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第41行： + + − 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|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, US|url=https://books.google.com/books?id=sExvSbe9MSsC|isbn=9780801868955}}</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>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:+ − + − 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。20世纪20年代，随着再生电路的引入，正反馈的概念已经流行起来。<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, US|url=https://books.google.com/books?id=sExvSbe9MSsC|isbn=9780801868955}}</ref> 弗里斯 Friis和延森 Jensen(1924)将一套电子放大器中的再生回路描述为"反馈"作用是正的例子，以此和他们顺便提及的负反馈作用相区别。<ref name=friis>Friis, H.T., and A.G.Jensen. "High Frequency Amplifiers" Bell System Technical Journal 3 (April 1924):181–205.</ref>哈罗德·史蒂芬·布莱克 Harold Stephen Black1934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。布莱克认为: − − − {{Quote|Positive feed-back increases the gain of the amplifier, negative feed-back reduces it.<ref name=black>H.S. Black, "Stabilized feed-back amplifiers", ''Electrical Engineering'', vol. 53, pp. 114–120, January 1934.</ref>}} − − {{Quote|正反馈增加放大器的增益，负反馈降低增益。<ref name=black>H.S. Black, "Stabilized feed-back amplifiers", ''Electrical Engineering'', vol. 53, pp. 114–120, January 1934.</ref>}} − − − According to Mindell (2002) confusion in the terms arose shortly after this: − − 据Mindell(2002年)说，在这之后不久就出现了术语上的混乱。 − − − {{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}}}} − − {{Quote|...Friis和Jensen对Black在 "正反馈 "和 "负反馈 "之间的区分是一样的，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。相反，Nyquist和Bode在Black的工作基础上，将负反馈称为符号相反的反馈。布莱克难以说服其他人相信他的发明的实用性，因为再基本的概念上存在混乱。<ref name=mindell/>{{rp|page=121}}}} − − − 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> − − 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. − − 甚至在这些术语被应用之前，詹姆斯·克莱克·麦克斯韦 James Clerk Maxwell就已经描述了几种与蒸汽机中使用的离心式调速器相关的 "运动分量"，并区分了那些导致扰动或振荡幅度持续''增加''的运动和那些导致其减少的运动。 <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> − − − ====Terminology==== − 术语 − − − The terms positive and negative feedback are defined in different ways within different disciplines. + + − − − # 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). + − # 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 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. − − #改变差距的行动或效果的<font color="#ff8000"> 效价 valence</font>，基于它对接受者或观察者是否具有''快乐''（积极）或''不快乐''（消极）的情感内涵。<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 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">{{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|page=424|url=https://archive.org/details/fifthdisciplineasen00seng}} − </ref> ''reinforcing/balancing'',<ref name="sterman">John D. Sterman, ''Business Dynamics: Systems Thinking and Modeling for a Complex World'', McGraw Hill/Irwin, 2000. {{ISBN|978-0-07-238915-9}}</ref> ''discrepancy-enhancing/discrepancy-reducing''<ref name="carver">Charles S. Carver, Michael F. Scheier: ''On the Self-Regulation of Behavior'' Cambridge University Press, 2001 </ref> or ''regenerative/degenerative''<ref>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">BF Skinner, ''The Experimental Analysis of Behavior'', American Scientist, Vol. 45, No. 4 (SEPTEMBER 1957), pp. 343-371</ref>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.<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." − For feedback in the educational context, see corrective feedback. − Ralph L. Levine, Hiram E. Fitzgerald. ''Analysis of the dynamic psychological systems: methods and applications'', {{ISBN|978-0306437465}} (1992) page 123</ref> − − − 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. 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. − − 这两种定义可能会引起混淆，比如当激励(奖励)被用来提高糟糕的表现(缩小差距)。针对定义1，一些作者使用了替代术语，分别用自强化/自纠正<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|page=424|url=https://archive.org/details/fifthdisciplineasen00seng}} + + − 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 and a quantitative component. As Connellan and Zemke (1993) put it: − − 这种混淆可能会出现，因为反馈既可以用于信息的目的，也可以用于激励的目的，而且往往同时具有定性和定量的成分。正如康奈兰 Connellan和泽姆克 Zemke(1993)所言: − − − {{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|''定量''反馈告诉我们多少。''定性''反馈告诉我们多好、多坏或二者之间。<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}}}} − − − − 正反馈和负反馈的限制 − − − 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. − + − {{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}}}}+ − − {{Quote|当只有两个部分连接在一起，以至于每个部分都会影响到另一个部分时，反馈的属性就能提供关于整体属性的重要有用信息。