TDLAStechnologyismainlyusedtodetectgasbydetectingasinglevibrationalabsorptionlineof thegasmoleculeWhendetectinglowconcentrationgas,becausetheabsorptionsignalisweak, itisusuallynecessarytocombinelongopticalpathtechnologyandharmonicdetectionmethod toimprovethesensitivityofgasdetectionAccordingtotheLambertBeerlaw,whenabeamof lightwilldecaywhenpassesthroughgas.
Gasdetectorisacommongasconcentrationdetectioninstrument,mainlyusinggassensorto detectthetypesofgasesintheenvironment.Itcandetecthydrogensulfide,carbonmonoxide, oxygen,sulfurdioxide,phosphine,ammonia,nitrogendioxide,hydrogencyanide,chlorine, chlorinedioxide,ozoneandcombustiblegas,etc.,whichiswidelyusedinpetrochemical,coal, metallurgy,chemicalindustry,municipalgas,environmentalmonitoring,agricultureandother sitesforsitetesting.Inaddition,itcanalsousedforthespecialoccasionmeasurementneeds, suchasconcentrationdetectionorleakageintunnel,pipe,tank,confinedspaceandsoon TunableDiodeLaserAbsorptionSpectroscopy(TDLAS)isatechnologythatusesaTunableDiode LaserandLaserAbsorptionSpectroscopytomeasuretheconcentrationofcertainsubstances (suchasmethaneandwatervapor)inagasmixtureTheadvantageofTDLASoverother concentrationmeasurementisitsabilitytoachieveverylowdetectionlimits(PPBclass).In additiontotheconcentration,thetemperature,pressure,velocity,andmassfluxoftheobserved gascanbealsodetermined.TDLASisbyfarthemostcommonlaserbasedabsorptiontechnique usedtoquantitativelyassesssubstancesinthegasphase
PrincipleofTDLASGasDetectionTechnology
SchematicdiagramofTDLASgasdetection
Whenlaserdiodelightgoesthroughgaschamber,PDlightdetectorwillreceiveLDopticalpower. Withthemodulation,theoutputopticalpowerandwavelengthofthelaserwillchange accordinglyAfterpassingthroughthegascavity,thecorrespondingoutputopticalpowerand wavelengthwillalsochange.Ifthelightisnotabsorbedbythegaswithinthewavelengthsweep
ApplicationofPiezoelectricTechnologyinTDLASGasDetection
TDLAStunablediodelaserabsorptionspectroscopytechnologyisusedtomeasuresingleor severalabsorptionlinesofmoleculesthatareveryclosetoeachotheranddifficulttoresolveby usingthecharacteristicsofnarrowlinewidthandwavelengthoftunablesemiconductorlaser withmodulation.
ApplicationofPiezoelectricTechnologyinTDLASGas Detection
Adjustingthecurrentdrivingthelaserdiodechangestherefractiveindexofthesemiconductor andthereforethefrequencyThetypicaltuningfactorisabout01GHz/mAThemodulation currentallowsmodulationoflaserfrequencieswithabandwidthofseveralMHzTherefore,itisa typical"actuator"forreducinglaserlinewidth
Inordertoreflectreallightabsorption,laserwavelengthorfrequencycurvemustbescanned
TheintracavitaryEOMmethodislesscommonandcanchangetherefractiveindexquickly,but therangeoffrequencyadjustmentsisusuallyverysmall.
ApplicationofPiezoelectricTechnologyinTDLASGasDetection
Piezoelectricadjustmentisaveryfastadjustment,whichcanadjustthegratingpositionand Angleinmillisecondorevensubmillisecondtomeettherequirementsofrapidfrequencychange. Moreover,thefrequencycanbeadjustedoverawiderange,fromafewHztokHz,by piezoelectricadjustmentmethod.
