loop.png|thumb|A positive feedback loop example]]
Yet even within a single discipline an example of feedback can be called either positive or negative, depending on how values are measured or referenced.
然而，即使在一个单一的学科中，一个反馈的例子也可以被称为正面或负面的，这取决于如何衡量或引用价值观。
Positive feedback: If the signal fed back from output is in phase with the input signal, the feedback is called positive feedback.
Positive feedback: If the signal fed back from output is in phase with the input signal, the feedback is called positive feedback.
This confusion may arise because feedback can be used for either informational or motivational purposes, and often has both a qualitative and a quantitative component. As Connellan and Zemke (1993) put it:
这种混淆可能是因为反馈既可以用于信息目的，也可以用于激励目的，而且通常既有定性的成分，也有定量的成分。正如康奈伦和泽姆克(1993)所说:
Negative feedback: If the signal fed back is of opposite polarity or out of phase by 180° with respect to input signal, the feedback is called as negative feedback.
Negative feedback: If the signal fed back is of opposite polarity or out of phase by 180° with respect to input signal, the feedback is called as negative feedback.
While simple systems can sometimes be described as one or the other type, many systems with feedback loops cannot be so easily designated as simply positive or negative, and this is especially true when multiple loops are present.
虽然简单的系统有时可以被描述为一种或另一种类型，但许多具有反馈回路的系统不能简单地被指定为正或负，当存在多个回路时尤其如此。
The terms "positive" and "negative" were first applied to feedback prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the [[regenerative circuit]].<ref name=mindell>
The terms "positive" and "negative" were first applied to feedback prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the [[regenerative circuit]].<ref name=mindell>
{{Cite book
{{Cite book
{{Quote|When there are only two parts joined so that each affects the other, the properties of the feedback give important and useful information about the properties of the whole. But when the parts rise to even as few as four, if every one affects the other three, then twenty circuits can be traced through them; and knowing the properties of all the twenty circuits does not give complete information about the system.
{{ Quote | 当只有两个部分相互连接时，反馈的属性提供了关于整体属性的重要而有用的信息。但是，当这些部件甚至上升到4个，如果每一个都影响其他3个，那么二十个电路可以通过他们追踪; 并且知道所有二十个电路的特性并不能给出关于这个系统的完整信息。
|author=David A. Mindell
|author=David A. Mindell
|title=Between Human and Machine : Feedback, Control, and Computing before Cybernetics.
Some systems with feedback can have very complex behaviors such as chaotic behaviors in non-linear systems, while others have much more predictable behaviors, such as those that are used to make and design digital systems.
一些具有反馈的系统可能具有非常复杂的行为，如非线性系统中的混沌行为，而另一些系统则具有更可预测的行为，如用于制造和设计数字系统的行为。
|year= 2002
|year= 2002
|publisher=Johns Hopkins University Press
|publisher=Johns Hopkins University Press
Feedback is used extensively in digital systems. For example, binary counters and similar devices employ feedback where the current state and inputs are used to calculate a new state which is then fed back and clocked back into the device to update it.
反馈在数字系统中被广泛应用。例如，二进制计数器和类似的设备使用反馈，当前状态和输入用于计算一个新的状态，然后反馈回设备并计时以更新它。
|location=Baltimore, MD, US
|location=Baltimore, MD, US
</ref> Friis and Jensen (1924) described regeneration in a set of electronic amplifiers as a case where ''the "feed-back" action is positive'' in contrast to negative feed-back action, which they mention only in passing.<ref name=friis>
</ref> Friis and Jensen (1924) described regeneration in a set of electronic amplifiers as a case where ''the "feed-back" action is positive'' in contrast to negative feed-back action, which they mention only in passing.<ref name=friis>
The stock market is an example of a system prone to oscillatory "hunting", governed by positive and negative feedback resulting from cognitive and emotional factors among market participants. For example:
Feedback can give rise to incredibly complex behaviors. The [[Mandelbrot set (black) within a continuously colored environment is plotted by repeatedly feeding back values through a simple equation and recording the points on the imaginary plane that fail to diverge|alt=]]
反馈可以导致难以置信的复杂行为。[[[ Mandelbrot 集(black)在一个连续着色的环境中绘制，方法是通过一个简单的方程反馈值，并记录假想平面上未能发散的点 | alt = ]]
Friis, H.T., and A.G.Jensen. "High Frequency Amplifiers" Bell System Technical Journal 3 (April 1924):181–205.</ref> [[Harold Stephen Black]]'s classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:
Friis, H.T., and A.G.Jensen. "High Frequency Amplifiers" Bell System Technical Journal 3 (April 1924):181–205.</ref> [[Harold Stephen Black]]'s classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:
By using feedback properties, the behavior of a system can be altered to meet the needs of an application; systems can be made stable, responsive or held constant. It is shown that dynamical systems with a feedback experience an adaptation to the edge of chaos.
通过使用反馈属性，系统的行为可以改变以满足应用程序的需要; 系统可以变得稳定、响应或保持不变。结果表明，具有反馈经验的动力系统具有对混沌边界的适应性。
{{Quote|Positive feed-back increases the gain of the amplifier, negative feed-back reduces it.<ref name=black>
{{Quote|Positive feed-back increases the gain of the amplifier, negative feed-back reduces it.<ref name=black>
According to Mindell (2002) confusion in the terms arose shortly after this:
According to Mindell (2002) confusion in the terms arose shortly after this:
{{Quote|...Friis and Jensen had made the same distinction Black used between "positive feed-back" and "negative feed-back", based not on the sign of the feedback itself but rather on its effect on the amplifier's gain. In contrast, Nyquist and Bode, when they built on Black's work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition.<ref name=mindell/>{{rp|page=121}}}}
In biological systems such as organisms, ecosystems, or the biosphere, most parameters must stay under control within a narrow range around a certain optimal level under certain environmental conditions. The deviation of the optimal value of the controlled parameter can result from the changes in internal and external environments. A change of some of the environmental conditions may also require change of that range to change for the system to function. The value of the parameter to maintain is recorded by a reception system and conveyed to a regulation module via an information channel. An example of this is insulin oscillations.
