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1、CHAPTER3:SENSORSSECTION3.1:POSITIONALSENSORS3.1LINEARVARIABLEDIFFERENTIALTRANSFORMERS(LVDT)3.1HALLEFFECTMAGNETICSENSORS3.6RESOLVERSANDSYNCHROS3.9INDUCTOSYNS3.13ACCELEROMETERS3.15?iMEMSANGULAR-RATE-SENSINGGYROSCOPE3.19GYROSCOPEDESCRIPTION3.19CORIOLISACCELEROMETERS3.20MOTIONIN2DIMENS

2、IONS3.21CAPACITIVESENSINGS3.23IMMUNITYTOSHOCKANDVIBRATION3.25REFERENCES3.27SECTION3.2:TEMPERATURESENSORS3.29INTRODUCTION3.29SEMICONDUCTORTEMPERATURESENSORS3.31CURRENTOUTTEMPERATURESENSORS3.33CURRENTANDVOLTAGEOUTPUTTEMPERATURESENSORS3.34THERMOCOUPLEPRINCIPLESANDCOLD-JUNCTIONCOMPENSA

3、TION3.38AUTO-ZEROAMPLIFIERFORTHERMOCOUPLEMEASUREMENTS3.45RESISTANCETEMPERATUREDETECTORS(RTDs)3.47THERMISTORS3.52DIGITALOUTPUTTEMPERATURESENSORS3.56THERMOSTATICSWITCHESANDSET-POINTCONTROLLERS3.58MICROPROCESSORTEMPERATUREMONITORING3.61REFERENCES3.64SECTION3.3:CHARGECOUPLEDDEVICES(CCD

4、s)3.65REFERENCES3.68SECTION3.4:BRIDGECIRCUITS3.69INTRODUCTION3.69AMPLIFINGANDLINEARIZINGBRIDGEOUTPUTS3,75DRIVINGREMOTEBRIDGES3.80SYSTEMOFFSETMINIMIZATION3.84REFERENCES3.87SECTION3.5:STRAIN,FORCE,PRESSUREANDFLOWMEASUREMENTS3.89STRAINGAGES3.89BASICLINEARDESIGNSECTION3.5:STRAIN,FORCE,

5、PRESSUREANDFLOWMEASUREMENTS(CONT)SEMICONDUCTORSTRAINGAGES3.92BRIDGESIGNALCONDITIONCIRCUITS3.95REFERENCES3.99SENSORSPOSITIONALSENSORSCHAPTER3:SENSORSSECTION3.1:POSITIONALSENSORSLinearVariableDifferentialTransformers(LVDTs)Thelinearvariabledifferentialtransformer(LVDT)isanaccurateand

6、reliablemethodformeasuringlineardistance.LVDTsfindusesinmodernmachine-tool,robotics,avionics,andcomputerizedmanufacturing.TheLVDT(seeFigure3.1)isaposition-to-electricalsensorwhoseoutputisproportionaltothepositionofamovablemagneticcore.Thecoremoveslinearlyinsideatransformerconsistin

7、gofacenterprimarycoilandtwooutersecondarycoilswoundonacylindricalform.TheprimarywindingisexcitedwithanACvoltagesource(typicallyseveralkHz),inducingsecondaryvoltageswhichvarywiththepositionofthemagneticcorewithintheassembly.Thecoreisusuallythreadedinordertofacilitateattachmenttoanon

8、ferromagneticrodwhichintur