但是，当部分增加到即使只有四个时，如果每一个都影响其他三个，那么就可以通过它们找到二十个回路；而知道所有这二十个回路的特性并不能提供有关系统的完整信息。<ref name=Ashby/>{{rp|page=54}}}} − − − − 其他反馈类型 − − 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. − − + − 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>{{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> − − − 术语<font color="#ff8000"> 双极反馈 bipolar feedback</font> 是指生物系统中正反馈系统和负反馈系统可以相互作用，一个系统的输出会影响另一个系统的输入，反之亦然。<ref name = Smit>{{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> − − − 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. − − 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. − − − 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. − + − + − + − − 应用 − − − − 数学和动力系统 − − [[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}} − − {{主要|动力系统|混沌理论|混沌边缘|控制理论}} − − − 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> − − 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. − + − − 生物 − − − {{See also|Homeostasis|Allostasis}} − {{另请参见|内环境稳态|稳态}} − − − 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. − − 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. − − − − 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. + − 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> 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>+ − − 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.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. − − 正常组织的完整性是通过粘附分子和作为介质的分泌分子介导的不同细胞类型之间的反馈相互作用来保持的；癌症中关键反馈机制的失效会破坏组织功能。.<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>在受伤或感染的组织中，炎症介质会引起细胞的反馈反应，改变基因表达，改变细胞表达和分泌的分子群，包括诱导不同细胞合作的分子和恢复组织结构和功能的分子。这种类型的反馈很重要，因为它能够协调免疫反应、使机体从感染和损伤中恢复。在癌症过程中，这种反馈的关键要素会失效，进而破坏组织功能和免疫力。<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>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). − − Mechanisms of feedback were first elucidated in bacteria, where a nutrient elicits changes in some of their metabolic functions.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). − − 反馈机制首次在细菌中得到阐明，是一种营养物质会引起其部分代谢功能的变化的机制。<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>反馈也是基因和基因调控网络运作的中心。用<font color="#ff8000"> 阻遏蛋白 Repressor</font>(参见 Lac 阻遏蛋白)和<font color="#ff8000"> 激活蛋白 activator protein</font>来创造<font color="#ff8000"> 基因操纵子 genetic operons protein</font>，这被弗朗索瓦·雅各布 Francois Jacob 和雅克·莫诺德 Jacques Monod 在1961年确定为反馈回路。<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>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结合) ，也可能是负的(例如代谢消耗中经常出现的情况)。 − − − 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> − − 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. − + − 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]]). − − In zymology, feedback serves as regulation of activity of an enzyme by its direct product(s) or downstream metabolite(s) in the metabolic pathway (see Allosteric regulation). − − 在酶学中，反馈在代谢途径中通过直接产物或的下游代谢产物来调节酶的活性(见'''<font color="#ff8000"> 变构调节allosteric regulation </font>''')。 − − − The [[hypothalamic–pituitary–adrenal axis]] is largely controlled by positive and negative feedback, much of which is still unknown. − − The hypothalamic–pituitary–adrenal axis is largely controlled by positive and negative feedback, much of which is still unknown. + − 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>+ − + − 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，从而导致激素的释放。然后，激素的释放可能会导致更多的激素被释放，从而形成正反馈循环。这种循环也存在于某些行为中。例如，容易脸红的人就会出现 "羞耻循环"。当他们意识到自己脸红的时候，他们会变得更加尴尬，从而导致进一步的脸红，等等。<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> − − − 气候科学 − − {{Main|Climate change feedback}} − {{主要|气候变化反馈}} − − − 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. − − 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. − − − − − ===Control theory=== − 控制理论 − − − {{Main|Control theory}} − {{主要|控制理论}} − − − 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> − − 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". + − − {{Further|PID controller}} − − {{进一步|PID控制器}}。、 − − 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> − − 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. + + − + − 教育 − − For feedback in the educational context, see [[corrective feedback]]. − For feedback in the educational context, see corrective feedback. − − 关于教育方面的反馈，见<font color="#ff8000"> 纠正性反馈 corrective feedback</font>。 − − − ===Mechanical engineering=== − 机械工程 − − − 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]]. − − 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. − + − 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 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 Cornelius Drebbel (1572-1633)制造了恒温器(c1620)用于控制鸡的孵化器和化学炉的温度。1745年，铁匠埃德蒙·李 Edmund Lee对风车进行了改进，他增加了一个扇形尾翼，使风车的正面始终面向风。1787年，汤姆·米德Tom Mead通过使用离心摆调节基石和动石之间的距离(即调节负荷)来调节风车的转速。 − − − 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 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，詹姆斯·瓦特 James Watt 使用离心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阀和泄压阀作为机械调节装置。詹姆斯·克拉克·麦克斯韦 James Clerk Maxwell在1868年对Watt的调节器进行了数学分析。<ref name=maxwell/> − − − 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> − − 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. − − “Great Eastern”是当时最大的汽轮之一，采用了由[[约翰·麦克法兰·格雷 John McFarlane Gray]]在1866年设计的带有反馈机制的蒸汽舵。约瑟夫·法尔科 [Joseph Farcot在1873年创造了“<font color="#ff8000"> 伺服系统 servo</font>”一词来描述蒸汽动力转向系统，后来伺服系统被用来定位喷枪。 斯佩里公司 Sperry Corporatio的[埃尔默·安布罗斯·斯佩里Elmer Ambrose Sperry在1912年设计了的第一台自动驾驶仪 autopilot。尼古拉斯·米诺尔斯基 Nicolas Minorsky在1922年发表了关于自动船舶操纵的理论分析，并描述了PID控制器。<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. − − 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. − + − − − − [[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">{{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]] − − [[File:Ideal feedback model.svg|thumb|反馈放大器的最简单形式可以用由单向元件组成的“理想框图”来表示。<ref name="Chen">{{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]] − − − 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. − − 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. − − − − 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. − − 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. − + − [[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. − − 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. − − − − − 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> − − 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. + + − When two or more amplifiers are cross-coupled using positive feedback, complex behaviors can be created. These ''[[multivibrator]]s'' are widely used and include: − − 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。这些多谐振荡器被广泛使用，包括: − − − * astable circuits, which act as oscillators − *非稳态电路，作为振荡器使用 − − * 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 + + − + − − 负反馈 − − − 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]]. − − 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. − − 当反馈的输出信号相对于输入信号有180°的相对相位（上下颠倒）时，就会出现负反馈。这种情况有时被称为失相，但该术语也用于表示其他相位分离，如 "90°失相"。负反馈可用于纠正输出误差或使系统对不需要的波动脱敏。<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>在反馈放大器中，这种校正一般是为了减少波形失真或建立一个指定的增益水平。负反馈放大器的增益的一般表达式是渐进增益模型。 − − − ====Positive feedback==== − 正反馈 − − − 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. − − 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. − − − − 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. − − 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. + + − + − 振荡器 − − [[File:OpAmpHystereticOscillator.svg|thumb|A popular [[Relaxation oscillator#Comparator–based electronic relaxation oscillator|op-amp relaxation oscillator]].]] − − [[File:OpAmpHystereticOscillator.svg|thumb|一个流行的运放弛缓振荡器]]。 − − − 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. − − 电子振荡器是一种产生周期性的、振荡信号的电子电路，通常是正弦波或方波。振荡器将电源中的直流电（DC）转换为交流信号。振荡器被广泛应用于许多电子设备中。 振荡器产生的信号的常见例子包括无线电和电视发射机广播的信号，调节计算机和石英钟的时钟信号，以及电子传呼机和视频游戏产生的声音。 − − − ====Lactches and flip-flops==== − − − A 4-bit [[ring counter using D-type flip flops]] − − 4位的使用d型触发器的环形计数器 − − − 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. − + − 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(因而也取决于以前的输入)。它也可用于脉冲的计数，以及将可变时序输入信号同步到某个参考时序信号。 − − 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。+ − − − 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。 − − − − 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. − − − − Feedback is also a useful design principle for designing user interfaces. − − − − − 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. − + − + − 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: − − 股市是一个易于出现振荡 "捕猎"的系统的例子，它受市场参与者之间的认知和情感因素所产生的正负反馈所支配。例如： − − − − George Soros used the word reflexivity, to describe feedback in the financial markets and developed an investment theory based on this principle. − − − − − − 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.