在诸如生物体、生态系统或生物圈等生物系统中，在某些环境条件下，大多数参数必须保持在围绕某一最佳水平的狭窄范围内。受控参数最优值的偏差可以由内外环境的变化引起。一些环境条件的改变也可能需要改变这个范围来改变系统的功能。要维持的参数值由接收系统记录并通过信息通道传输到调节模块。胰岛素振荡就是一个例子。
Even prior to the terms being applied, [[James Clerk Maxwell]] had described several kinds of "component motions" associated with the [[centrifugal governor]]s used in steam engines, distinguishing between those that lead to a continual ''increase'' in a disturbance or the amplitude of an oscillation, and those that lead to a ''decrease'' of the same.<ref name=maxwell>{{cite journal|last=Maxwell|first=James Clerk|title=On Governors|url=http://en.wikipedia.org/wiki/File:On_Governors.pdf|journal=Proceedings of the Royal Society of London|volume= 16|year= 1868 |pages= 270–283|doi=10.1098/rspl.1867.0055|s2cid=51751195}}</ref>
Biological systems contain many types of regulatory circuits, both positive and negative. As in other contexts, positive and negative do not imply that the feedback causes good or bad effects. A negative feedback loop is one that tends to slow down a process, whereas the positive feedback loop tends to accelerate it. The mirror neurons are part of a social feedback system, when an observed action is "mirrored" by the brain—like a self-performed action.
生物系统包含许多类型的调节回路，有正回路也有负回路。正如在其他情况下一样，正反馈并不意味着反馈会产生好的或坏的影响。负反馈回路会减慢一个过程，而正反馈回路则会加速这个过程。镜像神经元是社会反馈系统的一部分，当观察到的行为被大脑“镜像” ，就像一个自我执行的行为。
====Terminology====
====Terminology====
Normal tissue integrity is preserved by feedback interactions between diverse cell types mediated by adhesion molecules and secreted molecules that act as mediators; failure of key feedback mechanisms in cancer disrupts tissue function.
正常组织的完整性是通过粘附分子介导的不同类型细胞之间的反馈相互作用和作为介质的分泌分子来保持的; 癌症中关键反馈机制的失败扰乱了组织功能。
The terms positive and negative feedback are defined in different ways within different disciplines.
The terms positive and negative feedback are defined in different ways within different disciplines.
In an injured or infected tissue, inflammatory mediators elicit feedback responses in cells, which alter gene expression, and change the groups of molecules expressed and secreted, including molecules that induce diverse cells to cooperate and restore tissue structure and function. This type of feedback is important because it enables coordination of immune responses and recovery from infections and injuries. During cancer, key elements of this feedback fail. This disrupts tissue function and immunity.
在受伤或感染的组织中，炎症介质在细胞中引发反馈反应，改变基因表达，改变表达和分泌的分子群，包括诱导不同细胞合作和恢复组织结构和功能的分子。这种类型的反馈是重要的，因为它能够协调免疫反应和从感染和伤害中恢复。在癌症期间，这种反馈的关键因素失效了。这会破坏组织功能和免疫力。
# the altering of the ''gap'' between reference and actual values of a parameter, based on whether the gap is ''widening'' (positive) or ''narrowing'' (negative).<ref name="Ramaprasad" />
# the altering of the ''gap'' between reference and actual values of a parameter, based on whether the gap is ''widening'' (positive) or ''narrowing'' (negative).<ref name="Ramaprasad" />
Mechanisms of feedback were first elucidated in bacteria, where a nutrient elicits changes in some of their metabolic functions.
反馈机制首次在细菌中得到阐明，在细菌中营养物质引起了它们某些代谢功能的变化。
# the [[Valence (psychology)|valence]] of the ''action'' or ''effect'' that alters the gap, based on whether it has a ''happy'' (positive) or ''unhappy'' (negative) emotional connotation to the recipient or observer.<ref name=herold1977>Herold, David M., and Martin M. Greller. "Research Notes. FEEDBACK THE DEFINITION OF A CONSTRUCT." Academy of management Journal 20.1 (1977): 142-147.</ref>
# the [[Valence (psychology)|valence]] of the ''action'' or ''effect'' that alters the gap, based on whether it has a ''happy'' (positive) or ''unhappy'' (negative) emotional connotation to the recipient or observer.<ref name=herold1977>Herold, David M., and Martin M. Greller. "Research Notes. FEEDBACK THE DEFINITION OF A CONSTRUCT." Academy of management Journal 20.1 (1977): 142-147.</ref>
Feedback is also central to the operations of genes and gene regulatory networks. Repressor (see Lac repressor) and activator proteins are used to create genetic operons, which were identified by Francois Jacob and Jacques Monod in 1961 as feedback loops. These feedback loops may be positive (as in the case of the coupling between a sugar molecule and the proteins that import sugar into a bacterial cell), or negative (as is often the case in metabolic consumption).
反馈也是基因和基因调控网络运作的中心。阻遏蛋白(参见 Lac 阻遏蛋白)和激活蛋白被用来创造基因操纵子，这被 Francois Jacob 和 Jacques Monod 在1961年确定为反馈回路。这些反馈回路可能是正的(例如糖分子和将糖输入细菌细胞的蛋白质之间的耦合) ，也可能是负的(例如代谢消耗中经常出现的情况)。
The two definitions may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to definition 1, some authors use alternative terms, replacing ''positive/negative'' with ''self-reinforcing/self-correcting'',<ref name="senge">
The two definitions may cause confusion, such as when an incentive (reward) is used to boost poor performance (narrow a gap). Referring to definition 1, some authors use alternative terms, replacing ''positive/negative'' with ''self-reinforcing/self-correcting'',<ref name="senge">
On a larger scale, feedback can have a stabilizing effect on animal populations even when profoundly affected by external changes, although time lags in feedback response can give rise to predator-prey cycles.
在更大的范围内，即使受到外部变化的深刻影响，反馈也能对动物种群产生稳定作用，尽管反馈反应的时间滞后可能导致捕食者-被捕食者循环。
{{Cite book
{{Cite book
|author=Peter M. Senge
|author=Peter M. Senge
In zymology, feedback serves as regulation of activity of an enzyme by its direct or downstream in the metabolic pathway (see Allosteric regulation).
在酶学中，反馈是通过酶在代谢途径中的直接或下游来调节酶的活性的(见别构调节)。
|title=The Fifth Discipline: The Art and Practice of the Learning Organization
|title=The Fifth Discipline: The Art and Practice of the Learning Organization
|year=1990
|year=1990
The hypothalamic–pituitary–adrenal axis is largely controlled by positive and negative feedback, much of which is still unknown.
