Gas Flow Meters Piston Prover and Bell Prover Facilities

1 Page 1 I NISTMeasu liUmiii"'' *TECHR.I.C. IIIImilnilIII IInilnil NIST HBNC^: ' PUBLICATIONS AlllQS MfitiT7t, iMi::>iCalibrationServicesfor GasFlowMeters PistonProverandBellProver GasFlowFacilities NIST Special Publication 250^9... Open at page → 2 Page 2 rhe NationalInstituteofStandardsandTechnologywasestablishedin1988byCongressto"assistindustryin thedevelopmentoftechnology ...neededtoimproveproductquality,tomodernizemanufacturingprocesses, toensureproductreliability . .... Open at page → 3 Page 3 NISTSpecialPublication250-49 NISTMEASUREMENTSERVICES: NISTCalibrationServicesforGasFlowMeters PistonProverandBellProverGasFlowFacilities JohnD.WrightandGeorgeE.Mattingly ProcessMeasurements Division ChemicalScienceandTec... Open at page → 4 Page 4 I NationalInstituteofStandardsandTechnologySpecialPublication250-49 Natl.Inst.Stand.Technol.Spec.Publ.250-49,47pages(Aug.1998) CODEN:NSPUE2 U.S.GOVERNMENTPRINTINGOFFICE WASHINGTON: 1998 ForsalebytheSuperintendent ofDocum... Open at page → 5 Page 5 TABLEOFCONTENTS ABSTRACT vi 1.INTRODUCTION 1 2.THEORETICALBACKGROUND 3 3.POSITIVEDISPLACEMENTPROVERS 5 3.1.MEASUREMENTPRINCIPLE 5 3.2.CALIBRATIONPROCEDURE 6 3.2.1.PISTONPROVER 6 3.2.2.BELLPROVER 7 4.SOURCESOFUNCERTAINTY... Open at page → 6 Page 6 5.1.3COLLECTIONTIME,/ 14 5.1.3.1.TIMERCALIBRATION 14 5.1.3.2.TIMERACTUATION 14 5.1.3.3.PISTONROCKING 15 5.1.4.STORAGEEFFECTS 15 5.1.5.LEAKAGEANDSEALANTVAPORPRESSURE 16 5.1.6PISTONPROVERUNCERTAINTYSTATEMENT 16 5.2.UNCERTA... Open at page → 7 Page 7 5.2.4.STORAGEEFFECTS 25 5.2.5.LEAKAGEANDSEALANTVAPORPRESSURE 25 5.2.6.BELLPROVERUNCERTAINTYSTATEMENT 26 6.SUMMARY 27 7.REFERENCES 27 APPENDIXA-SAMPLECALIBRATIONREPORT 33 APPENDIXB-ESTIMATEOFEFFECTOFELLIPTICITYOFBELL 38 A... Open at page → 8 Page 8 ABSTRACT Thisdocumentprovidesadescriptionofthesmallandmediumrangegasflowcalibration facilitiesattheNationalInstituteofStandardsandTechnology(NIST)FluidFlowGroup,asreportedin NISTSpecialPublication250[1]forTestNos.18010C-... Open at page → 9 Page 9 1.INTRODUCTION Influidflowratemeasurements,no"standard"devicesorartifactsareavailablecomparableto thoseforlengthormassmeasurements. Instead,referenceflowratesmustbederivedfrom measurements thatcanberelatedtomorefundament... Open at page → 10 Page 10 1.90cm,4.44cm,and14.38cm(0.75in,1.75in,and5.66in).Thethreeproversaremountedtogetherin aconsoleandconnectedbyamanifoldtoasingleairsourceandinflowline.Thisarrangementallows morethanoneprovertobeusedforcalibrationofaflowmet... Open at page → 11 Page 11 2.THEORETICALBACKGROUND Atypicalsystemformeasuringbulkflowrateiscomposedofinletpipingtothemeterundertest, themeterundertest,pipingconnectingthemeterundertesttoacollectionvolume(theapproach volume),andadivertervalvewhichi... Open at page → 12 Page 12 Thesecondtermontherighthandsideof(2)accountsfor"storageeffects"intheconnecting volume.Fa :ifthedensityofthegasinFaincreasesabovesomeinitialvalue(duetodecreasingtemperature orincreasingpressure),thengasiseffectively"store... Open at page → 13 Page 13 3.POSITIVEDISPLACEMENTPROVERS 3.1.MeasurementPrinciple