无编辑摘要
当一个系统的输出作为输入被送回，并作为形成回路或循环的因果链的一部分时，就会产生'''反馈 feedback'''。<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>这个系统可以说是反馈到了自身。在因果关系应用于反馈系统时，必须谨慎处理其概念。
当一个系统的输出作为输入被送回，并作为形成回路或循环的因果链的一部分时，就会产生'''反馈 feedback'''。<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>这个系统可以说是反馈到了自身。在因果关系应用于反馈系统时，必须谨慎处理其概念。
对于一个反馈系统，很难进行简单的因果推理，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，产生了一个循环论证。这就使得基于因果关系的推理变得很困难，因此有必要将系统作为一个整体进行分析。——卡尔·约翰·阿斯特洛姆·马丁 Karl Johan Åström和查德·M·默里 Richard M.Murray
::对于一个反馈系统，很难进行简单的因果推理，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，产生了一个循环论证。这就使得基于因果关系的推理变得很困难，因此有必要将系统作为一个整体进行分析。——卡尔·约翰·阿斯特洛姆·马丁 Karl Johan Åström和查德·M·默里 Richard M.Murray
[[文件:复杂系统.jpg|缩略图|右|复杂系统]]
[[文件:复杂系统.jpg|缩略图|右|复杂系统]]
该图表示的汽车中的巡航控制系统可以作为负反馈的一个例子，它使车速与目标速度（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路面变化的坡度（干扰）的组合扭矩。汽车的速度（状态）由速度表测量。误差信号是速度计测量的速度与目标速度（设定点）的偏差。这个测量的误差由控制器来解译并以此来调整加速器，控制燃料流到发动机（效应器）。由此产生的发动机扭矩的变化，即反馈，与路面变化的坡度所施加的扭矩相结合，以减少速度误差，减少道路干扰。
该图表示的汽车中的巡航控制系统可以作为负反馈的一个例子，它使车速与目标速度（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路面变化的坡度（干扰）的组合扭矩。汽车的速度（状态）由速度表测量。误差信号是速度计测量的速度与目标速度（设定点）的偏差。这个测量的误差由控制器来解译并以此来调整加速器，控制燃料流到发动机（效应器）。由此产生的发动机扭矩的变化，即反馈，与路面变化的坡度所施加的扭矩相结合，以减少速度误差，减少道路干扰。
“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。20世纪20年代，随着再生电路的引入，正反馈的概念已经流行起来。<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, US|url=https://books.google.com/books?id=sExvSbe9MSsC|isbn=9780801868955}}</ref> 弗里斯 Friis和延森 Jensen（1924）将一套电子放大器中的再生回路描述为"反馈"作用是正的例子，以此和他们顺便提及的负反馈作用相区别。<ref name=friis>Friis, H.T., and A.G.Jensen. "High Frequency Amplifiers" Bell System Technical Journal 3 (April 1924):181–205.</ref>哈罗德·史蒂芬·布莱克 Harold Stephen Black1934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。布莱克认为:
::正反馈增加放大器的增益，负反馈降低增益。<ref name=black>H.S. Black, "Stabilized feed-back amplifiers", ''Electrical Engineering'', vol. 53, pp. 114–120, January 1934.</ref>}}
据Mindell（2002年）说，在这之后不久就出现了术语上的混乱。
::……Friis和Jensen对Black在“正反馈”和“负反馈”之间的区分是一样的，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。相反，Nyquist和Bode在Black的工作基础上，将负反馈称为符号相反的反馈。布莱克难以说服其他人相信他的发明的实用性，因为再基本的概念上存在混乱。<ref name=mindell/>
甚至在这些术语被应用之前，詹姆斯·克莱克·麦克斯韦 James Clerk Maxwell就已经描述了几种与蒸汽机中使用的离心式调速器相关的“运动分量”，并区分了那些导致扰动或振荡幅度持续增加的运动和那些导致其减少的运动。<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>
====术语====
正反馈和负反馈在不同的学科中有不同的定义。
正反馈和负反馈在不同的学科中有不同的定义。
# 根据差距是扩大（正）还是缩小（负）改变一个参数的参考值和实际值之间的差距；<ref name="Ramaprasad" />
# 根据差距是扩大（正）还是缩小（负）改变一个参数的参考值和实际值之间的差距；<ref name="Ramaprasad" />
# 改变差距的行动或效果的'''效价 valence'''，基于它对接受者或观察者是否具有快乐（积极）或不快乐（消极）的情感内涵。<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>
这两种定义可能会引起混淆，比如当激励（奖励）被用来提高糟糕的表现（缩小差距）。针对定义1，一些作者使用了替代术语，分别用自强化/自纠正<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|page=424|url=https://archive.org/details/fifthdisciplineasen00seng}}
</ref>、强化/平衡<ref name="sterman">John D. Sterman, ''Business Dynamics: Systems Thinking and Modeling for a Complex World'', McGraw Hill/Irwin, 2000. {{ISBN|978-0-07-238915-9}}</ref>、离散增强/离散减少<ref name="carver">Charles S. Carver, Michael F. Scheier: ''On the Self-Regulation of Behavior'' Cambridge University Press, 2001 </ref>或再生/退化<ref>Hermann A Haus and Richard B. Adler, ''Circuit Theory of Linear Noisy Networks'', MIT Press, 1959</ref>来替代正/负。对于定义2，一些作者主张将行为或效果描述为积极/消极的强化或惩罚，而不是反馈。<ref name="Ramaprasad" /><ref name="skinner">BF Skinner, ''The Experimental Analysis of Behavior'', American Scientist, Vol. 45, No. 4 (SEPTEMBER 1957), pp. 343-371</ref>然而，即使是在一个单一的学科中，反馈的例子也可以被称为正的或负的，这取决于如何衡量或引用其含义。<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."
