基于嵌入式ARM平台的远程IO数据采集系统的研究和开发.docx
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基于嵌入式ARM平台的远程IO数据采集系统的研究和开发.docx
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基于嵌入式ARM平台的远程IO数据采集系统的研究和开发
ResearchandDevelopmentoftheRemoteI/ODataAcquisitionSystemBasedonEmbeddedARMPlatform
INTRODUCTION
Withthewideuseofthenetworked,intelligentanddigitaldistributedcontrolsystem,thedataacquisitionsystembasedonthesingle-chipisnotonlylimitedinprocessingcapacity,butalsotheproblemofpoorreal-timeandreliability.Inrecentyears,withtherapiddevelopmentofthefieldofindustrialprocesscontrolandthefastpopularizationofembeddedARMprocessor,ithasbeenatrendthatARMprocessorcansubstitutethesingle-chiptorealizedataacquisitionandcontrol.EmbeddedARMsystemcanadapttothestrictrequirementsofthedataacquisitionsystem,suchasthefunction,reliability,cost,size,powerconsumption,andsoon.Inthispaper,anewkindofremoteI/OdataacquisitionsystembasedonARMembeddedplatformhasbeenresearchedanddeveloped,whichcanmeasureallkindsofelectricalandthermalparameterssuchasvoltage,current,thermocouple,RTD,andsoon.ThemeasureddatacanbedisplayedonLCDofthesystem,andatthesametimecanbetransmittedthroughRS485orEthernetnetworktoremoteDASorDCSmonitoringsystembyusingModbus/RTUorModbus/TCPprotocol.Thesystemhasthedualredundantnetworkandlong-distancecommunicationfunction,whichcanensurethedisturbrejectioncapabilityandreliabilityofthecommunicationnetwork.Thenewgenerationremotedataacquisitionandmoni-toringsystembasedonthehigh-performanceembeddedARMmicroprocessorhasimportantapplicationsignificance.
STRUCTRUEDESIGNOFTHEWHOLESYSTEM
ThewholestructurechartoftheremotedataacquisitionandmonitoringsystembasedonembeddedARMplatformisshowninFigure1.Intheschemeofthesystem,theremoteI/OdataacquisitionmodulesaredevelopedbyembeddedARMprocessor,whichcanbewidelyusedtodiversifiedindustriessuchaselectricpower,petroleum,chemical,metallurgy,steel,transportationandsoon.Thissystemismainlyusedfortheconcentrativeacquisitionanddigitalconversionofavarietyofelectricalandthermalsignalssuchasvoltage,current,thermalresistance,thermo-coupleintheproductionprocess.ThentheconverteddatacanbedisplayedontheLCDdirectly,andalsocanbesenttotheembeddedcontrollerthroughRS485orEthernetnetworkcommunicationinterfacebyusingModbus/RTUorModbus/TCPprotocol.Thedataintheembeddedcontrollerplatformistransmittedtothework-stationsofremotemonitoringcenterbyEthernetafterfurtheranalyzedandpro-cessed.Atthesametime,thesedatacanbestoredintherealtimedatabaseofthedatabaseserverinremotemonitoringcenter.Thesystemhasthedualredun-dantnetworkandlong-distancecommunicationfunction,whichcanensurethedisturbrejectioncapabilityandreliabilityofthecommunicationnetwork.
ThehardwareplatformoftheRemoteI/Odataacquisitionsystembasedonemb-eddedARMuses32-bitARMembeddedmicroprocessor,andthesoftwareplat-formusesthereal-timemulti-taskoperatingsystemuC/OS-II,whichisopen-sourceandcanbegrafted,cutoutandsolidified.Therealtimeoperatingsystem(RTOSmakesthedesignandexpansionoftheapplicationbecomesveryeasy,andwithoutmorechangeswhenaddnewfunctions.Throughthedivisionoftheappli-cationintoseveralindependenttasks,RTOSmakesthedesignprocessoftheapplicationgreatlysimple.
Figure1Structureofthewholesystem
THEHARDWAREDESIGNOFTHESYSTEM
TheremoteI/OdataacquisitionsystembasedonembeddedARMplatformhashighuniversality,eachacquisitiondeviceequippedwith24-wayacquisitionI/Ochannelsandisolatedfromeachother.EachI/Ochannelcanselectavarietyofvoltageandcurrentsignals,aswellastemperaturesignalssuchasthermalresis-tance,thermocoupleandsoon.Thevoltagesignalsintherangeof0-75mV,1-5V,0-5V,andsoon,thecurrentsignalsintherangeof0-10mAand4-20mA,thethermalresistancemeasurementcomponentsincludingCu50,Cu100,Pt50,Pt100,andthethermocouplemeasurementcomponentsincludingK,E,S,T,andsoon.
Figure2.StructureoftheremoteI/Odataacquisitionsystembasedon
ARMprocessor
ThestructuraldesignoftheembeddedremoteI/OdataacquisitionsystemisshowninFigure2.Thesystemequippedwithsomeperipheralssuchaspower,keyboard,reset,LCDdisplay,ADC,RS485,Ethernet,JTAG,I2C,E2PROM,andsoon.TheA/Dinterfacecircuitisindependentwiththeembeddedsystem,whichisindependentwiththeembeddedsystem,whichissystemhassettingbuttonsand128*64LCD,whichmakesthedebuggingandmodificationoftheparameterseasy.ThecollecteddatacanbesenttotheremoteembeddedcontrollerorDAS,DCSsystembyusingModbus/RTUorModbus/TCPprotocolthroughRS485orEth-ernetcommunicationinterfacealso,andthenbeusedformonitoringandcontrolafterfartherdisposal.
