PLC外文翻译S7200的特性.docx

PLC外文翻译S7200的特性.docx

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PLC外文翻译S7200的特性

大学

毕业设计

（外文翻译材料）

2012年6月

FeaturesoftheS7-200

TheS7-200providesseveralspecialfeaturesthatallowyoutocustomizehowtheS7-200functionstobetterfityourapplication.

TheS7-200AllowsYourProgramtoImmediatelyReadorWritetheI/O

TheS7-200instructionsetprovidesinstructionsthatimmediatelyreadfromorwritetothephysicalI/O.TheseimmediateI/Oinstructionsallowdirectaccesstotheactualinputoroutputpoint,eventhoughtheimageregistersarenormallyusedaseitherthesourceorthedestinationforI/Oaccesses.

Thecorrespondingprocess-imageinputregisterlocationisnotmodifiedwhenyouuseanimmediateinstructiontoaccessaninputpoint.Thecorrespondingprocess-imageoutputregisterlocationisupdatedsimultaneouslywhenyouuseanimmediateinstructiontoaccessanoutputpoint.

Tip

TheS7-200handlesreadsofanaloginputsasimmediatedata,unlessyouenableanaloginputfiltering.Whenyouwriteavaluetoananalogoutput,theoutputisupdatedimmediately.

Itisusuallyadvantageoustousetheprocess-imageregisterratherthantodirectlyaccessinputsoroutputsduringtheexecutionofyourprogram.Therearethreereasonsforusingtheimageregisters:

Thesamplingofallinputsatthestartofthescansynchronizesandfreezesthevaluesoftheinputsfortheprogramexecutionphaseofthescancycle.Theoutputsareupdatedfromtheimageregisteraftertheexecutionoftheprogramiscomplete.Thisprovidesastabilizingeffectonthesystem.

YourprogramcanaccesstheimageregistermuchmorequicklythanitcanaccessI/Opoints,allowingfasterexecutionoftheprogram.

I/Opointsarebitentitiesandmustbeaccessedasbitsorbytes,butyoucanaccesstheimageregisterasbits,bytes,words,ordoublewords.Thus,theimageregistersprovideadditionalflexibility.

TheS7-200AllowsYourProgramtoInterrupttheScanCycle

Ifyouuseinterrupts,theroutinesassociatedwitheachinterrupteventarestoredaspartoftheprogram.Theinterruptroutinesarenotexecutedaspartofthenormalscancycle,butareexecutedwhentheinterrupteventoccurs（whichcouldbeatanypointinthescancycle）.

InterruptsareservicedbytheS7-200onafirst-come-first-servedbasiswithintheirrespectivepriorityassignments.

TheS7-200AllowsYoutoAllocateProcessingTimeforRunModeEditandExecutionStatus

Youcanconfigureapercentageofthescancycletobededicatedforprocessingarunmodeeditcompilationorexecutionstatus.（RunmodeeditandexecutionstatusareoptionsprovidedbySTEP7--Micro/WINtomakedebuggingyourprogrameasier.）Asyouincreasethepercentageoftimethatisdedicatedtothesetwotasks,youincreasethescantime,whichmakesyourcontrolprocessrunmoreslowly.

Thedefaultpercentageofthescandedicatedtoprocessingrunmodeeditsandexecutionstatusissetto10%.Thissettingwaschosentoprovideareasonablecompromiseforprocessingthecompilationandstatusoperationswhileminimizingtheimpacttoyourcontrolprocess.Youcanadjustthisvalueby5%incrementsuptoamaximumof50%.Tosetthescancycletime-sliceforbackgroundcommunications:

1.SelecttheView>Component>SystemBlockmenucommandandselectBackgroundTime.

2.IntheBackgroundtab,usethedropdownboxtoselectthecommunicationsbackgroundtime.

3.ClickOKtosaveyourselection.

4.DownloadthemodifiedsystemblocktotheS7-200.

Figure1CommunicationsBackgroundTime

TheS7-200AllowsYoutoSettheStatesofDigitalOutputsforStopMode

TheoutputtableoftheS7-200allowsyoutodeterminewhethertosetthestateofthedigitaloutputpointstoknownvaluesuponatransitiontotheSTOPmode,ortoleavetheoutputsinthestatetheywereinbeforethetransitiontotheSTOPmode.TheoutputtableispartofthesystemblockthatisdownloadedandstoredintheS7-200.

1.SelecttheView>Component>SystemBlockmenucommandandselectOutputTable.ClickontheDigitaltab.

2.Tofreezetheoutputsintheirlaststate,selecttheFreezeOutputscheckbox.

3.Tocopythetablevaluestotheoutputs,entertheoutputtablevaluesbyclickingthecheckboxforeachoutputbityouwanttosettoOn

（1）afterarun-to-stoptransition.Thedefaultvaluesofthetableareallzeroes.

4.ClickOKtosaveyourselections.

5.DownloadthemodifiedsystemblocktotheS7-200.

Figure2DigitalOutputTable

TheS7-200AllowsYoutoConfiguretheValueofAnalogOutputs

TheAnalogOutputTableallowsyoutosetanalogoutputpointstoknownvaluesafteraRUN-to-STOPtransition,ortopreservetheoutputvaluesthatexistedbeforethetransitiontoSTOPmode.TheAnalogOutputtableispartofthesystemblockthatisdownloadedandstoredintheS7-200CPU.

