《電氣信息類專業(yè)英語》課件第3章

Part3ControlTheory3.1ControlEngineering3.2BasicControlActions3.3TimeResponseAnalysisofControlSystems3.4NonlinearModelsandNon-linear3.5State-SpaceAnalysisofControlSystems3.6Controllability,ObservabilityandStability

3.1.1語言現(xiàn)象——形容詞的翻譯

英語形容詞起修飾作用，是修飾名詞的。譯得準確、生動，與名詞搭配相得益彰，可以起到畫龍點睛的作用，使文章顯得生動活潑，使被修飾的人物、事物躍然紙上。否則，詞不達意，晦澀難懂，連名詞的意思也黯然失色。因此，應高度重視對英語形容詞的準確理解與恰當翻譯。3.1ControlEngineering形容詞在英文句中一般做表語或修飾名詞的定語，因而在翻譯時要把形容詞與其所修飾的客體統(tǒng)一考慮，對二者的割裂會導致牛頭不對馬嘴的錯誤。

1．正確體會一詞多義

有些形容詞的詞義不是一兩個解釋所能說清楚的，其含義比較復雜，要先了解它們的本義，抓住其基本概念，再結(jié)合被修飾的名詞，探索其演變出的各種意義。對形容詞詞義的理解必須同上下文聯(lián)系起來，明確它所指的范圍，即明確它所修飾的對象，確定它在此表達的意思，再從漢語中挑選恰當?shù)脑~語，準確恰當?shù)匕阉磉_出來。

heavy的基本詞義是“重”，但在翻譯時結(jié)合修飾的對象則譯法各異。如heavycurrent強電流；heavycrop大豐收；heavytraffic交通擁擠；heavyindustry重工業(yè)等。英語詞義對上下文的依賴性是很大的。一個孤立的詞，其詞義通常是游移不定的，但當詞處于特定的聯(lián)立關(guān)系中時，其含義就受到相關(guān)詞的制約而明朗和穩(wěn)定了。因此，根據(jù)詞的聯(lián)立關(guān)系確定詞義是詞義辨析的重要且最為可行的手段。

universal有“宇宙的、世界的、普遍的、一般的和通用的”等含義。具體用法舉例如下：

universalmeter萬用表；universalconstant通用常數(shù)；universalmotor交直流兩用電動機；universaluse普遍應用；universalagent全權(quán)代理人；universalaccess通用存??；universalcoupling/joint萬向軸節(jié)；universalgrammar普遍文法，通用文法；universalgravitation萬有引力；universallanguage通用語言，世界語；UniversalMusic環(huán)球音樂集團(公司名稱)；universalserialbus通用串行總線；universalset通用集(合)，泛集，萬有集；UniversalStudio環(huán)球影城(主題公園名)；universalsuffrage普選權(quán)；universaltestingmachine萬能試驗機；universaltime世界時間，格林威治時間，國際標準時間；universalpeace世界和平；universalrules一般法則；universaltruth普遍真理；universaltravel環(huán)球旅行等等。

sophisticated源出希臘語的詭辯家sophist一詞，現(xiàn)其使用范圍很廣。如sophisticatedequipment尖端設備，高級設備；sophisticatedinvestor成熟投資者，精明投資人；sophisticatedplaner精密刨床；sophisticatedtechnology精良工藝；sophisticatedarguments強詞奪理的論據(jù)；sophisticatedweapons尖端武器；sophisticatedman老于世故的人；thenewandsophisticatedpatternsofintervention花樣翻新的干涉活動等等。同一個high在highnoon中譯為正午，在highsummer中譯為盛夏，在highmanner中譯為傲慢的態(tài)度，而在highvoice中譯為尖聲，這些都和漢語的習慣用法密切相關(guān)。

一般的常用專業(yè)詞組搭配都可以在英漢技術(shù)字典中查到，所以對含義不清楚的詞組應借助字典來理解，閉門造車式的翻譯只能導致主觀臆斷的錯誤。

對形容詞的翻譯還可采取詞性轉(zhuǎn)換的技巧，使對原文的表達更通順和易于理解。

2．一些原義并無否定意思的形容詞和別的詞搭配，有時可譯成否定句

如：

Thesegoodsareinshortsupply.

這些貨物供應不足。

Thisequationisfarfrombeingcomplicated.

