中英文翻译传感器共14页.docx
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中英文翻译传感器共14页
传感器的基础知识
Basicknowledgeoftransducers
Atransducerisadevicewhichconvertsthequantitybeingmeasuredintoan
optical,mechanical,or-morecommonly-electricalsignal.Theenergy-conversionprocess
thattakesplaceisreferredtoastransduction.Transducersareclassifiedaccordingtothe
transductionprincipleinvolvedandtheformofthemeasured.Thusaresistance
transducerformeasuringdisplacementisclassifiedasaresistancedisplacement
transducer.Otherclassificationexamplesarepressurebellows,forcediaphragm,pressure
flapper-nozzle,andsoon.
1.TransducerElements
Althoughthereareexception,mosttransducersconsistofasensingelementanda
conversionorcontrolelement.Forexample,diaphragms,bellows,straintubesandrings,
bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressure
orforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmay
thenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,or
inductance.Suchcombinationofmechanicalandelectricalelementsform
electromechanicaltransducingdevicesortransducers.Similarcombinationcanbemade
forotherenergyinputsuchasthermal.Photo,magneticandchemical,giving
thermoelectric,photoelectric,electromaanetic,andelectrochemicalrespectively.
2.TransducerSensitivity
Therelationshipbetweenthemeasuredandthetransduceroutputsignalisusually
obtainedbycalibrationtestsandisreferredtoasthetransducersensitivityKl=output-
signalincrement/measuredincrement.Inpractice,thetransducersensitivityisusually
known,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominput=
output-signalincrement/Kl.
3.CharacteristicsofanIdealTransducer
Thehightransducershouldexhibitthefollowingcharacteristics.
ahighfidelity-thetransduceroutputwaveformshapebeafaithful
reproductionofthemeasured;thereshouldbeminimumdistortion.bThereshould
beminimuminterferencewiththequantitybeingmeasured;thepresenceofthe
transducershouldnotalterthemeasuredinanyway.
cSize.Thetransducermustbecapableofbeingplacedexactlywhereitisneeded.
dThereshouldbealinearrelationshipbetweenthemeasuredandthetransducer
signal.
eThetransducershouldhaveminimumsensitivitytoexternaleffects,pressure
transducers,forexample,areoftensubjectedtoexternaleffectssuchvibrationand
temperature
fThenaturalfrequencyofthetransducershouldbewellseparatedfromthe
frequencyandharmonicsofthemeasurand.
4.ElectricalTransducers
Electricaltransducersexhibitmanyoftheidealcharacteristics.Inadditiontheyoffer
highsensitivityaswellaspromotingthepossibleofremoteindicationor
mesdurement.Electricaltransducerscanbedividedintotwodistinctgroups:
avariable-control-parametertypes,whichinclude:
iresistance
iicapacitance
iiiinductance
ivmutual-inductancetypes
Thesetransducersallrelyonexternalexcitationvoltagefortheiroperation.
bself-generatingtypes,whichinclude
ielectromagnetic
iiphotoemissive
ivpiezo-electrictypes
Theseallthemselvesproduceanoutputvoltageinresponsetothemeasurandinput
andtheireffectsarereversible.Forexample,apiezo-electrictransducernormally
producesanoutputvoltageinresponsetothedeformationofacrystallinematerial;
however,ifanalternatingvoltageisappliedacrossthematerial,thetransducerexhibits
the
reversibleeffectbydeformingorvibratingatthefrequencyofthealternating
voltage.
5.ResistanceTransducers
Resistancetransducersmaybedividedintotwogroups,asfollows:
iThosewhich
experiencealargeresistancechange,measuredbyusingpotential-dividermethods.
Potentiometersareinthisgroup.
iiThosewhichexperienceasmallresistancechange,measuredbybridge-circuit
methods.Examplesofthisgroupincludestraingaugesandresistancethermometers.
5.1Potentiometers
Alinearwire-woundpotentiometerconsistsofanumberofturnsresistancewire
woundaroundanon-conductingformer,togetherwithawipingcontactwhichtravels
overthebarwires.Theconstructionprinciplesareshowninfigurewhichindicatethatthe
wiperdisplacementcanberotary,translational,oracombinationofbothtogivea
helical-typemotion.Theexcitationvoltagemaybeeithera.c.ord.c.andtheoutput
voltageisproportionaltotheinputmotion,providedthemeasuringdevicehasaresistance
whichismuchgreaterthanthepotentiometerresistance.Suchpotentiometerssufferfrom
thelinkedproblemofresolutionandelectricalnoise.
Resolutionisdefinedasthesmallestdetectablechangeininputandisdependenton
thecross-sectionalareaofthewindingsandtheareaoftheslidingcontact.Theoutput
voltageisthusaserialsofstepsasthe