High Vacuum Standard and Its Use

1 Page 1 NISTMeasurementServices: NEWNISTPUBLICATION April20,1989 HighVacuumStandard andItsUse SharrillDittmann U.S.DepartmentofCommerce NationalInstituteofStandardsandTechnology (formerlyNationalBureauofStandards) Open at page → 2 Page 2 CenterforBasicStandards TheCenterforBasicStandardsdevelopsandmaintainsthescientificcompetenciesandlaboratoryfacilitiesnec- essarytopreserveandcontinuetorefinethebasephysicalquantitiesuponwhichtheNation'smeasurement syste... Open at page → 3 Page 3 NISTMEASUREMENTSERVICES: HighVacuumStandardandItsUse SharrillDittmann CenterforBasicStandards NationalMeasurementLaboratory NationalInstituteofStandardsandTechnology Gaithersburg,MD20899 March1989 U.S.DEPARTMENTOFCOMMERC... Open at page → 4 Page 4 LibraryofCongressCatalogCardNumber.88-600605 NationalInstituteofStandardsandTechnologySpecialPublication250-<34 Natl.Inst.Stand.Technol.Spec.Publ.250-34,68pages(March1989) CODEN:NSPUE2 U.S.GOVERNMENTPRINTINGOFFICE WASHIN... Open at page → 5 Page 5 PREFACE CalibrationsandrelatedmeasurementservicesoftheNationalInstituteof StandardsandTechnologyprovidethemeansformakersandusersofmeasuring toolstoachievelevelsofmeasurementaccuracythatarenecessarytoattain quality,produc... Open at page → 6 Page 6 documentsmaybedirectedtotheauthorortooneofthetechnicalcontact personsidentifiedintheUsersGuide(SP -250) . Suggestionsforimprovingtheeffectiveness andusefulnessofthenewseries wouldbeverymuchappreciatedatNIST. Likewise,sug... Open at page → 7 Page 7 TABLEOFCONTENTS Page Preface iii I.Introduction 1 II.DescriptionoftheNISIVacuumCalibrationService 1 III.Theory,DesignPhilosophyandDescriptionoftheCalibration System 2 TheChamber 3 TheFlowmeter 4 TheOrifice 6 ExtensiontoL... Open at page → 8 Page 8 TABLEOFCONTENTSrCONTINUED) Appendices A.SampleReportofCalibrationforIonizationGage B.SampleReportofCalibrationforMolecularDragGage G.DimensionsandConductanceoftheOrificeintheNIST DynamicExpander vi Open at page → 9 Page 9 LISTOFTABLES Page I.Stunmaryofthevacuumcalibrationservice 2 II.Primarystandardconfigurations usedforcalibrations 15 III.Primarystandardnonllnearltles 25 IV.Uncertainties oftheNISThighvacuumstandardwithnitrogen 29 V.Resul... Open at page → 11 Page 11 I INTRODUCTION Vacuummeasurements areanimportanttoolformanysegmentsofthe AmericaneconomyandforAmericandefenseefforts. Theaccuracyofthese measurementsaffectsalargevarietyofindustriesrangingfromspacesimula- tiontosemicondu... Open at page → 12 Page 12 TABLEI.SummaryoftheVacuumCalibrationService Sensor Calibration Range Standard Uncertainty Pa percent MDG 5x10-3 Primaryhigh 1.4-1.6 vacuum IG IG 10"^ -10-1 10-6 .iQ-t, CalibratedMDG Primaryhigh vacuum 1.4-2.6 1.4-5.2 Ifc... Open at page → 13 Page 13 THECHAMBER Thedesignofthevacuumchamber,illustrated infigure2,islargely determinedbytheneedtomaintainalowbackgroundpressure, toprovideroom tomountthegagestobecalibrated, andtomaintainageometrywherethe orificeconductanceca... Open at page → 14 Page 14 thelowerchamberandbythe15-cmi.d,connectionbetweenthelowerchamber andthepijmp. Theturbomolecular pumpwaschosenforitsstablehighpumping speed,lowbasepressure,andcompatibilitywithallgases. Ultra-highvacuumconstructionpractic... Open at page → 15 Page 15 afterasufficiently longtimefollowingestablishment ofasteadygasflow. Second,stablepressuresarereadilygeneratedforlongperiodsoftime. Third,theonlydimensionswhichneedtobecharacterized arethoseofthe orificeandthevolumeofthep... Open at page → 16 Page 16 Thenextstepistoisolatetheworkingreservoir (E)fromtheballast