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