1.SelecttheView>Component>SystemBlockmenucommandandselectOutputTable.ClickontheAnalogtab.

2.Tofreezetheoutputsintheirlaststate,selecttheFreezeOutputscheckbox.

3.TheFreezeValuestableallowsyoutosettheanalogoutputstoaknown

value（--32768to37262）,onaRUN-to-STOPtransition.

4.ClickOKtosaveyourselections.

5.DownloadthemodifiedsystemblocktotheS7-200.

Figure3AnalogOutputTable

TheS7-200AllowsYoutoDefineMemorytoBeRetainedonLossofPower

Youcandefineuptosixretentiverangestoselecttheareasofmemoryyouwanttoretainthroughpowercycles.Youcandefinerangesofaddressesinthefollowingmemoryareastoberetentive:

V,M,C,andT.Fortimers,onlytheretentivetimers（TONR）canberetained.Thedefaultsettingforthefirst14bytesofMMemoryistobenon-retentive.

Onlythecurrentvaluesfortimersandcounterscanberetained:

thetimerandcounterbitsarenotretentive.

Tip

ChangingtherangeMB0toMB13toberetentiveenablesaspecialfeaturethatautomaticallysavestheselocationstothepermanentmemoryonpowerdown.

Todefinetheretentivememory:

1.SelecttheView>Component>SystemBlockmenucommandandselectRetentiveRanges.

2.SelecttherangesofmemorytoberetainedfollowinglossofpowerandclickOK.

3.DownloadthemodifiedsystemblocktotheS7-200.

Figure4RetentiveMemory

TheS7-200AllowsYoutoFiltertheDigitalInputs

TheS7-200allowsyoutoselectaninputfilterthatdefinesadelaytime（selectablefrom0.2msto12.8ms）forsomeorallofthelocaldigitalinputpoints.Thisdelayhelpstofilternoiseontheinputwiringthatcouldcauseinadvertentchangestothestatesoftheinputs.

TheinputfilterispartofthesystemblockthatisdownloadedandstoredintheS7-200.Thedefaultfiltertimeis6.4ms.AsshowninFigure4,eachdelayspecificationappliestogroupsofinputpoints.

Toconfigurethedelaytimesfortheinputfilter:

1.SelecttheView>Component>SystemBlockmenucommandandselectInputFilters.ClickontheDigitaltab.

2.EntertheamountofdelayforeachgroupofinputsandclickOK.

3.DownloadthemodifiedsystemblocktotheS7-200.

Tip

Thedigitalinputfilteraffectstheinputvalueasseenbyinstructionreads,inputinterrupts,andpulsecatches.Dependingonyourfilterselection,yourprogramcouldmissaninterrupteventorpulsecatch.Thehighspeedcounterscounttheeventsontheunfilteredinputs.

TheS7-200AllowsYoutoFiltertheAnalogInputs

TheS7-200allowsyoutoselectsoftwarefilteringonindividualanaloginputs.Thefilteredvalueistheaveragevalueofapreselectednumberofsamplesoftheanaloginput.Thefilterspecification（numberofsamplesanddeadband）isthesameforallanaloginputsforwhichfilteringisenabled.

Thefilterhasafastresponsefeaturetoallowlargechangestobequicklyreflectedinthefiltervalue.Thefiltermakesastepfunctionchangetothelatestanaloginputvaluewhentheinputexceedsaspecifiedchangefromthecurrentvalue.Thischange,calledthedeadband,isspecifiedincountsofthedigitalvalueoftheanaloginput.

ThedefaultconfigurationistoenablefilteringforallanaloginputsexceptAIW0andAIW2onCPU224XP.

1.SelecttheView>Component>SystemBlockmenucommandandselectInputFilters.ClickontheAnalogtab.

2.Selecttheanaloginputsthatyouwanttofilter,thenumberofsamples,andthedeadband.

3.ClickOK.

4.DownloadthemodifiedsystemblocktotheS7-200.

Figure5AnalogInputFilter

Tip

Donotusetheanalogfilterwithmodulesthatpassdigitalinformationoralarmindicationsintheanalogwords.AlwaysdisableanalogfilteringforRTD,Thermocouple,andAS-InterfaceMastermodules.

Tip

AIW0andAIW2ontheCPU224XParefilteredbytheanalogtodigitalconverter,andusuallywillnotneedtheadditionalsoftwarefilter.

TheS7-200AllowsYoutoCatchPulsesofShortDuration

TheS7-200providesapulsecatchfeaturewhichcanbeusedforsomeorallofthelocaldigitalinputpoints.Thepulsecatchfeatureallowsyoutocapturehigh-goingpulsesorlow-goingpulsesthatareofsuchashortdurationthattheywouldnotalwaysbeseenwhentheS7-200readsthedigitalinputsatthebeginningofthescancycle.Whenpulsecatchisenabledforaninput,achangeinstateoftheinputislatchedandhelduntilthenextinputcycleupdate.ThisensuresthatapulsewhichlastsforashortperiodoftimeiscaughtandhelduntiltheS7-200readstheinputs.

Youcanindividuallyenablethepulsecatchoperationforeachofthelocaldigitalinputs.

Toaccessthepulsecatchconfigurationscreen:

1.SelecttheView>Component>SystemBlockmenucommandandselectPulseCatchBits.

2.ClickthecorrespondingcheckboxandclickOK.

3.DownloadthemodifiedsystemblocktotheS7-200.

Figure6PulseCatch

Figure7show