傳感器外文翻譯

1、 BasicknowledgeoftransducersAtransducerisadevicewhichconvertsthequantitybeingmeasuredintoanoptical,mechanical,or-morecommonly-electricalsignal.Theenergy-conversionprocessthattakesplaceisreferredtoastransduction.Transducersareclassifiedaccordingtothetransductionprincipleinvolvedandtheformofthemeasure

2、d.Thusaresistancetransducerformeasuringdisplacementisclassifiedasaresistancedisplacementtransducer.Otherclassificationexamplesarepressurebellows,forcediaphragm,pressureflapper-nozzle,andsoon.1、TransducerElementsAlthoughthereareexception,mosttransducersconsistofasensingelementandaconversionorcontrole

3、lement.Forexample,diaphragms,bellows,straintubesandrings,bourdontubes,andcantileversaresensingelementswhichrespondtochangesinpressureorforceandconvertthesephysicalquantitiesintoadisplacement.Thisdisplacementmaythenbeusedtochangeanelectricalparametersuchasvoltage,resistance,capacitance,orinductance.S

4、uchcombinationofmechanicalandelectricalelementsformelectromechanicaltransducingdevicesortransducers.Similarcombinationcanbemadeforotherenergyinputsuchasthermal.Photo,magneticandchemical,givingthermoelectric,photoelectric,electromaanetic,andelectrochemicaltransducersrespectively.2、TransducerSensitivi

5、tyTherelationshipbetweenthemeasuredandthetransduceroutputsignalisusuallyobtainedbycalibrationtestsandisreferredtoasthetransducersensitivityK1=output-signalincrement/measuredincrement.Inpractice,thetransducersensitivityisusuallyknown,and,bymeasuringtheoutputsignal,theinputquantityisdeterminedfrominpu

6、t=output-signalincrement/K1.3、CharacteristicsofanIdealTransducerThehightransducershouldexhibitthefollowingcharacteristicshighfidelity-thetransduceroutputwaveformshapebeafaithfulreproductionofthemeasured;thereshouldbeminimumdistortion.Thereshouldbeminimuminterferencewiththequantitybeingmeasured;thepr

7、esenceofthetransducershouldnotalterthemeasuredinanyway.Size.Thetransducermustbecapableofbeingplacedexactlywhereitisneeded.Thereshouldbealinearrelationshipbetweenthemeasuredandthetransducersignal.Thetransducershouldhaveminimumsensitivitytoexternaleffects,pressuretransducers,forexample,areoftensubject

8、edtoexternaleffectssuchvibrationandtemperature.Thenaturalfrequencyofthetransducershouldbewellseparatedfromthefrequencyandharmonicsofthemeasurand.4、ElectricalTransducersElectricaltransducersexhibitmanyoftheidealcharacteristics.Inadditiontheyofferhighsensitivityaswellaspromotingthepossibleofremoteindi

9、cationormesdurement.Electricaltransducerscanbedividedintotwodistinctgroups:variable-control-parametertypes,whichinclude:resistancecapacitanceinductancemutual-inductancetypesThesetransducersallrelyonexternalexcitationvoltagefortheiroperation.self-generatingtypes,whichincludeelectromagneticthermoelect

10、ricphotoemissivepiezo-electrictypesTheseallthemselvesproduceanoutputvoltageinresponsetothemeasurandinputandtheireffectsarereversible.Forexample,apiezo-electrictransducernormallyproducesanoutputvoltageinresponsetothedeformationofacrystallinematerial;however,ifanalternatingvoltageisappliedacrossthemat

11、erial,thetransducerexhibitsthereversibleeffectbydeformingorvibratingatthefrequencyofthealternatingvoltage.5、ResistanceTransducersResistancetransducersmaybedividedintotwogroups,asfollows:Thosewhichexperiencealargeresistancechange,measuredbyusingpotential-dividermethods.Potentiometersareinthisgroup.Th

12、osewhichexperienceasmallresistancechange,measuredbybridge-circuitmethods.Examplesofthisgroupincludestraingaugesandresistancethermometers.PotentiometersAlinearwire-woundpotentiometerconsistsofanumberofturnsresistancewirewoundaroundanon-conductingformer,togetherwithawipingcontactwhichtravelsoverthebar

13、wires.Theconstructionprinciplesareshowninfigurewhichindicatethatthewiperdisplacementcanberotary,translational,oracombinationofbothtogiveahelical-typemotion.Theexcitationvoltagemaybeeithera.c.ord.c.andtheoutputvoltageisproportionaltotheinputmotion,providedthemeasuringdevicehasaresistancewhichismuchgr

14、eaterthanthepotentiometerresistance.Suchpotentiometerssufferfromthelinkedproblemofresolutionandelectricalnoise.Resolutionisdefinedasthesmallestdetectablechangeininputandisdependentonthecross-sectionalareaofthewindingsandtheareaoftheslidingcontact.Theoutputvoltageisthusaserialsofstepsasthecontactmove

15、sfromonewiretonext.Electricalnoisemaybegeneratedbyvariationincontactresistance,bymechanicalwearduetocontactfriction,andbycontactvibrationtransmittedfromthesensingelement.Inaddition,themotionbeingmeasuredmayexperiencesignificantmechanicalloadingbytheinertiaandfrictionofthemovingpartsofthepotentiomete

16、r.Thewearonthecontactingsurfacelimitsthelifeofapotentiometertoafinitenumberoffullstrokesorrotationsusuallyreferredtointhemanufacturesspecificationasthenumberofcyclesoflifeexpectancy,atypicalvaluebeing20*1000000cycles.TheoutputvoltageV0oftheunloadpotentiometercircuitisdeterminedasfollows.Letresistanc

17、eR1=xi/xt*Rtwherexi=inputdisplacement,xt=maximumpossibledisplacement,Rttotalresistanceofthepotentiometer.ThenoutputvoltageV0=V*R1/(R1+(Rt-R1)=V*R1/Rt=V*xi/xt*Rt/Rt=V*xi/xt.Thisshowsthatthereisastraight-linerelationshipbetweenoutputvoltageandinputdisplacementfortheunloadedpotentiometer.Itwouldseentha

18、thighsensitivitycouldbeachievedsimplybyincreasingtheexcitationvoltageV.however,themaximumvalueofVisdeterminedbythemaximumpowerdissipationPofthefinewiresofthepotentiometerwindingandisgivenbyV=(PRt)1/2.ResistanceStrainGaugesResistancestraingaugesaretransducerswhichexhibitachangeinelectricalresistancei

19、nresponsetomechanicalstrain.Theymaybeofthebondedorunbondedvariety.bondedstraingaugesUsinganadhesive,thesegaugesarebonded,orcemented,directlyontothesurfaceofthebodyorstructurewhichisbeingexamined.Examplesofbondedgaugesarefinewiregaugescementedtopaperbackingphoto-etchedgridsofconductingfoilonanepoxy-r

20、esinbackingasinglesemiconductorfilamentmountedonanepoxy-resinbackingwithcopperornickelleads.Resistancegaugescanbemadeupassingleelementstomeasuringstraininonedirectiononly,oracombinationofelementssuchasrosetteswillpermitsimultaneousmeasurementsinmorethanonedirection.unbondedstraingaugesAtypicalunbond

21、ed-strain-gaugearrangementshowsfineresistancewiresstretchedaroundsupportsinsuchawaythatthedeflectionofthecantileverspringsystemchangesthetensioninthewiresandthusalterstheresistanceofwire.Suchanarrangementmaybefoundincommerciallyavailableforce,load,orpressuretransducers.ResistanceTemperatureTransduce

22、rsThematerialsforthesecanbedividedintotwomaingroups:a)metalssuchasplatinum,copper,tungsten,andnickelwhichexhibitandincreaseinresistanceasthetemperaturerises;theyhaveapositivetemperaturecoefficientofresistance.b)semiconductors,suchasthermistorswhichuseoxidesofmanganese,cobalt,chromium,ornickel.Thesee

23、xhibitlargenon-linearresistancechangeswithtemperaturevariationandnormallyhaveanegativetemperaturecoefficientofresistance.a)metalresistancetemperaturetransducersThesedepend,formanypracticalpurposeandwithinanarrowtemperaturerange,upontherelationshipRl=R0*l+a*(bl-b2)whereacoefficientofresistanceinC-l,a

24、ndROresistanceinohmsatthereferencetemperatureb0=0CatthereferencetemperaturerangeC.Theinternationalpracticaltemperaturescaleisbasedontheplatinumresistancethermometer,whichcoversthetemperaturerange-259.35Cto63O.5C.b)thermistorresistancetemperaturetransducersThermistorsaretemperature-sensitiveresistors

