《电子信息专业英语》-Chapter 3 Sensors

Text1CircuitElementsandParametersAnelectriccircuit(ornetwork)isaninterconnectionofphysicalelectricaldevices.Thepurposeofelectriccircuitsistodistributeandconvertenergyintosomeotherforms.Accordingly，thebasiccircuitcomponentsareanenergysource(orsources)，anenergyconverter(orconverters)andconductorsconnectingthem.Anenergysource(aprimaryorsecondarycell，ageneratorandthelike)convertschemical，mechanical，thermalorsomeotherformsofenergyintoelectricenergy.Anenergyconverter，alsocalledload(suchasalamp，heatingapplianceorelectricmotor)，convertselectricenergyintolight，heat,mechanicalworkandsoon.下一页返回Text1CircuitElementsandParametersEventsinacircuitcanbedefinedintermsofe.m.f.(orvoltage)andcurrent.Whenelectricenergyisgenerated，transmittedandconvertedundersuchconditionsthatthecurrentsandvoltagesinvolvedremainconstantwithtime，oneusuallyspeaksofdirect-current(D.C.)circutts.Withtime-invariantcurrentsandvoltages，themagneticandelectricfieldsoftheassociatedelectricplantarealsotime-invariant.Thisisthereasonwhynoe.m.f.sofself-(ormutual-)inductionappearsinD.C.circuits，norarethereanydisplacementcurrentsinthedielectricsurroundingtheconductors.下一页返回上一页Text1CircuitElementsandParametersFig.3-1showsinsimplifiedformahypotheticalcircuitwithastoragebatteryasthesourceandalampastheload.Theterminalsofthesourceandloadareinterconnectedbyconductors(generallybutnotalwayswires).Asisseen，thesource，loadandconductorsformaclosedconductingpath.Thee.m.f.ofthesourcecausesacontinuousandunidirectionalcurrenttocirculateroundthisclosedpath.Thissimplecircuitmadeupofasource，aloadandtwowiresisseldom，ifever，metwithinpractice.Practicalcircuitsmaycontainalargenumberofsourcesandloadsinterconnectedinavarietyofways.下一页返回上一页Text1CircuitElementsandParametersTosimplifyanalysisofactualcircuits，itisusualtoshowthemsymbolicallyinadiagramcalledacircuitdiagram，whichisinfactafictitiousor,rather,idealizedmodelofanactualcircuitofnetwork.Suchadiagramconsistsofinterconnectedsymbolscalledcircuitelementsorcircuitparameters.TwoelementsarenecessarytorepresentprocessesinaD.C.circuit.Theseareasourceofe.m.f.Eandofinternal(or“source")resistanceRs，andtheloadresistance(whichincludestheresistanceoftheconductors)R(Fig.3-2).下一页返回上一页Text1CircuitElementsandParametersWhateveritsorigin(thermal，contact，etc.)，thesourcee.m.f.E(Fig.3-2(a))isnumericallyequaltothepotentialdififierencebetweenterminals1and2withtheexternalcircuitopen，thatis，whenthereisnocurrentflowingthroughthesource:(3.1)Thesourcee.m.fisdirectedfromtheterminalatalowerpotentialtothatatahigherone.Ondiagram，thisisshownbyarrows.Whenaloadisconnectedtothesourceterminals(Thecircuitisthensaidtobeloaded)andthecircuitisclosed，acurrentbeginstoflowroundit.