</ref>、强化/平衡<ref name="sterman">John D. Sterman, ''Business Dynamics: Systems Thinking and Modeling for a Complex World'', McGraw Hill/Irwin, 2000. {{ISBN|978-0-07-238915-9}}</ref>、离散增强/离散减少<ref name="carver">Charles S. Carver, Michael F. Scheier: ''On the Self-Regulation of Behavior'' Cambridge University Press, 2001 </ref>或再生/退化<ref>Hermann A Haus and Richard B. Adler, ''Circuit Theory of Linear Noisy Networks'', MIT Press, 1959</ref>来替代正/负。对于定义2，一些作者主张将行为或效果描述为积极/消极的强化或惩罚，而不是反馈。<ref name="Ramaprasad" /><ref name="skinner">BF Skinner, ''The Experimental Analysis of Behavior'', American Scientist, Vol. 45, No. 4 (SEPTEMBER 1957), pp. 343-371</ref>然而，即使是在一个单一的学科中，反馈的例子也可以被称为正的或负的，这取决于如何衡量或引用其含义。<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."
For feedback in the educational context, see corrective feedback.
For feedback in the educational context, see corrective feedback.
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>
这种混淆可能会出现，因为反馈既可以用于信息的目的，也可以用于激励的目的，而且往往同时具有定性和定量的成分。正如康奈兰 Connellan和泽姆克 Zemke（1993）所言：
::定量反馈告诉我们多少。定性反馈告诉我们多好、多坏或二者之间。<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>
====正反馈和负反馈的限制====
====Limitations of negative and positive feedback====
虽然单一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指定为正或负，尤其是存在多个回路时。
虽然单一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指定为正或负，尤其是存在多个回路时。
::当只有两个部分连接在一起，以至于每个部分都会影响到另一个部分时，反馈的属性就能提供关于整体属性的重要有用信息。但是，当部分增加到即使只有四个时，如果每一个都影响其他三个，那么就可以通过它们找到二十个回路；而知道所有这二十个回路的特性并不能提供有关系统的完整信息。<ref name=Ashby/>
===其他反馈类型===
===Other types of feedback===
一般来说，反馈系统可以有许多信号反馈，反馈回路中经常包含混合在一起的正反馈和负反馈，其中正反馈和负反馈可以在系统状态空间的不同频率或不同点占主导地位。
一般来说，反馈系统可以有许多信号反馈，反馈回路中经常包含混合在一起的正反馈和负反馈，其中正反馈和负反馈可以在系统状态空间的不同频率或不同点占主导地位。
术语'''双极反馈 bipolar feedback'''是指生物系统中正反馈系统和负反馈系统可以相互作用，一个系统的输出会影响另一个系统的输入，反之亦然。<ref name = Smit>{{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>
一些带有反馈的系统会有非常复杂的行为，比如非线性系统中的混沌行为，而另一些系统则有更多可预测的行为，比如那些用于制造和设计数字系统的系统。
一些带有反馈的系统会有非常复杂的行为，比如非线性系统中的混沌行为，而另一些系统则有更多可预测的行为，比如那些用于制造和设计数字系统的系统。
反馈在数字系统中得到了广泛的应用。例如，二进制计数器和类似的设备采用了反馈，即利用当前的状态和输入来计算一个新的状态，然后反馈到设备并计时更新它。
反馈在数字系统中得到了广泛的应用。例如，二进制计数器和类似的设备采用了反馈，即利用当前的状态和输入来计算一个新的状态，然后反馈到设备并计时更新它。
==应用==
===数学和动力系统===
[[File:Mandel zoom 00 mandelbrot set.jpg|322px|thumb|反馈可以产生令人难以置信的复杂行为。通过一个简单的方程反复反馈数值，并记录虚平面上未能偏离的点，绘制出连续着色环境中的'''曼德尔布罗特集（布莱克） Mandelbrot(black) set'''。
==Applications==
===Mathematics and dynamical systems===
[[File:Mandel zoom 00 mandelbrot set.jpg|322px|thumb|反馈可以产生令人难以置信的复杂行为。通过一个简单的方程反复反馈数值，并记录虚平面上未能偏离的点，绘制出连续着色环境中的<font color="#ff8000"> 曼德尔布罗特集（布莱克） Mandelbrot set]] (black)</font>。
通过使用反馈属性，可以更改系统的行为以满足应用程序的需求；可以使系统稳定、响应迅速或保持恒定。结果表明，具有反馈的动力系统会适应混沌边缘现象。<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>
通过使用反馈属性，可以更改系统的行为以满足应用程序的需求；可以使系统稳定、响应迅速或保持恒定。结果表明，具有反馈的动力系统会适应混沌边缘现象。<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>
===生物===
===Biology===
