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

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