《电气信息类专业英语》课件第3章

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

3.1.1语言现象——形容词的翻译

英语形容词起修饰作用，是修饰名词的。译得准确、生动，与名词搭配相得益彰，可以起到画龙点睛的作用，使文章显得生动活泼，使被修饰的人物、事物跃然纸上。否则，词不达意，晦涩难懂，连名词的意思也黯然失色。因此，应高度重视对英语形容词的准确理解与恰当翻译。3.1ControlEngineering形容词在英文句中一般做表语或修饰名词的定语，因而在翻译时要把形容词与其所修饰的客体统一考虑，对二者的割裂会导致牛头不对马嘴的错误。

1．正确体会一词多义

有些形容词的词义不是一两个解释所能说清楚的，其含义比较复杂，要先了解它们的本义，抓住其基本概念，再结合被修饰的名词，探索其演变出的各种意义。对形容词词义的理解必须同上下文联系起来，明确它所指的范围，即明确它所修饰的对象，确定它在此表达的意思，再从汉语中挑选恰当的词语，准确恰当地把它表达出来。

heavy的基本词义是“重”，但在翻译时结合修饰的对象则译法各异。如heavycurrent强电流；heavycrop大丰收；heavytraffic交通拥挤；heavyindustry重工业等。英语词义对上下文的依赖性是很大的。一个孤立的词，其词义通常是游移不定的，但当词处于特定的联立关系中时，其含义就受到相关词的制约而明朗和稳定了。因此，根据词的联立关系确定词义是词义辨析的重要且最为可行的手段。

universal有“宇宙的、世界的、普遍的、一般的和通用的”等含义。具体用法举例如下：

universalmeter万用表；universalconstant通用常数；universalmotor交直流两用电动机；universaluse普遍应用；universalagent全权代理人；universalaccess通用存取；universalcoupling/joint万向轴节；universalgrammar普遍文法，通用文法；universalgravitation万有引力；universallanguage通用语言，世界语；UniversalMusic环球音乐集团(公司名称)；universalserialbus通用串行总线；universalset通用集(合)，泛集，万有集；UniversalStudio环球影城(主题公园名)；universalsuffrage普选权；universaltestingmachine万能试验机；universaltime世界时间，格林威治时间，国际标准时间；universalpeace世界和平；universalrules一般法则；universaltruth普遍真理；universaltravel环球旅行等等。

sophisticated源出希腊语的诡辩家sophist一词，现其使用范围很广。如sophisticatedequipment尖端设备，高级设备；sophisticatedinvestor成熟投资者，精明投资人；sophisticatedplaner精密刨床；sophisticatedtechnology精良工艺；sophisticatedarguments强词夺理的论据；sophisticatedweapons尖端武器；sophisticatedman老于世故的人；thenewandsophisticatedpatternsofintervention花样翻新的干涉活动等等。同一个high在highnoon中译为正午，在highsummer中译为盛夏，在highmanner中译为傲慢的态度，而在highvoice中译为尖声，这些都和汉语的习惯用法密切相关。

一般的常用专业词组搭配都可以在英汉技术字典中查到，所以对含义不清楚的词组应借助字典来理解，闭门造车式的翻译只能导致主观臆断的错误。

对形容词的翻译还可采取词性转换的技巧，使对原文的表达更通顺和易于理解。

2．一些原义并无否定意思的形容词和别的词搭配，有时可译成否定句

如：

Thesegoodsareinshortsupply.

这些货物供应不足。

Thisequationisfarfrombeingcomplicated.

这个方程一点也不复杂。

3．当形容词在句中做表语时，某些情况下可根据汉语习惯，将其和系词合译成动词形式

如：

InternetisdifferentfromIntranetinmanyaspectsthoughtheirspellingisalike．

虽然拼写相像，Internet仍在很多方面不同于Intranet。

Iflow-costpowerbecomesavailablefromnuclearpowerplants，theelectricitycrisiswouldbesolved．

如能从核电站获得低成本电力，电力紧张问题就会解决。

4．某些表示事物特征的形容词，可在其后加上“性”、“度”而转化为名词

如：

IPCismorereliablethancommoncomputer.

工控机的可靠性比普通计算机高。

Experimentindicatesthatthenewchipisabout1.5timesasintegrativeasthatoftheoldones.

