传感器外文翻译

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 传感器的基础知识传感器是一种把被测量转换为光的、机械的或者更平常的电信

35、号的装置。能量转换的过程称之为换能。按照转换原理和测量形式对传感器进行分类。用来测量位移的电阻式传感器被归为电阻式位移传感器。分类如压力波纹管、压力膜和压力阀等。1、传感器元件除特例外，大多数的传感器都由敏感元件、转换元件或控制元件组成。如振动膜、波纹管、应力管和应力环、低音管和悬臂都是敏感元件，它们对压力和力作出响应把物理量转变成位移。然后位移可以改变电参数，如电压、电阻、电容或者感应系数。机械式和电子式元件合并形成机电式传感设备或传感器。这样的组合可用来输入能量信号。热的，光的，磁的和化学的相互结合产生的热电式、光电式、电磁式和电化学式传感器。2、传感器灵敏度通过校正测量系统获得的被测物理

36、量和传感器输出信号的关系叫做传感器灵敏度K1,也就是K1=输出信号增量/测量增量。实际中，传感器的灵敏度是已知的，并且通过测量输出信号，输入量由下式决定，输入量=输出信号增量/K1。3、理想传感器的特性高保真性：传感器输出波形应该真实可靠地再现被测量，并且失真很小。可测量最小的干扰，任何时候传感器的出现不能改变被测量。尺寸：传感器必须能正确地放在所需的地方。被测量和传感器信号之间应该有一个线性关系。传感器对外部影响的灵敏度应该小，例如压力传感器经常受到外部振动和温度的响。传感器的固有频率应该避开被测量的频率和谐波。4、电传感器电传感器具有许多理想特性。它们不仅实现远程测量和显示，还能提供高灵敏

37、度。电传感器可分为两大类。a)变参数型，包括：电阻式；电容式；iii自感应式；互感应式；这些传感器的工作依靠外部电压。b)自激型，包括：电磁式；热电式；光栅式；压电式。这些传感器根据测量输入值产生输出电压，而且这一过程是可逆的。比如，在一般情况下，压电式传感器可根据晶体材料的变形产生一个输出电压；但是，如果在材料上施加一个可变电压，传感器可以通过变形或与变电压同频率的振动来体现可逆效应。5、电阻式传感器电阻式传感器可以分为两大类：那些表现为大电阻变化的物理量可通过分压方式进行测量，电位器就属于此类。那些表现为小电阻变化的物理量可通过桥电路方式进行测量，这一类包括应变仪和电阻温度计。电位器绕线式

38、电位器由许多绕在非导体骨架的电阻丝以及滑行在线圈上的触头组成。结构原理如图，触头能够转动、直线式运动或者两运动合成的螺旋式运动。如果测量设备的电阻比电位器的电阻大，那么电压既可以是交流也可以是直流，且输出电压与输入运动成正比。这样的电位器存在着分辨率和电子噪声的问题。分辨率是指传感器能检测到的最小的输入增量，分辨率大小取决于线圈与滑动触头围成的面积。因此，输出电压为触头从一端移到另一端时一系列阶跃。电子噪声可以通过接触电阻的振动、触头摩擦形成的机械磨损以及从敏感元件传出的触头振动产生。另外，测得的运动量可以通过惯性和电位器中移动元件的摩擦获得较大的机械载荷。触头表面的磨损将电位器的寿命限制为多少转。通常指的是生产商在说明书中提及的“寿命转数”，一个典型值为20*1000000转。空载电位器电路的输出电压V0由下式决定：设电阻R1=xi/xt*Rt,其中xi为输入位移，xt为最大可能位移，Rt为电位器的电阻。那么输入电压V0=V*R1/(R1+(Rt-R1)=V*R1/Rt=V*xi/xt*Rt/Rt=V*xi/xt上式表明，对于空载电位器输出电压和输入位移呈直线关系。通过提高激励电压V可以获得高的灵敏度。但是，V的最大值由电位器线圈金属丝的功率损耗P决定，即V=(PRt)l/2。电阻应变仪电阻应变仪是由机械应变产生电阻变化的传感