電氣專業(yè)英語翻譯

FoundationofPLC1.1THECENTRALPROCESSINGUNITAlthoughreferredtoasthebrainofthesystem,theCentralProcessingUnitinanormalinstallationistheunsunghero,buriedinacontrolcabinet,allbutforgotten.Inaprogrammablecontrollersystem,thecentralprocessingunit(CPU)providesboththeheartandthebrainrequiredforsuccessfulandtimelycontrolexecution.Itrapidlyandefficientlyscansallofthesysteminputs,examinesandsolvestheapplicationlogic,andupdatesallofthesystemoutputs.Inaddition,italsogivesitselfacheckupeachscantoensurethatitsstructureisstillintact.Inthischapterwewillexaminethecentralprocessingunitasitrelatestotheentiresystem.IncludedwillbethevariousfunctionalblocksintheCPU,typicalscantechniques,I/Ointerfaceandmemoryusers,powersupplies,andsystemdiagnostics.executedinparallel.Theresultofthisapproachistoachieveexecutionspeedsthatareordersofmagnitudefasterthantheirsingle-taskingcounterparts.InadditiontoefficientlyprocessingdirectI/Ocontrolinformationandbeingprogrammable,therealadvantagethatmicroprocessor-basedsystemhaveovertheirhardwiredrelaycounterpartsistheabilitytoacquireandmanipulatenumericaldataeasily.Itisthisattributethatmakesprogrammablecontrollersthepowerhousesthattheyaretodayinsolvingtoughfactoryautomationproblems.Thefactoryoftomorrowwillrunefficientlyonlyifqualityinformationaboutprocessneedsandstatusoftheprocessequipmentareknownonarealtimesbasis.Thiscanandwillcomeaboutonlyiftheunitlevelcontrollers,includingprogrammablecontrollers,areempoweredwiththeabilitytocollect,analyze,concentrate,anddeliverdataabouttheprocess.Asthemarketcontinuestoexhibitthisdemand,manufacturesarelikelytooutfittheircontrollerswithmoreandmorevariablememory,andenhancedinstructionsetstoperformthesetasks.Thepowersupplyshownhereisusedforprovidingsufficientelectricalcurrentforthevarioussemiconductorsandotherpower-consumingdevicesononeormoreoftheCPUcircuitboards.Itcanbearrangedinanumberofdifferentphysicalways.ItmaybelocatedinthesamechassisinwhichtheCPUboardsarelocated,orcanbemountedinastand-alonefashion,connectedexternallytotheCPUchassis.Dependingontheparticularmanufacturer?sconfiguration,itmayalsoprovidepowerforsomeoftheI/Ofunction,aswell2astheCPU.Bydefinitionanddesign,theprogrammablecontrollerisdedicatedtothecontinuous,repetitivetaskofexaminingthesysteminputs,solvingthecontinuous,repetitivetaskofexaminingthesysteminputs,solvingthecurrentcontrollogic，andupdatingthesystemoutputs.Thistaskisreferredtoasscanning(sometimescalledsweeping),andisaccomplishedinslightlydifferentwaysineachmanufacturer?sprogrammablecontroller.Sincemanyofthevariationsarenotmaterialtothebasicfunctionalityofthesystem,wewillonlyexaminethebasicestheexecutiveroutine,inwhichtheactualbaseintelligenceofthesystemisusedtointerpretthecurrentcontrolprogram.Thisinterpretationisthenusedinthenextsteptosolvethecurrentcontrollogicprogram.ThelaststepofthisbasicscanprocessistointegratethecurrentlyinterpretedcontrollogicprogramwiththemostcurrentinputstatusesfromtheI/Oscan,andtoupdatetheoutputstatuseswiththecurrentresults.TheprimaryvariationofthisbasicscanningtechniquecomesfromarchitecturesthatserviceandupdateI/Owithaseparateprocessor,asynchronoustothemainlogicsolutionscan.ThisalternativeiscommoninsystemswhereserialcommunicationisusedtocontrolandupdateracksofremotelymountedI/O.ItisalsousedwherealloftheI/Oisserial,andruninmultipleasynchronousscanningtechniquehastheadvantagethatitallowsextensiveflexibilityinconfiguringaprogrammablecontrollersystemforaparticularapplicationneed.Ithasthedisadvantagethatwhilethebasisscanratemaybefastenoughtosuitanapplication,theI/Oscan(s)actuallybelongerthantheprimaryCPUscan.Thiscancauseproblemsinafastactingsysteminthatthelogicsolutioncanoccurwithrelatively“old”inputdatafromtheremoteI/Ochannel.Whilethisisattimesbothersome,themoredramaticcaseinvolvesapeculiarityofsomeprogrammablecontrollersinthattheymayallowinputandoutputdatatobeupdatedonseparatetimebases,providingthepossibilityof“bad”logicsolutionsandunpredictablemachineactions.AspartofthebasicCPUstructure,anumberoferrorcheckingproceduresareusedtomaintainahighlevelofintegrityinthecommunicationsbetweenitselfanditssubsystems.Thiscaninvolveboththeinternalsubsystems,suchasthememory,andso-calledexternalsubsystems,forexampletheI/Osystem.Themorecommonerror-checkingschemesareoutlinedbelow.Thefirstandmostisparity.Thisisusedonmanycommunicationlinksubsystemstodetect4errorsbyexaminingthenumberof“ones”ineachbyteofinformationreceived,andcomparingthetotalnumberinanyonebytetoapredeterminedchoiceofevenoroddparity.Thiscorrespondstothetotalofonesinthebytesummingtoanevenoroddnumber.Thishastheadvantageofbeingabletodetectasingle-biterror,thatiswhereazerooronehaschangedstateduringsomeoperation;butcannotdetecttwosinglebutopposingbitchangesinabyteofmemorythatcanceleachotheroutandmethodforerrorchecking,involvestheexaminationofablockofmemoryforerrorsascomparedtoanindividualwordasdoneinparitychecking.Theprocedureinvolvestheaddingofasinglewordofmemorytoablockthatisuniquetothatblock.CommonvarietiesofthechecksumaretheCyclicRedundancyCheck(CRC)andtheparitycheckisthatitmoreefficientlyusesmemory.ThethirderrorcheckingmethodthatwewillconsiderisErrorDetectionandCorrection(EDC).Itisusedinthemoresophisticatedprogrammablecontrollersprovidedbyafewmanufacturerstoday.Inessenceitinvolvesanumberofcomplexerrorcorrectingcodesimplementedinthehardware.TheErrorDetectingandCorrectingmethodhastheaddedadvantagethatitcansenseandcorrectsingle-biterror,whileonlysensingdoublebiterrors.Today?smodernprogrammablecontrollerincludesasophisticatedmethodtocontroltheCPU?sexecutionoftheInput/Outputchain.ThisisreferredtoasI/Ocontrol,orsometimesBuscontrol.Thisisactuallyhandledindifferentways,dependingonthetypeandstyleofcontrollerinvolved.Inthesmallprogrammablecontroller,theI/Oservicingisperformedasanintegralpartoftheprimarymicroprocessorusedtocontrolallofthemajorfunctions.Inmediumandlarge-sizedsystems,itiscommontoincludeamicroprocessor5boardorsubsystemtohandletheexecutionoftheI/Oupdating.ThisisespeciallyimportantinthesystemsthatupdateI/Oseparately,orsynchronouslyfromthemainscan.Regardlessofthewayitisachieved,theI/Ocontrol,orupdating,isperformedforthesamereasons.Forasuccessfulscansequence,anaccurateexecutionofthesignallevelcommunicationtothephysicalInputandOutputmodulesisrequired.Itisthen,andonlythen,thatanychangesintheI/Ostatuscanbephysicallyupdatedtoactuatorsorfromthesensors.Therearetwobasicmemorycategoriesusedbyprogrammablecontrollers,orforthatmatter,anymicroprocessor-basesystem.Theyarevolatileandnonvolatile.Volatilemeansthatthecontentsofthememoryhavenomeanstoremainintactwithoutanexternalpowersourceconnectedtomaintainthedataintegrity.Nonvolatilemeansofthememoryremainintactwithoutanexternalpowersupply.Thesegmentsofmemoryinaprogrammablecontrollersystemarestraightforward.ApplicationMemory.Alsocalledlogicmemory,itisthesectionof6memoryusedtostoretheactualcontrolprogramthatthecontrollerusestocontrolthemanufacturingprocess.Thiscontrolprogramisusuallycreatedbythesystemuser.DataTableMemory.Thistermcollectivelyreferstothevariable(register)memory,andtheinput/outputstatusorimagetables.Thevariablememorycontainstimerandcountervalues,alongwithanydatausedinmathematicalcalculationsperformedbytheapplicationprogram.TheI/Oimagetablescontain,asthenamesuggests,arepresentationoftheactualinput/outputpointstatus,eitheronoroff.Executive.Alsocalledfirmware(orjustfirmware),thissectionofmemorycontainsthebaseintelligenceofthesystem.Theexecutiveprogramsupervisesthebasischoresoftheprogrammablecontrollersystemincludingcommunicationswithsubsystems,controlprograminterpretationandexecution,CPUdiagnostics,andotherhousekeepingtasksincludedineveryscan.ScratchPad.Thisisatemporarymemoryareausedbythesystemtostorethestep-by-stepandinterimresultsobtainedthroughsomecalculations.Insomesystems,thescratchpadmemorycontainstheprogrammablecontrollerstatistics,suchasmemorysize,amountused,andanyactivediagnosticflagsset.Varioussegmentsoftheprogrammablecontrollerusedifferentmemorytypestoaccomplishdifferentdesignorapplicationpurposes.Below.weshallexamineasampleofmemorytypes,andcontrasttheiruseinprogrammablecontrollers.ReadOnlyMemory(ROM).Thismemorywasoneofthefirstcommerciallyvariablenonvolatilememorytypesusedinmicroprocessor-basedsystem.ROMgetitsnamefromthefactthatthememorycanbereadfrom(informationextracted),butcannotbewritteninto(informationplacedin).AnumberofmanufacturersofprogrammablecontrollersuseROMmemoryto7storetheexecutiveprograms.Thisisbecauseitnormallytostoretheexecutiveprograms.Thisisbecauseitnormallyrequiresnoadjustmentoreditingoncethesystemisshippedfromthemanufacturer.ROMisrarely,ifever,usedasapplicationmemory,andcannotbeusedasdatatableorscratchpadmemorybecauseitcannotbeupdatedwithdatafromtheoperationoftheprogrammablecontrollerexecution.RandomAccessMemory(RAM).Thisisavolatilememory,buthastheadvantageoverROMofbeingcapableofbeingwrittentoaswellasreadfrom.Itisforthisreasonthatitissometimescalledread/writememory.Anylocationwithinthememorycanbeaccessible.Becauseitisvolatile,thememorycontentswillbelostifpowerislost.Withaproperlydesignedbatterybackupsystem,RAMcanretainitscurrentcontentsduringlargecontrollersarenormallyexpandablefromonememorysizetotheirmaximumsize.Smallcontrollersarenormallyarenormallyfixedintheirmemorysize.Sizeofthememorycapacitymustbeexaminedrelativetothewordsize(8bitor16bit)andutilization.Whileitisclearthattwicetheinformationcanbestoredina16bitwordthaninan8bitbyte,itmaynotbeimmediatelyclearthatsomecontrollersutilizememorymoreefficientlythanothers.Forexample,anormallyopencontactanditsassociatedreferenceaddress(e.g.Input1),mayusein8biteachforstorage.Combined,theyconsumeone16bitword.Somecontrollersmayusemorememorythanthisfortheseinstructionsorothers.Inalargeprogram,theseinefficienciescanbuildoneachothertocauseapoorutilizationofthesystemmemory.Acarefulanalysisofthevariousprogrammablecontrollermodelsisrequiredto20%~40%ofmemorysizetobespecifiedtoallowformodificationsandlaterexpansion.Thisanalysis,combinedwithknowledgeoftheapplicationneeds,willallowforanintelligentchoiceofprogrammablecontroller.Thememoryofaprogrammablecontrollerisorganizedinwhatiscalledamemorymap.Thissegments,throughaprocessknownaspartitioning,thememoryintofunctionalunits.Allmanufacturesuseaslightlydifferenttechniqueindesigningtheircontroller?smemorymap.Somehavevariablepartitionswhileothersarefixed.All,however,aredesignedtosegmentthefollowingfunctionalareas:Executiveprogram(s)ScratchpadInput/outputimagetablesDatatablesApplicationprogramWewillnowelaborate,inoverviewfashiononeachofthememorymapsegments.Asnotedearlier,somecontrollersoffertheusertheflexibility(sometimesconsideredaconstraint)ofbeingabletovarythepartitionswithinthememorymap.This,inessence,allowstheuserorsystembuildertocustomizethesizesoftheapplication,datatable,andothermemorysegmentstosuittheparticularapplication.Othercontrollersofferapreconfiguredsystem,makingassumptionsaboutappropriatesizesforthevariousmemorysegmentsandtheirassociatedpartitions.Thiseliminatestheneedfortheusertodealwiththissometimesconfusingoperation.Asthearchitectureofprogrammablecontrollerscontinuestoevolve,itislikelythatthevariablepartitionmethodwillgainfavorablemomentum.Thisislikelybecauseitaccommodatesawidervarietyofoperatingsystemsandapplicationprogramssinceitcanbetailoredmoreeffectively.Thismoreflexiblefuturemaymanufactureswithspecialapplicationsoftwaretoaccomplishanindustryspecificsolution.Executive.Thisisthebasicintelligenceoftheprogrammablecontroller.Itallowsanyapplicationprograminstructionstobeinterpretedandactedupon.It9istransparenttotheuserandisalmostneverconsideredtobeincludedinthemanufacturersratedmemorysizes.ScratchPad.Alsotransparenttotheuser,thismemoryallowsinterimcomputationsandsomesystemconfigurationparameterstobeestablished.Input/outputImageTables.Thisisoneofthemostbasicandstraightforwardsegmentsinthememorymap.ThissectionofmemorycontainsastoredrepresentationofboththeinternalandexternalI/O?points.?Aninternalpointisaninputoroutputthatisusedonlyinaninternalcontrollogicprocess,andisnotdirectlyassociatedwiththephysicalI/Omodules.AnexternalpointisonethatisdirectlyassociatedormappedtoaphysicalI/Omodule,whichinturnisphysicallyconnectedtoasensororactuator.ThesetablesoftheI/Oareaccessibleandviewedbytheprogrammingdeviceandsomeotherprogrammablecontrollerperipherals.Theycanthenbeobservedormanipulateddirectlyforprogramcreation,editing,orlatertroubleshootingafterthesystemhasbeeninstalled.ThismemorysegmentisnormallypartitionedtosomedefaultvaluecorrespondingtothemaximumI/Ocapacityoftheprogrammablecontroller.TheviewseenontheprogrammingdevicescreenisthemostcurrentinformationonthestatusoftheI/O,asitchangestheapplicationprograminstructionsandrealworldenvironment.DataTables.Sometimescalledtheregistertables,thissegmentofsystemmemorycontainsthevariablereferencesusedintheexecutionoftheapplicationprogram.Formattedin16bitwords(8bitinoldersystems),thiswordincludestorageoftimerandcounteraccumulatedvalues,insomecasestimerandcounterpresetvalues,variablestoragereferencesformathematicalfunctions,storageofanalogvaluesconvertedtodigital,storageofBCDorASCⅡinformation,andsoon.Thissegment,incontrollersthatallowit,issizedbytheusertotrade-offapplicationprogramsize.ApplicationProgram.Thissegmentcontainstheactualladderlogiccontrolprogram.Henceitissometimescalledthelogicmemorysection.Againvariableinsizeforsomesystems,itiscreated,edited,andlaterviewedduringoperationwiththehelpoftheprogrammingdeviceusingcontacts,coils,andotherreferences,andthenisconvertedtomachinelevelcodeforusebythecentralprocessingunit.Therearemanytechniquesanddevicestoaccomplishthistask.可編程序控制器(PLC)的基礎1.1中央處理單元雖然被稱為大腦的系統(tǒng)、中央處理單元在一個正常的安裝是無名英雄，被埋在一個控制柜,幾乎被忘記了。在實踐中，中央處理單元可以跟隨結構變化，但是由基本組成部分結構在圖1.1中說明。處理部門由一個或多個微處理器與它們相關的電路。雖然這是事實,有些奢侈的使用微處理器，大多數(shù)現(xiàn)代系統(tǒng)使用一個單獨的微處理器，如AMD2903，是個簡單的模塊。這多個微處理器系統(tǒng)打破了11控制系統(tǒng)的工作分成許多小的組分，可并行執(zhí)行。這樣比單通道執(zhí)行要快很多。除了直接有效地處理I/O控制信息和可編程的，真正的優(yōu)點是基于微處理器的系統(tǒng)對信息的獲取和處理實驗數(shù)據(jù)有著得天獨厚的能力。他們解決的復雜的工廠自動化為題的能力使得可編程控制器更受歡迎。眾所周知，質量信息工程和工藝過程符合發(fā)展要求是工廠有效發(fā)展的動力。