Theuseofthepistonproverisbasedontheprincipleofmeasuringthetimeintervalrequiredto collectaknownvolumeofgasatmeasuredtemperatureandpressure. Itisdesignedtooperateatorn... Open at page → 14 Page 14 3.2.CalibrationProcedure 3.2.1.PistonProver Beforeperformingaflowmetercalibration,themeterandassociatedinstrumentation (formeasuring temperaturesandpressures)areinstalledupstreamfromthepistonprover.Toobtainaflowmeasureme... Open at page → 15 Page 15 3.2.2.BellProver Tomakeacalibrationmeasurementusingthebellprover,themeteranditsinstrumentation are installedandthepipingsystemistestedforleaks.Flowisestablishedthroughtheflowmeterandthebypass valve(fig.2)isadjustedsothat... Open at page → 16 Page 16 Thefirsttermontherighthandsideof(2)isthelargesttermandrepresentsthebasic,uncorrected collectionrateinthecylindricalvolumeofeitherprover.Itissubjecttopotentialerrorsinthedetermination ofthecollectionvolume, ,thetiminginte... Open at page → 17 Page 17 Uncertaintyduetoextramassflowintotheproveriscalculatedfromvaporpressuredataforthemercuryor oilsealants. 5.COMPONENTSOFUNCERTAINTY Theuncertaintyanalysisofthissectionusestheestimationapproachesandtheterminology suggestedb... Open at page → 18 Page 18 molecularweight,theuniversalgasconstant,andthepurityofthegasesusedhavebeenexaminedand foundnegligiblewhencomparedtothecomponentscoveredbelow. 5.1.1.1.TemperatureCalibration Thetemperaturesensorsusedinthepistonproversyste... Open at page → 19 Page 19 withinthecyUnderwalls.Forlongcollectionintervals,thistemperaturegradient isimposedonthegas collectedwithinthecylinderaswell. Iftheheattransfercoefficient issufficientlylarge,thegasiscooled againbythelower,coolerportionof... Open at page → 20 Page 20 Forthehighestflowrate(corresponding toa15scollectiontime)thepressurelossbetweenthe measurementpointandtheprovertubeisestimatedtobe6.0x 10"^ kPa(basedonstandardhandbook pressurelosscalculationsthroughelbows,etc.),resultin... Open at page → 21 Page 21 5.1.2.CollectionVolume, Vc 5.1.2.1.CylinderDiameter Cylinderdiametersweremeasuredat3.8cm(1.5in)intervalsalongthe91cm(36in)lengthofthe glasstubesusingboregagesthatwerecalibratedwithNISTtraceableproverrings.Fourdiameterswe... Open at page → 22 Page 22 Theeffectsofthermalexpansiononthecollectionvolumeshouldbecombinedarithmeticallyrather thanbyRSSbecauseanincreaseintemperaturewillcauselengthanddiametertobothincrease(correlated) andtheseuncertaintieswillnevercanceleachot... Open at page → 23 Page 23 5.1.3.3.PistonRocking There isroomforaveryslight"rocking"ofthepistonasshowninfig.3duetotheslight differences indiameterbetweenthecylinderandpiston.Thiseffectcanbeconsideredeitheracollection volumelengthuncertaintyoracoll... Open at page → 24 Page 24 canbeamplifiedorreduceddependingontheratiooftheapproachvolumetothecollectionvolume.For thesmall,medium,andlargepistonprovers.Fa/ is1.5,0.5,and0.1respectively,resultinginrelative standarduncertainties inmassflowduetostora... Open at page → 25 Page 25 Table2.Asummaryofthepistonproveruncertainties.Thequantitiesinthecolumnlabeled"value"are standarduncertaintiesforeachuncertaintycategory.Thecolumnlabeled"%" givestherelativestandard