ASTM_E_1594_-_11.pdf

Designation:E159411Standard Guide forExpression of Temperature1This standard is issued under the fixed designation E1594;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.1.Scope1.1 This guide covers uniform methods for expressingtemperature,temperature values,and temperature differences.1.2 This guide is intended as a supplement to IEEE/ASTMSI-10.2.Referenced Documents2.1 ASTM Standards:2E344 Terminology Relating to Thermometry and Hydrom-etryIEEE/ASTM SI-10 Standard for Use of the InternationalSystem of Units(SI):The Modern Metric System3.Terminology3.1 GeneralStandard terms used in this guide are definedin Terminology E344 and in IEEE/ASTM SI-10.4.Basic Concepts4.1 Temperature is a fundamental measurable quantity des-ignated by the symbol T or the symbol t(see 5.1).Inexpressions of dimensions the symbol u is sometimes used toindicate the dimension temperature.4.2 A temperature value is expressed in terms of a tempera-ture scale.The complete description consists of a numericalvalue designating the magnitude,a unit,and,where appropri-ate,a tolerance or uncertainty.Both the numerical value andthe unit depend upon the scale.4.3 A unit of temperature is understood to mean an intervalon a temperature scale.4.4 A temperature difference,interval,or increment is alsodescribed by a numerical value designating the magnitude,aunit,and,where appropriate,a tolerance or uncertainty.5.Temperature Scales5.1 Thermodynamic Temperature Scales:5.1.1 By international agreement,the theoretical tempera-ture scale to which all temperature values should be ultimatelyreferable is the Kelvin Thermodynamic Temperature Scale(KTTS).A value of temperature expressed on the KTTS isknown as a thermodynamic temperature,symbol T.5.1.2 The unit of thermodynamic temperature is the kelvin,symbol K.The kelvin is a base unit in the International Systemof Units(SI).Note that the symbol for the kelvin is the capitalletter K only;the degree sign()is not used.5.1.3 The expression of a value of thermodynamic tempera-ture is written:T 5 nkK(1)where:nk=a numerical value designating the magnitude,K=the symbol for the unit kelvin.The magnitude may also be represented by the notation T/K.5.1.4 A thermodynamic temperature may be expressed as aCelsius temperature.The symbol t is to be used to designate aCelsius temperature,but if this symbol leads to a conflict innotation in a given context,it is acceptable to use the symbolT instead to designate a Celsius temperature.5.1.5 The unit of Celsius temperature is the degree Celsius,symbol C.The degree Celsius is a derived SI unit.Note thatthe symbol for the degree Celsius consists of the degree sign()followed by the capital letter C.Neither the degree sign nor theletter C alone represents the degree Celsius.5.1.6 The expression of a value of Celsius temperature iswritten:t 5 nc7C(2)where:nc=a numerical value designating the magnitude,C=the symbol for the unit degree Celsius.The magnitude may also be represented by the notation t/C.5.1.7 By definition,at any temperature,a temperature incre-ment of one degree Celsius is equal to a temperature incrementof one kelvin.1This guide is under the jurisdiction of ASTM Committee E20 on TemperatureMeasurement and is the direct responsibility of Subcommittee E20.91 on Editorialand Terminology.Current edition approved Nov.1,2011.Published December 2011.Originallyapproved in 1994.Last previous edition approved in 2006 as E1594 06.DOI:10.1520/E1594-11.2For 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 5.1.8 By definition,the Celsius temperature t=0 C is thesame as the thermodynamic temperature T=273.15 K.Therelation between numerical values associated with both expres-sions of a temperature is therefore given by:nc5 nk2 273.15(3)where:t=ncC is the same temperature as T=nkK.5.2 Practical Temperature Scales:5.2.1 Practical temperature scales have been established byinternational agreement for the practice of temperature mea-surement.Among them are the International Practical Tem-perature Scale of 1968,the International Practical TemperatureScale of 1948,and the International Temperature Scale of1927.35.2.2 Practical scales are designed so that a numerical valueof temperature expressed on the scale is close to the numericalvalue of thermodynamic temperature.Because the KTTS isdifficult to implement,the vast majority of temperature mea-surements are based on a practical scale.5.2.3 There are two practical temperature scales now in use,superseding all other