這個方程一點也不復雜。

3．當形容詞在句中做表語時，某些情況下可根據(jù)漢語習慣，將其和系詞合譯成動詞形式

如：

InternetisdifferentfromIntranetinmanyaspectsthoughtheirspellingisalike．

雖然拼寫相像，Internet仍在很多方面不同于Intranet。

Iflow-costpowerbecomesavailablefromnuclearpowerplants，theelectricitycrisiswouldbesolved．

如能從核電站獲得低成本電力，電力緊張問題就會解決。

4．某些表示事物特征的形容詞，可在其后加上“性”、“度”而轉(zhuǎn)化為名詞

如：

IPCismorereliablethancommoncomputer.

工控機的可靠性比普通計算機高。

Experimentindicatesthatthenewchipisabout1.5timesasintegrativeasthatoftheoldones.

試驗表明，新型芯片的集成度是舊型號的1.5倍。

5．有時形容詞也可根據(jù)需要譯成副詞

如：

Thesameprinciplesoflowinternalresistancealsoapplytomilli-ammeters．

低內(nèi)阻原理也同樣適用于毫安表。

Themodernworldisexperiencingrapiddevelopmentofinformationtechnique．

當今世界的信息技術(shù)正在迅速地發(fā)展。詞性轉(zhuǎn)換技巧同樣適用于其他詞類，拘泥于原文的詞性進行完全對應的翻譯往往會給翻譯帶來極大的障礙，同時使得譯文生澀而難以理解。翻譯應從整體著眼，采取適當?shù)脑~性轉(zhuǎn)換、句子成分轉(zhuǎn)換或句型轉(zhuǎn)換的翻譯技巧，可使譯文既忠實于原意又通順可讀。3.1.2SpecifiedEnglishWords

disciplinen.紀律；學科；訓練vt.訓練，訓導；懲戒

regulatevt.調(diào)節(jié)，規(guī)定；有系統(tǒng)的管理；控制；校準

derivevt.得自；源于vi.起源

actuatorn.執(zhí)行機構(gòu)；激勵者；促動器

yawdamper抗偏器；偏航阻尼器

on-siteadj.現(xiàn)場的

Laplacetransform拉普拉斯變換

scanvt.掃描vi.掃描；掃掠n.掃描；瀏覽；審視；細看

diversifyvt.使多樣化，使變化；增加產(chǎn)品種類以擴大

sampled-data采樣數(shù)據(jù)

nonlinearadj.非線性的

time-invariantadj.時不變的

stationaryadj.靜止的；固定的；定居的；常備軍的n.不動的人；駐軍

lumpedparameter集合參數(shù)；集中參數(shù)；總參數(shù)

distributedparameter分散(布)式參數(shù)

deterministicadj.確定性的；命運注定論的

stochasticadj.隨機的；猜測的

performancecriteria性能標準

overlapn.重疊；重復vi.部分重疊vt.與……重疊；與……同時發(fā)生3.1.3Text

ControlEngineering

Automaticcontrolhasplayedavitalroleintheadvancementofengineeringandscience.Inadditiontoitsextremeimportanceinspace-vehicle,missile-guidance,andaircraft-pilotingsystems,etc,automaticcontrolhasbecomeanimportantandintegralpartofmodernmanufacturingandindustrialprocesses.Forexample,automaticcontrolisessentialinsuchindustrialoperationsascontrollingpressure,temperature,humidity,viscosity,andflowintheprocessindustries;tooling,handling,andassemblingmechanicalpartsinthemanufacturingindustries,amongmanyothers.

Thewordcontrolisusuallytakentomeanregulate,direct,orcommand.Controlsystemsaboundinourenvironment.Inthemostabstractsenseitispossibletoconsidereveryphysicalobjectasacontrolsystem.

Controlengineeringorcontrolsystemsengineeringistheengineeringdisciplinethatappliescontroltheorytodesignsystemswithpredictablebehaviors.Thepracticeusessensorstomeasuretheoutputperformanceofthedevicebeingcontrolledandthosemeasurementscanbeusedtogivefeedbacktotheinputactuatorsthatcanmakecorrectionstowarddesiredperformance.Whenadeviceisdesignedtoperformwithouttheneedofhumaninputsforcorrectionitiscalledautomaticcontrol(suchascruisecontrolforregulatingacar’sspeed).Multi-disciplinaryinnature,controlsystemsengineeringfocusonimplementationofcontrolsystemsmainlyderivedbymathematicalmodelingofsystemsofadiverserange.