下一页返回上一页Text1CircuitElementsandParametersNowthevoltagebetweensourceterminals1and2(calledtheterminalvoltage)isnotequaltoitse.m.f,becauseofthevoltagedropVsinsidethesource,thatis,acrossthesourceresistanceRs:Vs=RsIFig.3-3showsatypicalso-calledexternalcharacteristicofaloadedsource(henceanothernameistheloadcharacteristicofasource).Asisseen,increaseofcurrentfiromzerotoI≈IE,causestheterminalvoltageofthesourcetodecreaselinearly:下一页返回上一页Text1CircuitElementsandParametersInotherwords，thevoltagedropVsacrossthesourceresistancerisesinproportiontothecurrent.Thisgoesonuntilacertainlimitisreached.Thenasthecurrentkeepsrising,theproportionalitybetweenitsvalueandthevoltagedropacrossthesourceisupset,andtheexternalcharacteristicceasestobelinear.Thisdecreaseinvoltagemaybecausedbyareductioninthesourcevoltage,byanincreaseintheinternalresistance,orboth.Thepowerdeliveredbyasourceisgivenbytheequality:PS=EI(3.2)wherePSisthepowerofthesource.下一页返回上一页Text1CircuitElementsandParametersItseemsrelevantatthispointtodispelacommonmisconceptionaboutpower.Thusonemayhearthatpowerisgenerated，delivered，consumed，transmitted，lost，etc.Inpointoffact,however,itisenergythatcanbegenerated，delivered，consumed，transmittedorlost.Powerisjusttherateofenergyinputorconversion，thatis，thequantityofenergygenerated，delivered,transmitted，etc.perunittime.So，itwouldbemorecorrecttousethetermenergyinsteadofpowerintheabovecontext.Yet，wewouldratherfallinwiththetradition.下一页返回上一页Text1CircuitElementsandParametersTheloadresistanceR(Fig.3-2(b)),asageneralizedcircuitelement，givesanideaabouttheconsumptionofenergy，thatis，theconversionofelectricenergyintoheat,andisdefinedasP=RI2(3.3)Inthegeneralcase，theloadresistancedependssolelyonthecurrentthroughtheload，whichinfactissymbolizedbythefunctionR(I).ByOhm'sLaw，thevoltageacrossaresistanceis:v=RI(3.4)Incircuitanalysis，useisoftenmadeofthereciprocaloftheresistance，termedtheconductance，whichisdefinedasg=1/R.下一页返回上一页Text1CircuitElementsandParametersInpracticalproblems，oneoftenspecifiesthevoltageacrossaresistanceasafunctionofcurrentV(I)，ortheinverserelationI(V)，whichhascometobeknownasvolt-amperecharacteristics.Fig.3-4showsvolt-amperecurvesforametal-filamentlampV1(I)，andforacarbonfilamentlampV2(I).Asisseen，therelationbetweenthevoltageandthecurrentineachlampisotherthanlinear.Theresistanceofthemetal-filamentlampincreases，andthatofthecarbonfilamentlampdecreaseswithincreaseofcurrent.Electriccircuitscontainingcomponentswithnon-linearcharacteristicarecallednon-linear.下一页返回上一页Text1CircuitElementsandParametersIfthee.m.f.andinternalresistancesofsourcesandassociatedloadresistancesareassumedtobeindependentofthecurrentandvoltage，respectively，theexternalcharacteristicV(I)ofthesourcesandthevolt-amperecharacteristicV1(I)oftheloadswillbelinear(Fig.3-5).Electriccircuitscontainingonlyelementswithlinearcharacteristicarecalledlinear.Mostpracticalcircuitsmaybeclassedaslinear.Therefore，astudyintothepropertiesandanalysisoflinearcircuitsisofboththeoreticalandappliedinterest.下一页返回上一页NOTES1.Whenelectricenergyisgenerated，transmittedandconvertedundersuchconditionsthatthecurrentsandvoltagesinvolvedremainconstantwithtime，oneusuallyspeaksofdirect-current(D.C.)circuits.这是一个主从复合句，"when...time”是一个由when引导的时间状语从句，"one...circuits”是整个句子的主句。只是在从句中又包含了一个由suchthat引导的结果状语从句，该从句的主语是thecurrentsandvoltages,involved是它的后置定语，意为“牵涉到的，涉及的”，remain是系动词做谓语，结果状语从句是系表结构。因此整句译成“当电能在产生、传输和转换时，在相关的电流和电压随着时间变化而保持恒定时，我们可以称之为直流电路。”下一页返回上一页NOTES可以看到，结果状语从句并未译出。在此采用了翻译方法中的“转换法”，将其转译成条件状语从句，这样中文的译文更地道。2.Theterminalsofthesourceandloadareinterconnectedbyconductors(generallybutnotalwayswires).句中的generallybutnotalwayswires=generallywires,butnotalwayswires,意为“通常这种导体是导线，但少数情况下也有例外”。