只有單位等級控制器，包括可編程控制器、被授權的能力,以收集、分析、集中注意力、并交付有關數(shù)據(jù)的過程，這也才會出現(xiàn)。隨著市場繼續(xù)展示這種需求，制造商正在可能裝載越來越多變量控制和存儲能力，以及增強指令集來完成這些任務。圖1.1內存段中顯示的是指可編程序控制器的活躍存儲介質。這可以是不穩(wěn)定或易失性的設計，并且可配置，它被用于各種途徑對于系統(tǒng)執(zhí)行指令的存儲和實際控制的應用要求程序庫。此處所示為電力供應的用于提供足夠的電流的各種半導體設備和其他power-consuming在一個或多個CPU的電路板。它可安排在多個不同的物理變化。這可能是位于相同底盤的CPU板所在位置,或者可以安裝在一個獨立的時尚,外部連接在一起到中央處理器底盤。根據(jù)特定的制造商的配置,它也可能提供電力的一些I/O中的作用,以及中央處理器。根據(jù)定義和設計，可編程控制器是專門為連續(xù)的、重復任務的檢測系統(tǒng)的輸入，解決持續(xù)的、重復任務的檢測系統(tǒng)，解決當前輸入控制邏輯，并即時更新系統(tǒng)輸出。這個任務是被稱為掃描（有時叫做掃），各廠家的可編程控制完成的方法不同。因為許多變化并非是物質的基本功能的系統(tǒng)，我們將只檢查基本功能系統(tǒng)。圖1.2顯示了一個典型的掃描、運行機制。你會注意到I/O維修是在掃描周期的結束，也是該掃描時間不可分割的一部分。這種類型的掃描是被稱作同步掃描和是用非?？斓臋C器，可以在沒有延長掃描時間的準備的12情況下更新所有的I/O。一個典型的掃描時間，在一個現(xiàn)代可編程控制器的范圍很廣，從10~100個毫秒。大多數(shù)控制器有一種機制，看門狗定時器，測量掃描的每一個周期，一般長度150~250毫秒。按照圖1.1，同步掃描包含激活I/O掃描的其他四項。家務是指少數(shù)雜活兒由可編程控制器，以確保其內部結構仍然健康并工作正常。接下來的交流窗口允許結構化的通訊系統(tǒng)，其他的裝置或在外部。包括在本集團的編程設備、特種以微處理器為基礎的允許終極溝通的可編程控制器系統(tǒng)通信模塊的另一種智能設備。下一批來執(zhí)行例行程序，在實際智力底線的系統(tǒng)是用于解釋電流控制程序。這個解釋，然后用在接下來的步驟來解決當前的控制邏輯程序。這些基本的最后一步是整合掃描程序控制邏輯程序當前解釋和最新的輸入狀態(tài)從I/O掃描,并更新輸出狀態(tài)與當前的結果。這個基本的主要變化的掃描技術的體系結構，這種結構的服務來自和更新I/O模塊的一個獨立的處理器所作出的異步的主要邏輯解掃描。這種靈活的地方是常見的串行通信系統(tǒng)是用來控制和更新系統(tǒng)的遠程安裝的I/O。它也被用于I/O串列的情況，以及運行在多個異步掃描技術中，其優(yōu)點是它允許廣泛的彈性系統(tǒng)配置一個可編程控制器為特定的應用需要。它有其弊端，在不同的應用領域掃描速度不是很快，實際上I/O掃描比主CPU掃描需要更長的時間。這在快速反應系統(tǒng)中可能會導致問題，即I/O傳送數(shù)據(jù)滯后。當出現(xiàn)問題時，可編程控制器會出現(xiàn)一些富有戲劇性的特點，在差的解決方案和不可預知的機器運行情況，可編程控制器的輸入輸出數(shù)據(jù)將分通道傳輸。作為部分的基本結構，大量的CPU進行錯誤檢查程序是用來保持高水準的正直的本身及其子系統(tǒng)之間的通信。這可能包括石墨的內部子系統(tǒng)，例如記憶，以及所謂的外部的子系統(tǒng)，例如I/O系統(tǒng)。更常見的查錯的方案略述如下。第一步，奇偶校驗位。這是用在許多通信鏈路子系統(tǒng)檢測錯誤通過檢查數(shù)目的“歸屬”在每個字節(jié)的信息得到認可，并且比較了在任何一個字節(jié)總數(shù)甚至到預定的選擇與奇奇偶校驗位。這相當于總字節(jié)總13結的一個奇偶校驗。這樣做的好處是可以探測到一個值的錯誤，那就是在一串數(shù)據(jù)中改變的某個狀態(tài)，但在一串數(shù)據(jù)中無法探測到兩處單獨的可能互相抵消的錯誤，找不到正確的方法進行錯誤檢查，在塊存儲器中所涉及的錯誤檢查，再對一個個位進行偶校驗。這個程序包括添加一個字的記憶體區(qū)獨一無二的存儲區(qū)。常見品種校驗、循環(huán)冗余校驗(CRC)和一致校驗是使它更有效地使用內存。第三個錯誤檢查方法，我們將考慮的是錯誤檢測和校正(EDC)。它被廣泛應用在更為復雜的可編程控制器由少數(shù)制造商提供的今天。本質上,這涉及到許多復雜的錯誤更正碼在硬件實現(xiàn)。誤差檢測與校正方法具有優(yōu)勢，可以感受到和正確的single-bit誤差，而只有傳感雙位誤差。今天的現(xiàn)代可編程控制器使用一個復雜的方法來控制CPU的執(zhí)行的輸入/輸出鏈。這是被稱為I/O控制，或總線控制。這實際上是不同處理方式，這與類型和款式的控制器有關。在小可編程序控制器中，I/O服務是不可分割的一部分，中央微處理器用來控制所有的主要功能。在大中型系統(tǒng)，它是常見的，包括一個微處理器板或子系統(tǒng)處理執(zhí)行的I/O更新。無論是在I/O分列更新，還在主要掃描的同步中，這都是十分重要的。雖然實現(xiàn)的方式不同，但I/O控制和進行更新的目的是相同的。作為一個成功的掃描序列，準確執(zhí)行信號電平輸入和輸出信息模塊是必需的。它是這樣,也只有這樣,有I/O狀態(tài)任何變更，都可以更新到執(zhí)行機構或其傳感器。圖1.1演示了可編程序控制器的記憶與CPU的其他功能塊。可編程控制器的記憶功能是現(xiàn)代微處理器和先前的微處理器的區(qū)別。記憶中的先進14的功能有利于編輯迅速建立并有效控制用來運行的生產工藝的程序。不同類型的記憶存儲功能被廣泛應用于不同的應用或設計領域的可編程控制器。讓我們詳細分析一下其中的區(qū)別。有兩種基本的存儲范疇所使用的可編程控制器，或者是任何以微處理器為基礎的系統(tǒng)。他們有易失性和非易失性。易失性意味著內容的記憶在缺外部電源的情況下也沒有辦法保持數(shù)據(jù)的完整性。非易失性存儲器的方式是在沒有一個外部電源情況下也是保持不變的。存儲的片段性在一個可編程控制器系統(tǒng)中是顯而易見的。應用程序存儲器。也被稱為內存，它是邏輯的一段記憶，用來存儲控制器用來控制制造的過程實際控制程序。該控制程序通常是由系統(tǒng)建立的用戶。數(shù)據(jù)存