《电气信息类专业英语》课件第5章

Part5ProcessControl5.1IntroductionstoProcessControl5.2SensorandItsCharacteristics 5.3StandardThermocouplesTypes5.4PIDControllers5.5IntelligentControl

5.1.1语言现象——面试(personalinterview)

去外企应聘工作或申请出国留学签证，都需要用英语面试。那么面试英语时自我介绍该怎样讲呢?在与西方人交谈时，应注意哪些问题呢？

尽管一般在简历中对自己的教育背景作了介绍，但在面试时，面试官还有可能就此方面提问，还是应该事先做点准备。5.1IntroductionstoProcessControl

1．面试时常问的问题

当问及教育背景时，应注意简明扼要，实话实说。如：

I：Whatisyourmajor？

A：MymajorisBusinessAdministration.Iamespeciallyinterestedin“Marketing”。

这样回答不仅回答了问题，还顺带一句介绍了自己较为感兴趣的方面，简明扼要。再如：

I：Whichuniversityareyouattending？

A：IamattendingxxxUniversity.

I：Haveyoureceivedanydegrees？

A：Yes.First,IreceivedmyBachelordegreeinEnglishLiterature,andthenanMBAdegree.

I：Whatcoursedidyoulikebest？

A：ProjectManagement.IwasveryinterestedinthiscoursewhenIwasastudent.AndIthinkit’sveryusefulformypresentwork.

I：Doyoufeelthatyouhavereceivedagoodgeneraltraining？

A：Yes,IhavestudiedinanEnglishtrainingprogramandacomputertrainingprogramsinceIgraduatedfromuniversity.IamcurrentlystudyingFinanceatatrainingschool.当问及工作经验时，应注意显露实力，避免炫耀。如：

I：Haveyoueverbeenemployed？Yourresumesaysyouhavehadone-yearexperienceworkinginaforeignrepresentativeofficeinShanghai,mayIaskwhyyouleft？

A：Iworkedinaforeignofficeforoneyear.However,Ilefttheretwoyearsagobecausetheworktheygavemewasratherdull.Ifoundanotherjobthatismoreinteresting.

I：Haveyoudoneanyworkinthisfield？Whathaveyoulearnedfromthejobsyouhavehad？

A：Ihavelearnedalotaboutbusiness,andknowsomebasicofficeskills.Inaddition,Ilearnedatmypreviousjobshowtocooperatewithmycolleagues.

I：What’syoumajorweakpoint？

A：Ihaven’tbeeninvolvedininternationalbusiness,soIdon’thaveanyexperience,butIhavestudiedthiscourseintheInternationalBusinessTrainingCenterofthexxxCompany.

I：Doesyourpresentemployerknowyouarelookingforanotherjob？

A：No,Ihaven’tdiscussedmycareerplanswithmypresentemployer,butIamsurehewillunderstand.当问及性格爱好时，应注意表现积极、合作的一面。如：

I：Whatkindofpersonalitydoyouthinkyouhave？

A：Ialwaysapproachthingsveryenthusiastically.WhenIbeginsomething,Idon’tliketoleaveithalfdone.Ican’tconcentrateonsomethingnewuntilthefirstthingisfinished.

I：Whatisthemostimportantthingforyoutobehappy？

A：Differentpeoplehavedifferentideas.Ithinkthemostimportantthingformeishavingagoodrelationshipwithmyfamilymembersandmyfriends.Myfamilyhasalwaysbeenverycloseknit,andmyfriendsandIspendalotoftimetogether.WithoutthatIwouldbemuchlesshappythanIam.

I：Whatmakesyouangry？

A：Dishonesty.It’sunacceptable.

I：Whatareyourpersonalweaknesses？

A：I’mafraidI’mapoortalker.I’mnotcomfortabletalkingwiththepeoplewhomIhavejustmetforthefirsttime.Thatisnotverygoodforbusiness,soIhavebeenstudyingpublicspeaking.

I：Areyoumoreofaleaderorafollower？

A：Idon’ttrytoleadpeople.I’drathercooperatewitheverybody,andgetthejobdonebyworkingtogether.