3.Thissimplecircuitmadeupofasource,aloadandtwowiresisseldom,ifever,metwithinpractice.=Thissimplecircuitmadeupofasource,aloadandtwowiresisseldommetwithinpractice,ifitisevermetwithinpracticesometimes.下一页返回上一页NOTES意为“这种由一个电源、一个负荷和两段导线组成的简单电路在实践中即使有时能遇到，也是很少见的”。4.Whateveritsorigin(thermal，contact，etc.)，thesourcee.m.f.E(Fig.3-2(a))isnumericallyequaltothepotentialdifferencebetweenterminals1and2withtheexternalcircuitopen.句中的betweenterminals1and2说明difference，而withtheexternalcircuitopen则修饰terminals1and2，因此此句译为“无论图3-2(a)中的电动势E的原动力是什么(即不论是热的、机械的，还是其他什么形式)，其大小就等于1和2两端之间的开路电压。”下一页返回上一页ReadingIntroductionTheinsulatedgatebipolartransistor(IGBT)，whichwasintroducedintheearly1980s，hasbecomeasuccessfuldevicebecauseofitssuperiorcharacteristics.TheIGBTisathree-terminalpowersemiconductorswitchusedtocontrolelectricalenergyandmanynewapplicationswouldnotbeeconomicallyfeasiblewithoutIGBTs.PriortotheadventoftheIGBT，powerbipolarjunctiontransistors(BJTs)andpowermetaloxidefieldeffecttransistors(MOSFETs)werewidelyusedinlowtomediumpowerandhighfrequencyapplications，wherethespeedofgateturn-offthyristorswasnotadequate.下一页返回上一页ReadingPowerBJTshavegoodon-statecharacteristicsbutlongswitchingtimesespeciallyatturn-off.Theyarecurrentcontrolleddeviceswithsmallcurrentgainbecauseofhighlevelinjectioneffectsandwidebasewidthrequiredtopreventreach-throughbreakdownforhighblockingvoltagecapability.Therefore，theyrequirecomplexbase-drivecircuitstoprovidethebasecurrentduringon-state，whichincreasesthepowerlossinthecontrolelectrode.Ontheotherhand，powerMOSFETsarevoltage-controlleddevices，whichrequireverysmallcurrentduringtheswitchingperiodandhencehavesimplegate-driverequirements.下一页返回上一页ReadingPowerMOSFETsaremajoritycarrierdevices，whichexhibitveryhighswitchingspeeds.However，theunipolarnatureofthepowerMOSFETscausesinferiorconductioncharacteristicsasthevoltageratingisincreasedabove200V.Therefore，theiron-stateresistanceincreaseswithincreasingbreakdownvoltage.Furthermore，asthevoltageratingincreases，theinherentbodydiodeshowsinferiorreverserecoverycharacteristics，whichleadstohigherswitchinglosses.Inordertoimprovethepowerdeviceperformanceitisadvantageoustohavethelowon-stateresistanceofpowerBJTswithaninsulatedgateinputsimilartothatofapowerMOSFET.下一页返回上一页ReadingTheDarlingtonconfigurationofthetwodeviceshassuperiorcharacteristicsascomparedtothetwodiscretedevices.ThishybriddevicecouldbegatedinthesamewayasapowerMOSFETwithlowon-stateresistancebecausemostoftheoutputcurrentishandledbytheBJT.BecauseofthelowcurrentgainofBJT，aMOSFETofequalsizeisrequiredasadriver.AmorepowerfulapproachtoobtainthemaximumbenefitsoftheMOSgatecontrolandbipolarcurrentconductionistointegratethephysicsofMOSFETandBJTwithinthesamesemiconductorregion.ThisconceptgaverisetothecommerciallyavailableIGBTswithsuperioron-statecharacteristics，goodswitchingspeedandexcellentsafeoperatingarea.