ASTM_E_1502_-_10.pdf

Designation:E150210Standard Guide forUse of Fixed-Point Cells for Reference Temperatures1This standard is issued under the fixed designation E1502;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONDuring melting and freezing,pure material transforms from the solid state to the liquid state or fromthe liquid state to the solid state at a constant temperature.That constant temperature is referred to asa fixed point.Fixed points approached in the melting direction are referred to as melting points andfixed points approached in the freezing direction are referred to as freezing points.Fixed points ofhighly purified materials can serve as reference temperatures,and in fact,the InternationalTemperature Scale of 1990(ITS-90)2relies on the melting and freezing points of some highly purifiedmetals as defining fixed points.Fixed points can be realized in commercially available systemsincorporating fixed-point cells.When the cells are properly made and used,they establish usefulreference temperatures for the calibration of thermometers and for other industrial and laboratorypurposes;with care,these fixed points can be realized with an uncertainty of a few millikelvins3orless.1.Scope1.1 This guide describes the essential features of fixed-pointcells and auxiliary apparatus,and the techniques required torealize fixed points in the temperature range from 29 to1085C.31.2 Design and construction requirements of fixed-pointcells are not addressed in this guide.Typical examples aregiven in Fig.1 and Fig.2.1.3 This guide is intended to describe good practice andestablish uniform procedures for the realization of fixed points.1.4 This guide emphasizes principles.The emphasis onprinciples is intended to aid the user in evaluating cells,inimproving technique for using cells,and in establishing pro-cedures for specific applications.1.5 For the purposes of this guide,the use of fixed-pointcells for the accurate calibration of thermometers is restrictedto immersion-type thermometers that,when inserted into thereentrant well of the cell,(1)indicate the temperature only ofthe isothermal region of the well,and(2)do not significantlyalter the temperature of the isothermal region of the well byheat transfer.1.6 This guide does not address all of the details ofthermometer calibration.1.7 This guide is intended to complement special operatinginstructions supplied by manufacturers of fixed-point appara-tus.1.8 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.9 The following hazard caveat pertains only to the testmethod portion,Section 7,of this guide.This standard does notpurport to address all of the safety concerns,if any,associatedwith its use.It is the responsibility of the user of this standardto establish appropriate safety and health practices anddetermine the applicability of regulatory limitations prior touse.2.Referenced Documents2.1 ASTM Standards:4E344 Terminology Relating to Thermometry and Hydrom-etry1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.07 on Funda-mentals in Thermometry.Current edition approved Nov.1,2010.Published January 2011.Originallyapproved in 1992.Last previous edition approved in 2003 as E1502 98R03E01.DOI:10.1520/E1502-10.2Preston-Thomas,H.,“The International Temperature Scale of 1990(ITS-90),”Metrologia,Vol 27,No.1,1990,pp.310.For errata see ibid,Vol 27,No.2,1990,p.107.3In this guide,temperature intervals are expressed in kelvins(K)and millikel-vins(mK).Values of temperature are expressed in degrees Celsius(C),ITS-90.4For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 E644 Test Methods for Testing Industrial Resistance Ther-mometers3.Terminology3.1 Definitions:3.1.1 reference temperature,na fixed,reproducibletemperature,to which a value is assigned,that can be used forthe calibration of thermometers or other purposes.3.1.2 Additional terms used in this guide are defined inTerminology E344.3.2 Definitions of Terms Specific to This Standard:3.2.1 first cryoscopic constant,A,na constant of propor-tionality between the freezing point depression of,and concen-tration of impurities in,a sample of reference material,givenby the ratio of the molar heat of fusion of the pure material,L,to the product of the molar gas constant,R,and the square ofthe thermodynamic temperature of fusion,T,of the purematerial(freezing po