Controlsystemsdesignedbyhumansareusedtoextendtheirphysicalcapabilities,tocompensatefortheirphysicallimitations,torelievethemofroutineortedioustasks,ortosavemoney.Inamodernaircraft,forexample,thepowerboostcontrolsamplifytheforceappliedbythepilottomovethecontrolsurfacesagainstlargeaerodynamicforces.ThereactiontimeofahumanpilotistooslowtoenablehimorhertoflyanaircraftwithalightlydampedDutchrollmodewithouttheadditionofayawdampersystem.Anautopilot(flightcontrolsystem)relievesthepilotofthetaskofcontinuouslyoperatingthecontrolstomaintainthedesiredheading,altitude,andattitude.Freedofthisroutinetask,thepilotcanperformothertasks,suchasnavigationand/orcommunications,thusreducingthenumberofcrewrequiredandconsequentlytheoperatingcostoftheaircraft.

Inmanycases,thedesignofcontrolsystemisbasedonsometheoryratherthanintuitionortrail-and-error.Controltheoryisusedfordealingwiththedynamicresponseofasystemtocommands,regulations,ordisturbances.Controlengineeringconsistsofanalysisanddesignofcontrolconfigurations.Analysisistheinvestigationofthepropertiesofanexistingsystem.Itisconcernedwithdeterminationoftheresponseofaplant(thecontrolledobject)tocommands,disturbances,andchangesintheplantparameters.Thedesignproblemisonechoiceandarrangementofsystemcomponentstoperformaspecifictask.Ifthedynamicresponseissatisfactory,thereneedbenosecondphase.Iftheresponseisunsatisfactoryandmodificationoftheplantisunacceptable,adesignphaseisnecessarytoselectthecontrolelements(thecontroller)toimprovethedynamicperformancetoacceptablelevels.

Therearetwomajordivisionsincontroltheory,namely,classicalandmodern.Thescopeofclassicalcontroltheoryislimitedtosingle-inputandsingle-output(SISO)systemdesign.Thesystemanalysisiscarriedoutintimedomainusingdifferentialequations,incomplex-sdomainwithLaplacetransformorinfrequencydomainbytransformingfromthecomplex-sdomain.Thesystemsareassumedtobesecondorderandsinglevariable,andhigher-ordersystemresponsesandmultivariableeffectsareignored.Acontrollerdesignedusingclassicaltheoryusuallyrequireson-sitetuningduetodesignapproximations.Yet,duetoeasierphysicalimplementationofclassicalcontrollerdesignsascomparedtosystemsdesignedusingmoderncontroltheory,thesecontrollersarepreferredinmostindustrialapplications.ThemostcommoncontrollersdesignedusingclassicalcontroltheoryarePIDcontrollers.

Incontrast,moderncontroltheoryiscarriedoutinthestatespace,andcandealwithmulti-inputandmulti-output(MIMO)systems.Thisovercomesthelimitationsofclassicalcontroltheoryinmoresophisticateddesignproblems,suchasfighteraircraftcontrol.Inmoderndesign,asystemisrepresentedasasetoffirstorderdifferentialequationsdefinedusingstatevariables.Nonlinear,multivariable,adaptiveandrobustcontroltheoriescomeunderthisdivision.Beingfairlynew,moderncontroltheoryhasmanyareasyettobeexplored.ScholarslikeRudolfE.KalmanandAleksandrLyapunovarewellknownamongthepeoplewhohaveshapedmoderncontroltheory.

Controlsystemsareclassifiedintermsthatdescribeeitherthesystemitselforitsvariables:

Open-loopandclosed-loopcontrolsystems(seeFig.3.1).Anopen-loopsystemisoneinwhichthecontrolactionisindependentoftheoutput.Aclosed-loopsystem,however,theinputoftheplantissomehowdependentontheactualoutput.Sincetheoutputisfedbackinafunctionalformdeterminedbythenatureofthefeedbackelementsandthensubtractedfromtheinput,aclosed-loopsystemisreferredtoasanegativefeedbacksystemorsimplyasafeedbacksystem.