下一页返回上一页ReadingComparedtopowerMOSFETstheabsenceoftheintegralbodydiodecanbeconsideredasanadvantageordisadvantagedependingontheswitchingspeedandcurrentrequirements.Anexternalfast-recoverydiodeoradiodeinthesamepackagecanbeusedforspecificapplications.TheIGBTsarereplacingMOSFETsinhigh-voltageapplicationswithlowerconductionlosses.Theyhaveon-statevoltageandcurrentdensitycomparabletoapowerBJTwithhigherswitchingfrequency.Althoughtheyexhibitfastturn-on,theirturn-offisslowerthanaMOSFETbecauseofcurrentfalltime.Also，IGBTshaveconsiderablylesssiliconareathansimilarratedpowerMOSFETs.下一页返回上一页ReadingTherefore，byreplacingpowerMOSFETswithIGBTs，theefficiencyisimprovedandcostisreduced.Additionally，IGBTisknownasaconductivity-modulatedFET(COMFET)，insulatedgatetransistor(IGT)，andbipolar-modeMOSFET.Assoft-switchingtopologiesoffernumerousadvantagesoverthehard-switchingtopologies，theiruseisincreasingintheindustry.Byuseofsoft-switchingtechniquesIGBTscanoperateatfrequenciesuptohundredsofkilohertz.However，IGBTsbehavedifferentlyundersoft-switchingconditioncomparedtotheirbehaviorunderhard-switchingconditions.下一页返回上一页ReadingTherefore，thedevicetrade-offsinvolvedinsoft-switchingcircuitsaredifferentthanthoseinthehard-switchingcase.ApplicationofIGBTsinhigh-powerconverterssubjectsthemtohigh-transientelectricalstresssuchasshort-circuitandturn-offunderclampedinductiveload，andthereforerobustnessofIGBTsunderstressconditionsisanimportantrequirement.Traditionally，therehasbeenlimitedinteractionbetweendevicemanufacturersandpowerelectroniccircuitdesigners.Therefore，theshortcomingsofdevicereliabilityareobservedonlyafterthedevicesareusedinactualcircuits.下一页返回上一页ReadingThissignificantlyslowsdowntheprocessofpowerelectronicsystemoptimization.However，thedevelopmenttimecanbesignificantlyreducedifallissuesofdeviceperformanceandreliabilityaretakenintoconsiderationatthedesignstage.Ashighstressconditionsarequitefrequentincircuitapplications，itisextremelycostefficientandpertinenttomodeltheIGBTperformanceundertheseconditions.However,developmentofthemodelcanfollowonlyafterthephysicsofdeviceoperationunderstressconditionsimposedbythecircuitisproperlyunderstood.下一页返回上一页ReadingPhysicallybasedprocessanddevicesimulationsareaquickandcheapwayofoptimizingtheIGBT.Theemergenceofmixed-modecircuitsimulatorsinwhichsemiconductorcarrierdynamicsisoptimizedwithintheconstraintsofcircuitlevelswitchingisakeydesigntoolforthistask.返回上一页

Text2Voltage/FrepuencyConvertersTheuseofvoltage/frequency(V/F)convertersindigitalvoltmetersanddataloggershasledtothedevelopmentofawiderangeofunitswhichareavailableasmodularunitsorasintegratedcircuits.Thishasledtotheiruseinanumberoftransducersandinstrumentationsystemswhereananaloguevoltagecanbedevelopedthatisproportionaltoameasuredparameter.Theseunitscanberelativelylowincostandprovideahighlyaccuratemeansofdatatransmissionthatrequirestheminimumofsignalconditioningatthereceivingend.Asignaltransmittedintheformofafrequencyis，ineffect，aserialdigitalsignalandthereforehastheadvantagesofdigitalsystemsbutrequiresonlytwowiresfordatatransmission.下一页返回

Text2Voltage/FrepuencyConvertersInfact,ithasanadvantageoverordinaryserialdigitaldatatransmissionbecauseitisselfclockinganddoesnotneedsynchronization.Afurtheradvantageisthatthetechniqueiseasilyadaptabletothoseinstallationswherecompletephysicaland/orelectricalisolationisrequiredbetweenthetransducerandtheactualcounterorotherpartsofthesystem.ThisisillustratedinFig.3-6，inwhichatransducerandlow-poweredV/Fconverterarecouples'outputflashesatfrequencydevelopedbytheV/Fconverter.Thislightemissionisdetectedbylight-sensitivecellsandtheresultingsignalshapedandcounted,orcomputedforthemeasurement.下一页返回上一页

