用于測量液面高度的光纖光柵傳感器-英文-(完整版)實用資料

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

Opticalfibergratingsensorsforheightmeasurementofliquid用于測量液面高度的光纖光柵傳感器-英文--（完整版）實用資料(可以直接使用，可編輯完整版實用資料，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清華大學精密測量技術與儀器國家重點實驗室,北京,100084(b韓國科學技術研究院光子研究中心,漢城摘要:提出并實驗了一種精密的用光纖光柵作為敏感元件測量液面高度的方法,討論了傳感系統設計的關鍵問題。該傳感器可用于中等深度的液面高度的精密測量,其靈敏度可達0.15mm/pm。關鍵詞:測量傳感器光纖光柵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(4isthesensitivityofmeasurementwhichisdirectlyproportionaltoρandA.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,