用于測(cè)量液面高度的光纖光柵傳感器-英文-(完整版)實(shí)用資料

用于測(cè)量液面高度的光纖光柵傳感器-英文--（完整版）實(shí)用資料(可以直接使用，可編輯完整版實(shí)用資料，歡迎下載）

Opticalfibergratingsensorsforheightmeasurementofliquid用于測(cè)量液面高度的光纖光柵傳感器-英文--（完整版）實(shí)用資料(可以直接使用，可編輯完整版實(shí)用資料，歡迎下載）ZhangShuliana,LeeSangbaeb,XieFanga,ChoiSangsamb(aTheStateKeyLaboratoryofPrecisionMeasurementTechnologyandInstruments,TsinghuaUniversity,Beijing,100084(bPhotonicsResearchCenter,KoreaInstituteofScienceandTechnology,SeoulAbstract:Aprecisionapproachutilizingfibergratingaselementstomeasureheightofliquidispresentedandexperimentedandthebasicissuesofthesensorsystemdesignarediscussed.Thistypeofsensorcanbeusedinprecisionmeasurementofmediummeasurementranges.Thesensitivityof0.15mm/pmformeasuringtheheightofwaterhasbeenobtained.Keywords:measurementsensoropticalfibergrating用于測(cè)量液面高度的光纖光柵傳感器張書練a李相培b謝芳a崔相三b(a清華大學(xué)精密測(cè)量技術(shù)與儀器國家重點(diǎn)實(shí)驗(yàn)室,北京,100084(b韓國科學(xué)技術(shù)研究院光子研究中心,漢城摘要:提出并實(shí)驗(yàn)了一種精密的用光纖光柵作為敏感元件測(cè)量液面高度的方法,討論了傳感系統(tǒng)設(shè)計(jì)的關(guān)鍵問題。該傳感器可用于中等深度的液面高度的精密測(cè)量,其靈敏度可達(dá)0.15mm/pm。關(guān)鍵詞:測(cè)量傳感器光纖光柵IntroductionComparedwithtemperatureandpressuremeasurement,themethodstomeasuretheheightofliquidarenotgoodenough.Insomecircumstances,suchastheliquidsurfaceisfluctuating,theliquidisboilingandtherearesmallfloatingmaterialsontheliquidsurface,itisdifficulttomeasuretheheightofliquidprecisely.Nowadays,thereareseveralmethodstomeasuretheheightofliquid.Forexample,usingaruletomeasuretheheightofliquiddirectly,measuringtheheightofliquidthroughthevariationofthebuoyantforceorthroughthevariationofliquidpressureorthroughthevariationofelectricalcapacityinducedbytheliquidheightvariation.Becausetheprecisionofthetransferringfromthesevariationstoelectricalvariationisnothigh,thesensitivityofmeasuringtheheightofliquidisnotbetterthan1mm.Becauseoftheimmeasurableranges,thetechnologyofliquidheightmeasurementneedstobedevelopedalot.Itisaveryimportanttasktofindmoreprecisionandhigherresolutionmethodstomeasuretheliquidheight[1,2].Recentyearsanumberofpapershavebeenreportedonresearchofopticalfibergratingsensors,mostofwhichareusedtomeasurestrain,temperatureandpressure[3~9].Inthispaper,weexperimentprimarilyandpresentanin2fibergratingapplicationofmeasurementtheheightofliquid.Thistypeofopticalfibergratingsensorsmaybeusedinelectron2magneticinterferenceor/andinflammableor/andcorrosiveor/andconductingor/andfoamingsurfaceliquids.Becausea第25卷第1期2001年2月激光技術(shù)LASERTECHNOLOGYVol.25,No.1February,2001floatingbarisusedtotransfertheliquidheighttothestrainofanin2fibergrating,thecorrespondingissuesofdesign,includingthemeasurementrange,sensitivity,thediameterandlengthofthefloatingbaretc.,arediscussed.Asthemethodwepresentistoembedthein2fibergratingelementintothemeasuredliquid,thefluctuationandthefoamoftheliquidsurfacewillnotinfluencethemeasurementprecisionandtheimmeasurablerangecanbereducedbyusingashortin2fibergrating.OursensorsfitwithhighprecisionofmeasurementrangeofafewhundredFig.1Arrangementforliquidmeasurementutilizingfibergratingsmillimeters.1ExperimentalconfigurationTheexperimentalarrangementisshowninFig.1.AhollowfloatingbarFBishungbyspringSPsothattheweightofFBisbalanced.Abroadbandlightsourceilluminates,throughanisolatorISanda32dBcoupler,thefiberwithain2fiberBragggratingsG,ofwhichthenominalreflectingwavelengthis1549nm.ThereflectingsignalfromthegratingisdetectedwithaspectrumanalyzerSA(orwithotherinterrogativeapproaches,theheightvariationofliquidismeasuredwitharulerR.OneendofthefibergratingGismountedtothecenteroftheroundsurfaceofthelowerendofthebarwhiletheotherendofGisfirmlyfixedtotheunmovableshelf.Thespringsupportedontheshelfissoplacedthatitcanbemovedupanddowntopre2strainGFig.2Principalspringandfourside2springswithasmallquantity.WealsoemployedaspringsystemconsistingofaprincipalspringSPand4side2springs(fourrubberropestostabilizethefloatingbar(Fig.2.ThebuoyantforceFactingontheFBcanbepresentedasF=πr2ρΔh(1Where,ristheradiusofthefloatingbar,ρisthedensityoftheliquid,Δhisthevariationofliquidheight,whichcanbemeasuredwiththerulerR.FincreaseswiththeincreaseofΔh,whichinducesthereflectingwavelengthshiftwithaproportionalquantity.Duringtheexperiments,thechangeoftemperatureofwaterismaintainedwithin0.1℃,thereflectingwavelengthshiftofGwasmeasuredwiththespectrumanalyzerandthewaterheightwasrecordedwiththerulerRasthewaterwaspouredintothevessel.2ExperimentalresultsTheexperimentalresultsareillustratedinFig.3,inwhichthecurveAisforonespringSPandcurveBisfortheprincipalspringSPwiththefourside2springstogether.Comparingthetwocurves,weseetwoparallellinesthathaveilluminatedthesamehighlinearityandsensitivityinthetwocases,althoughtheside2springswhichprotectthegratingfrombreakingcanstrongly8激光技術(shù)2001年2月Fig.3Curveofwavelengthshiftagainstthewaterheightkeepthefloatingbarstable.Thesensitivityof0.15mm/pmhasbeenobtainedforafibergratingmadeof145μmdiameterKIST21104fiberandafloatingbarwith36.0mmdiameter.WecanexpressthesensitivityasKw=0.00619pm/mm?mm2,whichgivesthereflectingwavelengthshiftagainstpermmofheightchangeandpermm2ofsectionarea.Withthespectrumanalyzerinthelab,wewereabletodistinguish~3mmwaterheightchange.3ConsiderationsindesignFiveissueshavetobeconsideredtodesignanin2fibergratingliquidheightsensor:themaximumlimitationofthereflectingwavelengthshiftΔλmax,whichisdependentontheforcestretchingtheopticalfibersafely;measurementrangeΔhmax;lengthLandsectionareaAofthefloatingbar;sensitivityKandresolution.TherelationoftheseparameterscanbeexpressedbyFig.4Floatingbar:lengthanddiameterKwρAh=Δλ<Δλmax(2Where,Kwρisthesensitivityofliquid,ΔλisthereflectingwavelengthshiftwhichcannotbegreaterthanΔλmax,Aisthesectionareaofthefloatingbar.Forabarwitharoundsection(Fig.4,Eq.(2canberewrittenasKwρπr2h=Δλ<Δλmax(3Where,ristheradiusofthefloatingbar,andS=KwρA=Kwρπr2=Δλmax/hmax(4isthesensitivityofmeasurementwhichisdirectlyproportionaltoρa(bǔ)ndA.Δλmaxvarieswithdifferenttypesoffiber.Wanghasindicatedthat~7800pmreflectingwavelengthshiftcanbeinducedbystretchingafiberof~130μmdiameterwith7Nforce,thecorrespondingstrainis7860μstainbeyondwhichthefiberwillbesnapped[10].Thesearethemaximumlimitationofthewavelengthshift,strainandstretchingforceactingontheopticalfiber.Inordertobesafe,itisappropriatetolimitthegreatestwavelengthshifttoΔλmax5000pmwhichcorrespond-5nmtoa~5nmwavelengthshift.OnecanusethegivenmeasurementrangehmaxtocalculaterthenS,oronthecontraryusethegivenStocalculatehmaxandr.Themeasurementrangesoftraditionaltypesare0~300mmand0~2000mmetal.Wechosehmax=500mmasameasurementrangeoftheexampledesign,whichneedsthelengthoffloatingbarL>500mm(forexample550mm.FromEq.(3thediameterofthefloatingbarinwaterheightmeasurementcanbecalculatedasbelowΔλmax=Kwρhmaxπr2(5AsdiscussedabovewetakethatΔλmax=5000pm,hmax=500mm,ρ=1g/cm2andKw=9第24卷第6期ZhangShulianOpticalfibergratingsensorsforheightmeasurementofliquid01激光技術(shù)2001年2月0.00619pm/mm?mm2,thus5000pm(0.00619pm/mm?mm2×500mm×πr2wWhichmeansrw22.68mmandthediameteris45.36mmInaword,itissafeforafibergratingof~140μmdiameterstretchedbyafloatingbarof45.36mmdiametertomeasurethewaterheightof500mm.Forotherliquids,r=rw/ρFromEq.(4,weknowthatthesensitivityS=10pm/mm.Theresolutionvarieswiththeinterrogativeapproachesbecausetheyhavedifferentwavelengthshiftresolution.Forthegivenexample,10pmwavelengthshiftisagainst1mmwaterheightchange.Theordinaryresolutionsare:10mmforaspectrumanalyzerwithawavelengthresolutionof0.1nm;0.4mmforafiberFabry2Perotfilterwith4pmwavelengthresolution;and0.1mmfortheapproachoflength2tuningreferencefibergrating.4ConclusionanddiscussionAnovelapproachtomeasurewaterheightwaspresentedanddemonstrated.Asthein2fibergratingisembeddedintothemeasuredliquid,themeasurementisimmunetothefluctuationoftheliquidsurfaceandthefoamontheliquidsurface.Thesensitivityof6.49pm/mmofwaterheightmeasurementhasbeenobtainedforafloatingbarof36mmdiameter(orK=0.00619pm/mm?mm2.Thesensitivityofthetechnologyofinterrogatingwavelengthshifthasachieved1pm.Thesensitivityof6.49pm/mmmeansthesensitivityof0.15mmofliquidheight.Duringtheexperiments,wemaintainedthevariationoftemperaturelessthan0.1℃.Ageneraldesignconsiderationfittingforvariousliquidswasgiven.Bycalculating,theinfluenceofthewavelengthshiftinducedbywaterpressureunder500mmdepthissmall,