Inaddition,piezoadjustmentmethodsareoftenusedtocounteractslowerfrequencyshifts.
range,thatis,thereisnogasabsorptionline,thentheopticalpowerreceivedbyPDisthesame astheopticalpoweroutputbyLDIfthereisanabsorptionlineinthewavelengthrange,theline spectrumoftheopticalpowerreceivedbythePDterminalwillhaveadepression,andthetype andintensityofthegascanbedeterminedbythewavelengthanddepthofthedepression
Ingeneral,therearefourbasicwaystoadjustthefrequencyoflightcomingoutofalaser,namely, changingthetemperatureofthediode,changingthevoltageofthepiezoelectricactuator(which controlsthepositionandAngleofthegrating),adjustingthecurrentdrivingthelaserdiode,and changingthevoltageoftheEOMinsidethecavity
BasicMethodofFrequencyControlinTDLASGasDetection
Bychangingthetemperatureofthediode,thelaserfrequency(tuningcoefficientisgenerally 01nm/K)canbegreatlychanged,soastoachievethepurposeofwavelengthscanningButit takesalongtimeforthediodetemperaturetochange,usuallyafewseconds,whichisonly suitableforadjustingtheapproximaterangeofwavelengths
PiezoactuatorsarenotonlyusedinTDLASgasdetectiontechnology,butalsoinOPLAS opencircuitgasdetectionandanalysis
Typically,piezoactuatorsareactuatorcomponentsusedtolockphaseandfrequencyfeedback loopsItperformsphaseandfrequencyadjustmentsbasedoncontrolsignals
SelectionofPiezoActuatorsforTDLASGasDetection
CoreMorrowhasthousandsofpiezoactuatorsandthecorrespondingdrivecontrolproductsThe selectionofpiezoactuatorsmainlydependsonthespecificstructureofthecorrespondingTDLAS gasdetectionandthecorrespondingneedtoadjusttheopticalpathparameters
OPLAS(OpenPathLaserAbsorptionSpectroscopy)issimilartoTDLAS,butOPLASdoesnotneed topumpthesamplegasintothegasabsorptionunitforanalysisTheOPLASsystemhashigher requirementsforlaserpointqualityandopticalequipment.Forexample,thedetectionoflow concentrationofammoniaisrelativelydifficult,inthedetectionoflowconcentrationof ammoniagasenvironment,thepiezoactuatorcanbeusedtoadjustthedirectionofthelight source,quicklylocatethelaserscanningcenterposition,andthentakefastlaserscanningina certainrangeThemethodcanevendetectgasconcentrationsoveradistanceof1,000meters
ApplicationofPiezoelectricTechnologyinTDLASGasDetection
1)CoreMorrowPiezoStackActuator
OPLASBasicStructureDrawing
CoreMorrowPZTstackactuatorscomeinawiderangeofsizesandmodels,withthesmallestsize upto122x13x17mm^3anddisplacementupto1μmThecrosssectionalareaofthepiezo stackis1.22x1.3mm^2,1.66x1.72mm^2,2x3mm^2,3.5x3.5mm^2,5x5mm^2,7x7 mm^225x25mm^2,thelargerthecrosssectionalarea,thehighertheoutputTheheightcan beselectedaccordingtothedesireddisplacementrangevalue.Thehighertheheight,thegreater
Usually,thevolumeofthegasdetectorissmall,sothesmallerthecomponentsize,thebetter
Becausetheabsorptionspectrallinesofdifferentgasestobemeasuredaredifferent,theoutput laserwavelengthofthelaserneedstochangeperiodically,sothatthecentralwavelengthofthe laserisadjustedtotheabsorptionspectrallineofthegastobemeasured,andselective absorptionisgenerated.Theperiodicchangeoftheoutputwavelengthofthelasercanbe adjustedbythepiezoactuatorThepiezoactuatorhasthecharacteristicsoffastresponsespeed andhighprecision,andisverysuitableforadjustingtheoutputspectralline.