Text2Voltage/FrepuencyConvertersTheLEDandlightsensitivecellareavailableasasingleunitknownasanLEDopticalcoupler.Thisformofisolationcanbeofvalueinsomemedicalinstruments.Thelow-powered“frontend”canbeoperatedfromadrycellandisthereforecompletelyisolatedfromtheremainderoftheequipmentwhichcouldrequireamainssupply.Themethodcanalsobeofvaluewhereatransducerisrequiredtoworkinhermeticallysealedareas，inwhichcasethedatacanbetransmittedacrossatransparentwindowbyaseparateLEDwithsuitablescreeningforthelight-sensitivecell.下一页返回上一页

Text2Voltage/FrepuencyConvertersThebasiccircuitofaV/Fconverter,whichproducespulsesproportionaltovoltageinput，isshowninFig.3-7.Inthiscircuit，eachpulsewillhavethesamewidthandheight，astheyrepresenttheoutputoftheone-shotgenerator.Thesimplecircuitrequiresconsiderablemodificationtoproducealinearoutputwithminimumchangesinpulserate，duetotemperaturechanges.Inparticular,thecapacitordischargecircuitcallsforconsiderablecircuitryand，therefore，anumberofalternativetechniqueshavebeenadopted.下一页返回上一页

Text2Voltage/FrepuencyConvertersThemaindisadvantageofV/Fconverter，whenusedaspartofadigitaltransducersystem，isthetimeneededtotakeareading.Ifacountofpulseistobemade，theaccuracycanonlybemaintainediftheperiodissufficientlylongtoproducetherequiredresolution.Forexample，fora13bitdigitalnumber,over4000pulserate，thecountingperiodcouldbetoolong.Thetimecan，however,bekeptwithinreasonablelimitsbybiasingtheinputsignal.Bymeasuringthetimebetweenpulsesthisproblemisnotsoacute，butsomeoftheadvantagesoftheV/Ftechniquearelost，i.e.thehighnoiserejectionthatthecountingmethodintroduces.下一页返回上一页

Text2Voltage/FrepuencyConvertersHighnoiserejectioniscausedbytheintegratingactionoverthecountingperiod，whichproducesameasureofaveragingoftheinputsignalduringthisperiod，andanycommonmodenoisewillnormallyhavelittleoveralleffect.Ifthesamplingperiodforacountissynchronizedwiththemainssupply，thenoiseproducedatthisfrequency，anditsharmonics，isalmostaveragedout.However，noiseandrippleontheanalogueinputmayalterthetimingoftheindividualpulses，andmeasurementoftimebetweenpulseswillnowincludethenoiseelement.下一页返回上一页ReadingSensorAsensorisadevicethatmeasuresaphysicalquantityandconvertsitintoasignalwhichcanbereadbyanobserverorbyaninstrument.Forexample，amercurythermometerconvertsthemeasuredtemperatureintoexpansionandcontractionofaliquidwhichcanbereadonacalibratedglasstube.Athermocoupleconvertstemperaturetoanoutputvoltagewhichcanbereadbyavoltmeter.Foraccuracy，allsensorsneedtobecalibratedagainstknownstandards.下一页返回上一页ReadingSensorsareusedineverydayobjectssuchastouch-sensitiveelevatorbuttonsandlampswhichdimorbrightenbytouchingthebase.Therearealsoinnumerableapplicationsforsensorsofwhichmostpeopleareneveraware.Applicationsincludecars，machines，aerospace，medicine，manufacturingandrobotics.Asensor'ssensitivityindicateshowmuchthesensor'soutputchangeswhenthemeasuredquantitychanges.Forinstance，ifthemercuryinathermometermoves1cmwhenthetemperaturechangesby10℃，thesensitivityis1cm/℃.Sensorsthatmeasureverysmallchangesmusthaveveryhighsensitivities.