当问及工作要求时，应表示出我能胜任。如：

I：DoyouthinkyoucanmakeyourselfeasilyunderstoodinEnglish？

A：Yes,inmostcircumstances.

I：Areyouavailablefortravel？

A：Yes,Iliketraveling.Iamyoung,andunmarried.It’snoproblemformetotravelfrequently.

I：Howaboutovertimework？

A：Overtimeworkisverycommonincompanies.Icanworkovertimeifit’snecessary,butIdon’tthinkwewillworkovertimeeveryday.

I：Doyoulikeregularwork？

A：No,Idon’tlikeregularwork.Iaminterestedindifferentprojectswithnewopportunitiesandnewchallenge,butIcandoregularworkifthecompanyneedsmetodoso.

I：Whatsalarydoyouexpect?

A：Shallwediscussmyresponsibilitieswithyourcompanyfirst？Ithinksalaryiscloselyrelatedtotheresponsibilitiesofthejob.

I：Doyouworkwellunderpressure?

A：Workingunderpressureisexcitingandchallenging.Idon’tmindworkingunderpressure.Iworkwellunderthesecircumstances.Peoplecan,Ican.

I：Doyouhaveanyparticularconditionsthatyouwouldlikethecompanytotakeintoconsideration？

A：No,nothinginparticular.

I：Howsooncanyoubeginworkingforus？

A：Ineedabouttwotothreeweeksfornecessaryformalities.Iwillquitthentransfertoyourcompany.

当面试结束时，应礼貌道别。如：

I：Anyquestions？

A：WhenwillIknowyourdecision？

I：Wewillnotifyyouofourdecisionbymail,isthisconvenientforyou？

I：Ofcourse,thankyouforyourinterestinourcompany.

A：Thankyou,Mr.Smith.Goodbye.(Thankyouforyourtime.)

I：Youwillbehearingfromusverysoon.Pleasesendthenextapplicationonyourwayout.

A：OK.Thankyouverymuch.

此外，面试官还可能问及你的家庭情况，如家人对你的影响等，也应事先有所准备。

2．面试英语自我介绍的常用基本句子

Inoticedthatyouadvertisedajobinthismorning’spaper.

我看到你们在今早的报纸上刊登的招聘广告。

I’mcomingforyouradvertisementfor…我是来应聘你们广告上的……职位的。

Ihaveappliedforthepositionof…我申请了贵公司的……职位。

Doyouhaveanyjobforapart-timer?你们需要兼职吗?

I’dliketoknowifyouneedanyfull-timesecretary.我想知道你们是否需要全职秘书?

I’mlookingforajob.Arethereanyvacancies?我在找工作，请问你们有空缺吗?

3．面试英语自我介绍的常用句型

IgottheBachelor’sDegreeinElectricalEngineeringandtookacourseintyping.

我获得了电气工程工学学士学位，还学过打字。

Ihaven’tdoneanythinglikethatbefore.我以前没有做过这种工作。

IthinkI’mquitefitforassistant’sjob.我觉得我很适合做助理的工作。

Iusedtoworkasasale’smanager.我以前做销售经理。

I’mquitefamiliarwithediting.我做过很多编辑工作。

Iwantajobwithavacationeveryyear.我想找个每年都能度假的工作。

Iwasthinkingofajobinaschool.我打算到学校找份工作。

Iworkedintheaccountingsectionofamanufacturerofelectricalproducts.