下丘脑-垂体-肾上腺轴在很大程度上受正反馈和负反馈控制，其中大部分仍然是未知的。
|publisher=Doubleday
|publisher=Doubleday
|location=New York
|location=New York
In psychology, the body receives a stimulus from the environment or internally that causes the release of hormones. Release of hormones then may cause more of those hormones to be released, causing a positive feedback loop. This cycle is also found in certain behaviour. For example, "shame loops" occur in people who blush easily. When they realize that they are blushing, they become even more embarrassed, which leads to further blushing, and so on.
在心理学中，身体接受来自环境或内部的刺激，从而导致荷尔蒙的释放。然后，荷尔蒙的释放可能会导致更多的荷尔蒙被释放，从而形成一个积极的反馈循环。在某些行为中也发现了这种循环。例如，“羞耻循环”发生在容易脸红的人身上。当他们意识到自己在脸红时，他们会变得更加尴尬，从而导致进一步的脸红，等等。
|isbn=978-0-385-26094-7
|isbn=978-0-385-26094-7
}}
}}
</ref> ''reinforcing/balancing'',<ref name="sterman">
The climate system is characterized by strong positive and negative feedback loops between processes that affect the state of the atmosphere, ocean, and land. A simple example is the ice-albedo positive feedback loop whereby melting snow exposes more dark ground (of lower albedo), which in turn absorbs heat and causes more snow to melt.
气候系统是影响大气、海洋和陆地状态的过程之间强烈的正反馈拥有属性。一个简单的例子是冰反照率正反馈循环，即融化的雪暴露出更多的黑色地面(反照率较低) ，反过来吸收热量，导致更多的雪融化。
John D. Sterman, ''Business Dynamics: Systems Thinking and Modeling for a Complex World'', McGraw Hill/Irwin, 2000. {{ISBN|978-0-07-238915-9}}
John D. Sterman, ''Business Dynamics: Systems Thinking and Modeling for a Complex World'', McGraw Hill/Irwin, 2000. {{ISBN|978-0-07-238915-9}}
</ref> or ''regenerative/degenerative''<ref>
</ref> or ''regenerative/degenerative''<ref>
Feedback is extensively used in control theory, using a variety of methods including state space (controls), full state feedback, and so forth. Note that in the context of control theory, "feedback" is traditionally assumed to specify "negative feedback".
反馈广泛应用于控制理论中，使用了包括状态空间(控件)、全状态反馈等多种方法。请注意，在控制理论的背景下，“反馈”传统上被假定为指定“负反馈”。
Hermann A Haus and Richard B. Adler, ''Circuit Theory of Linear Noisy Networks'', MIT Press, 1959
Hermann A Haus and Richard B. Adler, ''Circuit Theory of Linear Noisy Networks'', MIT Press, 1959
</ref> respectively. And for definition 2, some authors advocate describing the action or effect as positive/negative ''[[Reinforcement#Reinforcement|reinforcement]]'' or ''[[Reinforcement#Punishment|punishment]]'' rather than feedback.<ref name="Ramaprasad" /><ref name="skinner">
</ref> respectively. And for definition 2, some authors advocate describing the action or effect as positive/negative ''[[Reinforcement#Reinforcement|reinforcement]]'' or ''[[Reinforcement#Punishment|punishment]]'' rather than feedback.<ref name="Ramaprasad" /><ref name="skinner">
The most common general-purpose controller using a control-loop feedback mechanism is a proportional-integral-derivative (PID) controller. Heuristically, the terms of a PID controller can be interpreted as corresponding to time: the proportional term depends on the present error, the integral term on the accumulation of past errors, and the derivative term is a prediction of future error, based on current rate of change.
使用控制回路反馈机制的最常见的通用控制器是比例积分微分(PID)控制器。启发式地，PID 控制器的条款可以解释为对应的时间: 比例项取决于当前的错误，积分项积累过去的错误，导数项是一个预测未来的错误，基于当前的变化率。
BF Skinner, ''The Experimental Analysis of Behavior'', American Scientist, Vol. 45, No. 4 (SEPTEMBER 1957), pp. 343-371</ref>
BF Skinner, ''The Experimental Analysis of Behavior'', American Scientist, Vol. 45, No. 4 (SEPTEMBER 1957), pp. 343-371</ref>
"However, after scrutinizing the statistical properties of the structural equations, the members of the committee assured themselves that it is possible to have a significant positive feedback loop when using standardized scores, and a negative loop when using real scores."
"However, after scrutinizing the statistical properties of the structural equations, the members of the committee assured themselves that it is possible to have a significant positive feedback loop when using standardized scores, and a negative loop when using real scores."
For feedback in the educational context, see corrective feedback.
有关教育背景中的反馈，请参阅纠正反馈。
Ralph L. Levine, Hiram E. Fitzgerald. ''Analysis of the dynamic psychological systems: methods and applications'', {{ISBN|978-0306437465}} (1992) page 123</ref>
Ralph L. Levine, Hiram E. Fitzgerald. ''Analysis of the dynamic psychological systems: methods and applications'', {{ISBN|978-0306437465}} (1992) page 123</ref>
This confusion may arise because feedback can be used for either ''informational'' or ''motivational'' purposes, and often has both a ''[[Qualitative property|qualitative]]'' and a ''[[Quantitative property|quantitative]]'' component. As Connellan and Zemke (1993) put it:
This confusion may arise because feedback can be used for either ''informational'' or ''motivational'' purposes, and often has both a ''[[Qualitative property|qualitative]]'' and a ''[[Quantitative property|quantitative]]'' component. As Connellan and Zemke (1993) put it:
In ancient times, the float valve was used to regulate the flow of water in Greek and Roman water clocks; similar float valves are used to regulate fuel in a carburettor and also used to regulate tank water level in the flush toilet.
在古代，浮子阀被用来调节希腊和罗马水钟的水流; 类似的浮子阀被用来调节化油器的燃料，也被用来调节抽水马桶的水位。
{{Quote|''Quantitative'' feedback tells us how much and how many. ''Qualitative'' feedback tells us how good, bad or indifferent.<ref name=Connellan>Thomas K. Connellan and Ron Zemke, "Sustaining Knock Your Socks Off Service" AMACOM, 1 July 1993. {{ISBN|0-8144-7824-7}}</ref>{{rp|page=102}}}}
{{Quote|''Quantitative'' feedback tells us how much and how many. ''Qualitative'' feedback tells us how good, bad or indifferent.<ref name=Connellan>Thomas K. Connellan and Ron Zemke, "Sustaining Knock Your Socks Off Service" AMACOM, 1 July 1993. {{ISBN|0-8144-7824-7}}</ref>{{rp|page=102}}}}
The Dutch inventor Cornelius Drebbel (1572-1633) built thermostats (c1620) to control the temperature of chicken incubators and chemical furnaces. In 1745, the windmill was improved by blacksmith Edmund Lee, who added a fantail to keep the face of the windmill pointing into the wind. In 1787, Tom Mead regulated the rotation speed of a windmill by using a centrifugal pendulum to adjust the distance between the bedstone and the runner stone (i.e., to adjust the load).