下一页返回上一页ReadingSensorsalsohaveanimpactonwhattheymeasure;forinstance，aroomtemperaturethermometerinsertedintoahotcupofliquidcoolstheliquidwhiletheliquidheatsthethermometer.Sensorsneedtobedesignedtohaveasmalleffectonwhatismeasured，makingthesensorsmalleroftenimprovesthisandmayintroduceotheradvantages.TechnologicalprogressallowsmoreandmoresensorstobemanufacturedonamicroscopicscaleasmicrosensorsusingMEMStechnology.Inmostcases，amicrosensorreachesasignificantlyhigherspeedandsensitivitycomparedwithmacroscopicapproaches.下一页返回上一页ReadingAgoodsensorobeysthefollowingrules:Issensitivetothemeasuredproperty?Isinsensitivetoanyotherproperty?Doesnotinfluencethemeasuredproperty?Idealsensorsaredesignedtobelinear.Theoutputsignalofsuchasensorislinearlyproportionaltothevalueofthemeasuredproperty.Thesensitivityisthendefinedastheratiobetweenoutputsignalandmeasuredproperty.Forexample，ifasensormeasurestemperatureandhasavoltageoutput，thesensitivityisaconstantwiththeunit[V/K];thissensorislinearbecausetheratioisconstantatallpointsofmeasurement.下一页返回上一页ReadingSensorDeviationsIfthesensorisnotideal，severaltypesofdeviationscanbeobserved:Thesensitivitymayinpracticedifferfromthevaluespecified.Thisiscalledasensitivityerror，butthesensorisstilllinear.Sincetherangeoftheoutputsignalisalwayslimited，theoutputsignalwilleventuallyreachaminimumormaximumwhenthemeasuredpropertyexceedsthelimits.Thefullscalerangedefinesthemaximumandminimumvaluesofthemeasuredproperty.Iftheoutputsignalisnotzerowhenthemeasuredpropertyiszero，thesensorhasanoffsetorbias.Thisisdefinedastheoutputofthesensoratzeroinput.下一页返回上一页ReadingIfthesensitivityisnotconstantovertherangeofthesensor，thisiscallednonlinearity.Usuallythisisdefinedbytheamounttheoutputdiffersfromidealbehavioroverthefullrangeofthesensor,oftennotedasapercentageofthefullrange.Ifthedeviationiscausedbyarapidchangeofthemeasuredpropertyovertime，thereisadynamicerror.Often，thisbehaviorisdescribedwithaBodeplotshowingsensitivityerrorandphaseshiftasfunctionofthefrequencyofaperiodicinputsignal.Iftheoutputsignalslowlychangesindependentofthemeasuredproperty，thisisdefinedasdrift.下一页返回上一页ReadingLongtermdriftusuallyindicatesaslowdegradationofsensorpropertiesoveralongperiodoftime.Noiseisarandomdeviationofthesignalthatvariesintime.Hysteresisisanerrorcausedwhenthemeasuredpropertyreversesdirection，butthereissomefinitelagintimeforthesensortorespond，creatingadifferentoffseterrorinonedirectionthanintheother.Ifthesensorhasadigitaloutput，theoutputisessentiallyanapproximationofthemeasuredproperty.Theapproximationerrorisalsocalleddigitizationerror.Ifthesignalismonitoreddigitally，limitationofthesamplingfrequencyalsocancauseadynamicerror.下一页返回上一页ReadingThesensormaytosomeextentbesensitivetopropertiesotherthanthepropertybeingmeasured.Forexample，mostsensorsareinfluencedbythetemperatureoftheirenvironment.Allthesedeviationscanbeclassifiedassystematicerrorsorrandomerrors.Systematicerrorscansometimesbecompensatedforbymeansofsomekindofcalibrationstrategy.Noiseisarandomerrorthatcanbereducedbysignalprocessing，suchasfiltering，usuallyattheexpenseofthedynamicbehaviorofthesensor.