我曾在电子产品制造商的会计组工作。

Iloveplayingtennis.我喜欢打网球。5.1.2SpecifiedEnglishWords

thelike同样的东西，同类的事情

inletn.插入物；入口，进口

outletn.出口，排放孔；电源插座；销路；发泄的方法；批发商店

ensuevi.跟着发生，接着发生；继起vt.追求

deviationn.偏差；背离；误差

thermocouplen.热电偶

thermistorn.热敏电阻；电热调节器

throttlen.节流阀；风门vt.使……窒息；使……节流vi.节流，减速；窒息

tremendousadj.极大的，巨大的；惊人的

manipulatedvariable操纵量；被控变量

setpoint设定值；调整点；凝结点

foulingn.污染；污垢v.弄脏；犯规(foul的ing形式)

batchprocess间歇过程，断续过程，分批过程

psigabbr.poundspersquareinch,gauge磅/平方英寸(表压)

modelingn.建模，造型；立体感adj.制造模型的5.1.3Text

IntroductionstoProcessControl

Automaticprocesscontrolisconcernedwithmaintainingprocessvariables,temperatures,pressures,flows,compositions,andthelikeatsomedesiredoperationvalue.Processesaredynamicinnature.Changesarealwaysoccurring,andifactionsarenottaken,theimportantprocessvariables-thoserelatedtosafety,productquality,andproductionrates-willnotachievedesignconditions.

Athermostatisasimpleexampleforaclosedcontrolloop.Itconstantlymeasuresthecurrenttemperatureandcontrolstheheater’svalvesettingtoincreaseordecreasetheroomtemperatureaccordingtotheuser-definedsetting.Asimplemethodswitchestheheatereithercompletelyon,orcompletelyoff,andanovershootandundershootofthecontrolledtemperaturemustbeexpected.Amoreexpensivemethodvariestheamountofheatprovidedbytheheaterdependingonthedifferencebetweentherequiredtemperature(the“setpoint”)andtheactualtemperature.Thisminimizesover/undershoot.

Inordertofixideas,letusconsideraheatexchangerinwhichaprocessstreamisheatedbycondensingsteam.TheprocessissketchedinFig.5.1.Fig.5.1Heatexchanger

Thepurposeofthisunitistoheattheprocessfluidfromsomeinlettemperature,Ti(t),uptoacertaindesiredoutlettemperature,T(t).Asmentioned,theheatingmediumiscondensingsteam.

Theenergygainedbytheprocessfluidisequaltotheheatreleasedbythesteam,providedtherearenoheatlossestosurroundings,thatis,theheatexchangerandpipingarewellinsulated.

Inthisprocesstherearemanyvariablesthatcanchange,causingtheoutlettemperaturetodeviatefromitsdesiredvalue.Ifthishappens,someactionsmustbetakentocorrectforthisdeviation.Thatis,theobjectiveistocontroltheoutletprocesstemperaturetomaintainitsdesiredvalue.

OnewaytoaccomplishthisobjectiveisbyfirstmeasuringthetemperatureT(t),thencomparingittoitsdesiredvalue,and,basedonthiscomparison,decidingwhattodotocorrectforanydeviation.Theflowofsteamcanbeusedtocorrectforthedeviation.Thisis,ifthetemperatureisaboveitsdesiredvalue,thenthesteamvalvecanbethrottledbacktocutthesteamflow(energy)totheheatexchanger.Ifthetemperatureisbelowitsdesiredvalue,thesteamvalvecouldbeopenedsomemoretoincreasethesteamflow(energy)totheexchanger.Allofthesecanbedonemanuallybytheoperator,andsincetheprocedureisfairlystraightforward,itshouldpresentnoproblem.However,sinceinmostprocessplantstherearehundredsofvariablesthatmustbemaintainedatsomedesiredvalue,thiscorrectionprocedurewouldrequireatremendousnumberofoperators.Consequently,wewouldliketoaccomplishthiscontrolautomatically.Thatis,wewanttohaveinstrumentsthatcontrolthevariableswithoutrequiringinterventionfromtheoperator.Thisiswhatwemeanbyautomaticprocesscontrol.

