传感器的基础知识中英文对照外文翻译文献Word下载.docx
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传感器的基础知识中英文对照外文翻译文献Word下载.docx
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Theenergy-conversionprocessthattakesplaceisreferredtoastransduction.
Transducersareclassifiedaccordingtothetransductionprincipleinvolvedandtheformofthemeasured.Thusaresistancetransducerformeasuringdisplacementisclassifiedasaresistancedisplacementtransducer.Otherclassificationexamplesarepressurebellows,forcediaphragm,pressureflapper-nozzle,andsoon.
1、TransducerElements
Althoughthereareexception,mosttransducersconsistofasensingelementandaconversionorcontrolelement.Forexample,diaphragms,bellows,straintubesandrings,bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressureorforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmaythenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,orinductance.Suchcombinationofmechanicalandelectricalelementsformelectromechanicaltransducingdevicesortransducers.Similarcombinationcanbemadeforotherenergyinputsuchasthermal.Photo,magneticandchemical,givingthermoelectric,photoelectric,electromaanetic,andelectrochemicaltransducersrespectively.
2、TransducerSensitivity
TherelationshipbetweenthemeasuredandthetransduceroutputsignalisusuallyobtainedbycalibrationtestsandisreferredtoasthetransducersensitivityK1=output-signalincrement/measuredincrement.Inpractice,thetransducersensitivityisusuallyknown,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominput=output-signalincrement/K1.
3、CharacteristicsofanIdealTransducer
Thehightransducershouldexhibitthefollowingcharacteristics
a)
highfidelity-thetransduceroutputwaveformshapebeafaithfulreproductionofthemeasured;
thereshouldbeminimumdistortion.
b)
Thereshouldbeminimuminterferencewiththequantitybeingmeasured;
thepresenceofthetransducershouldnotalterthemeasuredinanyway.
c)
Size.Thetransducermustbecapableofbeingplacedexactlywhereitisneeded.
d)
Thereshouldbealinearrelationshipbetweenthemeasuredandthetransducersignal.
e)
Thetransducershouldhaveminimumsensitivitytoexternaleffects,pressuretransducers,forexample,areoftensubjectedtoexternaleffectssuchvibrationandtemperature.
f)
Thenaturalfrequencyofthetransducershouldbewellseparatedfromthefrequencyandharmonicsofthemeasurand.
4、ElectricalTransducers
Electricaltransducersexhibitmanyoftheidealcharacteristics.Inadditiontheyofferhighsensitivityaswellaspromotingthepossibleofremoteindicationormesdurement.
Electricaltransducerscanbedividedintotwodistinctgroups:
variable-control-parametertypes,whichinclude:
i)resistance
ii)
capacitance
iii)
inductance
iv)
mutual-inductancetypes
Thesetransducersallrelyonexternalexcitationvoltagefortheiroperation.
self-generatingtypes,whichinclude
i)
electromagnetic
ii)thermoelectric
iii)photoemissive
iv)piezo-electrictypes
Theseallthemselvesproduceanoutputvoltageinresponsetothemeasurandinputandtheireffectsarereversible.Forexample,apiezo-electrictransducernormallyproducesanoutputvoltageinresponsetothedeformationofacrystallinematerial;
however,ifanalternatingvoltageisappliedacrossthematerial,thetransducerexhibitsthereversibleeffectbydeformingorvibratingatthefrequencyofthealternatingvoltage.
5、ResistanceTransducers
Resistancetransducersmaybedividedintotwogroups,asfollows:
Thosewhichexperiencealargeresistancechange,measuredbyusingpotential-dividermethods.Potentiometersareinthisgroup.
ii)Thosewhichexperienceasmallresistancechange,measuredbybridge-circuitmethods.Examplesofthisgroupincludestraingaugesandresistancethermometers.
5.1Potentiometers
Alinearwire-woundpotentiometerconsistsofanumberofturnsresistancewirewoundaroundanon-conductingformer,togetherwithawipingcontactwhichtravelsoverthebarwires.Theconstructionprinciplesareshowninfigurewhichindicatethatthewiperdisplacementcanberotary,translational,oracombinationofbothtogiveahelical-typemotion.Theexcitationvoltagemaybeeithera.c.or
d.c.andtheoutputvoltageisproportionaltotheinputmotion,providedthemeasuringdevicehasaresistancewhichismuchgreaterthanthepotentiometerresistance.
Suchpotentiometerssufferfromthelinkedproblemofresolutionandelectricalnoise.Resolutionisdefinedasthesmallestdetectablechangeininputandisdependentonthecross-sectionalareaofthewindingsandtheareaoftheslidingcontact.Theoutputvoltageisthusaserialsofstepsasthecontac
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