volumesothatflowisoutoftheworkingreservoiraloneintothechamber. Thisflowofgaswilltendtoreducethepressureintheworkingreservoirbut constantpressureismaintainedbyad... Open at page → 17 Page 17 uppersidetoadepthof0.61cmfromthecenterouttoadiameterof8.89cm, andacentered1.12-cmdiameterholewasboredthroughtheplate. The undersideoftheplatewasmachinedtoformahollow,truncated80°half-angle cone,leavingathicknessof0.74mma... Open at page → 18 Page 18 thepressureisreduced,therandomerroroftheMDG,typically10"^Paor greater,precludesitsuseforadirectdetermination ofRp .Rpwillbea functiononlyoftheorificeconductanceandthepumpspeed,andinthe molecularflowrange,theonlyvariablec... Open at page → 19 Page 19 lessthan1%althoughthismaybefortuitoussincefluxandpressuregradients ofseveralpercentareknowntoexistinthelowerchamber. Theflowratiocannotbedirectlymeasuredforpressureslowerthanthose thatcanbereliablygeneratedbyameasuredflo... Open at page → 20 Page 20 MDGperformanceatpressuresabove10"^Paislimitedbynonlinearities arisingfrominteractionsbetweenthegassurroundingtheballandthewalls ofthesteelthimblewhichcontainstheballinthevacuumchamber. The resultingchangesmaybeempiricall... Open at page → 21 Page 21 COMPONENTSELECTIONCRITERIA Eachpartofthecalibrationsystemmustmeetcertainperformance criteriatoinsurethatthesystemisoperatingunderoptimumconditions .The chamberandorificecriteriaarediscussedabove. Thethreeremainingparts o... Open at page → 22 Page 22 Theperformanceofthesegagesisdiscussedinthesectiononerrors. Withcarefuluse,thecalibrationofthegagewillchangenomorethan2%over a2-yearperiod. TheFlowmeter ,Allletterreferencesinthissectionaretofigure1. TheGases Becausetheor... Open at page → 23 Page 23 pistons,respectively. Thepistonsarecoupledtosteppingmotorsthrough bellowsandtwenty-turns-per-inchmicrometerscrews. Thereisabout one-quarterturnbacklashinthepistondrivebutthishasnoeffectasthe pistonisalwaysdriveninthesame... Open at page → 24 Page 24 Theflowmeteristhermallyinsulatedbutnottemperature-controlled. It isinsulatedwithpolystyrene toprotectitfromshort-termtemperature fluctuationsandinsureinternaluniformity. Asecondquartzthermometer is locatedinsidethepolyst... Open at page → 25 Page 25 foundturbomolecular pumpstobesatisfactory iftheMDGsaremountedwith care . IV.OPERATIONALPROCEDURESFORCALIBRATIONUSING THENISTHIGHVACUUMSTANDARD Thissectiondescribesinsomedetailtheoperationoftheorifice-flow standard. Users... Open at page → 26 Page 26 INSTALLATIONANDPREPARATIONOFGAGES Bake-Out Eachventingofthesystemmustbefollowedbyacompletebakingofthe chamberandinletlines. Thechamberisdesignedtobebakedattemperatures upto250°C.Thegaspisonflowmetermaynotbebakedbecauseof... Open at page → 27 Page 27 becausetheinletlineisgroundedattheflowmeterandatthechamber. The inletlineshouldsizzlewhenwaterisdroppedonit.Inaddition, theheater ontheturbomolecular pumpshouldbestarted. Theovenshouldremainattemperatureforatleast8hours.... Open at page → 28 Page 28 checkedandadjustedifnecessaryandthezerosoftheelectrometers shouldbe setbymechanicaladjustmentonahigh-rangescaleandelectricaladjustment atlow-rangescalereadingsafterremovingthecollectorlead. Forpressuresatthelowendofthera... Open at page → 29 Page 29 Pa.Then,gasmaybeintroducedintotheappropriatehalfofthechamberfrom theflowmeter. Dependingonthecalibrations tobedone,theflowmetermaybeusedto generateaknownflowofgasoritmaybeusedsimplytoestablishasteady flow.Thesecondcaseis... Open at page → 30 Page 30 finalreadingshouldbeslightlypositive. Oncethevalveisclosed,the pressureintheworkingreservoirwillstarttofallbecausegasisflowing outofthereservoirintothechamber. Anytimebeforethedifferential