Temperature international scale

The new international temperature scale, known as ITS-90, was adopted in September 1989. However, neither the definition of thermodynamic temperature nor the definition of the kelvin or the Celsius temperature scales has changed it is the way in which we are to realize these definitions that has changed. The changes concern the recommended thermometers to be used in different regions of the temperature scale and the list of secondary standard fixed points. The changes in temperature determined using ITS-90 from the previous IPTS-68 are always less than 0.4 K, and almost always less than 0.2 K, over the range 0-1300 K. 

Defining fixed points of the International Temperature Scale of 1990 (ITS-90). Except for the triple points, the assigned values of temperature are for equilibrium states at a pressure of one standard atmosphere (101 325 Pa). 

Vapor pressure data for soHd carbon dioxide are given in Table 2 (10). The sublimation temperature of soHd carbon dioxide, 194.5 K at 101 kPa (1 atm), was selected as one of the secondary fixed points for the International Temperature Scale of 1948. 

Gas thermometers that employ equation (1.10) can be constructed to measure either pressure while holding the volume constant (the most common procedure) or volume while holding the pressure constant. The (pV) product can be extrapolated to zero p. but this is an involved procedure. More often, an equation of state or experimental gas imperfection data are used to correct to ideal behavior. Helium is the usual choice of gas for a gas thermometer, since gas imperfection is small, although other gases such as hydrogen have also been used. In any event, measurement of absolute temperature with a gas thermometer is a difficult procedure. Instead, temperatures are usually referred to a secondary scale known as the International Temperature Scale or ITS-90. 

The International Temperature Scale — ITS-90 For ITS-90, temperatures of a series of fixed points are measured as accurately as possible with a gas thermometer. A complete description of ITS-90 is given in the literature5 7 and... 

ITS-90 is the latest in a series of international temperature scales. Each represents an improvement over an earlier scale as more reliable values for the fixed points are established. It has been the practice to update the ITS temperature scale approximately every twenty years. Earlier scales include (ITS-27), (ITS-48), (IPTS-68), and a provisional scale in 1976. 

The ability to measure temperature and temperature differences accurately and reproducibly is essential to the experimental study of thermodynamics. A thermometer constructed with an ideal gas as its working fluid yields temperatures that correspond to the fundamental thermodynamic temperature scale. However, such thermometers are extremely difficult to use, are not amenable to miniaturization, and are very expensive. Therefore, other means to measure temperatures that reproduce the ideal gas or thermodynamic temperature scale (Kelvin) have had to be developed. The international temperature scale represents a method to determine temperatures over a wide range with measuring devices that are easier to use than the ideal gas thermometer. The goal is to make temperature measurements that correspond to the thermodynamic temperature as accurately as possible. 

The international temperature scale is based upon the assignment of temperatures to a relatively small number of fixed points , conditions where three phases, or two phases at a specified pressure, are in equilibrium, and thus are required by the Gibbs phase rule to be at constant temperature. Different types of thermometers (for example, He vapor pressure thermometers, platinum resistance thermometers, platinum/rhodium thermocouples, blackbody radiators) and interpolation equations have been developed to reproduce temperatures between the fixed points and to generate temperature scales that are continuous through the intersections at the fixed points. 

Approximately every twenty years, the international temperature scale is updated to incorporate the most recent measurements of the equilibrium thermodynamic temperature of the fixed points, to revise the interpolation equations, or to change the specifications of the interpolating measuring devices. The latest of these scales is the international temperature scale of 1990 (ITS-90). It supersedes the earlier international practical temperature scale of 1968 (IPTS-68), along with an interim scale (EPT-76). These temperature scales replaced earlier versions (ITS-48 and ITS-27). 

Table A2.1 Fixed points for the International Temperature Scale, ITS-90...

The original reports on 1TS-90 are found in B. W. Mangum. "Special Report on the International Temperature Scale of 1990. Report on the 17th Session of the Consultative committee on Thermometry." J. Res. Natl. Inst. Stand. TeehnoL. 95. 69 (1990) H. Preston-Thomas, The International Scale of 1990 (ITS-90)." Metro/ogia. 27. 3 (1990). 

The XVIII Conference Generale des Poids et Mesures adopts the version of the International Temperature Scale ITS-90 The ITS-90 provides die best to-date practical approximation of die thermodynamic scale and offers a reproducibility that is better than the thermodynamic scale. 

BIPM Techniques for Approximating the International Temperature Scale of 1990, Bureau International des Poids et Mesures, Sevres (1990)... 

Techniques for accurate and reproducible measurement of temperature and temperature differences are essential to all experimental studies of thermodynamic properties. Ideal gas thermometers give temperatures that correspond to the fundamental thermodynamic temperature scale. These, however, are not convenient in most applications and practical measurement of temperature is based on the definition of a temperature scale that describes the thermodynamic temperature as accurately as possible. The analytical equations describing the latest of the international temperature scales, the temperature scale of 1990 (ITS-90) [1, 2]... 

Above the freezing point of silver, Tgq is defined in terms of a defining fixed point and the Planck radiation law, and optical pyrometers are frequently used as temperature probes. The Comite Consultatif de Thermometrie gives a thorough discussion of the different techniques for approximation of the international temperature scale of 1990 [2, 4],... 

Supplementary Information for the International Temperature Scale of1990. Paris Bureau International des Poids etMesures, 1990. 

Vittadini, E., Dickinson, L.C., and Chinachoti, P. 2002. NMR water mobility in xanthan and locust bean gum mixtures Possible explanation of microbial response. Carbohydr. Polym. 49, 261-269. Wachner, A.M. and Jeffrey, K.R. 1999. A two-dimensional deuterium nuclear magnetic resonance study of molecular reorientation in sugar/water glasses. J. Chem. Phys. Ill, 10611-10616. Wagner, W. and Pruss, A. 1993. International equations for the saturation properties of ordinary water substance Revised according to the international temperature scale of 1990. J. Phys. Chem. Ref. Data 22, 783-787. 

International Titanium Association, The (ITA), safety committee of, 24 865 International Technical Roadmap for Semiconductors (ITRS), 75 181 International temperature scales (ITS), 75 749 24 436... 

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