3电气工程及其自动化专业外文文献英文文献外文翻译plc方面.docx

3电气工程及其自动化专业外文文献英文文献外文翻译plc方面.docx

《3电气工程及其自动化专业外文文献英文文献外文翻译plc方面.docx》由会员分享，可在线阅读，更多相关《3电气工程及其自动化专业外文文献英文文献外文翻译plc方面.docx（13页珍藏版）》请在冰豆网上搜索。

3电气工程及其自动化专业外文文献英文文献外文翻译plc方面

1、外文原文

A:

FundamentalsofSingle-chipMicrocomputer

Thesingle-chipmicrocomputeristheculminationofboththedevelopmentofthedigitalcomputerandtheintegratedcircuitarguablythetowmostsignificantinventionsofthe20thcentury[1].

Thesetowtypesofarchitecturearefoundinsingle-chipmicrocomputer.Someemploythesplitprogram/datamemoryoftheHarvardarchitecture,showninFig.3-5A-1,othersfollowthephilosophy,widelyadaptedforgeneral-purposecomputersandmicroprocessors,ofmakingnologicaldistinctionbetweenprogramanddatamemoryasinthePrincetonarchitecture,showninFig.3-5A-2.

Ingeneraltermsasingle-chipmicrocomputerischaracterizedbytheincorporationofalltheunitsofacomputerintoasingledevice,asshowninFig3-5A-3.

Fig.3-5A-1AHarvardtype

Fig.3-5A-2.AconventionalPrincetoncomputer

Reset

Interrupts

Power

Fig3-5A-3.Principalfeaturesofamicrocomputer

Readonlymemory（ROM）.ROMisusuallyforthepermanent,non-volatilestorageofanapplicationsprogram.Manymicrocomputersandmareintendedforhigh-volumeapplicationsandhencetheeconomicalmanufactureofthedevicesrequiresthatthecontentsoftheprogrammemorybecommittedpermanentlyduringthemanufactureofchips.Clearly,thisimpliesarigorousapproachtoROMcodedevelopmentsincechangescannotbemadeaftermanufacture.Thisdevelopmentprocessmayinvolveemulationusingasophisticateddevelopmentsystemwithahardwareemulationcapabilityaswellastheuseofpowerfulsoftwaretools.

SomemanufacturersprovideadditionalROMoptionsbyincludingintheirrangedeviceswith（orintendedforusewith）userprogrammablememory.Thesimplestoftheseisusuallydevicewhichcanoperateinamicroprocessormodebyusingsomeoftheinput/outputlinesasanaddressanddatabusforaccessingexternalmemory.ThistypeofdevicecanbehavefunctionallyasthesinglechipmicrocomputerfromwhichitisderivedalbeitwithrestrictedI/Oandamodifiedexternalcircuit.Theuseofthesedevicesiscommoneveninproductioncircuitswherethevolumedoesnotjustifythedevelopmentcostsofcustomon-chipROM[2];therecanstillbeasignificantsavinginI/Oandotherchipscomparedtoaconventionalmicroprocessorbasedcircuit.MoreexactreplacementforROMdevicescanbeobtainedintheformofvariantswith'piggy-back'EPROM（ErasableprogrammableROM）socketsordeviceswithEPROMinsteadofROM。

ThesedevicesarenaturallymoreexpensivethanequivalentROMdevice,butdoprovidecompletecircuitequivalents.EPROMbaseddevicesarealsoextremelyattractiveforlow-volumeapplicationswheretheyprovidetheadvantagesofasingle-chipdevice,intermsofon-chipI/O,etc.,withtheconvenienceofflexibleuserprogrammability.

Randomaccessmemory（RAM）.RAMisforthestorageofworkingvariablesanddatausedduringprogramexecution.Thesizeofthismemoryvarieswithdevicetypebutithasthesamecharacteristicwidth（4,8,16bitsetc.）astheprocessor,Specialfunctionregisters,suchasstackpointerortimerregisterareoftenlogicallyincorporatedintotheRAMarea.ItisalsocommoninHarardtypemicrocomputerstotreattheRAMareaasacollectionofregister;itisunnecessarytomakedistinctionbetweenRAMandprocessorregisterasisdoneinthecaseofamicroprocessorsystemsinceRAMandregistersarenotusuallyphysicallyseparatedinamicrocomputer.

Centralprocessingunit（CPU）.TheCPUismuchlikethatofanymicroprocessor.Manyapplicationsofmicrocomputersandmicrocontrollersinvolvethehandlingofbinary-codeddecimal（BCD）data（fornumericaldisplays,forexample）,henceitiscommontofindthattheCPUiswelladaptedtohandlingthistypeofdata.Itisalsocommontofindgoodfacilitiesfortesting,settingandresettingindividualbitsofmemoryorI/Osincemanycontrollerapplicationsinvolvetheturningonandoffofsingleoutputlinesorthereadingthesingleline.Theselinesarereadilyinterfacedtotwo-statedevicessuchasswitches,thermostats,solid-staterelays,valves,motor,etc.

Parallelinput/output.Parallelinputandoutputschemesvarysomewhatindifferentmicrocomputer;inmostamechanismisprovidedtoatleastallowsomeflexibilityofchoosingwhichpinsareoutputsandwhichareinputs.Thismayapplytoallorsomeoftheports.SomeI/Olinesaresuitablefordirectinterfacingto,forexample,fluorescentdisplays,orcanprovidesufficientcurrenttomakeinterfacingothercomponentsstraightforward.SomedevicesallowanI/Oporttobeconfiguredasasystembustoallowoff-chipmemoryandI/Oexpansion.Thisfacilityispotentiallyusefulasaproductrangedevelops,sincesuccessiveenhancementsmaybecometoobigforon-chipmemoryanditisundesirablenottobuildontheexistingsoftwarebase.