荷兰发明家克尼利厄斯·雅布斯纵·戴博尔(1572-1633)建造了恒温器(c1620)来控制鸡的孵化器和化学炉的温度。1745年，铁匠埃德蒙 · 李对风车进行了改进，他在风车的正面加上了扇尾，使风车面朝向风。1787年，汤姆 · 米德通过使用离心摆来调节底石和流水石之间的距离(即调节负荷)来调节风车的转速。
====Limitations of negative and positive feedback====
====Limitations of negative and positive feedback====
While simple systems can sometimes be described as one or the other type, many systems with feedback loops cannot be so easily designated as simply positive or negative, and this is especially true when multiple loops are present.
While simple systems can sometimes be described as one or the other type, many systems with feedback loops cannot be so easily designated as simply positive or negative, and this is especially true when multiple loops are present.
The use of the centrifugal governor by James Watt in 1788 to regulate the speed of his steam engine was one factor leading to the Industrial Revolution. Steam engines also use float valves and pressure release valves as mechanical regulation devices. A mathematical analysis of Watt's governor was done by James Clerk Maxwell in 1868.
1788年 James Watt 使用离心式调速器来调节他的蒸汽机的速度是导致工业革命的一个因素。蒸汽发动机也使用浮子阀和释压阀作为机械调节装置。詹姆斯·克拉克·麦克斯韦在1868年对瓦特的调节器进行了数学分析。
{{Quote|When there are only two parts joined so that each affects the other, the properties of the feedback give important and useful information about the properties of the whole. But when the parts rise to even as few as four, if every one affects the other three, then twenty circuits can be traced through them; and knowing the properties of all the twenty circuits does not give complete information about the system.<ref name=Ashby/>{{rp|page=54}}}}
Internal combustion engines of the late 20th century employed mechanical feedback mechanisms such as the vacuum timing advance but mechanical feedback was replaced by electronic engine management systems once small, robust and powerful single-chip microcontrollers became affordable.
20世纪后期的内燃机采用了机械反馈机制，如真空定时推进，但机械反馈被电子发动机管理系统所取代，一旦小型、强大和功能强大的单片微控制器变得可以负担得起。
===Other types of feedback===
In general, feedback systems can have many signals fed back and the feedback loop frequently contain mixtures of positive and negative feedback where positive and negative feedback can dominate at different frequencies or different points in the state space of a system.
right
对
The term bipolar feedback has been coined to refer to biological systems where positive and negative feedback systems can interact, the output of one affecting the input of another, and vice versa.<ref name=Smit>
The use of feedback is widespread in the design of electronic components such as amplifiers, oscillators, and stateful logic circuit elements such as flip-flops and counters. Electronic feedback systems are also very commonly used to control mechanical, thermal and other physical processes.
反馈在电子元件设计中的应用非常广泛，例如放大器、振荡器和有状态逻辑电路元件，例如触发器和计数器。电子反馈系统也非常常用于控制机械，热和其他物理过程。
{{cite book |title=Introduction to Bioregulatory Medicine |author1=Alta Smit |author2=Arturo O'Byrne |chapter-url=https://books.google.com/books?id=RzXAOUnCM3oC&pg=PA6 |page=6 |chapter=Bipolar feedback |isbn=9783131469717 |year=2011 |publisher=Thieme}}
</ref>
If the signal is inverted on its way round the control loop, the system is said to have negative feedback; otherwise, the feedback is said to be positive. Negative feedback is often deliberately introduced to increase the stability and accuracy of a system by correcting or reducing the influence of unwanted changes. This scheme can fail if the input changes faster than the system can respond to it. When this happens, the lag in arrival of the correcting signal can result in over-correction, causing the output to oscillate or "hunt". While often an unwanted consequence of system behaviour, this effect is used deliberately in electronic oscillators.
如果在控制回路中信号是反向的，系统就称为负反馈; 否则，反馈就称为正反馈。负反馈通常是有意引入的，通过纠正或减少不必要的变化的影响来提高系统的稳定性和准确性。如果输入变化快于系统的响应速度，则此方案可能失败。当这种情况发生时，校正信号到达的滞后可能导致过度校正，导致输出振荡或“捕获”。虽然这种效应通常是系统行为的一个不希望出现的结果，但它却被有意地用于电子振荡器中。
Some systems with feedback can have very complex behaviors such as [[Chaos theory|chaotic behaviors]] in non-linear systems, while others have much more predictable behaviors, such as those that are used to make and design digital systems.
Harry Nyquist at Bell Labs derived the Nyquist stability criterion for determining the stability of feedback systems. An easier method, but less general, is to use Bode plots developed by Hendrik Bode to determine the gain margin and phase margin. Design to ensure stability often involves frequency compensation to control the location of the poles of the amplifier.
贝尔实验室的 Harry Nyquist 推导出了判定反馈系统稳定性的奈奎斯特稳定判据。一个比较简单但不太普遍的方法是使用 hendrikbode 开发的 Bode 图来确定增益裕度和相位裕度。保证稳定性的设计往往涉及频率补偿来控制放大器的极点位置。
Feedback is used extensively in digital systems. For example, binary counters and similar devices employ feedback where the current state and inputs are used to calculate a new state which is then fed back and clocked back into the device to update it.
Electronic feedback loops are used to control the output of electronic devices, such as amplifiers. A feedback loop is created when all or some portion of the output is fed back to the input. A device is said to be operating open loop if no output feedback is being employed and closed loop if feedback is being used.