Fig.3.1open-loopcontrolsystemandclosed-loopcontrolsystem

Continuousanddiscretesystems.Thesystemthatallitsvariablesarecontinuousfunctionsoftimeiscalledcontinuous-variableoranalogsystem;thedescribingequationsaredifferentialequations.Adiscrete-variableordigitalsystemhasoneormorevariablesknownonlyatparticularinstantsoftime,asinFig.3.2,theequationsaredifferenceequations.Ifthetimeintervalsarecontrolled,thesystemistermedasampled-datasystem.Discretevariablesoccurnaturally,asfromascanningradarthatobtainspositiondataonceperscanoradatachannelthattransmitsmanypiecesofinformationinturn.Adiscretevariablewillobviouslyapproachacontinuousvariableasthesamplingintervalisdecreased.

Fig.3.2Continuoussystemanddiscretesystem

Discontinuousvariables,suchasshowninFig.3.2(c)occurin“on-off”or“bang-bang”controlsystemsandaretreatedseparatelyinasubsequentpaper.

Linearandnonlinearsystems.Asystemislinearifallitselementsarelinear,andnonlinearifanyelementisnonlinear.

Time-invariantandtime-variantsystems.Atime-invariant(orstationary)systemisonewhoseparametersdonotvarywithtime.Theoutputofastationarysystemisindependentofthetimeatwhichaninputisapplied,andthecoefficientsofthedescribingdifferentialequationsareconstants.Atime-variant(ornonstationary)systemisasystemwithoneormoreparametersthatvarywithtime.Thetimeatwhichaninputisappliedmustbeknown,andthecoefficientsofthedifferentialequationsaretime-dependent.

Lumpedparameteranddistributedparametersystems.Lumpedparametersystemsarethoseforwhichphysicalcharacteristicsareassumedtobeconcentratedinoneormore“l(fā)umps”andthusindependentofanyspatialdistribution.Ineffect,bodiesareassumedrigidandtreatedaspointmassed;springsaremasslessandelectricalleadsresistanceless,orsuitablecorrectionsaremadetothesystemmassorresistance;temperaturesareuniform;etc.Indistributedparametersystems,thecontinuousspatialdistributionofaphysicalcharacteristicistakenintoaccount.Bodiesareelastic,springshaveadistributedmass,electricalleadshaveadistributeresistance,andthetemperaturesvaryacrossabody.Lumpedparametersystemsaredescribedbyordinarydifferentialequations;whiledistributedparametersystemsaredescribedbypartialdifferentialequations.

Deterministicandstochasticsystems.Asystemorvariableisdeterministicifitsfuturebehaviorisbothpredictableandrepeatablewithinreasonablelimits.Ifnot,thesystemorvariableiscalledstochasticorrandom.Analysesofstochasticsystemsandofdeterministicsystemwithstochasticinputsarebasedonprobabilitytheory.

Single-variableandmultivariablesystem.Asingle-variablesystemisdefinedasonewithonlyoneoutputforonereferenceorcommandinputandisoftenreferredtoasasingleinputsingleoutput(SISO)system.Amultivariable(MIMO)systemhasanynumberofinputsandoutputs.

Atmanyuniversities,controlengineeringcoursesaretaughtinElectricalandElectronicEngineering,MechatronicsEngineering,Mechanicalengineering,andAerospaceengineering;inothersitisconnectedtocomputerscience,asmostcontroltechniquestodayareimplementedthroughcomputers,oftenasEmbeddedsystems(asintheautomotivefield).Thefieldofcontrolwithinchemicalengineeringisoftenknownasprocesscontrol.Itdealsprimarilywiththecontrolofvariablesinachemicalprocessinaplant.Itistaughtaspartoftheundergraduatecurriculumofanychemicalengineeringprogram,andemploysmanyofthesameprinciplesincontrolengineering.Otherengineeringdisciplinesalsooverlapwithcontrolengineering,asitcanbeappliedtoanysystemforwhichasuitablemodelcanbederived.

Controlengineeringhasdiversifiedapplicationsthatincludescience,financemanagement,andevenhumanbehavior.Studentsofcontrolengineeringmaystartwithalinearcontrolsystemcoursedealingwiththetimeandcomplex-sdomain,whichrequiresathoroughbackgroundinelementarymathematicsandLaplacetransform(calledclassicalcontroltheory).Inlinearcontrol,thestudentdoesfrequencyandtimedomainanalysis.DigitalcontrolandnonlinearcontrolcoursesrequireZtransformationandalgebrarespectively,andcouldbesaidtocompleteabasiccontroleducation.