Toaccomplishthisobjectiveacontrolsystemmustbedesignedandimplemented.ApossiblecontrolsystemanditsbasiccomponentsareshowninFig.5.2.Thefirstthingtodoistomeasuretheoutlettemperatureoftheprocessstream.Asensor(thermocouple,thermistors,etc)doesthis.Thissensor,alsooftencalledtheprimaryelement,isconnectedphysicallytoatransmitter,alsocalledthesecondaryelement,whichtakestheoutputfromthesensorandconvertsittoasignalstrongenoughtobetransmittedtoacontroller.Thecontroller,alsocalledthe“brain”ofthecontrolsystem,thenreceivesthesignal,whichisrelatedtothetemperature,andcomparesitwithdesiredvalue.Dependingonthiscomparison,thecontrollerdecideswhattodotomaintainthetemperatureatitsdesiredvalue.Basedonthisdecision,thecontrollerthensendsanothersignaltofinalcontrolelement,oftenacontrolvalvebutnotalways,whichinturnmanipulatesthesteamflow.

Fig.5.2Heatexchangercontrolloop

Ineverycontrolsystem,thethreebasicoperationsmustbepresentperformed.TheyareMeasurement(M),Decision(D)andAction(A).Thedecision-makingoperationinsomesystemisrathersimple,whileinothersitismorecomplex.Theengineerdesigningacontrolsystemmustbesurethattheactiontakenaffectsthevariabletobecontrolled,thatis,thattheactiontakenaffectsthemeasuredvalue.Otherwise,thesystemisnotcontrollingandwillprobablydomoreharmthangood.

Tobesuccessfulinpracticeofautomaticprocesscontrol,theengineermustfirstunderstandtheprinciplesofprocessengineering.Forthestudyofprocessautomaticcontrolitisalsoimportanttounderstandhowprocessesbehavedynamically.Consequently,itisnecessarytodevelopthesetofequationsthatdescribedifferentprocesses.Thisiscalledmodeling.Todothis,theknowledgeofthebasicprinciplesmentionedinthepreviousparagraphandofmathematicsthroughdifferentialisneeded.InprocesscontroltheLaplacetransformsareusedheavily.Thisgreatlysimplifiesthesolutionofdifferentialequationsandthedynamicanalysisofprocessesandtheircontrolsystems.

Anotherimportant“tool”forthestudyandpracticeofprocesscontroliscomputersimulation.Manyoftheequationsdevelopedtodescribeprocessarenonlinearinnatureand,consequently,themostexactwaytosolvethemisbynumericalmethods;thismeanscomputersolution.Thecomputersolutionofprocessmodelsiscalledsimulation.

Notes

1．Theenergygainedbytheprocessfluidisequaltotheheatreleasedbythesteam,providedtherearenoheatlossestosurroundings,thatis,theheatexchangerandpipingarewellinsulated.

只要周围没有热损耗，即热交换器和管道是绝热的，过程流体获得的热量就等于蒸汽释放的热量。

2．Inthisprocesstherearemanyvariablesthatcanchange,causingtheoutlettemperaturetodeviatefromitsdesiredvalue.

在这个过程中很多变量会发生变化，继而导致出口温度偏离期望值｡

3．Thatis,wewanttohaveinstrumentsthatcontrolthevariableswithoutrequiringinterventionfromtheoperator.

就是说，我们想利用设备来控制变量，而无需操作人员介入｡5.1.4ReadingMaterials

TypesofControlSystems

Processcontrolisextensivelyusedinindustryandenablesmassproductionofcontinuousprocessessuchasoilrefining,papermanufacturing,chemicals,powerplantsandmanyotherindustries.Processcontrolenablesautomation,withwhichasmallstaffofoperatingpersonnelcanoperateacomplexprocessfromacentralcontrolroom.

Itisnecessarytodefinesometermsusedinthefieldofautomaticprocesscontrol.Thefirsttermiscontrolledvariable.Thisisthevariablethatmustbemaintainedorcontrolledatsomedesiredvalue.Intheprecedingexample,theprocessoutlettemperature,T(t),isthecontrolledvariable.Thesecondtermissetpoint,thedesiredvalueofcontrolledvariable.Themanipulatedvariableisthevariableusedtomaintainthecontrolledvariableatitssetpoint.Intheexample,theflowofsteamisthemanipulatedvariable.Finally,anyvariablethatcancausethecontrolledvariabletodeviateawayfromsetpointisdefinedasadisturbanceorupset.Inmostprocessthereareanumberofdifferentdisturbances.Asanexample,intheheatexchangershowninFig.5.1,possibledisturbancesareinletprocesstemperatureTi(t),theprocessflowq(t),thequalityoftheenergyofthesteam,ambientconditions,processfluidcomposition,fouling,andsoon.Whatisimportanthereistounderstandthatintheprocessindustries,mostoftenitisbecauseofthisdisturbancethatautomaticprocesscontrolisneeded.Iftherewerenodisturbances,design-operatingconditionswouldprevailandtherewouldbenonecessityofcontinuously“policing”theprocess.

