版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
ModernSensors
Lecture3X.WuLecture3BasicIntentReviewsomebackgroundonelectricalmeasurementofsensoroutputsSomedetailsregardingthebehaviorofsimplepassivefiltersandoperationalamplifiersProvideanoverviewofpiezoresistivedevices.SomeexamplesareworkedoutusingthissensingtechniqueAReviewofLecture2CharacteristicsofsensorsTransferfunctionSensitivityDynamicRangeHysteresisTemperatureCoefficientLinearityAccuracyNoiseResolutionBandwidthIntroductiontoSensorsElectronicsTheelectronicswhichgoalongwiththephysicalsensorelementareveryimportant:Limittheperformance,cost,andrangeofapplicabilityIfcarriedoutproperly,thedesigncanimprovethecharacteristicsoftheentiredevice,FocusonbasictechniquesfroprocessingthesignalsmosttypicallyproducedbyasensorMostsensoractlikepassivedeviceResistiveCapacitiveInductiveResistiveSensorCircuitsResistivesensorsobeyOhm’slawHowtogetavoltagesignaloutofthesensor?NeedaconstantcurrentsourceTheeasiestwaytobuildacurrentsource:voltagedividerCondition:loadR>>sensorRShortcoming:smallsignalmightneedsomeamplificationManysensorsrespondtophysicalsignalsbyproducingachangeincapacitanceImpedance:VerymuchlikearesistoratAC,maymeasurecapacitancebybuildingvoltagedividercircuits,useeitherresistororcapacitorastheloadresistanceResistorshavemuchsmallertempcoeff.thancaps:0.3ppm/ºCv.s.200ppm/ºCCapacitancemeasuringcircuitsCapacitancemeasuringcircuitsAsubstantialhassle:providinganACbiasConvertingtheACformicroprocessorinterfaceUseclocksignalorintegratedclock/samplingcircuitModulatedsignalcreatesanopportunityforuseofsomeadvancedsamplingandprocessingtechniquesLock-in:biasthesensorandtriggerthesampling,getthelownoisesignalDisadvantage:clockedswitchinjectnoisechargeintocircuitVeryaccuratecapacitancemeasurementstillrequiresexpensiveprecisioncircuitry
InductancemeasurementcircuitsImpedance:iL->essentiallyresistiveelements
Inductivesensorsgenerallyrequireexpensivetechniquesforthefabricationofthesensormechanicalstructure:3DstructureInexpensivecircuitsarenotofmuchuse,expensiveanyway!LimitationsLimitationstoresistancemeasurementLeadresistace->4-wireconfigurationOutputimpedanceThemeasuringnetworkresistanceplacesalowerlimitonthevalueofaresistancewhichmayacrosstheoutputterminalsAnexample:10Kthermister+1Mload,ifconnectedtoan1Kmeasuringinstrument->outputvoltagewouldbereducedby~90%LimitationstomeasurementofcapacitanceStrayCapacitanceAppearasadditionalcapacitancesinthemeasuringcircuitWiresmovingaboutwithrespecttoground,causingcapacitancefluctuationsTheseeffectsareduetopressure-inducedvibrationsinthepositionsofobjects,referredtoasmicrophonics.Piezoresistivedevices–anoverviewSilicon-basedSpecificadvantagesare:Highsensitivity,>0.5mV/mbarGoodlinearityatconstanttemperature
Abilitytotrackpressurechangeswithoutsignalhysteresis,uptothedestructivelimitStructureandAssemblyPrincipleofOperationDeformationbyappliedpressurecauseshighlevelsofmechanicaltensionattheedgeofdiaphragmSemiconductorresistorsonthefrontsidetransducethistensionintoresistancechangesbymeansofthepiezoresistiveeffect..SpecSheetNominalPressureRange(mbar)1002004001000Sensitivity(mV/mbar)0.50.250.120.06Linearity(%FSO)<1
BridgeResistance(k)5.6
ChipSize(mm3)3x3x1
2.2x2.2x1
DiaphragmSize(mm2)2x21.5x1.51.1x1.10.8x0.8BASICPROCESSINGSTEPSPressureandTemperatureSensorCluster
Diffusion(n-typeandp-type)MetallizationAnisotropicback-sideetching(byusingwellknownchemicalsasTMAHorKOH)Theoreticalbackground:piezoresistanceApiezoresistor:adevicewhichexhibitsachangeinresistancewhenitisstrained.Therearetwocomponentsofthepiezoresistiveeffectthegeometriccomponent
theresistivecomponent.
Thegeometriccomponentofpiezoresistivity:astrainedelementundergoesachangeindimension.Thesechangesincrosssectionalareaandlengthaffecttheresistanceofthedevice.
Strain:DefinitionStrainistheamountofdeformationofabodyduetoappliedforceDimensionless:mm/mmstrainisoftenexpressedasmicrostrain(),whichisx10-6.
Poisson’sRatio
Poisson’sratioWhenabarisstrainedwithauniaxialforce,aphenomenonknownasPoissonStraincausesthegirthofthebar,D,tocontractinthetransversedirection.ThemagnitudeofthistransversecontractionisamaterialpropertyindicatedbyitsPoisson'sRatio:
Definedasthenegativeratioofthestraininthetransversedirection(perpendiculartotheforce)tothestrainintheaxialdirection(paralleltotheforce),Poisson’sratio=eT/eLPoisson'sRatioforsteel,forexample,rangesfrom0.25to0.3
ClassicalDevice:MercuryTube
Anelastictubefilledwithaincompressibleconductivefluid,suchasmercury(really!)R=(Resistivityofmercury)(lengthoftube)/(crosssectionalareaoftube)
Gaugefactor:K=2forliquidstraingaugeWhatdoesitmean?ifaliquidstraingaugeisstretchedby1%,itsresistanceincreasesby2%.