下一页返回上一页ReadingResolutionTheresolutionofasensoristhesmallestchangeitcandetectinthequantitythatitismeasuring.Ofteninadigitaldisplay，theleastsignificantdigitwillfluctuate，indicatingthatchangesofthatmagnitudeareonlyjustresolved.Theresolutionisrelatedtotheprecisionwithwhichthemeasurementismade.Forexample，ascanningtunnelingprobe(Afinetipnearasurfacecollectsanelectrontunnelingcurrent)canresolveatomsandmolecules.返回上一页Text3OpticalSensorsforLightweightsModernlightweightmaterialsareincreasinglybeingusedinaerospaceapplicationsandinotherbranches，suchastrafficandconstructionengineering，mechanicalengineeringandtheenergybusiness.Fibercompositetechnologyinparticularisresultinginhugeweightsavings.Thereareincreasedattemptstoimplementsensortechnology，eitherforevaluatingongoingmechanicalstress/temperaturesorfordamagedetection，tomeetincreasedsafetyandwarrantystandards.Asthenumberofmeasurementpointstobemonitoredinanairplaneisveryhigh，sensorconceptsareneededthatarecapableofdealingappropriatelywithinformationtransmissionanddatahandling.下一页返回Text3OpticalSensorsforLightweightsDuetoitssmalldimensions，materialconformityandimmunityagainstelectromagneticinterference，fiber-opticmeasurementtechnologyisofparticularsignificanceinthisarea.Thecomplexityoftheentiremeasurementsystemcanbereducedbytransmittingthedataforallconnectedmeasurementpointsatthesametimethroughonethinwaveguide，resultinginincreasedstabilityandavailability.1.FraunhoferInstituteusesopticalsensorsoncompositematerialFig.3-9showsabearingsurfacesectionforfeasibilitytestingofaprototypetestcarrier(VLA-VeryLightAircraft)attheFraunhoferInstituteforstructuraldurabilityLBFinDarmstadt，Germany.下一页返回上一页Text3OpticalSensorsforLightweightsThemonitoringinthiscaseisofthemechanicalstressofthestructure，buttheautomaticacquisitionofweightandcenterofgravityareequallyimportant.2.Firstfiber-opticmonitoringsystemforcompositematerialsinaircraftconstructionFiber-opticBraggsensorsandinterrogatorsarealsobeingusedinthenewBusinessJetCompAirCA-12.TheUSCompanyCompAircommissionedChandlerMonitoringSystemsInc.(CMS)withthesystemdevelopment，usinginterrogators，strainandtemperaturesensorsfromHBM'stechnologypartnerMicronOpticsInc.下一页返回上一页Text3OpticalSensorsforLightweightsandopticaltransducersofthecompanyClevelandElectricLaboratoriesforthefireprotectionzoneoftheenginecompartment.This10-personturbopropaircraftisthefirstaircraftintheworldtobebuiltcompletelyofcompositematerials.Aprototypewithinstalledstrainandtemperaturesensorswastestedin2007;thenecessaryFAAcertificationoftheaircraftshouldbeassignedjust30monthslater.CompAirAviationwillonceagainbefulfillingatrendsetterroleinaircraftconstructionasthisisthefirsttimeafiber-opticmonitoringsystemwillbeused.Fig.3-10showsthewiringcovermadeofcompositematerialwithembeddedsensors(FraunhoferInstituteLBF，Germany).下一页返回上一页ReadingLEDasLightSensorFromWikipedia,thefreeencyclopediaAnLEDlightsensorisalight-emittingdiodeusedasaphotodiode.Thepropertiesoflightemittingdiodes(LEDs)canbeexploitedtorenderthemusefulforlightdetectionaswellasemission.Thiscapabilityhasbeendemonstratedandusedinavarietyofapplicationsincludingambientlightdetectionandbidire