Acommonlyusedcontroldevicecalledaprogrammablelogiccontroller,oraPLC,isusedtoreadasetofdigitalandanaloginputs,applyasetoflogicstatements,andgenerateasetofanaloganddigitaloutputs.Usingtheexampleinthepreviousparagraph,theroomtemperaturewouldbeaninputtothePLC.Thelogicalstatementswouldcomparethesetpointtotheinputtemperatureanddeterminewhethermoreorlessheatingwasnecessarytokeepthetemperatureconstant.APLCoutputwouldtheneitheropenorclosethehotwatervalve,anincrementalamount,dependingonwhethermoreorlesshotwaterwasneeded.LargermorecomplexsystemscanbecontrolledbyaDistributedControlSystem(DCS)orSupervisoryControlandDataAcquisition(SCADA)System.

Inpractice,processcontrolsystemscanbecharacterizedasoneormoreofthefollowingforms:

Discrete.

Foundinmanymanufacturing,motionandpackagingapplications.Roboticassembly,suchasthatfoundinautomotiveproduction,canbecharacterizedasdiscreteprocesscontrol.Mostdiscretemanufacturinginvolvestheproductionofdiscretepiecesofproduct,suchasmetalstamping.

Batch.Someapplicationsrequirethatspecificquantitiesofrawmaterialsbecombinedinspecificwaysforparticulardurationstoproduceanintermediateorendresult.Oneexampleistheproductionofadhesivesandglues,whichnormallyrequiresthemixingofrawmaterialsinaheatedvesselforaperiodoftimetoformaquantityofendproduct.Otherimportantexamplesaretheproductionoffood,beveragesandmedicine.Batchprocessesaregenerallyusedtoproducearelativelylowtointermediatequantityofproductperyear(afewpoundstomillionsofpounds).

Continuous.Often,aphysicalsystemisrepresentedthroughvariablesthataresmoothanduninterruptedintime.Thecontrolofthewatertemperatureinaheatingjacket,forexample,isanexampleofcontinuousprocesscontrol.Someimportantcontinuousprocessesaretheproductionoffuels,chemicalsandplastics.Continuousprocessesinmanufacturingareusedtoproduceverylargequantitiesofproductperyear(millionstobillionsofpounds).

Applicationshavingelementsofdiscrete,batchandcontinuousprocesscontrolareoftencalledhybridapplications.5.1.5Homework

1．Pleasesumupthemainpointsofthetextinseveralsentences.

2．TranslatethefollowingsentencesintoChinese.

(1)ThiskindofnonlinearPIDcontrollerholdsaflexiblegain-schedulebyselectingitsparameterssimply.

(2)AsabasicpartofaVirtualManufacturingPlatform,manufacturingsystemmodelingiscriticaltothesuccessofprocesscontrolinamultirobotvirtualmanufacturingenvironment.

(3)Aprocesscontrolalertoccurswhenasuccessionofdatapointsshowsatypicalpatternthatwaspossiblycausedbychangestothelaboratoryormanufacturingprocess.

(4)Thatis,wewanttohaveinstrumentsthatcontrolthevariableswithoutrequiringinterventionfromtheoperator.

(5)Theexperimentresultdemonstratesitsperformanceandcontroleffectivenesscanmeettherequirementofpracticalprocesscontrol.

