自动化专业外文文献英文文献外文翻译plc方面.docx
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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(复印件)
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
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,wherethesequenceandmaintainingtheprocessvariableareintertwinedsocloselythatthebenefitsofhavingaprogrammablecontrollertodothesequentiallogicaloutweighssomeofthedisadvantagesofnothavingadistributedcontrolsystem.”
BillBarkovitz,presidentofTriconex,predictsthat"allfuturecontrollersthatcomeoutintheprocesscontrolsystembusinesswillembracealotofmorePLCtechnologyandalotmorePLCfunctionalitythantheyeverdidbefore。
"
CommunicationsandMAP
Communicationsarevitaltoanindividualautomationcellandtobeautomatedfactoryasawhole.We’veheardalotaboutMAPinthelastfewyears,andalotofcompanieshavejumpedonthebandwagon。
[2]Many,however,weredisappointedwhenafully-definedandcompletedMAPspecificationdidn’tappearimmediately.SaysLarryKomarek:
”Rightnow,MAPisstillamovingtargetforthemanufacturers,aspecificationthatisnotfinal.Presently,forexample。
peopleareintroducingproductstomeettheMAP2。
1standard。
Yet2.1—basedproductswillbeobsoletewhenthenewstandardforMAP3.0isintroduced.”
Becauseofthis,manyPLCvendorsareholdingoffonfullMAPimplementations。
Omron,forexample,hasanongoingMAP-compatibilityprogram;[3]butFrankNewburn,vicepresidentofOmron'sIndustrialDivision,reportsthatbecauseofthelackofafirmdefinition,Omron’sPLCsdon’tyettalktoMAP.
Sinceit’sunlikelythatanindividualPLCwouldtalktobroadMAPanyway,makersareconcentratingonproprietarynetworks。
AccordingtoSalProvanzano,usersfearthatiftheydogetonboardandvendorswithdrawfromMAP,they'llbetheonesleftholdingacommunicationsstructurethat’snotsupported.
UniversalI/O
WhilethereareconcernsaboutthelackofcompatiblecommunicationsbetweenPLCsfromdifferentvendors,theconnectionattheotherend—theI/O—isevenmorefragmented。
Withrareexceptions,I/Oisstillproprietary。
YettherearethosewhofeelthatI/Owilleventuallybecomemoreuniversal.GEFanucishopin