电子反馈回路用于控制放大器等电子设备的输出。当输出的全部或部分被反馈给输入时，就创建了一个反馈循环。如果没有采用输出反馈，则称装置为操作开环，如果采用反馈，则称装置为闭环。
==Applications==
When two or more amplifiers are cross-coupled using positive feedback, complex behaviors can be created. These multivibrators are widely used and include:
当两个或两个以上的放大器使用正反馈进行交叉耦合时，可以产生复杂的行为。这些多重振动器被广泛使用，包括:
===Mathematics and dynamical systems===
[[File:Mandel zoom 00 mandelbrot set.jpg|322px|thumb|Feedback can give rise to incredibly complex behaviors. The [[Mandelbrot set]] (black) within a continuously colored environment is plotted by repeatedly feeding back values through a simple equation and recording the points on the imaginary plane that fail to diverge|alt=]]
{{Main|Dynamical system|Chaos theory|Edge of chaos|Control theory}}
By using feedback properties, the behavior of a system can be altered to meet the needs of an application; systems can be made stable, responsive or held constant. It is shown that dynamical systems with a feedback experience an adaptation to the [[edge of chaos]].<ref>{{cite journal|last1=Wotherspoon|first1=T.|last2=Hubler|first2=A.|title=Adaptation to the edge of chaos with random-wavelet feedback|journal=J. Phys. Chem. A|date=2009|doi=10.1021/jp804420g|pmid=19072712|volume=113|issue=1|pages=19–22|bibcode=2009JPCA..113...19W}}</ref>
===Biology===
{{See also|Homeostasis|Allostasis}}
A Negative feedback occurs when the fed-back output signal has a relative phase of 180° with respect to the input signal (upside down). This situation is sometimes referred to as being out of phase, but that term also is used to indicate other phase separations, as in "90° out of phase". Negative feedback can be used to correct output errors or to desensitize a system to unwanted fluctuations. In feedback amplifiers, this correction is generally for waveform distortion reduction or to establish a specified gain level. A general expression for the gain of a negative feedback amplifier is the asymptotic gain model.
当反馈输出信号相对于输入信号的相位为180 ° (上下颠倒)时，就会产生负反馈。这种情况有时被称为不同相，但这一术语也用来表示其他相分离，如“90 ° 不同相”。负反馈可以用来纠正输出错误，或者使系统对有害的波动不敏感。在反馈放大器中，这种校正通常用于降低波形失真或建立指定的增益电平。获得负反馈放大器的一个通用表达式是渐进增益模型。
In [[biology|biological]] systems such as [[organism]]s, [[ecosystem]]s, or the [[biosphere]], most parameters must stay under control within a narrow range around a certain optimal level under certain environmental conditions. The deviation of the optimal value of the controlled parameter can result from the changes in internal and external environments. A change of some of the environmental conditions may also require change of that range to change for the system to function. The value of the parameter to maintain is recorded by a reception system and conveyed to a regulation module via an information channel. An example of this is [[insulin oscillation]]s.
Biological systems contain many types of regulatory circuits, both positive and negative. As in other contexts, ''positive'' and ''negative'' do not imply that the feedback causes ''good'' or ''bad'' effects. A negative feedback loop is one that tends to slow down a process, whereas the positive feedback loop tends to accelerate it. The [[mirror neuron]]s are part of a social feedback system, when an observed action is "mirrored" by the brain—like a self-performed action.
Positive feedback occurs when the fed-back signal is in phase with the input signal. Under certain gain conditions, positive feedback reinforces the input signal to the point where the output of the device oscillates between its maximum and minimum possible states. Positive feedback may also introduce hysteresis into a circuit. This can cause the circuit to ignore small signals and respond only to large ones. It is sometimes used to eliminate noise from a digital signal. Under some circumstances, positive feedback may cause a device to latch, i.e., to reach a condition in which the output is locked to its maximum or minimum state. This fact is very widely used in digital electronics to make bistable circuits for volatile storage of information.
当反馈信号与输入信号同相时，就会产生正反馈。在一定的增益条件下，正反馈增强输入信号，使器件的输出在其最大和最小可能状态之间振荡。正反馈也可能在电路中引入滞后现象。这会导致电路忽略小信号，只响应大信号。它有时被用来消除数字信号中的噪声。在某些情况下，正反馈可能导致设备闭锁，即，达到输出锁定到其最大或最小状态的条件。这个事实在数字电子产品中被广泛应用，用来制造信息挥发性记忆体的双稳态电路。
Normal tissue integrity is preserved by feedback interactions between diverse cell types mediated by adhesion molecules and secreted molecules that act as mediators; failure of key feedback mechanisms in cancer disrupts tissue function.<ref>{{cite journal|last1=Vlahopoulos|first1=SA|last2=Cen|first2=O|last3=Hengen|first3=N|last4=Agan|first4=J|last5=Moschovi|first5=M|last6=Critselis|first6=E|last7=Adamaki|first7=M|last8=Bacopoulou|first8=F|last9=Copland|first9=JA|last10=Boldogh|first10=I|last11=Karin|first11=M|last12=Chrousos|first12=GP|title=Dynamic aberrant NF-κB spurs tumorigenesis: A new model encompassing the microenvironment.|journal=Cytokine & Growth Factor Reviews|date=20 June 2015|pmid=26119834|doi=10.1016/j.cytogfr.2015.06.001|volume=26|issue=4|pages=389–403|pmc=4526340}}</ref>
The loud squeals that sometimes occurs in audio systems, PA systems, and rock music are known as audio feedback. If a microphone is in front of a loudspeaker that it is connected to, sound that the microphone picks up comes out of the speaker, and is picked up by the microphone and re-amplified. If the loop gain is sufficient, howling or squealing at the maximum power of the amplifier is possible.
有时在音频系统、扩音系统和摇滚乐中发出的响亮的尖叫声被称为音频反馈。如果麦克风位于与之相连的扬声器前面，麦克风拾取的声音就会从扬声器中发出，然后被麦克风拾取并重新放大。如果环路增益是足够的，嚎叫或尖叫在最大功率的放大器是可能的。
In an injured or infected tissue, inflammatory mediators elicit feedback responses in cells, which alter gene expression, and change the groups of molecules expressed and secreted, including molecules that induce diverse cells to cooperate and restore tissue structure and function. This type of feedback is important because it enables coordination of immune responses and recovery from infections and injuries. During cancer, key elements of this feedback fail. This disrupts tissue function and immunity.<ref>{{cite journal | last1 = Vlahopoulos | first1 = SA | title = Aberrant control of NF-κB in cancer permits transcriptional and phenotypic plasticity, to curtail dependence on host tissue: molecular mode. | journal = Cancer Biology & Medicine | date = August 2017 | pmid = 28884042 | doi = 10.20892/j.issn.2095-3941.2017.0029 | volume = 14 | issue = 3 | pages = 254–270 | pmc = 5570602}}</ref><ref>{{cite journal|last1=Korneev|first1=KV|last2=Atretkhany|first2=KN|last3=Drutskaya|first3=MS|last4=Grivennikov|first4=SI|last5=Kuprash|first5=DV|last6=Nedospasov|first6=SA|title=TLR-signaling and proinflammatory cytokines as drivers of tumorigenesis.|journal=Cytokine|date=January 2017|volume=89|pages=127–135|doi=10.1016/j.cyto.2016.01.021|pmid=26854213}}</ref>
Mechanisms of feedback were first elucidated in bacteria, where a nutrient elicits changes in some of their metabolic functions.<ref>{{cite journal|last1= Sanwal|first1=BD| title= Allosteric controls of amphilbolic pathways in bacteria.|journal= Bacteriol. Rev.|date=March 1970|volume=34|issue=1|pages=20–39 |pmid=4315011 |pmc=378347|doi=10.1128/MMBR.34.1.20-39.1970}}</ref>
op-amp relaxation oscillator.]]
