外文翻译传感器和传感器激励和测量技术.docx

外文翻译传感器和传感器激励和测量技术.docx

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外文翻译传感器和传感器激励和测量技术

附录A

Transducerandsensorexcitationandmeasurementtechniques

Manyoftoday'sindustrialandinstrumentationapplicationsinvolvingsensor.Thefunctionofthesensorsystemistomonitorchanges,andthenthisdatabacktothemaincontroller.Forasimplevoltageorcurrentmeasurementsensorsmayberesistanceinnature.However,somesensorsystemmaybeinductiveorcapacitiveinnature,thatistosay,thefrequencyrangeofthesensorresistancechangeisnonlinear.Impedancesensorssuchtypicalexampleistheproximitysensor-acampaignforthedetectionoftherelativedistanceofobjects;Inaddition,capacitivesensorsorsensorsensibility-inthemedicaldevicesusedtomeasurebloodfloworbloodpressureorbloodqualitativeanalysis.Inordertousethese"compleximpedancesensors,"therealizationofmeasurement,toprovideanexchangeof（AC）excitationsourcefrequencyinthefrequencyrangeofthesensorforscanning.Thisarticleattemptstoexplainhowtheuseofsingle-chipdigitalwaveformgeneratortoeasilyachievethisupto10MHzfrequencyscanning.Alsointroducedakindofintegratedincentive,responseanddigitalsignalprocessor（DSP）featuresacompletesingle-chipsensorsolutionthatsuitedtherequirementsofuptonearly50kHzfrequencyapplications.Sensors:

workingprinciple.

InspiredbythefrequencyofsensorsignalsbasedonsensorvaluesofLorCtoshowthecorrespondinginstantaneousmagnitude,frequencyorphasechanges.Forexample,theultrasoundwillshowaflowofphaseoffset,whiletheproximitysensorwillcausetheratetochange.Trackingchangesinimpedancethatisthemostcommonlyusedtomonitortheresonantfrequencycircuit.Capacitancevalueoftheresonantfrequencyisequaltothefrequencywheretheinductancevaluepoint.Thisisalsothelargestfrequencycurvefrequencyimpedancevalueofthecorrespondingpoint.Undernormalcircumstances,forexample,instaticconditions,thesensorL,RandChasauniquevalue,intheresonantfrequencyimpedancetoDepartmentwiththegreatestvalue.Whenamovingobjectnearthesensor,thensensorLandCvalueswillbechangedandanewresonantfrequency.Bymonitoringthechangesinresonantfrequency（andthusleadtochangesinimpedance）,itispossibletospeculatethattherelativemovementofobjectsmovingawayfromthesensor.

Calculatedresonantfrequency:

calculationcircuitmeasuringtheresonantfrequencyoftheneedfortherelationshipbetweenfrequencyandimpedance,inparticular,needacertainfrequencyrangewiththeabilitytoscanthewaveformgenerator.Asimple,low-costmethodisbasedontheAD5930waveformgenerator.AD5930withagroupofpre-setinthefrequencyrangeoftheabilitytoprovidealinearscan.Oncetheconditionsforsetting,ontheneedforfurthercontrol,inadditiontoafrequencyscanforthestartofthetrigger.

AD5930hasmanyadvantages:

theoutputfrequencyresolutionof28bit,soyoucanbelessthanthecontrolaccuracyof0.1Hzoutputfrequency.Theoutputfrequencyrangeof0~10MHz,thustheselectionofsensorswithalotofflexibility.Forexample,somesensorsaverynarrowfrequencyrange,buttherequirementsinthisfrequencyrangewithhighresolution.Somesensorsmayrequireawidefrequencyrange,butlowerresolutionrequirements.Thisapproachiseasytocalculatetheresonantfrequencyofthesensor.

Systemblockdiagram:

typicalblockdiagramofsuchasystemasshowninFigure3.ThroughtheBF-535DSPprocessorAD5930digitalwaveformgeneratorset.AD5930needsarisingfromthesinusoidaloutputvoltagewaveformforlow-passfilteringandamplificationinordertoeliminatethemasterclock（MCLK）,mirroringthefrequencyandhighfrequencynoisegeneratedbyfeedthrough.Afterfilteringthesensorsignalcanbeusedasasourceofexcitationfrequency.AccordingtotheimpedanceofthesensorresponsesignalamplificationmaybeneededinordertoentertheADC（ADC）dynamicrange.SensoroutputandthefrequencyofthesourceofbothincentivesintotheAD726612bit,2MSPSdualsimultaneoussamplingADC.ADCoutputdatawillbestoredinmemoryinordertodofurtheranalysistocalculatethephaseandamplitudeofthesensoroffset.

Completeintegratedsensorsolutions:

separationdescribedaboveisacommonsolutionforimpedancemeasurementofthesensorsolution.Theprogrammayrequiremanydiscretecomponents,sothesensorisacost-analysissolution.Theseseparatecomponentswillincreasetheirownsourcesoferror.Thedesignofactivecomponentswillincreasethenumberofphaseerror,whichistheneedforcorrection.Inaddition,theDSPalsoneedtodealwithsomecomplexmathematicalcalculations,thismayrequireexternalmemorytostoretheoriginaldataoftheADC,whichwouldfurtherincreasecosts.