uncertaintiesforeachuncertaintycategory... Open at page → 26 Page 26 5.2.UncertaintyoftheBellProvers Theuncertaintyanalysisforthebellproverisbasedprimarilyonexperimentalmeasurementsfrom thesmallest bell.Itisexpectedthatthemediumandlargebellproverswillhavesimilarorbetter uncertaintiesthant... Open at page → 27 Page 27 5.2.1.2.PressureCalibration Thesamepressuretransducersareusedforboththepistonandbellprovers.Therelativestandard uncertaintyofthepressurecalibration is0.022%{A}. 5.2.1.3.PressureSampling Betweenthepressuretapintheinflowpi... Open at page → 28 Page 28 Substitutingtheabovelosscoefficientsintothepressurelossequationaboveresultsinapressurelossof 0.002kPa,ora0.002%reduction{B}. Inadditiontothesamplinglocation,thereisanissueofchangesinpressureinthecollection volumeduringth... Open at page → 29 Page 29 measuredbycomparingtheriseinoillevelduetobellimmersionwiththeriseobservedduetothe immersionofaknownvolume. 5.2.2.1.BellArea Theoutsidediametermeasurementsofthebellanddrywellweremadeusingstrappingtechniques withanNIST-cal... Open at page → 30 Page 30 5.2.2.3.CollectionLength Thelengthofthebelltravelisdeterminedbymeasuringthedistancebetweentwophotodiode switchesattachedtothedrywell.Theseareusedtogeneratearisingandfallingvoltageedgewhich triggersacountertostartandstop.... Open at page → 31 Page 31 introduced.AtheorytoquantifythisbiaswasdevelopedbySmith[14].Thevolumeofliquidadhering tothebell,Fl,isgivenas \_ ^'.=—{— J (4) whereuisthekinematicviscosityofthesealingoil,Uisthebellrisevelocity,gistheaccelerationdue togr... Open at page → 32 Page 32 5.2.3.CollectionTime,A? 5.2.3.1TimerCalibration Thesametimerisusedforboththebellsandthepistons,anditscalibrationstandarduncertainty is1x10'"s,orlessthan0.001%fortheshortestcollectiontime(15s){B}. 5.2.3.2.TimerActuation T... Open at page → 33 Page 33 5.2.4.StorageEffects Asforthepistonprover,temperatureandpressurechangesinthegaswithintheapproach volumeresultin beingasourceorsinkofmassflow.Experimentalmeasurementsonallthreebells showthatthepressurewithintheapproachvol... Open at page → 34 Page 34 5.2.6.BellProverUncertaintyStatement Forthebellprovertheflowrateuncertaintycanbeobtainedbytakingtherootsumofthe squaresoftheuncertainties fordensity,volume,timeandstorageeffectsaslistedinTable3.The relativecombinedstanda... Open at page → 35 Page 35 6.SUMMARY Theforegoinganalysispresentsadescriptionofthesystemperformanceofthesmallairflow calibrationfacilitiesintheNISTFluidFlowGroup. Metersformeasuringgasflowcanbecalibrated overtherangefrom3.7x 10'^mVminto1.4mVmin(0.... Open at page → 36 Page 36 [7] Taylor,B.N.andKuyatt,C.E.,GuidelinesforEvaluatingandExpressingtheUncertainty ofNISTMeasurementResults,NISTTechnicalNote1297(1994). [8] TablesofThermalPropertiesofGases,Natl.Bur.Stand.