5.2.1语言现象——科技文献检索

文献是在存储、检索、利用或传递记录信息的过程中，可作为一个单元处理的，在载体内、载体上或依附载体而存储有信息或数据的载体。文献具有知识、载体、记录方式三要素。文献本身固有的性质分别是知识性、客观物质性、人工记录性和动态发展性。5.2SensorandItsCharacteristics随着科学技术的迅速发展，科技文献，尤其是尖端科学文献增加速度更快，且倍增周期逐年缩短。科技文献种类繁多，有学术论文、科技报告、学位论文和科技会议文献等原始文献，也有在此基础上经整理、加工、压缩、提炼后编制成的各种检索工具，如书目、题录、索引、文摘、百科全书、手册、年鉴和名录等。进行科学研究、撰写学位和学术论文、进行毕业设计、从事产品的开发和进行发明创造等工作，都要检索相关的文献。因此，文献检索是科技人员必备的基本技能，是科学研究的先期工作，是知识更新的手段，也是能力培养的重要途径。

1．文献的形式

各类专业文献种类繁多，形态各异。从形式/载体上分为以下几种：

纸质型(Printedform)。也叫印刷型，是以纸张为存储介质，以手写、印刷为记录手段而存在的一种传统的文献形式。

缩微型(Microform)。缩微型以感光材料为存储介质，以缩微照相为记录手段而存在的一种文献形式。

声像/视听型(Audio-Visualform)。声像/视听型又称为视听资料或直感资料，以磁性材料和光学材料为存储介质。机读/电子型(MachineReadableform)。机读/电子型全称为计算机可读型文献，以磁性材料(磁带、磁盘或光盘等)为存储介质。

2．文献的级别

专业文献从级别上可分为下面几种：

一次文献/信息(primaryLiterature/info)，即原始文献，如期刊文献(Journalliterature)、科技报告(Sci-Techreport)、学术会议论文集(Proceedings)、专利(Patentspecification)、论文(Paper)、学位论文(Thesis)等。

二次文献/信息(secondaryliterature/info)，即检索工具，如条目(entryreferencecitationrecord)、文摘(Abstract)、索引(Index)、目录(Catalog)、题录(Bibliography)等。

三次文献(Tertiaryliterature/info)，如词典或百科全书等参考书(Referencebook)，属于参考性文献。

3．文献的类型与识别

文献的类型有很多，一般分为以下几类：

科技图书(Sci-Techbook)，主要包括专著(Monograph)、文选(Anthology)、教材(Textbook)和参考书(Referencebook)等；科技期刊(Sci-TechJournal)，主要包括杂志(magazine)、不定期的连续出版物(serial)和期刊(periodical)等；科技报告(Sci-TechReport)；专利文献(PatentDocument)，主要包括专利说明书(Patentspecification)和专利公告(bulletin)等；会议文献(Conferencepaper)；学位论文(Dissertation,Thesis)；其他标准文献、产品资料、技术档案、政府出版物等。

4．文献/信息检索(Literature/

InformationRetrieval/

Access)

文献检索的手段分为手检(书本型工具/期刊)和机检(数据库系统)。其中手检是对相关的印刷型资源进行检索，包括各种检索工具和专业期刊。计算机检索包括光盘数据库检索、网络数据库检索(比较流行的检索方式)和互联网信息检索(使用搜索引擎进行互联网信息检索)。目前常用的中文网络数据库有CNKI系列数据库(，包括中国期刊全文数据库、中国优秀博硕论文数据库和中国专利数据库)、超星数字图书馆()、万方数据库(/qikan)和维普数据库()等。

英文数据库有CSA数据库、SpringerLINK全文电子期刊、EBSCO数据库、OCLC数据库、IEL数据库、《不列颠百科全书》网络版和WorldSciNet电子期刊等。

互联网信息检索是指借助于搜索引擎进行互联网信息检索，常用的WWW搜索引擎主要有：

/

除了常规的WWW搜索引擎外，还可以使用FTP搜索引擎，其功能是搜集匿名FTP服务器提供的目录列表以及向用户提供文件信息的查询服务。由于FTP搜索引擎专门针对各种文件，因而相对WWW搜索引擎，寻找软件、图像、电影和音乐等文件时，使用FTP搜索引擎更加便捷。常用的FTP搜索引擎主要有：

