河北建筑工程學(xué)院畢業(yè)設(shè)計(jì)（論文）外文資料翻譯系別電氣工程系專業(yè)電氣工程及其自動(dòng)化班級(jí)姓名學(xué)號(hào)外文出處SPECIALIZEDENGLISHFORARCHITECTURALELECTRICENGINEERINGANDAUTOMATION附件1、外文原文；2、外文資料翻譯譯文。指導(dǎo)教師評(píng)語(yǔ)簽字年月日注請(qǐng)將該封面與附件裝訂成冊(cè)。1、外文原文INTRODUCTIONSTOTEMPERATURECONTROLANDPIDCONTROLLERSPROCESSCONTROLSYSTEMAUTOMATICPROCESSCONTROLISCONCERNEDWITHMAINTAININGPROCESSVARIABLESTEMPERATURESPRESSURESFLOWSCOMPOSITIONS,ANDTHELIKEATSOMEDESIREDOPERATIONVALUEPROCESSESAREDYNAMICINNATURECHANGESAREALWAYSOCCURRING,ANDIFACTIONSARENOTTAKEN,THEIMPORTANTPROCESSVARIABLESTHOSERELATEDTOSAFETY,PRODUCTQUALITY,ANDPRODUCTIONRATESWILLNOTACHIEVEDESIGNCONDITIONSINORDERTOFIXIDEAS,LETUSCONSIDERAHEATEXCHANGERINWHICHAPROCESSSTREAMISHEATEDBYCONDENSINGSTEAMTHEPROCESSISSKETCHEDINFIG1FIG1HEATEXCHANGERTHEPURPOSEOFTHISUNITISTOHEATTHEPROCESSFLUIDFROMSOMEINLETTEMPERATURE,TIT,UPTOACERTAINDESIREDOUTLETTEMPERATURE,TTASMENTIONED,THEHEATINGMEDIUMISCONDENSINGSTEAMTHEENERGYGAINEDBYTHEPROCESSFLUIDISEQUALTOTHEHEATRELEASEDBYTHESTEAM,PROVIDEDTHEREARENOHEATLOSSESTOSURROUNDINGS,IIITHATIS,THEHEATEXCHANGERANDPIPINGAREWELLINSULATEDINTHISPROCESSTHEREAREMANYVARIABLESTHATCANCHANGE,CAUSINGTHEOUTLETTEMPERATURETODEVIATEFROMITSDESIREDVALUE21IFTHISHAPPENS,SOMEACTIONMUSTBETAKENTOCORRECTFORTHISDEVIATIONTHATIS,THEOBJECTIVEISTOCONTROLTHEOUTLETPROCESSTEMPERATURETOMAINTAINITSDESIREDVALUEONEWAYTOACCOMPLISHTHISOBJECTIVEISBYFIRSTMEASURINGTHETEMPERATURETT,THENCOMPARINGITTOITSDESIREDVALUE,AND,BASEDONTHISCOMPARISON,DECIDINGWHATTODOTOCORRECTFORANYDEVIATIONTHEFLOWOFSTEAMCANBEUSEDTOCORRECTFORTHEDEVIATIONTHISIS,IFTHETEMPERATUREISABOVEITSDESIREDVALUE,THENTHESTEAMVALVECANBETHROTTLEDBACKTOCUTTHESTEARRFLOWENERGYTOTHEHEATEXCHANGERIFTHETEMPERATUREISBELOWITSDESIREDVALUE,THENTHESTEAMVALVECOULDBEOPENEDSOMEMORETOINCREASETHESTEAMFLOWENERGYTOTHEEXCHANGERALLOFTHESECANBEDONEMANUALLYBYTHEOPERATOR,ANDSINCETHEPROCEDUREISFAIRLYSTRAIGHTFORWARD,ITSHOULDPRESENTNOPROBLEMHOWEVER,SINCEINMOSTPROCESSPLANTSTHEREAREHUNDREDSOFVARIABLESTHATMUSTBEMAINTAINEDATSOMEDESIREDVALUE,THISCORRECTIONPROCEDUREWOULDREQUIREDATREMENDOUSNUMBEROFOPERATORSCONSEQUENTLY,WEWOULDLIKETOACCOMPLISHTHISCONTROLAUTOMATICALLYTHATIS,WEWANTTOHAVEINSTNNNENTSTHATCONTROLTHEVARIABLESWJTBOMREQURINGINTERVENTIONFROMTHEOPERATORSITHISISWHATWEMEANBYAUTOMATICPROCESSCONTROLTOACCOMPLISHHISOBJECTIVEACONTROLSYSTEMMUSTBEDESIGNEDANDIMPLEMENTEDAPOSSIBLECONTROLSYSTEMANDITSBASICCOMPONENTSARESHOWNINFIG2FIG2HEATEXCHANGERCONTROLLOOPTHEFIRSTTHINGTODOISTOMEASURETHEOUTLETTEMPERAVAREOFTHEPROCESSSTREAMASENSORTHERMOCOUPLE,THERMISTORS,ETCDOESTHISTHISSENSORISCONNECTEDPHYSICALLYTOATRANSMITTER,WHICHTAKESTHEOUTPUTFROMTHESENSORANDCONVERTSITTOASIGNALSTRONGENOUGHTOBETRANSMITTERTOACONTROLLERTHECONTROLLERTHENRECEIVESTHESIGNAL,WHICHISRELATEDTOTHETEMPERATURE,ANDCOMPARESITWITHDESIREDVALUEDEPENDINGONTHISCOMPARISON,THECONTROLLERDECIDESWHATTODOTOMAINTAINTHETEMPERATUREATITSDESIREDVALUEBASEONTHISDECISION,THECONTROLLERTHENSENDSANOTHERSIGNALTOFINALCONTROLELEMENT,WHICHINTURNMANIPULATESTHESTEAMFLOWTHEPRECEDINGPARAGRAPHPRESENTSTHEFOURBASICCOMPONENTSOFALLCONTROLSYSTEMSTHEYARE1SENSOR,ALSOOFTENCALLEDTHEPRIMARYELEMENT2TRANSMITTER,ALSOCALLEDTHESECONDARYELEMENT3CONTROLLER,THE“BRAIN“OFTHECONTROLSYSTEM4FINALCONTROLSYSTEM,OFTENACONTROLVALVEBUTNOTALWAYSOTHERCOMMONFINALCONTROLELEMENTSAREVARIABLESPEEDPUMPS,CONVEYORS,ANDELECTRICMOTORSTHEIMPORTANCEOFTHESECOMPONENTSISTHATTHEYPERFORMTHETHREEBASICOPERATIONSTHATMUSTBEPRESENTINEVERYCONTROLSYSTEMTHESEOPERATIONSARE1MEASUREMENTMMEASURINGTHEVARIABLETOBECONTROLLEDISUSUALLYDONEBYTHECOMBINATIONOFSENSORANDTRANSMITTER2DECISIONDBASEDONTHEMEASUREMENT,THECONTROLLERMUSTTHENDECIDEWHATTODOTOMAINTAINTHEVARIABLEATITSDESIREDVALUE3ACTIONAASARESULTOFTHECONTROLLERSDECISION,THESYSTEMMUSTTHENTAKEANACTIONTHISISUSUALLYACCOMPLISHEDBYTHEFINALCONTROLELEMENTASMENTIONED,THESETHREEOPERATIONS,M,D,ANDA,MUSTBEPRESENTINEVERYCONTROLSYSTEMPIDCONTROLLERSCANBESTANDALONECONTROLLERSALSOCALLEDSINGLELOOPCONTROLLERS,CONTROLLERSINPLCS,EMBEDDEDCONTROLLERS,ORSOFTWAREINVISUALBASICORCCOMPUTERPROGRAMSPIDCONTROLLERSAREPROCESSCONTROLLERSWITHTHEFOLLOWINGCHARACTERISTICSCONTINUOUSPROCESSCONTROLANALOGINPUTALSOKNOWNAS“MEASUREMEM“OR“PROCESSVARIABLE“OR“PV“ANALOGOUTPUTREFERREDTOSIMPLYAS“OUTPUT“SETPOINTSPPROPORTIONALP,INTEGRALI,AND/ORDERIVATIVEDCONSTANTSEXAMPLESOF“CONTINUOUSPROCESSCONTROL“ARETEMPERATURE,PRESSURE,FLOW,ANDLEVELCONTROLFOREXAMPLE,CONTROLLINGTHEHEATINGOFATANKFORSIMPLECONTROL,YOUHAVETWOTEMPERATURELIMITSENSORSONELOWANDONEHIGHANDTHENSWITCHTHEHEATERONWHENTHELOWTEMPERATURELIMITSENSORTUMSONANDTHENMMTHEHEATEROFFWHENTHETEMPERATURERISESTOTHEHIGHTEMPERATURELIMITSENSORTHISISSIMILARTOMOSTHOMEAIRCONDITIONINGHEATINGTHERMOSTATSINCONTRAST,THEPIDCONTROLLERWOULDRECEIVEINPUTASTHEACTUALTEMPERATUREANDCONTROLAVALVETHATREGULATESTHEFLOWOFGASTOTHEHEATERTHEPIDCONTROLLERAUTOMATICALLYFINDSTHECORRECTCONSTANTFLOWOFGASTOTHEHEATERTHATKEEPSTHETEMPERATURESTEADYATTHESETPOINTINSTEADOFTHETEMPERATUREBOUNCINGBACKANDFORTHBETWEENTWOPOINTS,THETEMPERATUREISHELDSTEADYIFTHESETPOINTISLOWERED,THENTHEPIDCONTROLLERAUTOMATICALLYREDUCESTHEAMOUNTOFGASFLOWINGTOTHEHEATERIFTHESETPOINTISRAISED,THENTHEPIDCONTROLLERAUTOMATICALLYINCREASESTHEAMOUNTOFGASFLOWINGTOTHEHEATERLIKEWISETHEPIDCONTROLLERWOULDAUTOMATICALLYFORHOT,SUNNYDAYSWHENITISHOTTEROUTSIDETHEHEATERANDFORCOLD,CLOUDYDAYSTHEANALOGINPUTMEASUREMENTISCALLEDTHE“PROCESSVARIABLE“OR“PV“YOUWANTTHEPVTOBEAHIGHLYACCURATEINDICATIONOFTHEPROCESSPARAMETERYOUARETRYINGTOCONTROLFOREXAMPLE,IFYOUWANTTOMAINTAINATEMPERATUREOFORONEDEGREETHENWETYPICALLYSTRIVEFORATLEASTTENTIMESTHATORONETENTHOFADEGREEIFTHEANALOGINPUTISA12BITANALOGINPUTANDTHETEMPERATURERANGEFORTHESENSORIS0TO400DEGREESTHENOUR“THEORETICAL“ACCURACYISCALCULATEDTOBE400DEGREESDIVIDEDBY4,09612BITS009765625DEGREESWESAY“THEORETICAL“BECAUSEITWOULDASSUMETHEREWASNONOISEANDERRORINOURTEMPERATURESENSOR,WIRING,ANDANALOGCONVERTERTHEREAREOTHERASSUMPTIONSSUCHASLINEARITY,ETCTHEPOINTBEINGWITH1/10OFADEGREE“THEORETICAL“ACCURACYEVENWITHTHEUSUALAMOUNTOFNOISEANDOTHERPROBLEMSONEDEGREEOFACCURACYSHOULDEASILYBEATTAINABLETHEANALOGOUTPUTISOFTENSIMPLYREFERREDTOAS“OUTPUT“OFTENTHISISGIVENAS0100PERCENTINTHISHEATINGEXAMPLE,ITWOULDMEANTHEVALVEISTOTALLYCLOSED0ORTOTALLYOPEN100THESETPOINTSPISSIMPLYWHATPROCESSVALUEDOYOUWANTINTHISEXAMPLEWHATTEMPERATUREDOYOUWANTTHEPROCESSATTHEPIDCONTROLLERSJOBISTOMAINTAINTHEOUTPUTATALEVELSOTHATTHEREISNODIFFERENCEERRORBETWEENTHEPROCESSVARIABLEPVANDTHESETPOINTSPINFIG3,THEVALVECOULDBECONTROLLINGTHEGASGOINGTOAHEATER,THECHILLINGOFACOOLER,THEPRESSUREINAPIPE,THEFLOWTHROUGHAPIPE,THELEVELINATANK,ORANYOTHERPROCESSCONTROLSYSTEMWHATTHEPIDCONTROLLERISLOOKINGATISTHEDIFFERENCEOR“ERROR“BETWEENTHEPVANDTHESPSETPOINTP，I，DCONSTANTSDIFFERENCEERRORPIDCONTROLALGORITHMPROCESSOUTPUTVARIABLEFIG3PIDCONTROLITLOOKSATTHEABSOLUTEERRORANDTHERATEOFCHANGEOFERRORABSOLUTEERRORMEANSISTHEREABIGDIFFERENCEINTHEPVANDSPORALITTLEDIFFERENCERATEOFCHANGEOFERRORMEANSISTHEDIFFERENCEBETWEENTHEPVORSPGETTINGSMALLERORLARGERASTIMEGOESONWHENTHEREISA“PROCESSUPSET“,MEANING,WHENTHEPROCESSVARIABLEORTHESETPOINTQUICKLYCHANGESTHEPIDCONTROLLERHASTOQUICKLYCHANGETHEOUTPUTTOGETTHEPROCESSVARIABLEBACKEQUALTOTHESETPOINTIFYOUHAVEAWALKINCOOLERWITHAPIDCONTROLLERANDSOMEONEOPENSTHEDOORANDWALKSIN,THETEMPERATUREPROCESSVARIABLECOULDRISEVERYQUICKLYTHEREFORETHEPIDCONTROLLERHASTOINCREASETHECOOLINGOUTPUTTOCOMPENSATEFORTHISRISEINTEMPERATUREONCETHEPIDCONTROLLERHASTHEPROCESSVARIABLEEQUALTOTHESETPOINT,AGOODPIDCONTROLLERWILLNOTVARYTHEOUTPUTYOUWANTTHEOUTPUTTOBEVERYSTEADYNOTCHANGINGIFTHEVALVEMOTOR,OROTHERCONTROLELEMENTISCONSTANTLYCHANGING,INSTEADOFMAINTAININGACONSTANTVALUE,THISCOULDCAUSEMOREWEARONTHECONTROLELEMENTSOTHEREARETHESETWOCONTRADICTORYGOALSFASTRESPONSEFASTCHANGEINOUTPUTWHENTHEREISA“PROCESSUPSET“,BUTSLOWRESPONSESTEADYOUTPUTWHENTHEPVISCLOSETOTHESETPOINTNOTETHATTHEOUTPUTOFTENGOESPASTOVERSHOOTSTHESTEADYSTATEOUTPUTTOGETTHEPROCESSBACKTOTHESETPOINTFOREXAMPLE,ACOOLERMAYNORMALLYHAVEITSCOOLINGVALVEOPEN34TOMAINTAINZERODEGREESAFTERTHECOOLERHASBEENCLOSEDUPANDTHETEMPERATURESETTLEDDOWNIFSOMEONEOPENSTHECOOLER,WALKSIN,WALKSAROUNDTOFINDSOMETHING,THENWALKSBACKOUT,ANDTHENCLOSESTHECOOLERDOORTHEPIDCONTROLLERISFREAKINGOUTBECAUSETHETEMPERATUREMAYHAVERAISED20DEGREESSOITMAYCRANKTHECOOLINGVALVEOPENTO50,75,OREVEN100PERCENTTOHURRYUPANDCOOLTHECOOLERBACKDOWNBEFORESLOWLYCLOSINGTHECOOLINGVALVEBACKDOWNTO34PERCENTLETSTHINKABOUTHOWTODESIGNAPIDCONTROLLERWEFOCUSONTHEDIFFERENCEERRORBETWEENTHEPROCESSVARIABLEPVANDTHESETPOINTSPTHEREARETHREEWAYSWECANVIEWTHEERRORTHEABSOLUTEERRORTHISMEANSHOWBIGISTHEDIFFERENCEBETWEENTHEPVANDSPIFTHEREISASMALLDIFFERENCEBETWEENTHEPVANDTHESPTHENLETSMAKEASMALLCHANGEINTHEOUTPUTIFTHEREISALARGEDIFFERENCEINTHEPVANDSPTHENLETSMAKEALARGECHANGEINTHEOUTPUTABSOLUTEERRORISTHE“PROPORTIONAL“PCOMPONENTOFTHEPIDCONTROLLERTHESUMOFERRORSOVERTIMEGIVEUSAMINUTEANDWEWILLSHOWWHYSIMPLYLOOKINGATTHEABSOLUTEERRORPROPORTIONALONLYISAPROBLEMTHESUMOFERRORSOVERTIMEISIMPORTANTANDISCALLEDTHE“INTEGRAL“ICOMPONENTOFTHEPIDCONTROLLEREVERYTIMEWERUNTHEPIDALGORITHMWEADDTHELATESTERRORTOTHESUMOFERRORSINOTHERWORDSSUMOFERRORSERROR1QERROR2ERROR3ERROR4THEDEADTIMEDEADTIMEREFERSTOTHEDELAYBETWEENMAKINGACHANGEINTHEOUTPUTANDSEEINGTHECHANGEREFLECTEDINTHEPVTHECLASSICALEXAMPLEISGETTINGYOUROVENATTHERIGHTTEMPERATUREWHENYOUFIRSTMMONTHEHEAT,ITTAKESAWHILEFORTHEOVENTO“HEATUP“THISISTHEDEADTIMEIFYOUSETANINITIALTEMPERATURE,WAITFORTHEOVENTOREACHTHEINITIALTEMPERATURE,ANDTHENYOUDETERMINETHATYOUSETTHEWRONGTEMPERATURETHENITWILLTAKEAWHILEFORTHEOVENTOREACHTHENEWTEMPERATURESETPOINTTHISISALSOREFERREDTOASTHE“DERIVATIVE“DCOMPONENTOFTHEPIDCONTROLLERTHISHOLDSSOMEFUTURECHANGESBACKBECAUSETHECHANGESINTHEOUTPUTHAVEBEENMADEBUTARENOTREFLECTEDINTHEPROCESSVARIABLEYETABSOLUTEERROR/PROPORTIONALONEOFTHEFIRSTIDEASPEOPLEUSUALLYHAVEABOUTDESIGNINGANAUTOMATICPROCESSCONTROLLERISWHATWECALL“PROPORTIONAL“MEANING,IFTHEDIFFERENCEBETWEENTHEPVANDSPISSMALLTHENLETSMAKEASMALLCORRECTIONTOTHEOUTPUTIFTHEDIFFERENCEBETWEENTHEPVANDSPISLARGETHENLETSMAKEALARGERCORRECTIONTOTHEOUTPUTTHISIDEACERTAINLYMAKESSENSEWESIMULATEDAPROPORTIONALONLYCONTROLLERINMICROSOFTEXCELFIG4ISTHECHARTSHOWINGTHERESULTSOFTHEFIRSTSIMULATIONDEADTIME0,PROPORTIONALONLYPROPORTIONALANDINTEGRALCONTROLLERSTHEINTEGRALPORTIONOFTHEPIDCONTROLLERACCOUNTSFORTHEOFFSETPROBLEMINAPROPORTIONALONLYCONTROLLERWEHAVEANOTHEREXCELSPREADSHEETTHATSIMULATESAPIDCONTROLLERWITHPROPORTIONALANDINTEGRALCONTROLHEREFIG5ISACHARTOFTHEFIRSTSIMULATIONWITHPROPORTIONALANDINTEGRALDEADTIME0,PROPORTIONAL04ASYOUCANTELL,THEPICONTROLLERISMUCHBETTERTHANJUSTTHEPCONTROLLERHOWEVER,DEADTIMEOFZEROASSHOWNINTHEGRAPHISNOTCOMMONFIG4THESIMULATIONCHARTDERIVATIVECONTROLDERIVATIVECONTROLTAKESINTOCONSIDERATIONTHATIFYOUCHANGETHEOUTPUT,THENITTAKESTIMFORTHATCHANGETOBEREFLECTEDINTHEINPUTPVFOREXAMPLE,LETSTAKEHEATINGOFTHEOVENFIG5THESIMULATIONCHARTIFWESTARTTURNINGUPTHEGASFLOW,ITWILLTAKETIMEFORTHEHEATTOBEPRODUCED,THEHEATTOFLOWAROUNDTHEOVEN,ANDFORTHETEMPERATURESENSORTODETECTTHEINCREASEDHEATDERIVATIVECONTROLSORTOF“HOLDSBACK“THEPIDCONTROLLERBECAUSESOMEINCREASEINTEMPERATUREWILLOCCURWITHOUTNEEDINGTOINCREASETHEOUTPUTFURTHERSETTINGTHEDERIVATIVECONSTANTCORRECTLYALLOWSYOUTOBECOMEMOREAGGRESSIVEWITHTHEPICONSTANTS2、外文資料翻譯譯文溫度控制簡(jiǎn)介和PID控制器過程控制系統(tǒng)自動(dòng)過程控制系統(tǒng)是指將被控量為溫度、壓力、流量、成份等類型的過程變量保持在理想的運(yùn)行值的系統(tǒng)。過程實(shí)際上是動(dòng)態(tài)的。變化總是會(huì)出現(xiàn)，此時(shí)如果不采取相應(yīng)的措施，那些與安全、產(chǎn)品質(zhì)量和生產(chǎn)率有關(guān)的重要變量就不能滿足設(shè)計(jì)要求。為了說明問題，讓我們來看一下熱交換器。流體在這個(gè)過程中被過熱蒸汽加熱，如圖1所示。這一裝置的主要目的是將流體由入口溫度乃F加熱到某一期望的出口溫度TF。如前所述，加熱介質(zhì)是過熱蒸汽。只要周圍沒有熱損耗，過程流體獲得的熱量就等于蒸汽釋放的熱量，即熱交換器和管道間的隔熱性很好。很多變量在這個(gè)過程中會(huì)發(fā)生變化，繼而導(dǎo)致出口溫度偏離期望值。如果出現(xiàn)這種情況，就該采取一些措施來校正偏差，其目的是保持出口溫度為期望值。實(shí)現(xiàn)該目的的一種方法是首先測(cè)量R0，然后與期望值相比較，由比較結(jié)果決定如何校正偏差。蒸汽的流量可用于偏差的校正。就是說，如果溫度高于期望值，就關(guān)小蒸汽閥來減小進(jìn)入換熱器的蒸汽流量；若溫度低于期望值，就開大蒸汽閥，以增加進(jìn)入換熱器的蒸汽流量。所有這些操作都可由操作員手工實(shí)現(xiàn)，操作很簡(jiǎn)單，不會(huì)出現(xiàn)什么問題。但是，由于多數(shù)過程對(duì)象都有很多變量需要保持為某一期望值，就需要許多的操作員來進(jìn)行校正。因此，我們想自動(dòng)完成這種控制。就是說，我們想利用無需操作人員介入就可以控制變量的設(shè)備。這就是所謂自動(dòng)化的過程控制。為達(dá)到上述目標(biāo)，就需要設(shè)計(jì)并實(shí)現(xiàn)一個(gè)系統(tǒng)。圖2所示為一個(gè)可行的控制系統(tǒng)及其基本構(gòu)件。首先要做的是測(cè)量過程流體的出口溫度，這一任務(wù)由傳感器熱電偶、熱電阻等完成。將傳感器連接到變送器上，由變送器將傳感器的輸出信號(hào)轉(zhuǎn)換為足夠大的信號(hào)傳送給控制器?？刂破鹘邮张c溫度相關(guān)的信號(hào)并與期望值比較。根據(jù)比較的結(jié)果，控制器確定保持溫度為期望值的控制作用?；谶@一結(jié)果，控制器再發(fā)一信號(hào)給執(zhí)行機(jī)構(gòu)來控制蒸汽流量。