试验表明，新型芯片的集成度是旧型号的1.5倍。

5．有时形容词也可根据需要译成副词

如：

Thesameprinciplesoflowinternalresistancealsoapplytomilli-ammeters．

低内阻原理也同样适用于毫安表。

Themodernworldisexperiencingrapiddevelopmentofinformationtechnique．

当今世界的信息技术正在迅速地发展。词性转换技巧同样适用于其他词类，拘泥于原文的词性进行完全对应的翻译往往会给翻译带来极大的障碍，同时使得译文生涩而难以理解。翻译应从整体着眼，采取适当的词性转换、句子成分转换或句型转换的翻译技巧，可使译文既忠实于原意又通顺可读。3.1.2SpecifiedEnglishWords

disciplinen.纪律；学科；训练vt.训练，训导；惩戒

regulatevt.调节，规定；有系统的管理；控制；校准

derivevt.得自；源于vi.起源

actuatorn.执行机构；激励者；促动器

yawdamper抗偏器；偏航阻尼器

on-siteadj.现场的

Laplacetransform拉普拉斯变换

scanvt.扫描vi.扫描；扫掠n.扫描；浏览；审视；细看

diversifyvt.使多样化，使变化；增加产品种类以扩大

sampled-data采样数据

nonlinearadj.非线性的

time-invariantadj.时不变的

stationaryadj.静止的；固定的；定居的；常备军的n.不动的人；驻军

lumpedparameter集合参数；集中参数；总参数

distributedparameter分散(布)式参数

deterministicadj.确定性的；命运注定论的

stochasticadj.随机的；猜测的

performancecriteria性能标准

overlapn.重叠；重复vi.部分重叠vt.与……重叠；与……同时发生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“lumps”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，在对压力、温度、湿度、粘度、流量实施的工业过程的控制中，必须进行自动控制。

2．ThereactiontimeofahumanpilotistooslowtoenablehimorhertoflyanaircraftwithalightlydampedDutchrollmodewithouttheadditionofayawdampersystem.

飞行员的反应速度太慢，如果不附加阻尼偏航系统，就无法通过小阻尼的荷兰滚方式来驾驶飞机。

3．Sincetheoutputisfedbackinafunctionalformdeterminedbythenatureofthefeedbackelementsandthensubtractedfromtheinput…

因为输出会以由反馈元件特性决定的函数形式反馈回来，然后从输入中减去……

4．Studentsofcontrolengineeringmaystartwithalinearcontrolsystemcoursedealingwiththetimeandcomplex-sdomain,whichrequiresathoroughbackgroundinelementarymathematicsandLaplacetransform.学习控制工程可以从线性控制系统起步，线性控制系统涉及时域及复域两个方面，要求必须具有良好的数学基础，掌握拉普拉斯变换。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语言现象——定语从句的翻译

科技英语中定语从句极为常见。定语从句也叫关系分句，是一种由关系词引导的分句形式的后置修饰语。关系分句所修饰的先行词和在句中作某种成分的关系代词、关系副词构成了定语从句的主要特征。3.2BasicControlActions不管一个句子有多长，句子里套有几个定语从句，定语从句是否紧随先行词之后，其基本类型有两种：限制性定语从句和非限制性定语从句。科技英语中使用定语从句能使结构紧凑，语义连贯，逻辑性强。但同时也会面临一个问题，即如果不能准确找出定语从句所修饰的先行词，理解之间的关系，就会产生误译甚至错译。

因此，在英汉翻译的过程中，首先通读句子，进行语法分析，借助专业知识，依靠上下文，准确理解句子所传达的信息和内涵意义，然后依据从句、先行词和主干句之间的关系，适当翻译。

1．翻译成“定语─中心语”的关系

大多数简单限制性定语从句和并列限制定语从句常翻译成带“的”字结构的定语，与先行词构成“定语—中心语”的关系，也有部分的非限制性定语从句可采用这种翻译方法。

例如：

Amotorwhichistoosmallwouldbesubjecttofrequentoverload.

过小的电动机时常会发生过载。

Thedegreetowhichtheyimpedetheflowofcurrentiscalledresistance.阻碍电流流动的程度叫电阻。

Itisthatpartofthestatespaceinwhichasymptoticallystabletrajectoriesoriginate.

它是引出渐近稳定轨迹的状态空间的一部分。

2．翻译成汉语的并列关系

当定语从句结构复杂，翻译成“定语—中心语”的关系不符合汉语的表达习惯时，可采用重复或省略英语先行词或先行词所代表的含义的方法，把定语从句译成后置或前置的并列分句。例如：

Inthecaseofaresistor,thevoltage-currentrelationshipisgivenbyOhm’slaw,whichstatesthatthevoltageacrosstheresistorisequaltothecurrentthroughtheresistormultipliedbythevalueoftheresistance.就电阻来说，电压—电流的关系由欧姆定律决定。欧姆定律指出，电阻两端的电压等于流过电阻上的电流乘以电阻值。

Arocketisindependentofairbecauseitcontainsanexplosivemixturewhichconsistsbothofafueltobeburnedandasupplyofoxygen.

