中英文翻译传感器共14页Word下载.docx

中英文翻译传感器共14页Word下载.docx

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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