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熱繼電器的選擇與應(yīng)用畢業(yè)論文-資料下載頁

2025-06-28 16:47本頁面
  

【正文】 ser,isnoncontactequipment,theprocedurescanbechangedtochangeproductionprocesses.Theprogrammablecontrollerhasbeeapowerfultoolforfactoryautomation,widelypopularreplication.Programmablecontrollerisuserorientedindustriesdedicatedcontrolputer,withmanydistinctivefeatures.①highreliability,antiinterferencecapability。②programmingvisual,simple。③adaptabilitygood。④functional improvements, strong functional interface. ProgrammableLogicControllers(PLC),aputingdeviceinventedbyRichardE.Morley,havebeenwidelyusedinindustryincludingmanufacturingsystems,transportationsystems,chemicalprocessfacilities,andmanyothers.Atthattime,thePLCreplacedthehardwiredlogicwithsoftwiredlogicorsocalledrelayladderlogic(RLL),aprogramminglanguagevisuallyresemblingthehardwiredlogic,andreducedtherebytheconfigurationtimefrom6monthsdownto6days.AlthoughPCbasedcontrolhasstartedtoeintoplace,PLCbasedcontrolwillremainthetechniquetowhichthemajorityofindustrialapplicationswilladhereduetoitshigherperformance,lowerprice,andsuperiorreliabilityinharshenvironments.Moreover,accordingtoastudyonthePLCmarketofFrostandSullivan,anincreaseoftheannualsalesvolumeto15millionPLCsperyearwiththehardwarevalueofmorethan8billionUSdollarshasbeenpredicted,thoughthepricesofputinghardwareissteadilydropping.TheinventorofthePLC,RichardEMorley,fairlyconsidersthePLCmarketasa5billionindustryatthepresenttime.ThoughPLCsarewidelyusedinindustrialpractice,theprogrammingofPLCbasedcontrolsystemsisstillverymuchrelyingontrialanderror.Alikesoftwareengineering,PLCsoftwaredesignisfacingthesoftwaredilemmaorcrisisinasimilarway.Morleyhimselfemphasizedthisaspectmostforcefullybyindicating:`Ifhouseswerebuiltlikesoftwareprojects,asinglewoodpeckercoulddestroycivilization.”Particularly,practicalproblemsinPLCprogrammingaretoeliminatesoftwarebugsandtoreducethemaintenancecostsofoldladderlogicprograms.ThoughthehardwarecostsofPLCsaredroppingcontinuously,reducingthescantimeoftheladderlogicisstillanissueinindustrysothatlowcostPLCscanbeused.Ingeneral,theproductivityingeneratingPLCisfarbehindparedtootherdomains,forinstance,VLSIdesign,whereefficientputeraideddesigntoolsareinpractice.ExistentsoftwareengineeringmethodologiesarenotnecessarilyapplicabletothePLCbasedsoftwaredesignbecausePLCprogrammingrequiresasimultaneousconsiderationofhardwareandsoftware.Thesoftwaredesignbees,thereby,moreandmorethemajorcostdriver.Inmanyindustrialdesignprojects,morethan50%ofthemanpowerallocatedforthecontrolsystemdesignandinstallationisscheduledfortestinganddebuggingPLCprograms.Inaddition,currentPLCbasedcontrolsystemsarenotproperlydesignedtosupportthegrowingdemandforflexibilityandreconfigurabilityofmanufacturingsystems.
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