在生物体、生态系统或生物圈等生物系统中，大多数参数必须在特定环境下保持在以最佳水平为中心的小范围内。受控参数和最佳值之间的偏差可能是由于内外部环境的变化造成的。环境条件的变化，也需要改变参数变化的范围来维持系统的运行。受控参数的值由接收系统记录下来，并通过信息通道传达给调节模块。胰岛素振荡就是一个例子。
在生物体、生态系统或生物圈等生物系统中，大多数参数必须在特定环境下保持在以最佳水平为中心的小范围内。受控参数和最佳值之间的偏差可能是由于内外部环境的变化造成的。环境条件的变化，也需要改变参数变化的范围来维持系统的运行。受控参数的值由接收系统记录下来，并通过信息通道传达给调节模块。胰岛素振荡就是一个例子。
生物系统包含许多类型的调节回路，包括正向和负向。与其他情况一样，正负并不意味着反馈会造成好的或坏的影响。负反馈回路是一种倾向于减缓过程的回路，而正反馈回路则倾向于加速过程。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”——就像一个自导自演的行为。
生物系统包含许多类型的调节回路，包括正向和负向。与其他情况一样，正负并不意味着反馈会造成好的或坏的影响。负反馈回路是一种倾向于减缓过程的回路，而正反馈回路则倾向于加速过程。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”——就像一个自导自演的行为。
正常组织的完整性是通过粘附分子和作为介质的分泌分子介导的不同细胞类型之间的反馈相互作用来保持的；癌症中关键反馈机制的失效会破坏组织功能。<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>在受伤或感染的组织中，炎症介质会引起细胞的反馈反应，改变基因表达，改变细胞表达和分泌的分子群，包括诱导不同细胞合作的分子和恢复组织结构和功能的分子。这种类型的反馈很重要，因为它能够协调免疫反应、使机体从感染和损伤中恢复。在癌症过程中，这种反馈的关键要素会失效，进而破坏组织功能和免疫力。<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>
反馈机制首次在细菌中得到阐明，是一种营养物质会引起其部分代谢功能的变化的机制。<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>反馈也是基因和基因调控网络运作的中心。用'''阻遏蛋白 Repressor'''（参见Lac阻遏蛋白）和'''激活蛋白 activator protein'''来创造'''基因操纵子 genetic operons protein'''，这被弗朗索瓦·雅各布 Francois Jacob和雅克·莫诺德 Jacques Monod在1961年确定为反馈回路。<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>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结合），也可能是负的（例如代谢消耗中经常出现的情况）。
尽管反馈反应的时间滞后可能引起捕食者-猎物循环，在受到外部变化的深刻影响的情况下，反馈也能对动物种群产生稳定作用。<ref>CS Holling. "Resilience and stability of ecological systems". Annual Review of Ecology and Systematics 4:1-23. 1973</ref>
尽管反馈反应的时间滞后可能引起捕食者-猎物循环，在受到外部变化的深刻影响的情况下，反馈也能对动物种群产生稳定作用。<ref>CS Holling. "Resilience and stability of ecological systems". Annual Review of Ecology and Systematics 4:1-23. 1973</ref>
在酶学中，反馈在代谢途径中通过直接产物或的下游代谢产物来调节酶的活性（见'''变构调节 allosteric regulation'''）。
下丘脑-垂体-肾上腺在很大程度上受到正反馈和负反馈的控制，其中的机制很大程度上仍然未知。
下丘脑-垂体-肾上腺在很大程度上受到正反馈和负反馈的控制，其中的机制很大程度上仍然未知。
在心理学中，身体接受来自环境或内部的刺激，从而导致激素的释放。然后，激素的释放可能会导致更多的激素被释放，从而形成正反馈循环。这种循环也存在于某些行为中。例如，容易脸红的人就会出现“羞耻循环”。当他们意识到自己脸红的时候，他们会变得更加尴尬，从而导致进一步的脸红，等等。<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>
===气候科学===
气候系统的特点是，影响大气、海洋和陆地状态的过程之间存在着强烈的正负反馈回路。一个简单的例子是冰-反射率正反馈环路，即雪的融化使更多的黑暗地面（反射率较低）暴露出来，反过来吸收热量，使更多的雪融化。
===Climate science===
气候系统的特点是，影响大气、海洋和陆地状态的过程之间存在着强烈的正负反馈回路。一个简单的例子是冰-反射率正反馈环路，即雪的融化使更多的黑暗地面(反射率较低)暴露出来，反过来吸收热量，使更多的雪融化。
===控制理论===
反馈广泛应用于控制理论中，使用的方法很多，包括状态矢量空间（控制）、全状态反馈等。需要注意的是，在控制理论的背景下，“反馈”通常特指“负反馈”。<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>
反馈广泛应用于控制理论中，使用的方法很多，包括状态矢量空间（控制）、全状态反馈等。需要注意的是，在控制理论的背景下，“反馈”通常特指“负反馈”。<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>
最常见的采用控制回路反馈机制的通用控制器是比例-积分-导数（PID）控制器。从启发式的角度看，PID控制器的项可以解释为与时间相对应：比例项取决于现在的误差，积分项取决于过去误差的积累，而导数项则是根据当前的变化率，对未来误差进行预测。<ref>{{Citation | url = http://www.eolss.net/ebooks/Sample%20Chapters/C18/E6-43-03-03.pdf | title = PID Control | last = Araki | first = M. }}</ref>