Notes

1．Forexample,automaticcontrolisessentialinsuchindustrialoperationsascontrollingpressure,temperature,humidity,viscosity,andflowintheprocessindustries.

例如，在對壓力、溫度、濕度、粘度、流量實施的工業(yè)過程的控制中，必須進行自動控制。

2．ThereactiontimeofahumanpilotistooslowtoenablehimorhertoflyanaircraftwithalightlydampedDutchrollmodewithouttheadditionofayawdampersystem.

飛行員的反應速度太慢，如果不附加阻尼偏航系統(tǒng)，就無法通過小阻尼的荷蘭滾方式來駕駛飛機。

3．Sincetheoutputisfedbackinafunctionalformdeterminedbythenatureofthefeedbackelementsandthensubtractedfromtheinput…

因為輸出會以由反饋元件特性決定的函數(shù)形式反饋回來，然后從輸入中減去……

4．Studentsofcontrolengineeringmaystartwithalinearcontrolsystemcoursedealingwiththetimeandcomplex-sdomain,whichrequiresathoroughbackgroundinelementarymathematicsandLaplacetransform.學習控制工程可以從線性控制系統(tǒng)起步，線性控制系統(tǒng)涉及時域及復域兩個方面，要求必須具有良好的數(shù)學基礎，掌握拉普拉斯變換。3.1.4ReadingMaterials

TypesofFeedback

Whenfeedbackactsinresponsetoanevent/phenomenon,itcaninfluencetheinputsignalinoneoftwoways.Anin-phasefeedbacksignal,whereapositive-goingwaveontheinputleadstoapositive-goingchangeontheoutput,willamplifytheinputsignal,leadingtomoremodification.Thisisknownaspositivefeedback.Afeedbacksignalwhichisinverted,whereapositive-goingchangeontheinputleadstoanegative-goingchangeontheoutput,willdampentheeffectoftheinputsignal,leadingtolessmodification.Thisisknownasnegativefeedback.

Notethatanincreaseordecreaseofthefeedbacksignalherereferstothemagnituderelativetotheinputsignal’sabsolutevalue,withoutregardtothepolarityorsignofthefeedbacksignal.Forexampleiftheinputsignalchangesby100thenachangeinfeedbacksignalvaluefrom+5to+10isapositivefeedback.Iftheinputsignalchangesby-100thenachangeinthefeedbacksignalfrom-5to-10isalsoapositivefeedback.

Positivefeedbacktendstoincreasetheeventthatcausedit,suchasinanuclearchain-reaction.Itisalsoknownasaself-reinforcingloop.Aneventinfluencedbypositivefeedbackcanincreaseordecreaseitsoutput/activationuntilithitsalimitingconstraint.Suchaconstraintmaybedestructive,asinthermalrunawayoranuclearchainreaction.Self-reinforcingloopscanbeasmallerpartofalargerbalancingloop,especiallyinbiologicalsystemssuchasregulatorycircuits.

Negativefeedback,whichtendstoreducetheinputsignalthatcausedit,isalsoknownasaself-correctingorbalancingloop.Suchloopstendtobegoal-seeking,asinathermostat,whichcomparesactualtemperaturewithdesiredtemperatureandseekstoreducethedifference.Balancingloopsaresometimespronetohunting:anoscillationcausedbyanexcessiveordelayednegativefeedbacksignal,resultinginover-correction,whereinthesignalbecomesapositivefeedback.

Thetermsnegativeandpositivefeedbackcanbeusedlooselyorcolloquiallytodescribeorimplycriticismandpraise,respectively.Thismayleadtoconfusionwiththemoretechnicallyaccuratetermspositiveandnegativereinforcement,whichrefertosomethingthatchangesthelikelihoodofafuturebehavior.Moreover,whenusedtechnically,negativefeedbackleadstostabilitythatis,ingeneral,consideredgood,whereaspositivefeedbackcanleadtounstableandexplosivesituationsthatareconsideredbad.Thus,whenusedcolloquially,thesetermsimplytheoppositedesirabilitytothatwhenusedtechnically.

NegativefeedbackwasappliedbyHaroldStephenBlacktoelectricalamplifiersin1927,buthecouldnotgethisideapatenteduntil1937.ArturoRosenblueth,aMexicanresearcherandphysician,co-authoredaseminal1943paperBehavior,PurposeandTeleologythat,accordingtoNorbertWiener(anotherco-authorofthepaper),setthebasisforthenewsciencecybernetics.Rosenbluethproposedthatbehaviorcontrolledbynegativefeedback,whetherinanimal,humanormachine,wasadeterminative,directiveprincipleinnatureandhumancreations.Thiskindoffeedbackisstudiedincyberneticsandcontroltheory.3.1.5Homework

1．Pleasesumupthemainpointsofthetextinseveralsentences.

