数据采集系统文献翻译.docx

数据采集系统文献翻译.docx

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数据采集系统文献翻译

SelectingtheRightDataAcquisitionSystem

Engineersoftenmustmonitorahandfulofsignalsoverextendedperiodsoftime,andthengraphandanalyzetheresultingdata.Theneedtomonitor,recordandanalyzedataarisesinawiderangeofapplications,includingthedesign-verificationstageofproductdevelopment,environmentalchambermonitoring,componentinspection,benchtoptestingandprocesstrouble-shooting.

Thisapplicationnotedescribesthevariousmethodsanddevicesyoucanusetoacquire,recordandanalyzedata,fromthesimplepen-and-papermethodtousingtoday'ssophisticateddataacquisitionsystems.Itdiscussestheadvantagesanddisadvantagesofeachmethodandprovidesalistofquestionsthatwillguideyouinselectingtheapproachthatbestsuitsyourneeds.

Introduction

Ingeotechnicalengineering,wesometimeencountersomedifficultiessuchasmonitoringinstrumentsdistributedinalargearea,dangerousenvironmentofworkingsitethatcausesomedifficultyforeasyaccess.Inthiscase,operatorsmayadoptremotecontrol,bywhichalargeamountofmeasureddatawillbetransmittedtoaobservationroomwherethedataaretobecollected,storedandprocessed.

Theautomaticdataacquisitioncontrolsystemisabletocompletethetasksasregularautomaticdatamonitoring,acquisitionandstore,featuringhighautomation,largedatastorecapacityandreliableperformance.

Thesystemiscomposedofacquisitioncontrolsystemanddisplaysystem,withthefollowingfeatures:

1.No.ofChannels:

32（canbeincreasedordecreasedaccordingtouser'srealneeds.）

2.Scanningduration:

decidedbyuser,fastest32points/second

3.Storecapacity:

20G（maybeincreasedordecreased）

4.Display:

（a）Tableofparameter（b）Historytendency（c）Columngraphics.

5.Function:

realtimemonitoringcontrol,warning

6.Overalldimension:

50cm×50cm×72cm

Dataacquisitionsystems,asthenameimplies,areproductsand/orprocessesusedtocollectinformationtodocumentoranalyzesomephenomenon.Inthesimplestform,atechnicianloggingthetemperatureofanovenonapieceofpaperisperformingdataacquisition.Astechnologyhasprogressed,thistypeofprocesshasbeensimplifiedandmademoreaccurate,versatile,andreliablethroughelectronicequipment.Equipmentrangesfromsimplerecorderstosophisticatedcomputersystems.Dataacquisitionproductsserveasafocalpointinasystem,tyingtogetherawidevarietyofproducts,suchassensorsthatindicatetemperature,flow,level,orpressure.Somecommondataacquistiontermsareshownbelow:

Dataacquisitiontechnologyhastakengiantleapsforwardoverthelast30to40years.Forexample,40yearsago,inatypicalcollegelab,apparatusfortrackingthetemperatureriseinacrucibleofsodiumtungsten-bronzeconsistedofathermocouple,abridge,alookuptable,apadofpaperandapencil.

Today'scollegestudentsaremuchmorelikelytouseanautomatedprocessandanalyzethedataonaPCToday,numerousoptionsareavailableforgatheringdata.Theoptimalchoicedependsonseveralfactors,includingthecomplexityofthetask,thespeedandaccuracyyourequire,andthedocumentationyouwant.Dataacquisitionsystemsrangefromthesimpletothecomplex,witharangeofperformanceandfunctionality.

Pencilandpaper

Theoldpencilandpaperapproachisstillviableforsomesituations,anditisinexpensive,readilyavailable,quickandeasytogetstarted.Allyouneedtodoishookupadigitalmultimeter（DMM）andbeginrecordingdatabyhand.

Unfortunately,thismethodiserror-prone,tendstobeslowandrequiresextensivemanualanalysis.Inaddition,itworksonlyforasinglechannelofdata;whileyoucanusemultipleDMMs,thesystemwillquicklybecomesbulkyandawkward.Accuracyisdependentonthetranscriber'sleveloffastidiousnessandyoumayneedtoscaleinputmanually.Forexample,iftheDMMisnotsetuptohandletemperaturesensors,manualscalingwillberequired.Takingtheselimitationsintoaccount,thisisoftenanacceptablemethodwhenyouneedtoperformaquickexperiment.

Stripchartrecorder

Modernversionsofthevenerablestripchartrecorderallowyoutocapturedatafromseveralinputs.Theyprovideapermanentpaperrecordofthedata,andbecausethisdataisingraphicalformat,theyallowyoutoeasilyspottrends.Oncesetup,mostrecordershavesufficientinternalintelligencetorununattended—withouttheaidofeitheranoperatororacomputer.Drawbacksincludealackofflexibilityandrelativelylowaccuracy,whichisoftenconstrainedtoafewpercentagepoints.Youcantypicallyperceiveonlysmallchangesinthepenplots.Whilerecordersperformwellwhenmonitoringafewchannelsoveralongperiodoftime,theirvaluecanbelimited.Forexample,theyareunabletoturnanotherdeviceonoroff.Otherconcernsincludepenandpapermaintenance,papersupplyanddatastorage,allofwhichtranslateintopaperoveruseandwaste.Still,recordersarefairlyeasytosetupandoperate,andofferapermanentrecordofthedataforquickandsimpleanalysis.