25、whichexhibitlargenon-linerresistancechangeswithtemperaturevariation.Ingeneral,theyhaveanegativetemperaturecoefficient.Forsmalltemperatureincrementsthevariationinresistanceisreasonablylinear;but,iflargetemperaturechangesareexperienced,speciallinearizingtechniquesareusedinthemeasuringcircuitstoproduce

26、alinearrelationshipofresistanceagainsttemperature.Thermistorsarenormallymadeintheformofsemiconductordiscsenclosedinglassvitreousenamel.Sincetheycanbemadeassmallaslmm,quiterapidresponsetimesarepossible.PhotoconductiveCellsThephotoconductivecell,usesalight-sensitivesemiconductormaterial.Theresistanceb

27、etweenthemetalelectrodesdecreaseastheintensityofthelightstrikingthesemiconductorincreases.Commonsemiconductormaterialsusedforphoto-conductivecellsarecadmiumsulphide,leadsulphide,andcopper-dopedgermanium.Theusefulrangeoffrequenciesisdeterminedbymaterialused.Cadmiumsulphideismainlysuitableforvisibleli

28、ght,whereasleadsulphidehasitspeakresponseintheinfra-redregionandis,therefore,mostsuitableforflame-failuredetectionandtemperaturemeasurement.PhotoemissiveCellsWhenlightstrikesthecathodeofthephotoemissivecellaregivensufficientenergytoarrivethecathode.Thepositiveanodeattractstheseelectrons,producingacu

29、rrentwhichflowsthroughresistorRandresultinginanoutputvoltageV.PhotoelectricallygeneratedvoltageV=Ip.RlWhereIp=photoelectriccurrent(A),andphotoelectriccurrentIp=Kt.BWhereKt=sensitivity(A/im),andB=illuminationinput(lumen)Althoughtheoutputvoltagedoesgiveagoodindicationofthemagnitudeofillumination,thece

30、llsaremoreoftenusedforcountingorcontrolpurpose,wherethelightstrikingthecathodecanbeinterrupted.6、CapacitiveTransducersThecapacitancecanthusmadetovarybychangingeithertherelativepermittivity,theeffectivearea,orthedistanceseparatingtheplates.Thecharacteristiccurvesindicatethatvariationsofareaandrelativ

31、epermittivitygivealinearrelationshiponlyoverasmallrangeofspacings.Thusthesensitivityishighforsmallvaluesofd.Unlikethepotentionmeter,thevariable-distancecapacitivetransducerhasaninfiniteresolutionmakingitmostsuitableformeasuringsmallincrementsofdisplacementorquantitieswhichmaybechangedtoproduceadispl

32、acement.7、InductiveTransducersTheinductancecanthusbemadetovarybychangingthereluctanceoftheinductivecircuit.Measuringtechniquesusedwithcapacitiveandinductivetransducers:a)A.C.excitedbridgesusingdifferentialcapacitorsinductors.b)A.C.potentiometercircuitsfordynamicmeasurements.D.C.circuitstogiveavoltag

33、eproportionaltovelocityforacapacitor.Frequency-modulationmethods,wherethechangeofCorLvariesthefrequencyofanoscillationcircuit.Importantfeaturesofcapacitiveandinductivetransducersareasfollows:resolutioninfiniteaccuracy+-0.1%offullscaleisquoteddisplacementranges25*10-6mto10-3mrisetimelessthan50uspossi

34、bleTypicalmeasurandsaredisplacement,pressure,vibration,sound,andliquidlevel.8、LinearVariable-differentialTtransformer9、Piezo-electricTransducers10、ElectromagneticTransducers11、ThermoelectricTransducers12、PhotoelectricCells13、MechanicalTransducersandSensingElements 傳感器的基礎(chǔ)知識傳感器是一種把被測量轉(zhuǎn)換為光的、機械的或者更平常的電信

35、號的裝置。能量轉(zhuǎn)換的過程稱之為換能。按照轉(zhuǎn)換原理和測量形式對傳感器進行分類。用來測量位移的電阻式傳感器被歸為電阻式位移傳感器。分類如壓力波紋管、壓力膜和壓力閥等。1、傳感器元件除特例外，大多數(shù)的傳感器都由敏感元件、轉(zhuǎn)換元件或控制元件組成。如振動膜、波紋管、應(yīng)力管和應(yīng)力環(huán)、低音管和懸臂都是敏感元件，它們對壓力和力作出響應(yīng)把物理量轉(zhuǎn)變成位移。然后位移可以改變電參數(shù)，如電壓、電阻、電容或者感應(yīng)系數(shù)。機械式和電子式元件合并形成機電式傳感設(shè)備或傳感器。這樣的組合可用來輸入能量信號。熱的，光的，磁的和化學(xué)的相互結(jié)合產(chǎn)生的熱電式、光電式、電磁式和電化學(xué)式傳感器。2、傳感器靈敏度通過校正測量系統(tǒng)獲得的被測物理