[运放张弛振荡器]
Feedback is also central to the operations of [[gene]]s and [[gene regulatory network]]s. [[Repressor protein|Repressor]] (see [[Lac repressor]]) and [[activator protein|activator]] [[protein]]s are used to create genetic [[operon]]s, which were identified by [[Francois Jacob]] and [[Jacques Monod]] in 1961 as ''feedback loops''.<ref>{{cite journal|last1= Jacob|first1=F|last2=Monod|first2=J|title= Genetic regulatory mechanisms in the synthesis of proteins.|journal= J Mol Biol|date=June 1961|volume=3|issue=3|pages=318–356 |pmid=13718526|doi=10.1016/S0022-2836(61)80072-7}}</ref> These feedback loops may be positive (as in the case of the coupling between a sugar molecule and the proteins that import sugar into a bacterial cell), or negative (as is often the case in [[metabolic]] consumption).
An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current (DC) from a power supply to an alternating current signal. They are widely used in many electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games.
振盪器是一种产生周期性振荡电子信号的电子电路，通常是正弦波或方波。振荡器将直流电从电源转换成交流电信号。它们被广泛应用于许多电子设备中。振荡器产生信号的常见例子包括无线电和电视发射机发出的信号、调节计算机和石英钟的时钟信号，以及电子寻呼机和电子游戏发出的声音。
On a larger scale, feedback can have a stabilizing effect on animal populations even when profoundly affected by external changes, although time lags in feedback response can give rise to [[Lotka–Volterra equation|predator-prey cycles]].<ref>
CS Holling. "Resilience and stability of ecological systems". Annual Review of Ecology and Systematics 4:1-23. 1973</ref>
A 4-bit [[ring counter using D-type flip flops]]
4位[使用 d 型触发器的环形计数器]
In [[fermentation (biochemistry)|zymology]], feedback serves as regulation of activity of an enzyme by its direct {{Not a typo|product(s)}} or downstream {{Not a typo|metabolite(s)}} in the metabolic pathway (see [[Allosteric regulation]]).
A latch or a flip-flop is a circuit that has two stable states and can be used to store state information. They typically constructed using feedback that crosses over between two arms of the circuit, to provide the circuit with a state. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Latches and flip-flops are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems.
锁存器或触发器是具有两个稳定状态的电路，可用于存储状态信息。它们通常利用电路的两个臂之间交叉的反馈来构造，以便为电路提供一个状态。该电路可以通过施加到一个或多个控制输入的信号来改变状态，并且具有一个或两个输出。它是时序逻辑电路的基本存储元素。锁存器和触发器是用于计算机、通信和许多其他类型系统的数字电子系统的基本构件。
The [[hypothalamic–pituitary–adrenal axis]] is largely controlled by positive and negative feedback, much of which is still unknown.
Latches and flip-flops are used as data storage elements. Such data storage can be used for storage of state, and such a circuit is described as sequential logic. When used in a finite-state machine, the output and next state depend not only on its current input, but also on its current state (and hence, previous inputs). It can also be used for counting of pulses, and for synchronizing variably-timed input signals to some reference timing signal.
锁存器和触发器用作数据存储元件。这样的数据存储可以用来存储状态，这样的电路被描述为时序逻辑电路。当用于有限状态机时，输出和下一状态不仅取决于其当前输入，还取决于其当前状态(因此，以前的输入)。它也可以用于计数脉冲，并用于同步一些参考定时信号的变时输入信号。
In [[psychology]], the body receives a stimulus from the environment or internally that causes the release of [[hormone]]s. Release of hormones then may cause more of those hormones to be released, causing a positive feedback loop. This cycle is also found in certain behaviour. For example, "shame loops" occur in people who blush easily. When they realize that they are blushing, they become even more embarrassed, which leads to further blushing, and so on.<ref>{{cite magazine|last=Scheff |first=Thomas |url=http://www.psychologytoday.com/blog/lets-connect/200909/the-emotionalrelational-world |title=The Emotional/Relational World |magazine=Psychology Today |date=2009-09-02 |accessdate=2013-07-10}}</ref>
Flip-flops can be either simple (transparent or opaque) or clocked (synchronous or edge-triggered). Although the term flip-flop has historically referred generically to both simple and clocked circuits, in modern usage it is common to reserve the term flip-flop exclusively for discussing clocked circuits; the simple ones are commonly called latches.
触发器可以是简单的(透明的或者不透明的)或者是计时的(同步的或者边缘触发的)。虽然触发器这个术语在历史上一直泛指简单电路和时钟电路，但在现代用法中，通常将触发器这个术语专门用于讨论时钟电路，简单的电路通常称为锁存电路。
===Climate science===
Using this terminology, a latch is level-sensitive, whereas a flip-flop is edge-sensitive. That is, when a latch is enabled it becomes transparent, while a flip flop's output only changes on a single type (positive going or negative going) of clock edge.
使用这个术语，锁存器是电平敏感的，而触发器是边缘敏感的。也就是说，当锁存器启用时，它变得透明，而触发器的输出只在时钟边缘的单一类型(正向或负向)上发生变化。
{{Main|Climate change feedback}}
The climate system is characterized by strong positive and negative feedback loops between processes that affect the state of the atmosphere, ocean, and land. A simple example is the [[Ice-albedo feedback|ice-albedo positive feedback]] loop whereby melting snow exposes more dark ground (of lower [[albedo]]), which in turn absorbs heat and causes more snow to melt.
Feedback loops provide generic mechanisms for controlling the running, maintenance, and evolution of software and computing systems. Feedback-loops are important models in the engineering of adaptive software, as they define the behaviour of the interactions among the control elements over the adaptation process, to guarantee system properties at run-time. Feedback loops and foundations of control theory have been successfully applied to computing systems. In particular, they have been applied to the development of products such as IBM's Universal Database server and IBM Tivoli. From a software perspective, the autonomic (MAPE, monitor analyze plan execute) loop proposed by researchers of IBM is another valuable contribution to the application of feedback loops to the control of dynamic properties and the design and evolution of autonomic software systems.