pressurereadingbecomesnegative,... Open at page → 31 Page 31 chamberandthegagesaremonitoreduntilthereadingsaresteady. Atthis timethegagesareread:MDGreadingsarestarted,theIGsarereadonce,and thentheIGsarereadinreverseorder. Theanalysisofthegagereadings is describedbelowwiththeexcept... Open at page → 32 Page 32 Thereferencereservoirtemperaturebeforeandaftertherun, . Whentheflowisintotheupperchamber,theformulausedtocalculatethe pressureis Pu =(Q/C)(Rp)/(Rp-l) (3) whereQisthethroughputintotheupperchambergivenby Q=Pf,(dV/dt)(T,h/T... Open at page → 33 Page 33 S=(I, -I,„)/(I,P) (13) (14) where R,,isaresistorspecifictothecontrollerandtheemissioncurrent range, isthevoltagedropacross ,1^istheemissioncurrent, isthe measuredcollectorcurrent, EisarangefactorfortheelectrometerandPis... Open at page → 34 Page 34 sincetheorificeisanidealsink. Thiscontributionwilldecreasethe pressureatthegageportsfromthatgivenineq(7)byafactorof0.99956. Thesecondcontribution ismoredifficulttocalculatebecausethe scatteringoftheinletflowproducesadiff... Open at page → 35 Page 35 resultsarebasedonthereadingsof12MDGstakenoveraperiodofkdaysand aresummarizedintableIIIbelow. Totaldeviationsareexpressedasthemean differencebetweenthepressureindicatedbytheMDGsandpressuregenerated bythehighvacuumstandard... Open at page → 36 Page 36 pressuresassumesthatpumpspeeddoesnotchangewithdecreasingpressure. Anychangeinthepumpspeedwillcauseerrorsinthecalculatedpressure, withcorresponding errorsinthesensitivityofanygagecalibrated. In particular, adecreaseinpump... Open at page → 37 Page 37 RANDOMERRORS Upperboundsontherandomerrorscanbesetbyevaluatingthevariation ofrepeatedgagecalibrations. Thesenumberswill,ofcourse,includethe randomerrorsofthegagesaswellasthoseofthestandard. Ameasureoftheshort-termrepeatab... Open at page → 38 Page 38 Amorerealisticassessmentoftherandomerrorscanbeobtainedfrom calibrationsrepeatedondifferentdays. Forflowintotheupperchamberwe expectthaterrorsatthelowestpressureswillbedominatedbyrandom flowmetererrors. Thedatainfigure4a)... Open at page → 39 Page 39 ThetabulatedrandomerrorsareupperboundsbasedonrepeatedMDG calibrationswithnitrogenandargon. Theseincludedtherandomerrorsofthe standard,flowmeterandgages. Thevalueat 10"'' Paisbasedonthreetimes theshort-termdeviationsobser... Open at page → 40 Page 40 VI.OOALITYCONTROL Thedeterminationofsystematicandrandomerrorsinaprimarystandard isbutthefirststepincharacterizing itsperformance. Byitsverynature, aprimarystandardisdifficulttomonitoroverlongperiodsoftimeand variouslabor... Open at page → 41 Page 41 Bourdongage. Someinitialworkhasbeendonetocomparethetwoflowmeters usingbothstandardleaksandMDGsastransferstandards. Theleakworkhas beendoneatlowflowrateswhiletheMDGworkhasofnecessitybeendoneat muchhigherflowrates. ElevenM... Open at page → 42 Page 42 AsecondsetoffourballswassenttoNISTin1986inacontinuation of theroundrobin. PreliminaryresultsindicatethatthemeanofthefourNIST valuesforargonwaswithin0.5%ofthepilotlaboratory'svalue. Theresults forninelaboratories (represe... Open at page → 43 Page 43 IonGageComparisons IongagesarenotasstableasMDGsandwedonotexpecttogainasmuch informationaboutsystemperformancefromouriongagedata. However,because ofthebroadpressurerangecoveredbythesegages,wecanusethem tolook forsystemati... Open at page → 44 Page 44 of1-2%in2year'stime.Thesepa^rticularcustomersareknowledgeable users ofthegageandweexpectthattherotorshavebeentreatedcarefullybetween calibrations. VII.NEEDSANDPLANS Themajorlimitationsofthissystemare1)thepresenceofelasto... Open at page → 45 Page 45 