2．TranslatethefollowingsentencesintoChinese.

(1)

Indealingwithwaterpollutioninthearea,thetraditionalwastewatertreatmenttechnologycanbeemployedtodischargewaterqualityrequirements,inWaterPollutionControlplayedapositiverole.

(2)

AsabasicpartofaVirtualManufacturingPlatform,manufacturingsystemmodelingiscriticaltothesuccessofprocesscontrolinamultirobotvirtualmanufacturingenvironment.

(3)

Themotorshaveallthenecessarypowerandcontrolsystemsintegratedintothewheelhub,greatlyreducingthenumberofconnectionsbetweenthehubmotorsandtherestofthevehicle.

(4)

Atthesametime,digitalcontroltechnologybasedonmicroprocessorimplementssomecompletecontrolalgorithmthatcannotbeimplementedbytraditionalanalogcircuit.

(5)

Theorganizationshalldevelopcontrolplansatthesystem,subsystem,componentand/ormateriallevelfortheproductsupplied.

3.2.1語言現(xiàn)象——定語從句的翻譯

科技英語中定語從句極為常見。定語從句也叫關(guān)系分句，是一種由關(guān)系詞引導的分句形式的后置修飾語。關(guān)系分句所修飾的先行詞和在句中作某種成分的關(guān)系代詞、關(guān)系副詞構(gòu)成了定語從句的主要特征。3.2BasicControlActions不管一個句子有多長，句子里套有幾個定語從句，定語從句是否緊隨先行詞之后，其基本類型有兩種：限制性定語從句和非限制性定語從句?？萍加⒄Z中使用定語從句能使結(jié)構(gòu)緊湊，語義連貫，邏輯性強。但同時也會面臨一個問題，即如果不能準確找出定語從句所修飾的先行詞，理解之間的關(guān)系，就會產(chǎn)生誤譯甚至錯譯。

因此，在英漢翻譯的過程中，首先通讀句子，進行語法分析，借助專業(yè)知識，依靠上下文，準確理解句子所傳達的信息和內(nèi)涵意義，然后依據(jù)從句、先行詞和主干句之間的關(guān)系，適當翻譯。

1．翻譯成“定語─中心語”的關(guān)系

大多數(shù)簡單限制性定語從句和并列限制定語從句常翻譯成帶“的”字結(jié)構(gòu)的定語，與先行詞構(gòu)成“定語—中心語”的關(guān)系，也有部分的非限制性定語從句可采用這種翻譯方法。

例如：

Amotorwhichistoosmallwouldbesubjecttofrequentoverload.

過小的電動機時常會發(fā)生過載。

Thedegreetowhichtheyimpedetheflowofcurrentiscalledresistance.阻礙電流流動的程度叫電阻。

Itisthatpartofthestatespaceinwhichasymptoticallystabletrajectoriesoriginate.

它是引出漸近穩(wěn)定軌跡的狀態(tài)空間的一部分。

2．翻譯成漢語的并列關(guān)系

當定語從句結(jié)構(gòu)復雜，翻譯成“定語—中心語”的關(guān)系不符合漢語的表達習慣時，可采用重復或省略英語先行詞或先行詞所代表的含義的方法，把定語從句譯成后置或前置的并列分句。例如：

Inthecaseofaresistor,thevoltage-currentrelationshipisgivenbyOhm’slaw,whichstatesthatthevoltageacrosstheresistorisequaltothecurrentthroughtheresistormultipliedbythevalueoftheresistance.就電阻來說，電壓—電流的關(guān)系由歐姆定律決定。歐姆定律指出，電阻兩端的電壓等于流過電阻上的電流乘以電阻值。

Arocketisindependentofairbecauseitcontainsanexplosivemixturewhichconsistsbothofafueltobeburnedandasupplyofoxygen.

火箭飛行不依賴空氣，因為它本身裝有爆炸混合物，這種混合物是由待燃燒的燃料和氧氣組成的。

3．翻譯成漢語的同位關(guān)系

英語的定語從句和漢語的同位語關(guān)系密切，在英漢互譯的過程中往往可以相互轉(zhuǎn)換。例如：

Hydrogen,whichisthelightestelement,hasonlyoneelectron.