36、量和傳感器輸出信號的關(guān)系叫做傳感器靈敏度K1,也就是K1=輸出信號增量/測量增量。實際中，傳感器的靈敏度是已知的，并且通過測量輸出信號，輸入量由下式?jīng)Q定，輸入量=輸出信號增量/K1。3、理想傳感器的特性高保真性：傳感器輸出波形應(yīng)該真實可靠地再現(xiàn)被測量，并且失真很小。可測量最小的干擾，任何時候傳感器的出現(xiàn)不能改變被測量。尺寸：傳感器必須能正確地放在所需的地方。被測量和傳感器信號之間應(yīng)該有一個線性關(guān)系。傳感器對外部影響的靈敏度應(yīng)該小，例如壓力傳感器經(jīng)常受到外部振動和溫度的響。傳感器的固有頻率應(yīng)該避開被測量的頻率和諧波。4、電傳感器電傳感器具有許多理想特性。它們不僅實現(xiàn)遠程測量和顯示，還能提供高靈敏

37、度。電傳感器可分為兩大類。a)變參數(shù)型，包括：電阻式；電容式；iii自感應(yīng)式；互感應(yīng)式；這些傳感器的工作依靠外部電壓。b)自激型，包括：電磁式；熱電式；光柵式；壓電式。這些傳感器根據(jù)測量輸入值產(chǎn)生輸出電壓，而且這一過程是可逆的。比如，在一般情況下，壓電式傳感器可根據(jù)晶體材料的變形產(chǎn)生一個輸出電壓；但是，如果在材料上施加一個可變電壓，傳感器可以通過變形或與變電壓同頻率的振動來體現(xiàn)可逆效應(yīng)。5、電阻式傳感器電阻式傳感器可以分為兩大類：那些表現(xiàn)為大電阻變化的物理量可通過分壓方式進行測量，電位器就屬于此類。那些表現(xiàn)為小電阻變化的物理量可通過橋電路方式進行測量，這一類包括應(yīng)變儀和電阻溫度計。電位器繞線式

38、電位器由許多繞在非導(dǎo)體骨架的電阻絲以及滑行在線圈上的觸頭組成。結(jié)構(gòu)原理如圖，觸頭能夠轉(zhuǎn)動、直線式運動或者兩運動合成的螺旋式運動。如果測量設(shè)備的電阻比電位器的電阻大，那么電壓既可以是交流也可以是直流，且輸出電壓與輸入運動成正比。這樣的電位器存在著分辨率和電子噪聲的問題。分辨率是指傳感器能檢測到的最小的輸入增量，分辨率大小取決于線圈與滑動觸頭圍成的面積。因此，輸出電壓為觸頭從一端移到另一端時一系列階躍。電子噪聲可以通過接觸電阻的振動、觸頭摩擦形成的機械磨損以及從敏感元件傳出的觸頭振動產(chǎn)生。另外，測得的運動量可以通過慣性和電位器中移動元件的摩擦獲得較大的機械載荷。觸頭表面的磨損將電位器的壽命限制為多少轉(zhuǎn)。通常指的是生產(chǎn)商在說明書中提及的“壽命轉(zhuǎn)數(shù)”，一個典型值為20*1000000轉(zhuǎn)。空載電位器電路的輸出電壓V0由下式?jīng)Q定：設(shè)電阻R1=xi/xt*Rt,其中xi為輸入位移，xt為最大可能位移，Rt為電位器的電阻。那么輸入電壓V0=V*R1/(R1+(Rt-R1)=V*R1/Rt=V*xi/xt*Rt/Rt=V*xi/xt上式表明，對于空載電位器輸出電壓和輸入位移呈直線關(guān)系。通過提高激勵電壓V可以獲得高的靈敏度。但是，V的最大值由電位器線圈金屬絲的功率損耗P決定，即V=(PRt)l/2。電阻應(yīng)變儀電阻應(yīng)變儀是由機械應(yīng)變產(chǎn)生電阻變化的傳感