ThesystemofRS485hasadualredundantnetworkandlong-distancecommunicationfunction.AstheembeddedEthernetinterfacemakestheremotedataexchangeoftheapplicationsbecomeveryeasy,thesystemcanchooseRS485orEthernetinterfacethroughjumpertocommunicatewithhostcomputer.EthernetinterfaceuseindependentZNE-100TLintelligentembeddedEthernettoserialportconversionmoduleinordertofacilitatethesystemmaintenanceandupgrade.TheZNE-100TLmodulehasanadaptive10/100MEthernetinterface,whichhasalotofworkingmodessuchasTCPServer,TCPClient,UDP,RealCOM,andsoon,anditcansupportfourconnectionsatmost.
Figure3.Diagramofthesignalpretreatmentcircuit
Figure3showsthesignalpretreatmentcircuitdiagram.Thesignalsofthermo-couplesuchasK,E,S,Tetcand0-500mVvoltagesignalcanconnecttothepositiveendINPxandthenegativeendINNxofthesimulatemultiplexers(MUXdirectly.The4-20mAcurrentsignaland1-5Vvoltagesignalmustbetransformedbyresis-tancebeforeconnectingtothepositiveendINPxandthenegativeendINNxoftheMUXofcertainchannel.TheRTDthermalresistancesignalssuchasCu50,Cu100,Pt50andPt100shouldconnectone1mAconstantcurrentbeforeconnectingtothepositiveendINPxandthenegativeendINNxoftheMUXofcertainchannel.
Figure4.DiagramofADCsignalcircuit
Figure4showstheADCsignalcircuit,whichusingthe16-bitADCchipAD7715.TheconnectionofthechipandthesystemissimpleandonlyneedfivelineswhichareCS(chipselect,SCLK(systemclock,DIN(datainput,DOUT(dataoutputandDRDY(dataready.
AstheARMmicroprocessorhasthecharacteristicsofhighspeed,lowpower,lowvoltageandsoon,whichmakeitscapacityoflow-noise,therippleofpower,thetransientresponseperformance,thestabilityofclocksource,thereliabilityofpowercontrolandmanyotheraspectsshouldbehavehigherrequest.ThesystemresetcircuitusespecialmicroprocessorpowermonitoringchipofMAX708S,inordertoimprovethereliabilityofthesystem.ThesystemresetcircuitisshowninFigure5.
Figure5.Diagramofsystemresetcircuit
SOFTWAREDESIGNANDREALIZATIONOFTHESYSTEM
ThesystemsoftwareoftheremoteI/OdataacquisitionsystembasedonembeddedARMplatformusethereal-timeoperatingsystem(RTOSuC/OS-II,whichisopen-sourceandcanbegrafted,cutoutandsolidified.ThekeypartofRTOSisthereal-timemulti-taskcore,whosebasicfunctionsincludingtaskmanagement,resourcemanagement,systemmanagement,timermanagement,memorymanagement,informationmanagement,queuemanagementandsoon.ThesefunctionsareusedthoughAPIservicefunctionsofthecore.
ThesystemsoftwareplatformuseuC/OS-IIreal-timeoperatingsystemcoresimplifiedthedesignofapplicationsystemandmadethewholestructureofthesystemsimpleandthecomplexapplicationhierarchical.Thedesignofthewholesystemincludesthetasksoftheoperatingsystemandaseriesofuserapplications.Themainfunctionofthesystemismainlytorealizetheinitializationofthesystemhardwareandtheoperatingsystem.Theinitializationofhardwareincludesinterr-upt、keyboard、LCDandsoon.Theinitializationofoperatingsystemincludesthecontrolblocksandeventscontrolblocks,andbeforethestartofmulti-taskschedu-ling,onetaskmustbestartedatleast.Astarttaskhasbeencreatedinthissystem,whichismainlyresponsiblefortheinitializationandstartupofclock,thestart-upofinterruption,theinitializationofcommunicationtaskmodule,aswellasthedivisionoftasksandsoon.Thetasksmustbedividedinordertocompletevariousfunctionsofthereal-timemulti-tasksystem.
Figure6.Functionaltasksofthesystemsoftware
Figure6showsthefunctionaltasksofthesystemsoftware.Accordingtoimportanceofthetasksandthedemandsofreal-time,thesystemapplicationsaredividedintosixtaskswithdifferentpriority,whichincludingthetasksofA/Ddataacquisition,systemmonitoring,receivequeue,datasend,keyboardinput,LCDdisplay.TheA/Ddataacquisitiontaskdemandsthehighestreal-timerequirementsandtheLCDdisplaytaskisthelowest.Becauseeachtaskhasadifferentpriority,thehigher-prioritytaskcanaccessthereadyonebycallingthesystemhangupfunctionordelayfunction.
Figure7.ChartofAD7715datatransferflow
Figure7showsthedataconversionflowofAD7715.TheapplicationA/Dconversionisanimportantpartofthedataacquisitionsystem.IntheuC/OS-IIreal-timeoperatingsystemcore,therealizationprocessofA/DdriverdependsmainlyontheconversiontimeofA/Dconverter,theanalogfrequencyoftheconversionvalue,thenumberofinputchannels,theconversionfrequencyandsoon.ThetypicalA/Dconversioncircuitismadeupofanalogmultiplexer(MUX,amplifieranda
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