Scanningdigitalmultimeter

SomebenchtopDMMsofferanoptionalscanningcapability.Aslotintherearoftheinstrumentacceptsascannercardthatcanmultiplexbetweenmultipleinputs,with8to10channelsofmuxbeingfairlycommon.DMMaccuracyandthefunctionalityinherentintheinstrument'sfrontpanelareretained.Flexibilityislimitedinthatitisnotpossibletoexpandbeyondthenumberofchannelsavailableintheexpansionslot.AnexternalPCusuallyhandlesdataacquisitionandanalysis.

PCplug-incards

PCplug-incardsaresingle-boardmeasurementsystemsthattakeadvantageoftheISAorPCI-busexpansionslotsinaPC.Theyoftenhavereadingratesashighas100,000readingspersecond.Countsof8to16channelsarecommon,andacquireddataisstoreddirectlyintothecomputer,whereitcanthenbeanalyzed.Becausethecardisessentiallypartofthecomputer,itiseasytosetuptests.PCcardsalsoarerelativelyinexpensive,inpart,becausetheyrelyonthehostPCtoprovidepower,themechanicalenclosureandtheuserinterface.

Dataacquisitionoptions

Inthedownside,PCplug-incardsoftenhaveonly12bitsofresolution,soyoucan'tperceivesmallvariationswiththeinputsignal.Furthermore,theelectricalenvironmentinsideaPCtendstobenoisy,withhigh-speedclocksandbusnoiseradiatedthroughout.Often,thiselectricalinterferencelimitstheaccuracyofthePCplug-incardtothatofahandheldDMM.Thesecardsalsomeasureafairlylimitedrangeofdcvoltage.Tomeasureotherinputsignals,suchasacvoltage,temperatureorresistance,youmayneedsomesortofexternalsignalconditioning.Additionalconcernsincludeproblematiccalibrationandoverallsystemcost,especiallyifyouneedtopurchaseadditionalsignalconditioningaccessoriesoraPCtoaccommodatethecards.Takingthatintoconsideration,PCplug-incardsofferanattractiveapproachtodataacquisitionifyourrequirementsfallwithinthecapabilitiesandlimitationsofthecard.

Dataloggers

Dataloggersaretypicallystand-aloneinstrumentsthat,oncetheyaresetup,canmeasure,recordanddisplaydatawithoutoperatororcomputerintervention.Theycanhandlemultipleinputs,insomeinstancesupto120channels.AccuracyrivalsthatfoundinstandalonebenchDMMs,withperformanceinthe22-bit,0.004-percentaccuracyrange.Somedataloggershavetheabilitytoscalemeasurements,checkresultsagainstuser-definedlimits,andoutputsignalsforcontrol.

Oneadvantageofusingdataloggersistheirbuilt-insignalconditioning.Mostareabletodirectlymeasureanumberofdifferentinputswithouttheneedforadditionalsignalconditioningaccessories.Onechannelcouldbemonitoringathermocouple,anotheraresistivetemperaturedevice（RTD）andstillanothercouldbelookingatvoltage.

Thermocouplereferencecompensationforaccuratetemperaturemeasurementistypicallybuiltintothemultiplexercards.Adatalogger'sbuilt-inintelligencehelpsyousetupthetestroutineandspecifytheparametersofeachchannel.Onceyouhavecompletedthesetup,dataloggerscanrunasstandalonedevices,muchlikearecorder.Theystoredatalocallyininternalmemory,whichcanaccommodate50,000readingsormore.

PCconnectivitymakesiteasytotransferdatatoyourcomputerforin-depthanalysis. Mostdataloggersaredesignedforflexibilityandsimpleconfigurationandoperation,andmanyprovidetheoptionofremotesiteoperationviabatterypacksorothermethods.DependingontheA/Dconvertertechniqueused,certaindataloggerstakereadingsatarelativelyslowrate,especiallycomparedtomanyPCplug-incards.Still,readingspeedsof250readings/secondarenotuncommon.Keepinmindthatmanyofthephenomenabeingmonitoredarephysicalinnature—suchastemperature,pressureandflow—andchangeatafairlyslowrate.Additionally,becauseofadatalogger'ssuperiormeasurementaccuracy,multiplereadingsandaveragingarenotnecessary,astheyoftenareinPCplug-insolutions.

Dataacquisitionfrontends

DataacquisitionfrontendsareoftenmodularandaretypicallyconnectedtoaPCorcontroller.Theyareusedinautomatedtestapplicationsforgatheringdataandforcontrollingandroutingsignalsinotherpartsofthetestsetup.Frontendperformancecanbeveryhigh,withspeedandaccuracyrivalingthebeststandaloneinstruments.Dataacquisitionfrontendsareimplementedinanumberofformats,includingVXIversions,suchastheAgilentE1419AmultifunctionmeasurementandcontrolVXImodule,andproprietarycardcages..Althoughfront-endcosthasbeendecreasing,theses