(U.S.),NBSCircular564 (1955). [9]... Open at page → 37 Page 37 [17] Croarkin,M.C,MeasurementAssurancePrograms,PartII:Developmentand Implementation,NBSSpecialPublication676-11(1985). [18] Mattingly,G.E.,FluidMeasurement:Standards,Calibrations,andTraceabilities,Proc. 17thMeas.ScienceC... Open at page → 38 Page 38 LightSource MercurySeal Piston AluminumPlate GlassTube Flow TestSection Va LightDetector Stop Q Start Valve Figure1.Thepistonproverapparatusshowingthecollectionvolume(Fc),theapproach volume(Fa),thelocationoftemperature(T... Open at page → 39 Page 39 Figure2.Thebellproverapparatusshowingthecollectionvolume(Fc),theapproach volume(Fa),thelocationoftemperature(T)andpressuresensors(P),andthesensors usedtomeasurethecollectiontime(At). 31 Open at page → 40 Page 40 Glass AluminumPlate Slit 0.0038cm Figure3.Diagramofthepistonrockingphenomenonandtheresultingcollectionlength(ortime) uncertainty.Thelightslitisnotdrawntoscale. 32 Open at page → 41 Page 41 APPENDIXA:SampleCalibrationReport U.S.DEPARTMENTOFCOMMERCE NATIONALINSTITUTEOFSTANDARDSANDTECHNOLOGY Gaithersburg,MD20899 REPORTOFCALIBRATION OF CRITICALFLOWMETERS May4,1998 Mfg:MeterBuilders,Inc SerialNo:1234 ThroatDiam... Open at page → 42 Page 42 (TmeterSN30032,thermistor#7andPmeterSN0387/0055).Arecoveryfactor,r,of0.70was usedtoconvertmeasuredtemperaturetostagnationtemperature, Tq.Stagnationtemperaturewas calculatedfromtheequation: T-T \+^-M'-(l-r) (1) andthestag... Open at page → 43 Page 43 C=0.68309+1.42025 10'' •-2.80046 •10"' •+3.47447 10"' • +. . . ...-1.80997 •10"' • Po • To+2.46278 •10"'° • (6) withC*dimensionless, TqinK,andPqinkPa.Equation(6)isbasedonafittoreferencedata."* Thecalibrationresultsarepre... Open at page → 44 Page 44 Ananalysiswasperformedtoassesstheuncertaintyofthedischargecoefficientsobtainedforthe meterunder test.^' ^ Thisprocessinvolvesidentifying allofthesignificant uncertainty componentsandobtainingstandarduncertaintyvalues(67%... Open at page → 45 Page 45 Therelativestandarduncertaintyofthemeterpressuremeasurement is0.02%{B}basedon pressurecahbrationdata,andthesensitivitycoefficient is1.0.Therelativestandarduncertainty ofthemetertemperaturemeasurement is0.03%{B}(0.1K)base... Open at page → 46 Page 46 APPENDIXB:EstimateoftheEffectofEllipticityofBell Assumethatthedeparturefromcircularitycanbeexpressedintermsofeasshownbelow: Theperimeteroftheellipse,P,is: a+0 P=2-n (Bl) IntermsofRande,thisbecomes: P=2-n-R-J\+ R 2-n-R- 1... Open at page → 47 Page 47 Aq=7T-R' 1+ R (B4) Buttheactualareaoftheellipseis: A=n-a-b=n-R' R (B5) sothatthefractionalerrorintheareais: A Vr (B6) Thisareadifference isrelativelysmall.Forexample,withe= 1mmandR=196mm,thearea errorwouldbe0.005%. 39 Open at page → 48 Page 48 APPENDIXC:DeterminationofBellWallVolumebyImmersion Theimmersedvolume, Fr,isacylindricalrod77.8cm(30.625in)longand2.54cm(1in)in diameter.Whenitissuspendedbyawireandfullyimmersedintheoil(fromwhichthebellhas beenremoved)ofs... Open at page → 49 Page 49 respectively, is0.052%.Becausethebellposition issetmanuallyforthesemeasurements, a 0.025cm(0.01in)standarduncertainty isassigned ateachend,givingarelativestandard uncertaintyinLof0.076%,thestandarduncertainty in //bbeing... Open at page → 51 Page 51 THESP250SERIESONNISTMEASUREMENTSERVICES* SP250-1 SpectralRadianceCalibrations PB87179883 SP250-2 FarUltravioletDetectorStandards PB87227609 SP250-3 RadiometricStandardsintheVacuumUltraviolet PB87227625 SP250-4 FrickeDosi... 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