最常见的采用控制回路反馈机制的通用控制器是比例-积分-导数（PID）控制器。从启发式的角度看，PID控制器的项可以解释为与时间相对应：比例项取决于现在的误差，积分项取决于过去误差的积累，而导数项则是根据当前的变化率，对未来误差进行预测。<ref>{{Citation | url = http://www.eolss.net/ebooks/Sample%20Chapters/C18/E6-43-03-03.pdf | title = PID Control | last = Araki | first = M. }}</ref>
===教育===
关于教育方面的反馈，见'''纠正性反馈 corrective feedback'''。
===Education===
===机械工程===
在古代，浮阀被用来调节希腊和罗马水钟的水流; 类似的浮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。
在古代，浮阀被用来调节希腊和罗马水钟的水流; 类似的浮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。
荷兰发明家克尼利厄斯·雅布斯纵·戴博尔 Cornelius Drebbel（1572-1633）制造了恒温器（c1620）用于控制鸡的孵化器和化学炉的温度。1745年，铁匠埃德蒙·李 Edmund Lee对风车进行了改进，他增加了一个扇形尾翼，使风车的正面始终面向风。1787年，汤姆·米德 Tom Mead通过使用离心摆调节基石和动石之间的距离（即调节负荷）来调节风车的转速。
1788年，詹姆斯·瓦特 James Watt使用离心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阀和泄压阀作为机械调节装置。詹姆斯·克拉克·麦克斯韦 James Clerk Maxwell在1868年对Watt的调节器进行了数学分析。<ref name=maxwell/>
“Great Eastern”是当时最大的汽轮之一，采用了由约翰·麦克法兰·格雷 John McFarlane Gray在1866年设计的带有反馈机制的蒸汽舵。约瑟夫·法尔科 Joseph Farcot在1873年创造了“'''伺服系统 servo'''”一词来描述蒸汽动力转向系统，后来伺服系统被用来定位喷枪。斯佩里公司 Sperry Corporatio的埃尔默·安布罗斯·斯佩里 Elmer Ambrose Sperry在1912年设计了的第一台自动驾驶仪 autopilot。尼古拉斯·米诺尔斯基 Nicolas Minorsky在1922年发表了关于自动船舶操纵的理论分析，并描述了PID控制器。<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>
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，但当小型、坚固和功能强大的单片机变得经济实惠后，机械反馈就被电子发动机管理系统所取代。
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，但当小型、坚固和功能强大的单片机变得经济实惠后，机械反馈就被电子发动机管理系统所取代。
===电子工程===
===Electronic engineering===
电子工程
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。电子反馈系统也常用于控制机械，热和其他物理过程。
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。电子反馈系统也常用于控制机械，热和其他物理过程。
如果信号在绕过控制环路的过程中发生了反转，则称系统有负反馈；<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>否则，称反馈为正反馈。负反馈常常被刻意引入，通过纠正或减少不需要的变化的影响来提高系统的稳定性和准确性 如果输入的变化速度快于系统对它的响应速度，这种方案就会失效。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”。<ref>With mechanical devices, hunting can be severe enough to destroy the device.</ref>虽然这种效应通常是系统行为不希望出现的结果，但它却被有意地用于电子振荡器中。
如果信号在绕过控制环路的过程中发生了反转，则称系统有负反馈；<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>否则，称反馈为正反馈。负反馈常常被刻意引入，通过纠正或减少不需要的变化的影响来提高系统的稳定性和准确性 如果输入的变化速度快于系统对它的响应速度，这种方案就会失效。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”。<ref>With mechanical devices, hunting can be severe enough to destroy the device.</ref>虽然这种效应通常是系统行为不希望出现的结果，但它却被有意地用于电子振荡器中。
贝尔实验室的哈里·奈奎斯特 Harry Nyquist推导出了判定反馈系统稳定性的'''奈奎斯特稳定判据 Nyquist stability criterion Chaos theory'''。一个比较简单但不太常用的方法是使用亨德里克博德 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使用频率补偿来控制放大器的极点位置。
贝尔实验室的哈里·奈奎斯特 Harry Nyquist 推导出了判定反馈系统稳定性的<font color="#ff8000"> 奈奎斯特稳定判据 Nyquist stability criterion Chaos theory</font>。一个比较简单但不太常用的方法是使用亨德里克博德 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使用频率补偿来控制放大器的极点位置。
电子反馈回路用于控制电子设备的输出，如放大器。当所有或部分输出反馈到输入时，就形成了一个反馈回路。如果没有采用输出反馈，则称为开环运行，如果采用反馈，则称为闭环运行。<ref>P. Horowitz & W. Hill, ''The Art of Electronics'', Cambridge University Press (1980), Chapter 3, relating to operational amplifiers.</ref>
