How to Select and Mount Transducers in …

1 1 SNAA266A April2015 RevisedNovember2015 SubmitDocumentationFeedbackCopyright 2015,TexasInstrumentsIncorporatedHowto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand FluidIDApplicationReportSNAA266A April2015 RevisedNovember2015 Howto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand FluidIDMatthewMinasiABSTRACTU ltrasonicsensingutilizingTimeOf Flight(TOF)measurementtechniquesare usedin liquidleveland fluididentificationsensingin the automotive,consumerand (TOF)sensingcanyieldhighaccuracyand highreliabilitywith low-powerconsumptionfor all of ordertoachievethe best cost-to-performancecombination,caremustb e takenin selectingthe servicedby utilizingbare(unsealed) selectthe mostappropriatetransducerfor liquidlevelsensingand additionto sensorselection,propertechniquesfor mountingtransducerson the outsideof tanksfor rapidprototypingis alsoaddressedin this of Glueto (FrontView).

2 87 TransducerReceptacleClearance(SideView). .88 TransducerReceptacle(TopView)..99 TransducerReceptacle(SideView)..9 List of April2015 RevisedNovember2015 SubmitDocumentationFeedbackCopyright 2015,TexasInstrumentsIncorporatedHowto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand FluidID1 TransducerSelectionSelectingthe righttransducerstartswith understandingwhatand how you wantto makeyourlevelsensingor fluid s TDC1000handlesultrasonicTOFmeasurementsa nd canworkwith transducersthat havea resonancefrequencyfrom30 KHz to 4 ,the followingquestionsneedto be answered:Whatfrequency?

3 Whatsize?WhichPiezomaterial?Wheredoesit needto be mounted?Whattemperaturerange?Eachof thesequestionswill bediscussedin frequencyyou choosedependson resonateat multiplefrequenciesdependingon its piezoelectricmaterialcompositionand its deepdiscussionofthis topicis not withinthe scopeof this such,this applicationnoteonly discussestransducersof the disc varietyworkingin axialor The frequencyof yourtransducerand the transmitpulselengthcan determineaxial(depth) higherthe frequency,the tighterthe resolution[1]. In generala 1 MHztransduceryieldsbetterthan1 mm resolutionin theotherhanduse 40 kHz Transducers ,whilegas flow metersuse 200 kHz general,propagatingan ultrasonicwavethroughliquidsallowssystem designersto use transducersin the MHzrangewhileapplicationswherethe ultrasonicwavewill propagatethrougha gas requiretransducersanywherefrom40 kHz to 500 kHz dependingon the distancethe waveneedsto traveland theaccuracyrequirementof the ( * # cycles)/2(1)2.

4 The higherthe transducerfrequency,the tighterthe beamwidth[2,3].3. The smallerthe transducerdiameter,the widerthe beamwidth[2,3].Sine( ) = * V/(DF)(2)where: = BeamdivergenceangleV = SoundVelocityin the material(m/sec)D = diameterof transducer (m)F = Frequencyof transducer (Hz) The smallerthe transducerdiameter,the less efficientthe transduceris at creatingan addition,smallerdiametersmakethe transducerless sensitivewhiletryingto detecta in general,largertransducersimprovesignalto noiseratioat the expenseof surfaceareaon acontainerwall and The size of a transduceris also influencedby its severaldifferentmaterialsofferedby piezomanufacturesand ,they differin sensitivity(abilityto convertvoltageinto mechanicaldisplacement).

5 Hereis a list ofthe Bariumtitanate(oldertechnology)2. Leadzirconatetitanateor PZT is moreinformation,the followingis agoodwebsitefor informationon the differenttypesof PZTs: is commonfor a piezomanufacturerto not includeinformationaboutmaterialin thatis the case,it is recommendedto ask the manufacturerin orderto makesurethat the performancewouldbe similarto the PZT sensorsthat are recommendedin applicationnotesSNIA020(WaterFlowMeter)a nd SNAA265(FluidIdentificationand Contamination). April2015 RevisedNovember2015 SubmitDocumentationFeedbackCopyright 2015,TexasInstrumentsIncorporatedHowto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand MHzTransducersfor LiquidLevelSensingand FluidIdentificationFor the scopeof this ApplicationNote,1 MHztransducerswill be the the tablebelowarethe transducersthat havebeentestedwith the TDC1000for levelsensingand ofthe transducersare approximately2 mm is due to the requirementof axial(thickness)