下面介紹控制系統(tǒng)中的4種基本元件，分別是1傳感器，也稱為一次元件。2變送器，也稱二次元件。3調(diào)節(jié)器，控制系統(tǒng)的“大腦”。4執(zhí)行機(jī)構(gòu)，通常是一個(gè)控制閥，但并不全是。其他常用的執(zhí)行機(jī)構(gòu)有變速泵、傳送裝置和電動(dòng)機(jī)。這些元件的重要性在于它們執(zhí)行每個(gè)控制系統(tǒng)中都必不可少的3個(gè)基本操作，即1測(cè)量被控量的測(cè)量通常由傳感器和變送器共同完成。2決策根據(jù)測(cè)量結(jié)果，為了維持輸出為期望值，控制器必須決定如何操作。3操作根據(jù)控器的處理,系統(tǒng)必須執(zhí)行某種操作,這通常由執(zhí)行機(jī)構(gòu)來完成如上所述,每個(gè)控制系統(tǒng)都有M,D和A這3種操作有些系統(tǒng)的決策任務(wù)簡(jiǎn)單,而有些很復(fù)雜設(shè)計(jì)控制系統(tǒng)的工程師必須確保所采取確保所采取的操作能影響被控變量,也就是說,該操作要影響測(cè)量值否則,系統(tǒng)是不可控的,還會(huì)帶來許多危害PID控制器可以是獨(dú)立控制器（也可以叫做單回路控制器），可編程控制器（PLCS）中的控制器，嵌入式控制器或者是用VB或C編寫的計(jì)算機(jī)程序軟件。PID控制器是過程控制器，它具有如下特征連續(xù)過程控制；模擬輸入（也被稱為“測(cè)量量”或“過程變量”或“PV”）；模擬輸出（簡(jiǎn)稱為“輸出”）；基準(zhǔn)點(diǎn)（SP）；比例、積分以及/或者微分常數(shù)；“連續(xù)過程控制”的例子有溫度、壓力、流量及水位控制。例如控制一個(gè)容器的熱量。對(duì)于簡(jiǎn)單的控制，你使用兩個(gè)具有溫度限定功能的傳感器一個(gè)限定低溫，一個(gè)限定高溫。當(dāng)?shù)蜏叵薅▊鞲衅鹘油〞r(shí)就會(huì)打開加熱器，當(dāng)溫度升高到高溫限定傳感器時(shí)就會(huì)關(guān)加熱器。這類似于大多數(shù)家庭使用的空調(diào)及供暖系統(tǒng)的溫度自動(dòng)調(diào)節(jié)器。反過來，PID控制器能夠接受像實(shí)際溫度這樣的輸入，控制閥門，這個(gè)閥門能夠控制進(jìn)入加熱器的氣體流量。PID控制器自動(dòng)地找到加熱器中氣體的合適流量，這樣就保持了溫度在基準(zhǔn)點(diǎn)穩(wěn)定。溫度穩(wěn)定了，就不會(huì)在高低兩點(diǎn)間上下跳動(dòng)了。如果基準(zhǔn)點(diǎn)降低，PID控制器就會(huì)自動(dòng)降低加熱器中氣體的流量。如果基準(zhǔn)點(diǎn)升高，PID控制器就會(huì)自動(dòng)的增加加熱器中氣體的流量。同樣地，對(duì)于高溫，晴朗的天氣當(dāng)外界溫度高于加熱器時(shí)及陰冷，多云的天氣，PID控制器都會(huì)自動(dòng)調(diào)節(jié)。模擬輸入測(cè)量量也叫做“過程變量”或“PV。你希望PV能夠達(dá)到你所控制過程參數(shù)的高精確度。例如，如果我們想要保持溫度為1度或1度，我們至少要為此努力，使其精度保持在01度。如果是一個(gè)12位的模擬輸入，傳感器的溫度范圍是從0度到400度，我們計(jì)算的理論精確度就是4096除400度0097656度。我們之所以說這是理論上因?yàn)槲覀兗俣囟葌鞲衅?，電線及模擬轉(zhuǎn)換器上沒有噪音和誤差。還有其他的假定。例如，線性等等。即使是有大量的噪音和其他問題，按理論精確度的110計(jì)算，1度精確度的數(shù)值應(yīng)該很容易得到的。模擬輸出經(jīng)常被簡(jiǎn)稱為“輸出”。經(jīng)常在0到100之間給出。在這個(gè)熱量的例子中閥門完全關(guān)閉0，完全打開100?；鶞?zhǔn)點(diǎn)SP很簡(jiǎn)單，即你想要什么樣的過程量。在這個(gè)例子中一你想要過程處于怎樣的溫度。PID控制器的任務(wù)是維持輸出在一個(gè)程度上，這樣在過程變量PV和基準(zhǔn)點(diǎn)SP上就沒有偏差誤差。在圖3中，閥門用來控制進(jìn)入加熱器的氣體，冷卻器的制冷，水管的壓力，水管的流量，容器的水位或其他的過程控制系統(tǒng)。PID控制器所觀察的是PV和SP之間的偏差或誤差。它觀察絕對(duì)偏差和偏差變換率。絕對(duì)偏差就是一PV和SP之間偏差大還是小。偏差變換率就是PV和SP之間的偏差隨著時(shí)間的變化是