lecture 17 transducers - read the docs · pressure transducers come in several types • absolute -...
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Transducers
J.R.LeemanandC.Marone
TechniquesofGeoscien8ficExperimenta8on
October18,2016
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Transducersaredevicesthatconvertoneformofenergytoanother-wecommonlyusethemasreal-worldinterfaces
Ac8ve Passive Actuator Bidirec8onal
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TransducerSelec8on
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Whenselec8ngatransducer,youmusthaveawelldefinedapplica8onandconsideranumberofvariables
Image:Wikipedia
• Range• Linearity• Sensi8vity• ResponseTime• Stability• Accuracy• Durability• Cost• SignalCondi8oning
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Rangeisthespanofvaluesoverwhichthetransducerisratedtoperformat
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Linearityishowmuchthesensordivergesfromanideallinearsensoroutput
Image:dataforth.com
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Linearityishowmuchthesensordivergesfromanideallinearsensoroutput
Image:dataforth.com
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Sensi8vityistheslopeoftheoutput-inputcurve
Image:USGS
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Response8meishowlongthetransducertakestoregisterachangeinthephysicalquan8ty
Image:Intech
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Stabilityishowconstanttheoutputofatransducerremainswhenthephysicals8mulusissta8c
Image:Setra
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Precisionreferstothereproducibilityofagivenmeasurement
Accuracyisthemaximumdifferencebetweentherealandindicatedvalues
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Durabilityishowruggedthetransduceristothemeasurementenvironmentitwillbeexposedto
Image:APGSensors
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Signalcondi8oningrequirementscangreatlyimpacttheeaseofuseandcostofagiventransducer
Image:Na8onalInstruments
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OffsetreferstoaDCbiasisagiventransducer’soutput
Image:Na8onalInstruments
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Hysteresisisthetransducer’ssensi8vitytowhichdirec8on(up/down)thephysicalquan8tyischanging
Image:Na8onalInstruments
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Dynamiclinearitydescribeshowwellatransducer’soutputcanfollowarapidlychangingquan8ty
Image:Wikipedia
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Temperature
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Eachtypeoftemperaturesensorhasadifferentoutputcurve
Image:Na8onalInstruments
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ThermocouplesworkonaprinciplecalledtheSeebeckeffect
Image:EEVBlog
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Twodissimilarmetalsarejoinedtomakeatransducer
Image:SterlingSensors
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Therearemanymetalcombina8onsortypesofthermocouples
Image:OMEGA
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Thechallengeisuninten8onaljunc8onsinthesystem
Image:Wikipedia
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Thechallengeisuninten8onaljunc8onsinthesystem
Image:AnalogDevices
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Wemeasurethetemperatureofthe“coldjunc8on”andcompensateforitwithNISTtables
Image:NIST
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Oruseahighorderpolynomialfit
Image:OMEGA
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RTDschangeresistancebasedonthetemperature
Image:Wikipedia/OMEGA
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Mul8plesignalcondi8oningstrategiescanbeuseddependingontherequirementsandcosttradeoff
Image:Wikipedia
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Thermistorsalsochangetheirresistancewithtemperature
Image:Wikipedia
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Condi8oninghappenswithvariousresistorbridge/dividercircuits
Image:Adafruit
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Displacement
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Displacementmeasurementscanbeperformedinabsoluteorrela8vewayswithaWIDEvarietyoftransducers
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Capaci8vedisplacementsensorsareverylownoiseandhighresolu8on
Image:lionprecision.com
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Eddycurrentsensorsarelessexpensiveands8llrela8velylownoise
Image:electronicshub/lionprecision.com
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Pressure
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Pressuretransducerscomeinseveraltypes
• Absolute-measurew.r.t.aperfectvacuum• Gage-measurew.r.t.external(atmospheric)pressure• Vacuum-measurepressuresbelowatmospheric• Differen8al-measuredifferencebetweentwopoints• Sealed-measurew.r.t.asealedfixedpressure
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HousingscanvaryfromPCBmounttoindustrial
Images:Wikipedia/OMEGA
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Pressuresensorsaregenerallyadeflec8onmeasurementbasedtechnology
Image:hydraulicspneuma8cs.com/instrumenta8ontoolbox.com
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Strain
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Straingageschangeresistancebasedupontheirstretching/compression
Image:OU/SensorWiki
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Resistanceofamaterialdependsontheareaofcontact,resis8vity,andlength
Image:Wikipedia
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Sotensionincreasesresistance,compressiondecreasesresistance
Image:Wikipedia
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MoststraingagecircuitsarebasedontheWheatstoneBridge
Image:Na8onalInstruments
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Thegagefactoristherela8vechangeisresistancewithstrain
Image:Na8onalInstruments
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Thequarterbridgeistheleastsensi8ve,butonlyrequiresoneac8veelement
Image:Na8onalInstruments
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Halfbridgesrequireonlytwoac8veelements
Image:Na8onalInstruments
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Thefullbridgeisthemostsensi8vearrangement
Image:Na8onalInstruments
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Image:Na8onalInstruments
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Temperatureplaysaroleaswellthough
Image:Na8onalInstruments
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A“dummygauge”isocenusedfortemperaturecompensa8on
Image:Na8onalInstruments
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Ac8vity:Calculatethetemperaturemeasurementsfromthedataincludedwiththe“ThermistorCalcula8on”ac8vity
Due:10/20
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Assignment:Findsomethingtoaffixstraingaugestoforournextlabac8vity
Due:10/25