MetalwirebasedstraingaugeMetalwires:stretchingofthewirechangesthegeometryofthewireinawaywhichactstoincreasetheresistance:GaugefactorK=2~4=Poisson’sratioTofindK:MetalwirebasedstraingaugeIssuesindesignwewouldprefertohavealargechangeinresistancetosimplifythedesignoftherestofasensinginstrument,sowegenerallytrytochoosesmalldiameters,smallyoung'smodulus,andlargegagefactorswhenpossible.Theelasticlimitsofmostmaterialsarebelow1%,sowearegenerallytalkingaboutresistancechangeswhichareinthe1%-0.001%range.Clearly,themeasurementofsuchresistancesisnottrivial,andweoftenseeresistancebridgesdesignedtoproducevoltageswhichcanbefedintoamplificationcircuits.WheatstonebridgeTheWheatstonebridgeiswidelyusedforprecisionmeasurementsofresistanceHowtochooseR?Rx=R+RR1=R2=R3V=-R*(V/4R)
MetalWireStrainGauge:thinfilmpattern
Themetallicstraingaugeconsistsofaveryfinewireor,morecommonly,metallicfoilarrangedinagridpattern.ThegridpatternmaximizestheamountofmetallicwireorfoilsubjecttostrainintheparalleldirectionAvarietyofshapesavailableStrainGaugeMeasurementInpractice,thestrainmeasurementsrarelyinvolvequantitieslargerthanafewmillistrain(x10-3).
Tomeasurethestrainrequiresaccuratemeasurementofverysmallchangesinresistance
Forexample,supposeatestspecimenundergoesastrainof500m.Astraingaugewithagaugefactorof2willexhibitachangeinelectricalresistanceofonly2(500x10-6)=0.1%.Fora120gauge,thisisachangeofonly0.12.
FoilStrainGaugeGaugefactor:alittleover2Outputsinglegauge+3dummyresistorsArea:2-10mm2Measurement:Quarter-bridgecircuitIfthenominalresistanceofthestraingaugeisdesignatedasRG,thenthestrain-inducedchangeinresistance,R,canbeexpressedas
R=RG·K·.AssumingthatR1=R2andR3=RG,VO/VEX=-K/4(1+K·/2)4(1+K·/2)termthatindicatesthenonlinearityofthequarter-bridgeoutputwithrespecttostrainTackleTemperatureEffectStraingaugematerialalsorespondtochangesintemperatureMinimizesensitivitytotemperaturebyprocessingthegaugematerialUsingtwostraingaugesinthebridge,theeffectoftemperaturecanbefurtherminimized
IncreaseSensitivityHalf-bridgecircuitFull-bridgeStrainGaugeinIndustryadfSignalConditioningBridgecompletionExcitationRemotesensingAmplificationFilteringOffsetShuntcalibrationStrainGaugeinIndustryPackagedfoilstraingaugeSpecificationsPerformance
Hysteresis<0.02%RatedOutput(R.O.)LongTermStability<0.04%RatedOutput(R.O.)Nonlinearrity<0.1%R.O./YearNonRepeatability<0.01%R.OCreep/CreepRecovery,20minutes<0.05%R.O.Temp.EffectonZeroBalanceStandard<0.03%R.O./°COptional<0.004%R.O./°CTemp.EffectonOutput
Standard<0.025%Reading/°COptional<0.002%Reading/°CAsopposetoP33.2007handbookBridgeCompletionUnlessyouareusingafull-bridgestraingaugesensorwithfouractivegauges,youwillneedtocompletethebridgewithreferenceresistors.Therefore,straingaugesignalconditionerstypicallyprovidehalf-bridgecompletionnetworksconsistingofhigh-precisionreferenceresistors.
OtherIssuesExcitation–typicallyprovideaconstantvoltagesourcetopowerthebridge.3~10Varecommon.
Whileahigherexcitationvoltagegeneratesaproportionatelyhigheroutputvoltage,thehighervoltagecanalsocauselargererrorsbecauseofself-heating..
RemotesensingLongleadneedswirecompensationOtherApplication:DataStorage
A100micron-longpiezoresistivecantileverisdraggedalongapolycarbonatediskat10mm/s,bouncingupanddownasitpassesoversub-micronindentationsinthesurfaceofthedisk.Thisideaisessentiallyahigh-perfo
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 2024版临时居住中介协议3篇
- 2024版全面解读:卫星通信技术研发与服务合同
- 2024版房地产合作开发项目协议细则版B版
- 2024年道路运输安全协议3篇
- 2024模具采购合同标准范本
- 2022-2024年山东中考英语试题汇编:书面表达
- 2024年贷款实践合同样本
- 2024年园林园艺养护管理、绿化工程劳务分包合同样本9篇
- 2024年度房地产销售业绩达成及佣金分配合同范本3篇
- 2024年零售商品寄售协议标准文本一
- 六年级语文上册期末试卷及完整答案
- 人教版(2024)数学七年级上册期末测试卷(含答案)
- 医院护理10s管理
- 北京市东城区2023-2024学年八年级上学期期末生物试题
- ISO28000:2022供应链安全管理体系
- 人教版六年级数学下册全册分层作业设计含答案
- 闭水试验自动计算公式及说明
- “挑战杯”优秀组织奖申报材料
- 小学二年级上册道德与法治教学工作总结
- 超声波治疗仪的临床应用(软组织损伤篇)
- 汽油调和技术
评论
0/150
提交评论