SIGNAL CONDITIONING FOR RESISTIVE SENSORS 传感与检测技术ppt课件.ppt

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1、3SIGNALCONDITIONINGFORRESISTIVESENSORSThischapterpresents:Methodstoobtainfromresistivesensorsoutputvoltagesinarangesuitedtoanalog-to-digitalconverters.InterferencecompensationSensorlinearization3.1MEASUREMENTOFRESISTANCEThegeneralequationfortheresistancechangeofasensor:ForlinearsensorsThera

2、ngeofvaluesforxdependsstronglyonthetypeofsensorandonthemeasurandspan:xfrom0to-1forlinearpotentiometersxfrom10-5to10-2forstraingages……3.1MEASUREMENTOFRESISTANCETworequirementsforallconditionersforresistivesensors:DrivethesensorwithanelectricvoltageorcurrentThesupplyislimitedbysensorself-heat

3、ingunlessthesensingprincipleusessensorself-heatingThepowerdissipatebythesensorisTheveninEquivalentcircuitSensor3.1MEASUREMENTOFRESISTANCEConditionersforremotesensorsmustbeinsensitivetoconnectingleadresistanceorcompensateforit.ThevoltagemeasuredinFigure(a)V≈IRiftheoutputimpedanceofthecurrent

4、sourceandtheinputimpedanceofthevoltagemeterarelargeenough.3.1MEASUREMENTOFRESISTANCEMethodsforresistancemeasurement:Deflection(偏差的)method.Sensethedropinvoltageacrosstheresistancetobemeasuredorthecurrentthroughitorboth.Nullmethod.Basedonmeasurementbridges.3.1MEASUREMENTOFRESISTANCEThevoltage

5、output:Itmeansthatv0willconsistofsmallfluctuationsuperimposedonaverylargeoffsetvoltage.3.1MEASUREMENTOFRESISTANCEHowtodeletetheoffsetBysubtractingthedropinvoltageacrossRrdeletetheconstantvoltage.Itcanbeimplementedbyusingtwoidenticalcurrentsources.IfwhereRw1,Rw2andRw3aretheleadsresistance.3.

6、1MEASUREMENTOFRESISTANCEExample3.13.1MEASUREMENTOFRESISTANCEConsiderthesensitivity,say1mV/℃3.1MEASUREMENTOFRESISTANCEAnotherdeflectionmethodTwo-readingmethod.3.2VOLTAGEDIVIDERVoltagedividersiscommonlyusedtomeasurehigh-valueresistance.AssumetheinputresistanceofvoltmetermuchhigherthanR,wehave

7、IfswapRrandR,wehave3.2VOLTAGEDIVIDERExample3.2PowerdissipationimposestheconditionThemaximaldissipationwillhappenwhenR=RrThesensorresistancerangeisfrom1000kΩto3.2VOLTAGEDIVIDERThevoltage-resistancerelationinvoltagedividerisnotlinearbecausethecurrentinthec