automation,amongthosebeingtherecordingofthepistondriveinformation, therecordingofCDGandtemperatureinformation, andtherecordingofMDG transferstandardreadings. ThoseIGswhicharetestedonNIST-designed controllersmayalsoberead... Open at page → 46 Page 46 Martinforhiseffortsinthemanufactureandassemblyofthemanycomponents involved. IX.REFERENCES [I] K.E.McCulloh, C.R.Tilford, C.D.Ehrlich, andF.G.Long,"Low-Range FlowmetersforUsewithVacuumandLeakStandards," J.Vac.Sci.Technol.... Open at page → 47 Page 47 [15]P.L.M.Heydemann, C.R.Tilford,andR.W.Hyland,"Uitrasonic ManometersforLowandMediumVacuaunderDevelopmentattheNational BureauofStandards," J.Vac.Sci.andTechnol. 14,597(1977). [16]R.W.Hyland,"NISTMeasurementServices:Calib... Open at page → 48 Page 48 VacuumGageCalibration : "CalibrationofSpinningRotorGasFrictionGaugeAgainstaFundamentalVacuum PressureStandard," G.Comsa,J.K.Fremerey,andB.Lindenau(KFA)and G.MesserandP.Rohl(PTB) ,J.Vac.Sci.Technol. 17,642(1980). "TheCali... Open at page → 49 Page 49 Gas Inlet Line Gas Supply Cylinder n Ballast Volume A Working Reservoir Variable Leak H 1 to Chamber u Reference Volume B Figure1.SchematicofthePrimaryHighVacuumStandardIncludingthe Chamber,theFlowmeterandtheOrifice. Let... Open at page → 50 Page 50 Valve Gas Bakeable OrificePlateLifting Mechanism Baffle Orifice Plate Baffle Bakeable Valve ) Spinning Rotor Gage ^Bakeable Valve To Turbopump Figure2.SchematicoftheVacuumChamberShowingtheLifting ^ MechanismandSealingMet... Open at page → 51 Page 51 Figure3.AxialSectionoftheOrificePlate,withDimensions inInches. DetailsoftheCentralDuctareShowninfigure7.ThisPlate canbeRaisedtoProvideaLargeConductanceBetweentheUpper andLowerChambersoftheDynamicExpanderDuringEvacuation.... Open at page → 52 Page 52 Figure4.Representative MeasuredLow-PressureNitrogenSensitivities for DifferentIonGages. Sensitivities forEachGageareRelativeto itsValueat10'*Pa.The+'sIndicateFlowintotheLower Chamber,theO'sareintotheUpperChamber. TheData... Open at page → 53 Page 53 Figure5.DeviationsfromtheInitialValueoftheEffectiveAccommodation CoefficientofFiveMolecularDragGageRotorsasDeterminedby CalibrationsAgainsttheNISTPrimaryHighVacuumStandard. All DatawereTakenUsingNitrogenGas.Valueshavebee... Open at page → 54 Page 54 0.10 (0 a I0.05 - c (0 -5 -4 -3 LogPressure,Pa 0.06 (0 Q. 0.05 0) I0.04 XXXX 5 X >, X X * tA? 0.03 -8 -6 -5 -4 -3 LogPressure,Pa a)andb)IonGageSensitivity inNitrogenforTwoDifferent UltraHighVacuumIonizationGages'asDeterm... Open at page → 55 Page 55 I i (0,0,-a) I I z Figure7.DetailoftheCentralDuctThroughtheOrificePlate. The SurfacesMarkedAandBareSphericalSegmentsLappedto RadiusofCurvatureR,andTheirCentersofCurvatureare MarkedwithCoordinates (0,0,-a)and(0,0,a).Respe... Open at page → 57 Page 57 XI.APPENDICES APPENDIXA SAMPLEREPORTOFCALIBRATIONFOR IONIZATIONGAGE IonGageTubeandController Submittedby CUSTOMERNAME CITY,STATEZIP TPDCalibrationNumber: HVXX NISTIdentification ofGage:XXX SupplierofGage:SUPPLIER GageMod... Open at page → 58 Page 58 Pa.Usingcalibratedmoleculardraggages,theestimateduncertainty inthe generatedpressurebetween 10"'' and10" •'• Pais1.6%±2x10"^Pa, Thegagetubewasmountedonthecalibrationchamberandevacuatedand bakedovernightat250"C.Itwasdegas... Open at page → 59 Page 59 Theoperatingparametersoftheelectrometerwereindependently checked andarenotedbelow,foryourinformation. Thecontrollerrequired approximately 24hoursafterbeingturnedontoreachastableindication. CurrentatCollector Input.Amps I... Open at page → 61 Page 61 APPENDIXB SAMPLEREPORTOFCALIBRATIONFOR MOLECULARDRAGGAGE SpinningRotorVacuumGage Submittedby