用于测量液面高度的光纤光栅传感器-英文-(完整版)实用资料

用于测量液面高度的光纤光栅传感器-英文--（完整版）实用资料(可以直接使用，可编辑完整版实用资料，欢迎下载）

Opticalfibergratingsensorsforheightmeasurementofliquid用于测量液面高度的光纤光栅传感器-英文--（完整版）实用资料(可以直接使用，可编辑完整版实用资料，欢迎下载）ZhangShuliana,LeeSangbaeb,XieFanga,ChoiSangsamb(aTheStateKeyLaboratoryofPrecisionMeasurementTechnologyandInstruments,TsinghuaUniversity,Beijing,100084(bPhotonicsResearchCenter,KoreaInstituteofScienceandTechnology,SeoulAbstract:Aprecisionapproachutilizingfibergratingaselementstomeasureheightofliquidispresentedandexperimentedandthebasicissuesofthesensorsystemdesignarediscussed.Thistypeofsensorcanbeusedinprecisionmeasurementofmediummeasurementranges.Thesensitivityof0.15mm/pmformeasuringtheheightofwaterhasbeenobtained.Keywords:measurementsensoropticalfibergrating用于测量液面高度的光纤光栅传感器张书练a李相培b谢芳a崔相三b(a清华大学精密测量技术与仪器国家重点实验室,北京,100084(b韩国科学技术研究院光子研究中心,汉城摘要:提出并实验了一种精密的用光纤光栅作为敏感元件测量液面高度的方法,讨论了传感系统设计的关键问题。该传感器可用于中等深度的液面高度的精密测量,其灵敏度可达0.15mm/pm。关键词:测量传感器光纤光栅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月激光技术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激光技术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激光技术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,