反馈回路为控制软件和计算系统的运行、维护和进化提供了通用机制。反馈回路是自适应软件工程中的重要模型，它定义了自适应过程中控制元件之间相互作用的行为，以保证系统在运行时的性能。反馈环路和控制理论的基础已成功地应用于计算系统。特别是，它们已经应用于产品的开发，如 IBM 的 Universal Database server 和 IBM Tivoli。从软件的角度来看，IBM 研究人员提出的自主(MAPE，monitor analyze plan execute)回路是对反馈回路应用于动态特性控制和自主软件系统设计与演化的另一个有价值的贡献。
===Control theory===
{{Main|Control theory}}
Feedback is extensively used in control theory, using a variety of methods including [[state space (controls)]], [[full state feedback]], and so forth. Note that in the context of control theory, "feedback" is traditionally assumed to specify "negative feedback".<ref name=mees>
''"There is a tradition in control theory that one deals with a ''negative feedback loop'' in which a negative sign is included in the feedback loop..."''
A.I.Mees, "Dynamics of Feedback Systems", New York: J. Wiley, c1981. {{ISBN|0-471-27822-X}}. p69</ref>
{{Further|PID controller}}
The most common general-purpose [[controller (control theory)|controller]] using a control-loop feedback mechanism is a [[PID controller|proportional-integral-derivative]] (PID) controller. Heuristically, the terms of a PID controller can be interpreted as corresponding to time: the proportional term depends on the ''present'' error, the integral term on the accumulation of ''past'' errors, and the derivative term is a prediction of ''future'' error, based on current rate of change.<ref>{{Citation | url = http://www.eolss.net/ebooks/Sample%20Chapters/C18/E6-43-03-03.pdf | title = PID Control | last = Araki | first = M. }}</ref>
Feedback is also a useful design principle for designing user interfaces.
反馈也是设计用户界面的一个有用的设计原则。
===Education===
For feedback in the educational context, see [[corrective feedback]].
Video feedback is the video equivalent of acoustic feedback. It involves a loop between a video camera input and a video output, e.g., a television screen or monitor. Aiming the camera at the display produces a complex video image based on the feedback.
视频反馈是视频等效的声学反馈。它涉及一个循环之间的视频摄像机输入和视频输出，例如，一个电视屏幕或显示器。将摄像机对准显示器，根据反馈信息生成复杂的视频图像。
===Mechanical engineering===
In ancient times, the [[float valve]] was used to regulate the flow of water in Greek and Roman [[water clock]]s; similar float valves are used to regulate fuel in a [[carburettor]] and also used to regulate tank water level in the [[flush toilet]].
The Dutch inventor [[Cornelius Drebbel]] (1572-1633) built thermostats (c1620) to control the temperature of chicken incubators and chemical furnaces. In 1745, the windmill was improved by blacksmith Edmund Lee, who added a [[windmill fantail|fantail]] to keep the face of the windmill pointing into the wind. In 1787, [[Tom Mead]] regulated the rotation speed of a windmill by using a [[conical pendulum|centrifugal pendulum]] to adjust the distance between the bedstone and the runner stone (i.e., to adjust the load).
The use of the [[centrifugal governor]] by [[James Watt]] in 1788 to regulate the speed of his [[steam engine]] was one factor leading to the [[Industrial Revolution]]. Steam engines also use float valves and [[relief valve|pressure release valves]] as mechanical regulation devices. A [[mathematical analysis]] of Watt's governor was done by [[James Clerk Maxwell]] in 1868.<ref name=maxwell/>
The stock market is an example of a system prone to oscillatory "hunting", governed by positive and negative feedback resulting from cognitive and emotional factors among market participants. For example:
股票市场就是这样一个系统的例子，它倾向于振荡性的”捕猎” ，由市场参与者的认知和情感因素所产生的正反馈和负反馈来控制。例如:
The ''[[SS Great Eastern|Great Eastern]]'' was one of the largest steamships of its time and employed a steam powered rudder with feedback mechanism designed in 1866 by [[John McFarlane Gray]]. [[Joseph Farcot]] coined the word ''[[Servomechanism|servo]]'' in 1873 to describe steam-powered steering systems. Hydraulic servos were later used to position guns. [[Elmer Ambrose Sperry]] of the [[Sperry Corporation]] designed the first [[autopilot]] in 1912. [[Nicolas Minorsky]] published a theoretical analysis of automatic ship steering in 1922 and described the [[PID controller]].<ref name="Minorsky">{{cite journal |author=Minorsky, Nicolas |year=1922 |title=Directional stability of automatically steered bodies |journal=J. Amer. Soc of Naval Engineers |volume=34 |issue= 2|pages=280–309 |doi= 10.1111/j.1559-3584.1922.tb04958.x}}</ref>
Internal combustion engines of the late 20th century employed mechanical feedback mechanisms such as the [[Ignition timing#Vacuum timing advance|vacuum timing advance]] but mechanical feedback was replaced by electronic [[engine control unit|engine management systems]] once small, robust and powerful single-chip [[microcontroller]]s became affordable.
George Soros used the word reflexivity, to describe feedback in the financial markets and developed an investment theory based on this principle.
乔治•索罗斯(George Soros)用“反身性”(reflexivity)一词来描述金融市场的反馈，并根据这一原则发展了一套投资理论。
===Electronic engineering===
[[File:Ideal feedback model.svg|thumb|The simplest form of a feedback amplifier can be represented by the ''ideal block diagram'' made up of [https://www.google.com/search?tbo=p&tbm=bks&q=%22A+unilateral+block+or+network+is+one+in+which+power+may+be+transmitted+in+one+direction+only.%22&num=10&gws_rd=ssl unilateral elements].<ref name="Chen">
The conventional economic equilibrium model of supply and demand supports only ideal linear negative feedback and was heavily criticized by Paul Ormerod in his book The Death of Economics, which, in turn, was criticized by traditional economists. This book was part of a change of perspective as economists started to recognise that chaos theory applied to nonlinear feedback systems including financial markets.