Serialinput/output.Serialcommunicationwithterminaldevicesiscommonmeansofprovidingalinkusingasmallnumberoflines.Thissortofcommunicationcanalsobeexploitedforinterfacingspecialfunctionchipsorlinkingseveralmicrocomputerstogether.Boththecommonasynchronoussynchronouscommunicationschemesrequireprotocolsthatprovideframing（startandstop）information.ThiscanbeimplementedasahardwarefacilityorU（S）ART（Universal（synchronous）asynchronousreceiver/transmitter）relievingtheprocessor（andtheapplicationsprogrammer）ofthislow-level,time-consuming,detail.tismerelynecessarytoselectedabaud-rateandpossiblyotheroptions（numberofstopbits,parity,etc.）andload（orreadfrom）theserialtransmitter（orreceiver）buffer.Serializationofthedataintheappropriateformatisthenhandledbythehardwarecircuit.

Timing/counterfacilities.Manyapplicationofsingle-chipmicrocomputersrequireaccurateevaluationofelapsedrealtime.Thiscanbedeterminedbycarefulassessmentoftheexecutiontimeofeachbranchinaprogrambutthisrapidlybecomesinefficientforallbutsimplestprograms.Thepreferredapproachistousetimercircuitthatcanindependentlycountprecisetimeincrementsandgenerateaninterruptafterapresettimehaselapsed.Thistypeoftimerisusuallyarrangedtobereloadablewiththerequiredcount.Thetimerthendecrementsthisvalueproducinganinterruptorsettingaflagwhenthecounterreacheszero.Bettertimersthenhavetheabilitytoautomaticallyreloadtheinitialcountvalue.Thisrelievestheprogrammeroftheresponsibilityofreloadingthecounterandassessingelapsedtimebeforethetimerrestarted,whichotherwisewoundbenecessaryifcontinuouspreciselytimedinterruptswererequired（asinaclock,forexample）.Sometimesassociatedwithtimerisaneventcounter.Withthisfacilitythereisusuallyaspecialinputpin,thatcandrivethecounterdirectly.

Timingcomponents.Theclockcircuitryofmostmicrocomputersrequiresonlysimpletimingcomponents.Ifmaximumperformanceisrequired,acrystalmustbeusedtoensurethemaximumclockfrequencyisapproachedbutnotexceeded.Manyclockcircuitsalsoworkwitharesistorandcapacitoraslow-costtimingcomponentsorcanbedrivenfromanexternalsource.Thislatterarrangementisusefulisexternalsynchronizationofthemicrocomputerisrequired.

WORDSANDTERMS

culminationn.顶点

spiltadj.分离的

volatilen.易变的

commitv.保证

albeitconj.虽然

customadj.定制的

variantadj.不同的

piggy-backadj.背负式的

socketn.插座

B:

PLC[1]

PLCs（programmablelogicalcontroller）faceevermorecomplexchallengesthesedays.Whereoncetheyquietlyreplacedrelaysandgaveanoccasionalreporttoacorporatemainframe,theyarenowgroupedintocells,givennewjobandnewlanguages,andareforcedtocompeteagainstagrowingarrayofcontrolproducts.Forthisyear'sannualPLCtechnologyupdate,wequeriedPLCmakersonthesetopicsandmore.

Programminglanguages

HigherlevelPLCprogramminglanguageshavebeenaroundforsometime,butlatelytheirpopularityhasmushrooming."AsRaymondLeveille,vicepresident&generalmanager,SiemensEnergy&Automation.inc;Programmablecontrolsarebeingusedformoreandmoresophisticatedoperations,languagesotherthanladderlogicbecomemorepractical,efficient,andpowerful.Forexample,it'sverydifficulttowriteatrigonometricfunctionusingladderlogic."LanguagesgainingacceptanceincludeBoolean,controlsystemflowcharting,andsuchfunctionchartlanguagesasGraphcetanditsvariation.Andthere'sincreasinginterestinlanguageslikeCandBASIC.

PLCsinprocesscontrol

Thusfar,PLCshavenotbeenusedextensivelyforcontinuousprocesscontrol.Willthiscontinue?

"ThefeelingthatI'vegotten,"saysKenJannotta,manger,productplanning,seriesOneandSeriesSixproduct,atGEFanucNorthAmerica,'isthatPLCswillbeusedintheprocessindustrybutnotnecessarilyforprocesscontrol."

Severalvendors-obviouslybettingthattheoppositewillhappen-haveintroducedPLCsoptimizedforprocessapplication.RichRyan,manger,commercialmarketing,Allen-bradleyProgrammableControlsDiv.,citesPLCs'sincreasingusesuchindustriesasfood,chemicals,andpetroleum.Ryanfeelstherearetwotypesofapplicationsinwhichthey'reappropriate."one,"hesays,"iswherethesizeoftheprocesscontrolsystemthat'sbeingautomateddoesn'tjustifyDCS[distributedcontrolsystem].Withthestartingpricetagsofchoseproductsbeingrelativelyhigh,aprogrammablecontrollermakessenseforsmall,lowloopcountapplication.Thesecondiswhereyouhavetointegratetheloopcloselywiththesequentiallogical.Batchcontrollersareprimeexample,wherethesequenceandmaintainingtheprocessvariableareintertwinedsocloselythatthebenefitsofhavingaprogrammablecontroll