FrequencyControlBasedonPiezoelectricTechnology
Note:Duetoalargenumberofproductmodels,onlypartofthemareshownhereFormore
information,pleasecontactoursalesengineer.
ApplicationofPiezoelectricTechnologyinTDLASGasDetection
Thefinalselectionwilldependonfactorssuchasoutputrequirement,displacementrequirement andspacelimitation CoreMorrowPiezoStackActuator TechnicaldataofCoreMorrowPiezoStacks
thedisplacement.
Inaddition,thepiezoactuatorispreloadedinternallytomakeitmoresuitablefordynamic applications.
ApplicationofPiezoelectricTechnologyinTDLASGasDetection
Themovingendofthepreloadedpiezoactuatorscanbeconnectedwithflathead,ballhead, internalthread,externalthread,orcustomizedconnection.
Inordertogetbetterprotectionandapplication,CoreMorrowprovidespreloadedpiezo actuators,withpiezoceramicstackedandencapsulatedintheinterior,sothattheyareprotected fromtheimpactofknock,humidityandsoon
CoreMorrowPreloadedPiezoActuators
2)CoreMorrowPreloadedPiezoActuators
ApplicationofPiezoelectricTechnologyinTDLASGasDetection TechnicaldataofCoreMorrowPreloadedPiezoActuators Note:Duetoalargenumberofproductmodels,onlypartofthemareshownhereFormore information,pleasecontactoursalesengineer.
Forthedetectionoflowerconcentrationsofgases,highergasabsorptionsensitivityisrequired.
Ofcourse,theaboveisjustoneoftheTDLASstructures,andthestructureofeachTDLASdevice willbedifferent
ListofGasSensitiveWavelengths Gassensitivewavelengthparametersinthefollowingtableforyourreference: Molecule MIR NIR TypicalApplication (ppb) WaveLength (nm) (ppb) WaveLength (nm) H2O 20 5940 60 1390 ProcessControl CO2 0.13 4230 3000 1960 Combustionsystem,coa
ApplicationofPiezoelectricTechnologyinTDLASGasDetection
Note:Forreferenceonly,differentsystemshavedifferentstructures
Thesensitivityofgasabsorptioncanbeimprovedbyincreasingthelengthofthegaschamber, butthiswillresultinthevolumeofthegasdetectionequipmentbecominglargerTosolvethis problem,manygasdetectiondeviceshavespeciallowlossmirrorsatbothendsofthegas chamberThelightemittedbythelaserisreflectedbackandforthinthegascavitybythe reflectionlens,sothatthelighthasmorecontactwiththegas,andthedistanceofthelight throughthegasbecomeslonger,soastoimprovethehighsensitivityofthetest,andtheweak absorptionlinecanalsobedetected.
AbsorptionSensitivitycanbeImprovedbyIncreasingLengthofGas Chamber
Lightoscillatesbackandforthinthegaschamber,sotheLDlinewidthneedstobeasnarrowas possible
ApplicationofPiezoelectricTechnologyinTDLASGasDetection lmine,hypoxiaprotecti Con,smokecontrol O 075 4600 30000 1570 500 2330 NO 5.8 5250 60000 1800 1000 2650 NO2 30 6140 340 680 N2O 044 4470 1000 2260 SO2 14 7280 CH4 17 3260 600 1650 Naturalgasextractiona Cndpipelines 2H2 35 7400 80 1520 HF 10 1310 ProcessControl HCl 0.83 3400 150 1790 HOilRefinery Br 72 3820 600 1960 HI 2100 1540 HCN 12 6910 290 1540 ProcessControl H2S 20000 1570 O3 11 9500 Air contamination measurement NH3 08 10300 800 1500 Refrigeratedfoodmanuf acturing,processingand preservation, beverageproduction, iceskatingrink CH2O 84 3550 50000 1930 ProcessControl PH3 6.2 10100 1000 2150 O2 78000 760 Hypoxiaprotection