最輕的元素氫只有一個電子。

ThesecondmethodofLyapunov(whichisalsocalledthedirectmethodofLyapunov)isthemostgeneralmethodforthedeterminationofstabilityofnonlinearand/ortime-varyingsystems.李雅普諾夫第二方法(也稱為李雅普諾夫直接法)是確定非線性和/或時變系統(tǒng)穩(wěn)定性的最一般的方法。

4．翻譯成漢語的動賓關(guān)系

有時定語從句和先行詞之間存在著邏輯上的動賓關(guān)系，譯成漢語時，可把先行詞譯成英語定語從句里謂語動詞的賓語，構(gòu)成漢語的動賓關(guān)系。例如：

Therearethreestepswhichmustbetakenbeforewegraduatefromtheintegratedcircuittechnology.

我們要完全掌握集成電路工藝，必須采取三項措施。

5．翻譯成漢語的主謂關(guān)系

有時定語從句和先行詞之間存在著邏輯上的主謂關(guān)系(特別在Therebe句型中)，譯成漢語時，可把先行詞譯成英語定語從句里謂語動詞的主語，構(gòu)成漢語的主謂關(guān)系。例如：

Therewasnotonehousebut(作為關(guān)系代詞，相當于whichwasnot)wasburntdown.

所有的房子都被燒掉了。

Therearesomemetalswhichpossessthepowertoconductelectricityandtheabilitytobemagnetized.

有些金屬既能導電，又能被磁化。

6．翻譯成漢語的主從偏正復句

英語中有些定語從句與主干句之間語義上相互關(guān)聯(lián)，且二者之間的關(guān)系并不平等，含有因果、目的、讓步、條件和假設等關(guān)系，可根據(jù)語義譯成漢語的偏正復句。例如：

Abodythatcontainsonlyatomswithsamegeneralpropertiesiscalledanelement.

一切物質(zhì)，如果它包含的原子性質(zhì)都相同，則稱為元素。

Einstein,whoworkedoutthefamousPhotoelectricTheory,wontheNoblePrize.愛因斯坦因提出了著名的“光電理論”而獲得諾貝爾獎。

Computers,whichhavemanyadvantages,cannottaketheplaceofman.

計算機雖有很多優(yōu)點，卻不能代替人。

Thefirstcomputerusedthesametypesofcomponentwhichmadeequipmentverylargeandbulky.

首批計算機采用同類元件，致使設備又大又笨重。

Heunnecessarilyspentalotoftimeintroducingthisbook,whichthestudentsarefamiliarwith.

他花了很長時間介紹這本書，其實沒有必要，因為學生們對它已經(jīng)很熟悉了。

7．翻譯成獨立句

Onewasaviolentthunderstorm,theworstIhadeverseen,whichobscuredmyobjective.

有一次是暴風驟雨，猛烈的程度實為我生平所僅見，這陣暴風雨遮住了我的目標。3.2.2SpecifiedEnglishWords

faucetn.旋塞，龍頭，開頭

deviationn.明顯異化，偏差，偏離，背離，越軌

controlaction控制作用

errorsignal誤差(偏差)信號

two-positionoron-offcontroller雙位或繼電器型控制器

proportional-plus-derivative-plus-integralcontroller比例微分積分控制器(即PID控制器)

actuatevt.開動(機器等)，驅(qū)使，促使，激勵(某人做某事)

actuatorn.激勵者，制動器，執(zhí)行機構(gòu)，傳動裝置

displacementn.移置，轉(zhuǎn)移，取代，置換，位移，排水量

correspondencen.相應，通信，信件，符合，一致，和諧，相似adj.通信的，函授的

bringintocorrespondencewith使與……一致，使與……聯(lián)絡

diaphragmn.橫隔膜，膜片，控光裝置，鏡頭上的光圈，(電話等)振動膜

two-positionoron-offcontrolaction雙位或繼電器型控制

domesticadj.家庭的，國產(chǎn)的，國內(nèi)的，馴服的n.傭人，[pl.]國貨

solenoidn.螺線管，筒形線圈，電磁鐵，網(wǎng)絡，網(wǎng)絡管

inflown.流入，流入物

exponentialn.指數(shù)，倡導者，演奏者，例子adj.指數(shù)的，冪數(shù)的

thefillingcurve灌水曲線

theemptyingcurve放水曲線

differentialgap差動間隙

inverseadj.倒轉(zhuǎn)的，反轉(zhuǎn)的，顛倒的，相反的，倒數(shù)的n.反面，倒數(shù)vi.倒轉(zhuǎn)