Addresstheabove-mentionedanalysisoftheissueoflow-frequencysensorsolutionsAD5933/4device,itwillbythemainprocessingmoduleareintegratedintoonechip.Thecoreofthechip,includingthreemainmodules:

thefrequencyofscanningforthedirectdigitalsynthesizer（DDS）waveformgenerator;usedtomeasurethesensor'sresponsetothe12bit,1MSPSADC;and,finally,totheADCdatafor1024pointDiscreteFourierTransform（DFT）calculationsoftheDSPengine.

TheresultsofDFTcalculationstoprovidearealpart（R）andanimaginarypart（I）data,whichcaneasilycalculatetheimpedance.Usingthefollowingformulaiseasytocalculatetheimpedanceamplitudeandphase:

InordertodeterminetheactualvalueoftherealimpedanceZ（ω）,istypicallyrequiredtoperformfrequencyscanning.Cancalculatetheimpedanceofeachfrequencypoint,whichcandrawarelationshipbetweenfrequencyandamplitudecurves.Soitiseasytomeasure100Ω~20MΩresistancewithinthescope.Thesystemallowsuserstosetupa2Vpeak-to-peak（PK-PK）ofthesinusoidalsignalasanexternalfrequencysourceexcitationload.Outputrangecanbesetto1V,500mVand200mV.Frequencyresolutioncanbe27bit（<0.1Hz）.Therealizationofthefrequencyofscanning:

Inordertoachievethefrequencyofscanning,theusermustfirstsetuptherequiredfrequencyofscanningconditions:

theneedforastartfrequency,frequencyintervalandsweeppoints.Thentheneedforastartcommandtostartscanning.Frequencypointsineachscan,ADCcompletedthefirst1024samples,andthencalculatingtheDFTinordertoprovidethewaveformoftherealandimaginarypartsofthedata.TherealandimaginarypartsofthedatathroughtheI2Cinterfaceintheformoftwo16bitwordsavailabletotheuser.DSP-chipprocessingunituserdoesnothavetheadvantageofcomplexmathematicalcalculations,andneednotstoreADCrawdata,onlytwo16bitdata.Therefore,itallowstheDSPtochoosecheapersolutions,asgreatlyreducetheprocessingpowerofthefinalrequirements.

Withoutcalibrationofthesystemasaresultcanonlyusethetypicalvalueofsensitivityandoffsettheoutputvoltageisconvertedtopressure,thepressuremeasuredwillhaveamarginoferrorasshowninFigure.

Thisinitialerrorwithoutcalibrationbythefollowingcomponents:

1.offseterror:

Asthepressureintheentirerangeofverticalshifttomaintainaconstant,sotheproliferationandlaserconditioningconverterchangestheamendmentwouldhaveoffseterror.

2.Thesensitivityoferror,resultinginerrorsindirectproportiontothesizeandpressure:

Ifthedeviceishigherthanthetypicalvalueofthesensitivity,thesensitivityoftheerrorwillbeincrementalpressurefunction（seeFigure1）.Ifthesensitivityislowerthanthetypicalvalue,thenthesensitivityoftheerrorwillbedecreasingfunctionofpressure.Thecauseoftheerrordiffusionprocessistochange.

3.LinearityError:

Thisisaninitialerrorfactorlessaffected,theerroristhecauseofthephysicalnon-linearsilicon,butwiththesensoramplifier,shouldalsoincludenon-linearamplifier.Linearerrorcurvecanbeconcavecurve,itcouldbeaconvexcurve.

4.LagError:

Inmostcases,thelagerrorcanbeignoredcompletely,becausesiliconhasahigherdegreeofmechanicalstiffness.Changesingeneraljustalotofpressuretoconsiderthecaseofhysteresiserror.

Calibrationcaneliminateorgreatlyreducetheseerrors,andcompensationtechniqueisusuallyrequiredtoidentifytheparametersoftheactualtransferfunction,ratherthansimplytheuseoftypicalvalues.Potentiometer,adjustableresistance,andotherhardwarecanbeusedinthecompensationprocess,whilethesoftwareisabletoachievemoreflexibilityintheworkofthiserrorcompensation.

CalibrationmethodthatcaneliminatethetransferfunctionagainsttheAgencytocompensatetheoffsetdrifterror,suchastheauto-zerocalibrationmethod.Offsetzerocalibrationisusuallycarriedoutunderpressure,especiallyinthedifferentialsensor,becauseundertheconditionsofthenominaldifferentialpressureisusually0.Forpuresensoroffsetcalibrationwillbedifficult,becauseiteitherneedstoreadapressuresystemtomeasuretheatmosphericpressureintheenvironmentundertheconditionsofthecalibrationofpressureorneedtoobtainthepressureofexpectationsofthepressurecontroller.Zerodifferentialpressuresensorisveryaccuratecalibration,becausethepressureofstrictdemarcationis0.Ontheotherhand,thepressureof0:

00isnottheaccuracyofthecalibrationdependsonthepressurecontrollerortheperformancemeasurementsystem.

  Calibrationisveryimportantselectionpressure,whichdeterminestheaccuracytoobtainthebestpressurerange.Infact,aftercalibrationoffsetactualstandardfixed-pointerrorintheDepartmentandhasbeentomaintainasmaller