Designation:B77–81(Reapproved2001)
StandardTestMethodfor
ThermoelectricPowerofElectrical-ResistanceAlloys1ThisstandardisissuedunderthefixeddesignationB77;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(e)indicatesaneditorialchangesincethelastrevisionorreapproval.
1.Scope
1.1Thistestmethodcoversthedeterminationofthether-moelectricpowerofametaloralloywithrespecttocopperwhenthetemperaturesofthejunctionsliebetween0and100°C.
1.2Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.
1.3Thevaluesstatedininch-poundunitsarethepreferredunit.Thevaluesinparenthesesareforinformationonly.2.ReferencedDocuments2.1ASTMStandards:
B3SpecificationforSoftorAnnealedCopperWire23.Terminology
3.1thermoelectricpower,Q—theelectromotiveforceinanelectriccircuitconsistingoftwometalswhenthejunctionsbetweenthemhaveadifferenceintemperatureof1°C.
3.1.1Discussion—Experimentally,ithasbeenfoundthatthethermoelectricpoweroftwometalsisnotaconstantbutdependsonthemeantemperatureofthejunctions.However,overarangeoftemperaturefrom0to100°Citisusuallysufficienttoassumethatthethermoelectricpowerisindepen-dentoftemperaturesothatforthisrangeoftemperature:
Q5E/~t82t!
alowthermoelectricpowerisdesired.Asmostelectriccircuitsarelargelycomposedofcopper,thethermoelectricpowerofaresistancemetalwillgenerallybemeasuredagainstcopper.5.TestSpecimen
5.1Themetaloralloytobetestedshallbeintheformofsheet,ribbon,orwireandthetestspecimenshallbeofsuchlengththatthetwoendscanbereadilymaintainedatdifferenttemperatures.Ateachendofthespecimenacopperleadofconvenientsizeshallbefastened.Theseleadsshallmakegoodelectricalcontactwiththespecimen,suchasthatobtainedbywelding,brazing,orsoldering.Slightimpuritiesinthecopperhaveanegligibleeffectonthethermoelectricpower.
NOTE1—Whennecessarytospecifythequalityofthecopperleads,referenceshouldbemadetoSpecificationB3.
where:
E=theelectromotiveforcedevelopedinthecircuit,t8=thehighertemperatureatonejunction,°C,andt=thelowertemperatureattheotherjunction,°C.4.SignificanceandUse
4.1Thepurposeofthismethodistodeterminethesuitabil-ityofdifferentmetalsforuseinresistanceapparatusinwhich
ThistestmethodisunderthejurisdictionofASTMCommitteeB02onNonferrousMetalsandAlloysandisthedirectresponsibilityofSubcommitteeB02.10onThermostatMetals.
CurrenteditionapprovedNov.27,1981.PublishedJanuary1982.OriginallypublishedasB77–30T.LastpreviouseditionB77–33(1975).2AnnualBookofASTMStandards,Vol02.03.
16.Procedure
6.1MeasurementofTemperature—Asamatterofprecau-tion,theaveragetemperatureusedindeterminingthethermo-electricpowershallbeapproximatelythesameasthattowhichthematerialwillbesubjectedinpractice,andinnocaseshallthetemperaturedifferencebetweenthetwojunctionsbelessthan20°C.Thetemperatureateachoftwojunctionsshallbemeasuredbyadevicethatissufficientlyaccuratetodeterminethetemperaturedifferencewithin5%.Aconvenientmethodfordeterminingthetemperaturesofthejunctionsistoimmerseeachjunctioninseparateoilbathsmaintainedatthedesiredtemperatures.Bathsthatarestirredandthetemperaturesofwhicharethermostaticallycontrolledaretobepreferred.However,beakersofoilwhicharesupportedbyblocksofmetal,sandbaths,orothermeansmaybeused,providedthethermalcapacityoftheseassembliesissuchthatwhentheheatiscutofftheirtemperatureswilldecreaseatrateslessthan0.2°C/min.Thetemperatureoftheoilineachbathmaybedeterminedeitherbyacalibratedmercurythermometerorbyacalibratedthermocouple.Iftheoilisnotstirred,thejunctionsshallbeplacedincloseproximitytothetemperature-measuringinstrument.Toensurethatthetemperaturesofthejunctionsshallnotbeinfluencedbyheatofconductionalongthespecimen,thelengthofeachspecimenfromthejunctiontothepointwhereitleavesthesurfaceoftheoilshallnotbelessthan10timestheminimumcross-sectiondimensionofthe
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resistancematerial,norlessthan100timestheminimumcrosssectionofthecopperleads,andinnocaselessthan2in.(50.8mm).
6.2MeasurementofElectromotiveForce—Theelectromo-tiveforceshallbedeterminedbyamethodthatwillgivethevaluecorrectwithin5%.Threedifferentmethodsofmeasuringtheelectromotiveforceareincommonuse,namely:
6.2.1Themethodinwhichapotentiometerisusedtocomparetheunknownemfwiththatofastandardcell.
6.2.2Themethodinwhichtheunknownemfisequatedtothedifferenceofpotentialbetweentheterminalsofastandardresistorwhenameasuredcurrentflowsthroughit.
6.2.3Themethodinwhichtheemfismeasuredbythedeflectionofasuitablemeasuringinstrument.
6.2.4Inanycase,precautionsshallbetakentoensurethattherearenoparasiticelectromotiveforcesinthemeasuringcircuit,aconditionwhichmaybedeterminedbyplacingbothjunctionsinthesamebeaker,inwhichcasenoappreciableelectromotiveforceshallbeindicated.
7.PolarityoftheMetal
7.1Themetaloralloytestedshallbeconsideredtohavepositivepolaritywhen,inacircuitconsistingofcopperandthemetaloralloy,thedirectionofcurrentflowinthemetaloralloyisfromthejunctionhavingthehighertemperaturetotheonehavingthelowertemperature.
8.Report
8.1Thereportshallincludethefollowing:
8.1.1Thecharacterofthemetaloralloytestedandtheidentificationofthespecimen,
8.1.2Thesize,shape,andlengthofthespecimen,
8.1.3Methodofdeterminingthetemperaturesofthejunc-tions,
8.1.4ThetemperatureateachjunctionindegreeCelsius,8.1.5Thetypeofapparatususedinmeasuringtheelectro-motiveforce,
8.1.6Theobservedelectromotiveforce,8.1.7Thethermoelectricpower,and
8.1.8Thepolarityofthemetaloralloytested.
9.PrecisionandBias
9.1Thereproducibilityofthetestresultsdependsonthecontrolusedinmakingtheconnectionsandthecontroloftemperaturesatthejunctions.Thebiaswilldependontheparameterslistedforreproducibilityandinstrumentationusedtomeasureemf.
9.2Theprecisionofthistestmethodshouldbe1%orless.9.3Thebiasofthistestmethodiswithin6%.
10.Keywords
10.1copper;electricalresistantalloys;potentiometer;ther-moelectricpower
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