北大天网FTP：

清华大学：/，/北京大学：，/，/

中国科学技术大学：/

浙江大学：/

北京邮电大学：/，/

华中理工大学：/

上海交通大学：/，/哈尔滨工业大学：/

西安交通大学：/，/，/

香港中文大学：ftp://ftp.cuhk.hk/，.hk/，.hk/

5．检索点/途径(AccessPoint)

检索点是检索系统预先设置的用户可用于检索的途径。

分类(Classified)：按文献所属的学科类别来检索文献。在检索文献之前应根据课题的主要内容以及数据库所采用的分类表，确定分类号。

主题(Subject)：从文献的主题概念出发，通过主题词或关键词检索文献。

题名(Title)：根据文献题名来检索文献。文献题名主要指书名、刊名、篇名等。题名允许中、英文混合或者是题名的一部分。著者(Author)：通过著者[个人著者、团体著者(CorporateAuthor/Authors’Affiliation)]的名称来检索文献。

号码检索：通过号码(Code/Coden)如ISBN(InternationalStandardBookNumber)号、ISSN号、专利号、标准号、报告号等来检索文献。5.2.2SpecifiedEnglishWords

sensorn.传感器

mercury-in-glassthermometer玻璃水银温度计；水银温度计；汞柱玻璃温度计

calibratevt.测定……的口径，标定，校准……的刻度(或分度)，定……的刻度

straingauge应变仪；变形测量器；应变仪；变形测量器

foilvt.挫败；阻止，挡开；衬托；贴箔于n.箔，金属薄片；叶形片；衬托，烘托

etchvt.蚀刻；鲜明地描述；铭记vi.蚀刻n.刻蚀；腐蚀剂

serpentineadj.阴险的；蜿蜒的；弯弯曲曲的vt.使迂回曲折地行进n.蛇纹石

resinn.树脂；松香vt.涂树脂；用树脂处理

modestadj.谦虚的，谦逊的，纯洁的，不太多的，不过分的，适度的，适中的

responsivityn.响应率；反应性

piezoresistiveadj.压电电阻的；压电电阻效应的

microscopicadj.用显微镜可见的；微观的

MEMSabbr.微电子机械系统(Micro-electromechanicalSystems)

fullscalerange量程

degradationn.降格，降级；退化；堕落

hysteresisn.磁滞(现象)

aliasingn.别名使用；混淆现象

calibrationn.标定，校正，调节,口径测定，刻度，分等级5.2.3Text

SensorandItsCharacteristics

Thisisanintroductiontosomeofthephysicalprinciplesthatunderliesensorsininstrumentsystems.Itisnotintendedtobedefinitive,orverydetailed,buttogivethereaderanideaofwhatisreadilyachievablewiththevarioussystems.

Asensor(alsocalleddetectors)isadevicethatmeasuresameasurableattributeandconvertsitintoasignalwhichcanbereadbyanobserverorbyaninstrument.Forexample,amercury-in-glassthermometerconvertsthemeasuredtemperatureintoexpansionandcontractionofaliquidwhichcanbereadonacalibratedglasstube.Athermocoupleconvertstemperaturetoanoutputvoltagewhichcanbereadbyavoltmeter.Foraccuracy,mostsensorsarecalibratedagainstknownstandards.

Atconstanttemperature,theresistanceRofametalorsemiconductorelementofareaA,lengthl,resistivity

,is

R＝l

/A(5-2-1)

andwhentheelementisstrainedthischangesbyanamount

so

Atypicalstraingaugeconsistsofametalfoil,photo-etchedtoformaserpentinepattern,andmountedonaresinbackingfilm.Thisisthenattachedtothestructuretobemonitoredwithadhesive.Metalsensor-elementsaredominatedbythegeometrictermsintheaboveequationandthereforetheyarerelativelytemperatureindependentandhaveamodestgaugefactor(i.e.responsivity)ofabout2.Semiconductorelementscanexploitalargepiezoresistiveeffectyieldinggaugefactorsof150.However,thisisattheexpenseoftemperaturestabilityandsomesortofcompensationschemeisusuallyrequiredinpractice.