6 Resonancemodeof 1 MHzfor theseare listedon s importantto understandthey are bothcorrectand that careneedsto be takenwhenselectinga TestedTransducersFREQ(THICKNESSMODE)THIC KNESS(mm)RADIUS(mm)SEALEDMODEL#VENDORWEB SITE1 MHz210 NSMD10T2R111 MHz215 NSMD15T21R111 MHz27 NBSU-P7-1000B-W200 MHz210 NBSU-P10-1000B-W200 MHz215 NBSU-P15-1000B-W200 MHz215YT/R975-US0014L353-01 MHz214 NAW5Y14200 TransducerGet Mounted?1. Insideor outsidethe tank?Insideor outsidethe tank will greatlyaffectthe cost of the requiretransducersto be mountedon the insideof a tank needsealedtransducersthat are mechanicallymorecomplexas they needto withstandchemical(liquid)

7 Theotherhand,applicationsthat allowtransducersto be mountedon the outsideof a containercan utilizebare,unsealedtransducerswhichare havethe addedbenefitof beingnon-invasiveand can be retrofittedto general,if an applicationcantolerateexternalmounting,t otal systemcost is reducedand the systembenefitsfromhigherreliabilityand Top or bottomof the tank?Top or bottomwill also greatlyaffectthe cost of the transducerand the transduceris mountedon the bottomof the tank on the outerwall,the baretransducertype can be ,if the transduceris mountedon the top in the innerwall,forexampleto measurelevel,the conductingmediumfor the ultrasonicwaveis now a gas, and thus theresonancefrequencyof choiceneedsto be 40 kHz to 200 kHz dependingon the levelaccuracyrequirementand levelheightthat is fluid identificationapplications.

8 Transducersare typicallymountedon the outsideof the transducerswill not comein contactwith the liquidmediuminsidethe container,the less expensive,baretransducerscan be Temperaturerange?MostPZT shouldnot be usedabove80 C as it degradesthe piezoelectriccapabilityrenderingit high temperatureapplications,appropriatetrans ducersareavailablesuchas Modifiedlead metaniobatewhichis availablefromthe followingvendors: April2015 RevisedNovember2015 SubmitDocumentationFeedbackCopyright 2015,TexasInstrumentsIncorporatedHowto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand TankWallIt is possibleto transmitthroughmosttank wallsbecausethe ultrasonicwavestravelthroughtank wallswith no issuesdependingon the measurementrequirementsand tankmaterials,suchas automotiveHDPE(HighDensityPolyethylene)a nd StainlessSteel,havebeentestedwith processhas two key featuresto maximizesuccess:1.

9 Goodmechanicalconnectionbetweenthe transducerand the tank is achievedusingCyanoacrylateadhesiveas it curesquicklywith low compressibilityand high adhesionto Transducerbacksideacousticdampening(andw ire strainrelief).This is achievedusing Hot glue as ithas high adhesionto acrylicand moderateflexibilityallowingfor bothacousticdampeningand goodwire be usedinsteadbut requiresa longer(24 hr) The tank wall is homogeneous(hasno air gapsand/oris not porousin nature).Air gapscausereflectionsand can attenuatethe ultrasonicwaves,thus Roughen1 cm squareareaon lowerside of plasticcontainerwith TestContainerPreparation2.

10 De-greasewith Dry areawith air ApplyCYAglue to 1 cm April2015 RevisedNovember2015 SubmitDocumentationFeedbackCopyright 2015,TexasInstrumentsIncorporatedHowto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand FluidIDFigure2. ApplyingCYAto TestContainer5. Attachtransducerto glue spot with leadsout to side of MountingTransducerto TestContainer6. Whileapplyinggentlepressureto transducerto hold it in placeapply CYAA ccelerator to Waitapproximately15 sec for glue to Applyalcoholto areawith air Applyhot glue aroundthe circumferenceof the April2015 RevisedNovember2015 SubmitDocumentationFeedbackCopyright 2015,TexasInstrumentsIncorporatedHowto Selectand MountTransducersin UltrasonicSensingfor LevelSensingand FluidIDFigure4.