电子反馈回路用于控制电子设备的输出，如放大器。当所有或部分输出反馈到输入时，就形成了一个反馈回路。如果没有采用输出反馈，则称为开环运行，如果采用反馈，则称为闭环运行。<ref>P. Horowitz & W. Hill, ''The Art of Electronics'', Cambridge University Press (1980), Chapter 3, relating to operational amplifiers.</ref>
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。这些多谐振荡器被广泛使用，包括：
* 非稳态电路，作为振荡器使用
* 单稳态电路，可以将其推入一个状态，并在一段时间后恢复到稳定状态。
* 单稳态电路，可以将其推入一个状态，并在一段时间后恢复到稳定状态。
* 双稳态电路，它有两个稳定的状态，电路可以在这两个状态之间切换。
* 双稳态电路，它有两个稳定的状态，电路可以在这两个状态之间切换。
====负反馈====
当反馈的输出信号相对于输入信号有180°的相对相位（上下颠倒）时，就会出现负反馈。这种情况有时被称为失相，但该术语也用于表示其他相位分离，如“90°失相”。负反馈可用于纠正输出误差或使系统对不需要的波动脱敏。<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>在反馈放大器中，这种校正一般是为了减少波形失真或建立一个指定的增益水平。负反馈放大器的增益的一般表达式是渐进增益模型。
====正反馈====
====Negative feedback====
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，达到将输出锁定到其最大或最小状态的条件。这个功能在数字电子产品中被广泛应用于制作双稳态电路，用于信息的易失性存储。
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，达到将输出锁定到其最大或最小状态的条件。这个功能在数字电子产品中被广泛应用于制作双稳态电路，用于信息的易失性存储。
音响系统、扩音系统和摇滚音乐中有时会出现的响亮的尖叫声，这就是所谓的音频反馈。如果话筒在它所连接的扬声器前，话筒接收的声音就会从扬声器中传出，并被话筒结束并再次放大。如果环路增益足够，在放大器的最大功率下就可以发出啸叫或尖叫声。
音响系统、扩音系统和摇滚音乐中有时会出现的响亮的尖叫声，这就是所谓的音频反馈。如果话筒在它所连接的扬声器前，话筒接收的声音就会从扬声器中传出，并被话筒结束并再次放大。如果环路增益足够，在放大器的最大功率下就可以发出啸叫或尖叫声。
====振荡器====
电子振荡器是一种产生周期性的、振荡信号的电子电路，通常是正弦波或方波。振荡器将电源中的直流电（DC）转换为交流信号。振荡器被广泛应用于许多电子设备中。振荡器产生的信号的常见例子包括无线电和电视发射机广播的信号，调节计算机和石英钟的时钟信号，以及电子传呼机和视频游戏产生的声音。
====Oscillator====
====锁存器或触发器====
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。它们通常利用两臂电路之间交叉的反馈来构造，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，产生一个或两个输出。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。
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。它们通常利用两臂电路之间交叉的反馈来构造，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，产生一个或两个输出。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。
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（因而也取决于以前的输入）。它也可用于脉冲的计数，以及将可变时序输入信号同步到某个参考时序信号。
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。
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、维护和升级提供了通用机制。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又一宝贵贡献。
反馈回路为控制软件和计算系统的运行、维护和升级提供了通用机制。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又一宝贵贡献。
反馈也是设计用户界面时一个有用的设计原则。
反馈也是设计用户界面时一个有用的设计原则。
视频反馈是相当于声音反馈的视频。它涉及到摄像机输入和视频输出（如电视屏幕或显示器）之间的循环。将摄像机对准显示器，会生成基于反馈的复杂的视频图像。
视频反馈是相当于声音反馈的视频。它涉及到摄像机输入和视频输出（如电视屏幕或显示器）之间的循环。将摄像机对准显示器，会生成基于反馈的复杂的视频图像。
股市是一个易于出现振荡“捕猎”的系统的例子，它受市场参与者之间的认知和情感因素所产生的正负反馈所支配。例如：
乔治•索罗斯 George Soros用“'''反身性 reflexivity servo'''”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。
乔治•索罗斯 George Soros 用“<font color="#ff8000"> 反身性 reflexivity servo</font>”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。
传统的经济供求平衡模型只支持理想的线性负反馈，保罗·奥默罗德 Paul Ormerod在他的《经济学之死》一书中对这个模型提出了严厉的批评，而传统经济学家也对她提出了批评。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，这本书成为了转变观点的一部分。
传统的经济供求平衡模型只支持理想的线性负反馈，保罗·奥默罗德 Paul Ormerod在他的《经济学之死》一书中对这个模型提出了严厉的批评，而传统经济学家也对她提出了批评。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，这本书成为了转变观点的一部分。