CUSTOMERNAME CITY,STATEZIP TPDReferenceNumber: HVX NISTIdentification ofFlange: 654321 Manufacturer's Identification ofFlange:... Open at page → 62 Page 62 Atthetimeoftest,thepickupsignalfromtheball,theresidualdrag andthefrequencydependenceoftheresidualdragwereallmonitored. Allof thesefactorsmaychangeduringuseandmustberedetermined atthetimeof use.Theballwasremagnetizeduntil... Open at page → 63 Page 63 Theeffectiveaccommodationcoefficientgivenfortheballappliesonly fornitrogen. Beforethegageisused,thechambertemperature, inkelvins,mustbe enteredfromthefrontpanelofthecontrollerasaparameter. Temperature correctionsmustbema... Open at page → 65 Page 65 APPENDIXC DIMENSIONSANDCONDUCTANCEOFTHEORIFICE INTHENISTDYNAMICEXPANDER* Introduction TheorificeintheNISTdynamicexpansionapparatuswasdesignedand fabricatedin1980tosatisfythreeconditions; 1. Sufficientthicknesstoensuredim... Open at page → 66 Page 66 Gallagher,whoreportedavalueItCq=0.4425in±0.00003in,whererQisthe radius. Eachofthesphericalsegmentsterminatesatanaxialdistance b=0.0150in±0.0005infromtheplaneofthethroat. Transitiontothefull thicknessoftheorificeplateisma... Open at page → 67 Page 67 0.99995< <0.99997. Acarefullydesignedconicaltransitioninplaceofanabruptstepwould requireacorrectionfactormuchclosertounity. Unfortunately, designand fabricationprecededrecognitionofthispoint. Fromthecomputedresultsandunc... Open at page → 68 Page 68 -W= J h(z)p(z)dz, (C2) -b wherep(z),translating itsverbaldefinitionintomathematical form,isthe solutionoftheinhomogeneous Fredholmintegralequationofthesecondkind p(z)= Po(z) + [ g(z,u)p(u)du. (C3) J-b Thesetwoequationspr... Open at page → 69 Page 69 Becauseofeq(C6)itsuffices,toexpandtheintegraleq(C3)onlyinthe rangeofpositivez.Aftersomemanipulation theresultbecomes pb 2Rp(z)=R-a+A-2R g(-z,u)p(u)du; 0<z<b , where j.b p(u)du. Integratingeq(C8) where (2R-b)A=b(R-a) -B,... Open at page → 70 Page 70 Gas Conductance CL/s) H2 43.52 He 30.89 N2 11.675 Ar 9.777 Theeffectofdeviationsfromthecosinelawofscatteringisbeyondthe scopeofthisreport.Asimplemodel,basedontheassumptionthatasmall fractionofmoleculesundergoesspecularre... Open at page → 71 Page 71 APPENDIXC-I ListofSymbols R: radiusofcurvatureofsurfacesAandB(fig.7). r^, :radiusofthethroat , a: distancefromthecenterofthethroattothecenterofcurvatureof surfaceAorsurfaceB. a^= -r^,^ b: distancefromthecenteroftheentran... Open at page → 73 Page 73 APPENDIXC-II TheIntegralAandtheTransmissionProbabilityK TheIntegralAandthetransmissionprobabilityKhavebeennarrowly boundedwithoutsolvingintegraleq(C8) .Firsttheintegrals f ^ I(z)=2R g(z,u)du; -b<x<0 J 0 and J= I(z)dz J-b... Open at page → 74 Page 74 Assigningnominalvaluestotheorificedimensionsandsolvingthissystemfor thebounds, 0Ti476T<~i(zyT'O48l27^^^^^^ 0<z<b Fromeq(C12)andtheseboundsonA, ' 0.991672<t<(T.991677. HenceK=0.99167tofivedecimalplaces,withanuncertaintyof... Open at page → 75 Page 75 NBS-n4A(REV.2-80) U.S.DEPT.OFCOMM.. BIBLIOGRAPHICDATA SHEET(Seeinstructions) 1.PUBLICATIONOR REPORTNO. NIST/SP-250/34 2.PerformingOrgjui.ReportNo,3.PublicationDate March1989 4.TITLEANDSUBTITLE NISTMeasurementServices:Hig... Open at page → 79 Page 79 THESP250SERIESONNISTMEASUREMENTSERVICES* SP250-1 Spectra)RadianceCalibrations SN003-003-O2792-8 $3.50 SP250-2 FarUttravloletDetectorStandards PB87227609 SP250-3 RadiometricStandardsintheVacuum Uitraviolet PB87227625 SP25... Open at page → 80 Page 80 U.S.DepartmentofCommerce NationalInstituteofStandardsandTechnology (formerlyNationalBureauofStandards) Galthersburg.MD20899 OfficialBusiness PenaltyforPrivateUse$300 Open at page →