Straingaugesarewidelyusedinmanyapplications;theyaresmall,cheap,sensitiveandreliable,andmanyvariables(e.g.pressure)canbeusedtocausestrain.

Asensor’ssensitivityindicateshowmuchthesensor’soutputchangeswhenthemeasuredquantitychanges.Forinstance,ifthemercuryinathermometermoves1

cmwhenthetemperaturechangesby1℃,thesensitivityis1

cm/℃(itisbasicallytheslopeDy/Dxassumingalinearcharacteristic).Sensorsthatmeasureverysmallchangesmusthaveveryhighsensitivities.Sensorsalsohaveanimpactonwhattheymeasure;forinstance,aroomtemperaturethermometerinsertedintoahotcupofliquidcoolstheliquidwhiletheliquidheatsthethermometer.Sensorsneedtobedesignedtohaveasmalleffectonwhatismeasured;makingthesensorsmalleroftenimprovesthisandmayintroduceotheradvantages.

TechnologicalprogressallowsmoreandmoresensorstobemanufacturedonamicroscopicscaleasmicrosensorsusingMEMStechnology.Inmostcases,amicrosensorreachesasignificantlyhigherspeedandsensitivitycomparedwithmacroscopicapproaches.

Agoodsensorissensitivetothemeasuredpropertyonly,isinsensitivetoanyotherpropertylikelytobeencounteredinitsapplication,anddoesnotinfluencethemeasuredproperty.

Idealsensorsaredesignedtobelinearorlineartosomesimplemathematicalfunctionofthemeasurement,typicallylogarithmic.Theoutputsignalofsuchasensorislinearlyproportionaltothevalueorsimplefunctionofthemeasuredproperty.Thesensitivityisthendefinedastheratiobetweenoutputsignalandmeasuredproperty.Forexample,ifasensormeasurestemperatureandhasavoltageoutput,thesensitivityisaconstantwiththeunit[V/K];thissensorislinearbecausetheratioisconstantatallpointsofmeasurement.

Ifthesensorisnotideal,severaltypesofdeviationscanbeobserved:

Thesensitivitymayinpracticedifferfromthevaluespecified.Thisiscalledasensitivityerror,butthesensorisstilllinear.

Sincetherangeoftheoutputsignalisalwayslimited,theoutputsignalwilleventuallyreachaminimumormaximumwhenthemeasuredpropertyexceedsthelimits.Thefullscalerangedefinesthemaximumandminimumvaluesofthemeasuredproperty.

Iftheoutputsignalisnotzerowhenthemeasuredpropertyiszero,thesensorhasanoffsetorbias.Thisisdefinedastheoutputofthesensoratzeroinput.

Ifthesensitivityisnotconstantovertherangeofthesensor,thisiscallednonlinearity.Usuallythisisdefinedbytheamounttheoutputdifferencefromidealbehavioroverthefullrangeofthesensor,oftennotedasapercentageofthefullrange.

Ifthedeviationiscausedbyarapidchangeofthemeasuredpropertyovertime,thereisadynamicerror.Often,thisbehaviorisdescribedwithabodeplotshowingsensitivityerrorandphaseshiftasfunctionofthefrequencyofaperiodicinputsignal.

Iftheoutputsignalslowlychangesindependentofthemeasuredproperty,thisisdefinedasdrift.Longtermdriftusuallyindicatesaslowdegradationofsensorpropertiesoveralongperiodoftime.

Noiseisarandomdeviationofthesignalthatvariesintime.

Hysteresisisanerrorcausedbywhenthemeasuredpropertyreversesdirection,butthereissomefinitelagintimeforthesensortorespond,creatingadifferentoffseterrorinonedirectionthanintheother.

Ifthesensorhasadigitaloutput,theoutputisessentiallyanapproximationofthemeasuredproperty.Theapproximationerrorisalsocalleddigitizationerror.

Ifthesignalismonitoreddigitally,limitationofthesamplingfrequencyalsocancauseadynamicer