ASTM_E_1750_-_10.pdf

Designation:E175010Standard Guide forUse of Water Triple Point Cells1This standard is issued under the fixed designation E1750;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.INTRODUCTIONThe triple point of water is an important thermometric fixed point common to the definition of twotemperature scales of science and technology,the Kelvin Thermodynamic Temperature Scale(KTTS)and the International Temperature Scale of 1990(ITS-90).The ITS-90 was designed to be as close tothe KTTS as the experimental data available at the time of the adoption of the ITS-90 would permit.The temperatures(T)on the KTTS are defined by assigning the value 273.16 K to the triple point ofwater,thus defining the thermodynamic unit of temperature,kelvin(K),as 1/273.16 of thethermodynamic temperature of the triple point of water(1,2).2The triple point of water,one of thefixed points used to define the ITS-90,is the temperature to which the resistance ratiosW(T)=R(T)R(273.16 K)of the standard platinum resistance thermometer(SPRT)calibrations arereferred.The triple points of various materials(where three distinct phases,for example,their solid,liquid,and vapor phases,coexist in a state of thermal equilibrium)have fixed pressures and temperatures andare highly reproducible.Of the ITS-90 fixed points,six are triple points.The water triple point is oneof the most accurately realizable of the defining fixed points of the ITS-90;under the best ofconditions,it can be realized with an expanded uncertainty(k=2)of less than 60.00005 K.Incomparison,it is difficult to prepare and use an ice bath with an expanded uncertainty(k=2)of lessthan 60.002 K(3).1.Scope1.1 This guide covers the nature of two commercial watertriple-point cells(types A and B,see Fig.1)and provides amethod for preparing the cell to realize the water triple-pointand calibrate thermometers.Tests for assuring the integrity ofa qualified cell and of cells yet to be qualified are given.Precautions for handling the cell to avoid breakage are alsodescribed.1.2 The effect of hydrostatic pressure on the temperature ofa water triple-point cell is discussed.1.3 Procedures for adjusting the observed SPRT resistancereadings for the effects of self-heating and hydrostatic pressureare described in Appendix X1 and Appendix X2.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:3E344 Terminology Relating to Thermometry and Hydrom-etryE1594 Guide for Expression of Temperature3.Terminology3.1 DefinitionsThe definitions given in Terminology E344apply to terms used in this guide.3.2 Definitions of Terms Specific to This Standard:3.2.1 inner melt,na thin continuous layer of water be-tween the thermometer well and the ice mantle of a watertriple-point cell.1This 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 May 1,2010.Published June 2010.Originallyapproved in 1995.Last previous edition approved in 2009 as E1750-09.DOI:10.1520/E1750-10.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For 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 3.2.2 reference temperature,nthe temperature of a phaseequilibrium state of a pure substance at a specified pressure,forexample,the assigned temperature of a fixed point.3.2.2.1 DiscussionAt an equilibrium state of three phasesof a substance,that is,at the triple point,both the temperatureand pressure are fixed.4.Significance and Use4.1 This guide describes a procedure for placing a watertriple-point cell in service and for using it as a referencetemperature in thermometer calibration.4.2 The reference temperature attained is that of a funda-mental state of pure water,the equilibrium between coexistingsolid,liquid,and vapor phases.4.3 The cell is subject to qualification but not to calibration.The cell may be qualified as capable of representing thefundamental state(see 4.2)by comparison with a bank ofsimilar qualified cells of known history,and it may be soqualified and the qualification documented by its manufacturer.4.4 The temperature to be attributed to a qualified watertriple-point c