传统的经济均衡/需求模型只支持理想的线性负反馈，Paul Ormerod 在他的《经济学之死》一书中对此进行了严厉的批评，而这本书反过来又遭到了传统经济学家的批评。随着经济学家开始认识到混沌理论适用于包括金融市场在内的非线性反馈系统，这本书是观点转变的一部分。
{{cite book|title=Circuit Analysis and Feedback Amplifier Theory|author=Wai-Kai Chen|publisher=CRC Press|year=2005|isbn=9781420037272|location=423825181|pages=13–1|chapter=Chapter 13: General feedback theory|quote=[In a practical amplifier] the forward path may not be strictly unilateral, the feedback path is usually bilateral, and the input and output coupling networks are often complicated.|chapter-url=https://books.google.com/books?id=ZlJM1OLDQx0C&pg=SA13-PA1}}
</ref>|280px|right]]
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The use of feedback is widespread in the design of [[electronics|electronic]] components such as [[amplifier]]s, [[oscillator]]s, and stateful [[logic circuit]] elements such as [[flip-flop (electronics)|flip-flop]]s and [[counter (digital)|counter]]s. Electronic feedback systems are also very commonly used to control mechanical, thermal and other physical processes.
If the signal is inverted on its way round the control loop, the system is said to have ''[[negative feedback amplifier|negative feedback]]'';<ref name=KalS>
{{cite book |title=Basic Electronics: Devices, Circuits and IT Fundamentals |author=Santiram Kal |url=https://books.google.com/books?id=_Bw_-ZyGL6YC&q=%22it+is+called+negative+feedback%22+%22if+the+feedback+signal+reduces+the+input+signal%22&pg=PA191 |quote=If the feedback signal reduces the input signal, ''i.e.'' it is out of phase with the input [signal], it is called negative feedback. |isbn=9788120319523 |year=2009 |publisher=PHI Learning Pvt. Ltd |page=191}}
</ref> otherwise, the feedback is said to be ''positive''. Negative feedback is often deliberately introduced to increase the [[BIBO stability|stability]] and accuracy of a system by correcting or reducing the influence of unwanted changes. This scheme can fail if the input changes faster than the system can respond to it. When this happens, the lag in arrival of the correcting signal can result in over-correction, causing the output to [[oscillation|oscillate]] or "hunt".<ref>With mechanical devices, hunting can be severe enough to destroy the device.</ref> While often an unwanted consequence of system behaviour, this effect is used deliberately in electronic oscillators.
[[Harry Nyquist]] at [[Bell Labs]] derived the [[Nyquist stability criterion]] for determining the stability of feedback systems. An easier method, but less general, is to use [[Bode plot]]s developed by [[Hendrik Wade Bode|Hendrik Bode]] to determine the [[Gain margin|gain margin and phase margin]]. Design to ensure stability often involves [[frequency compensation]] to control the location of the [[pole (complex analysis)|pole]]s of the amplifier.
Electronic feedback loops are used to control the output of [[electronics|electronic]] devices, such as [[amplifiers]]. A feedback loop is created when all or some portion of the output is fed back to the input. A device is said to be operating ''open loop'' if no output feedback is being employed and ''closed loop'' if feedback is being used.<ref>P. Horowitz & W. Hill, ''The Art of Electronics'', Cambridge University Press (1980), Chapter 3, relating to operational amplifiers.</ref>
When two or more amplifiers are cross-coupled using positive feedback, complex behaviors can be created. These ''[[multivibrator]]s'' are widely used and include:
* astable circuits, which act as oscillators
* monostable circuits, which can be pushed into a state, and will return to the stable state after some time
* bistable circuits, which have two stable states that the circuit can be switched between
}}
}}
====Negative feedback====
A Negative feedback occurs when the fed-back output signal has a relative phase of 180° with respect to the input signal (upside down). This situation is sometimes referred to as being ''out of phase'', but that term also is used to indicate other phase separations, as in "90° out of phase". Negative feedback can be used to correct output errors or to desensitize a system to unwanted fluctuations.<ref name=Bhattacharya>
For an analysis of desensitization in the system pictured, see {{cite book |author=S.K Bhattacharya |title=Linear Control Systems |pages=134–135 |quote=The parameters of a system ... may vary... The primary advantage of using feedback in control systems is to reduce the system's sensitivity to parameter variations. |chapter=§5.3.1 Effect of feedback on parameter variations |isbn=9788131759523 |publisher=Pearson Education India |year=2011 |chapter-url=https://books.google.com/books?id=e5Z1A_6jxAUC&q=%22primary+advantage+of+using+feedback+in+control+system+is+to+reduce+the+system%27s+sensitivity+to+parameter+variations%22&pg=PA135}}
</ref> In feedback amplifiers, this correction is generally for waveform [[distortion]] reduction{{citation needed|date=October 2014}} or to establish a specified [[Gain (electronics)|gain]] level. A general expression for the gain of a negative feedback amplifier is the [[asymptotic gain model]].
====Positive feedback====
Positive feedback occurs when the fed-back signal is in phase with the input signal. Under certain gain conditions, positive feedback reinforces the input signal to the point where the output of the device [[oscillates]] between its maximum and minimum possible states. Positive feedback may also introduce [[hysteresis]] into a circuit. This can cause the circuit to ignore small signals and respond only to large ones. It is sometimes used to eliminate noise from a digital signal. Under some circumstances, positive feedback may cause a device to latch, i.e., to reach a condition in which the output is locked to its maximum or minimum state. This fact is very widely used in digital electronics to make [[Flip-flop (electronics)|bistable]] circuits for volatile storage of information.
The loud squeals that sometimes occurs in [[audio system]]s, [[public address system|PA systems]], and [[rock music]] are known as [[audio feedback]]. If a microphone is in front of a loudspeaker that it is connected to, sound that the microphone picks up comes out of the speaker, and is picked up by the microphone and re-amplified. If the [[loop gain]] is sufficient, howling or squealing at the maximum power of the amplifier is possible.
====Oscillator====
[[File:OpAmpHystereticOscillator.svg|thumb|A popular [[Relaxation oscillator#Comparator–based electronic relaxation oscillator|op-amp relaxation oscillator]].]]
An [[electronic oscillator]] is an [[electronic circuit]] that produces a periodic, [[oscillation|oscillating]] electronic signal, often a [[sine wave]] or a [[square wave]].<ref name="Snelgrove">{{cite encyclopedia
| last = Snelgrove
| first = Martin
| title = Oscillator
| encyclopedia = McGraw-Hill Encyclopedia of Science and Technology, 10th Ed., Science Access online service
Category:Control theory
Category:Control theory
范畴: 控制理论
范畴: 控制理论
| publisher = McGraw-Hill
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<noinclude>