火箭飞行不依赖空气，因为它本身装有爆炸混合物，这种混合物是由待燃烧的燃料和氧气组成的。

3．翻译成汉语的同位关系

英语的定语从句和汉语的同位语关系密切，在英汉互译的过程中往往可以相互转换。例如：

Hydrogen,whichisthelightestelement,hasonlyoneelectron.

最轻的元素氢只有一个电子。

ThesecondmethodofLyapunov(whichisalsocalledthedirectmethodofLyapunov)isthemostgeneralmethodforthedeterminationofstabilityofnonlinearand/ortime-varyingsystems.李雅普诺夫第二方法(也称为李雅普诺夫直接法)是确定非线性和/或时变系统稳定性的最一般的方法。

4．翻译成汉语的动宾关系

有时定语从句和先行词之间存在着逻辑上的动宾关系，译成汉语时，可把先行词译成英语定语从句里谓语动词的宾语，构成汉语的动宾关系。例如：

Therearethreestepswhichmustbetakenbeforewegraduatefromtheintegratedcircuittechnology.

我们要完全掌握集成电路工艺，必须采取三项措施。

5．翻译成汉语的主谓关系

有时定语从句和先行词之间存在着逻辑上的主谓关系(特别在Therebe句型中)，译成汉语时，可把先行词译成英语定语从句里谓语动词的主语，构成汉语的主谓关系。例如：

Therewasnotonehousebut(作为关系代词，相当于whichwasnot)wasburntdown.

所有的房子都被烧掉了。

Therearesomemetalswhichpossessthepowertoconductelectricityandtheabilitytobemagnetized.

有些金属既能导电，又能被磁化。

6．翻译成汉语的主从偏正复句

英语中有些定语从句与主干句之间语义上相互关联，且二者之间的关系并不平等，含有因果、目的、让步、条件和假设等关系，可根据语义译成汉语的偏正复句。例如：

Abodythatcontainsonlyatomswithsamegeneralpropertiesiscalledanelement.

一切物质，如果它包含的原子性质都相同，则称为元素。

Einstein,whoworkedoutthefamousPhotoelectricTheory,wontheNoblePrize.爱因斯坦因提出了著名的“光电理论”而获得诺贝尔奖。

Computers,whichhavemanyadvantages,cannottaketheplaceofman.

计算机虽有很多优点，却不能代替人。

Thefirstcomputerusedthesametypesofcomponentwhichmadeequipmentverylargeandbulky.

首批计算机采用同类元件，致使设备又大又笨重。

Heunnecessarilyspentalotoftimeintroducingthisbook,whichthestudentsarefamiliarwith.

他花了很长时间介绍这本书，其实没有必要，因为学生们对它已经很熟悉了。

7．翻译成独立句

Onewasaviolentthunderstorm,theworstIhadeverseen,whichobscuredmyobjective.

有一次是暴风骤雨，猛烈的程度实为我生平所仅见，这阵暴风雨遮住了我的目标。3.2.2SpecifiedEnglishWords

faucetn.旋塞，龙头，开头

deviationn.明显异化，偏差，偏离，背离，越轨

controlaction控制作用

errorsignal误差(偏差)信号

two-positionoron-offcontroller双位或继电器型控制器

proportional-plus-derivative-plus-integralcontroller比例微分积分控制器(即PID控制器)

actuatevt.开动(机器等)，驱使，促使，激励(某人做某事)

actuatorn.激励者，制动器，执行机构，传动装置

displacementn.移置，转移，取代，置换，位移，排水量

correspondencen.相应，通信，信件，符合，一致，和谐，相似adj.通信的，函授的

bringintocorrespondencewith使与……一致，使与……联络

diaphragmn.横隔膜，膜片，控光装置，镜头上的光圈，(电话等)振动膜

two-positionoron-offcontrolaction双位或继电器型控制

domesticadj.家庭的，国产的，国内的，驯服的n.佣人，[pl.]国货

solenoidn.螺线管，筒形线圈，电磁铁，网络，网络管

inflown.流入，流入物

exponentialn.指数，倡导者，演奏者，例子adj.指数的，幂数的

thefillingcurve灌水曲线

theemptyingcurve放水曲线

differentialgap差动间隙

inverseadj.倒转的，反转的，颠倒的，相反的，倒数的n.反面，倒数vi.倒转

duplicateadj.复制的，副的，两重的，两倍的n.复制品，副本vt.复写，复制

anticipatoryadj.预料的，预想的，预期的，预先做的，预先发生的

asamatterofcourse理所当然的(事)；自然地

transientperiod过渡周期，暂态过程，稳定时间

servomechanismn.伺服机构(系统)，随动系统，跟踪系统，自动控制装置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