duplicateadj.復制的，副的，兩重的，兩倍的n.復制品，副本vt.復寫，復制

anticipatoryadj.預料的，預想的，預期的，預先做的，預先發(fā)生的

asamatterofcourse理所當然的(事)；自然地

transientperiod過渡周期，暫態(tài)過程，穩(wěn)定時間

servomechanismn.伺服機構(gòu)(系統(tǒng))，隨動系統(tǒng)，跟蹤系統(tǒng)，自動控制裝置3.2.3Text

BasicControlActions

Afamiliarexampleofacontrolloopistheactiontakenwhenadjustinghotandcoldfaucets(valves)tomaintainthewateratadesiredtemperature.Thistypicallyinvolvesthemixingoftwoprocessstreams,thehotandcoldwater.Thepersontouchesthewatertosenseormeasureitstemperature.Basedonthisfeedbacktheyperformacontrolactiontoadjustthehotandcoldwatervalvesuntiltheprocesstemperaturestabilizesatthedesiredvalue.

Anautomaticcontrollercomparestheactualvalueoftheplantoutputwiththedesiredvalue,determinesthedeviation,andproducesacontrolsignalwhichwillreducethedeviationtozeroortoasmallvalue.Themannerinwhichtheautomaticcontrollerproducesthecontrolsignaliscalledthecontrolaction.

Hereweshallpresentthebasiccontrolactionscommonlyusedinindustrialautomaticcontrollers.Firstweshallintroducetheprincipleofoperationofautomaticcontrollersandthemethodsforgeneratingvariouscontrolsignals,suchastheuseofthederivativeandintegraloftheerrorsignal.Nextweshalldiscusstheeffectsofparticularcontrolmodesonthesystemperformance.Thenweshallgiveabriefdiscussionofmethodsforreducingtheeffectsofexternaldisturbancesonthesystemperformance.

Mostindustrialautomaticcontrollersuseelectricityorpressurizedfluidsuchasoilorairaspowersources.Automaticcontrollersmayalsobeclassifiedaccordingtothekindofpoweremployedintheoperation,suchaspneumaticcontrollers,hydrauliccontrollers,orelectroniccontrollers.Whatkindofcontrollertousemustbedecidedbythenatureoftheplantandtheoperatingconditions,includingsuchconsiderationsassafety,availability,reliability,accuracy,weight,andsize.

Anautomaticcontrollermustdetecttheactuatingerrorsignal,whichisusuallyataverylowpowerlevel,andamplifyittoasufficientlyhighlevel.Thus,anamplifierisnecessary.Theoutputofanautomaticcontrollerisfedtoapowerdevice,suchasapneumaticmotororvalve,ahydraulicmotor,oranelectricmotor.

Thecontrollerusuallyconsistsofanerrordetectorandamplifier.Themeasuringelementisadevicethatconvertstheoutputvariableintoanothersuitablevariable,suchasadisplacement,pressure,orelectricsignal,whichcanbeusedforcomparingtheoutputwiththereferenceinputsignal.Thiselementisinthefeedbackpathoftheclosed-loopsystem.Thesetpointofthecontrollermustbeconvertedtoareferenceinputofthesameunitsasthefeedbacksignalfromthemeasuringelement.Theamplifieramplifiesthepoweroftheactuatingerrorsignal,whichinturnoperatestheactuator.Theactuatorisanelementwhichalterstheinputtotheplantaccordingtothecontrolsignalsothatthefeedbacksignalmaybebroughtintocorrespondencewiththereferenceinputsignal.

Industrialautomaticcontrollersmaybeclassifiedaccordingtotheircontrolaction.Thefollowingbasiccontrolactionsareverycommonamongindustrialautomaticcontrollers:on-off,proportional,integral,derivative,proportional-plus-integral,proportional-plus-derivative,andproportional-plus-derivative-plus-integralcontrolaction.Notethatanunderstandingofthebasiccharacteristicsofthevariousactionsisnecessaryinorderforthecontrolengineertoselecttheonebestsuitedtoh