International Temperature Scale of 1990 ITS

Defining fixed points of the International Temperature Scale of 1990 (ITS-90)  

Vapor pressure equation of helium 3 to 5 -270.15to -454.27to 

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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). 

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). 

A temperature of 0 K is called absolute zero . It coincides with the minimum molecular activity, i.e., thermal energy of matter. The thermodynamic temperature was formerly called absolute temperature . In practice, the International Temperature Scale of 1990 (ITS-90) [i] serves as the basis for high-accuracy temperature measurements. Up to 700 K, the most accurate measurements of thermodynamic temperature are the NBS/NIST results for Constant Volume Gas Thermometry (CVGT). Above 700 K, spectral radiometry is used to measure the ratio of radiances from a reference... 

The International Practical Temperature Scale of 1968 (IPTS-68) has been replaced by the International Temperature Scale of 1990 (ITS-90). The ITS-90 scale is basically arbitraiy in its definition but is intended to approximate closely the thermodynamic temperature scale. It is based on assigned values of the temperatures of a number of defining fixed points and on interpolation formulas for standard instruments (practical thermometers) that have been cahbrated at those fixed points. The fixed points of ITS-90 are given in Table 1. 

The International Temperature Scale of 1990 (ITS-90) is in effect since January 1, 1990, (Mamayev et al., 1991). For oceanographic applications, a simple conversion formula (Saunders, 1990 Mamayev et al, 1991 Feistel and Hagen, 1995) is sufficiently accurate for theconversionbetween ITS-90 temperatures (tgo) and the former IPTS-68 temperatures (tgg), as... 

Temperature values to be used for the currently valid thermodynamic formulas (EOS-80) of seawater (Fofonoff and Millard, 1983 Mamayev et al., 1991) need to be expressed in the International Practical Temperature Scale of 1968 (IPTS-68). Practically measured temperatures are assumed to be in IPTS-68 before January 1, 1990, and in the International Temperature Scale of 1990 (ITS-90) afterward (Mamayev et al., 1991). Temperatures required for the thermodynamic potential functions for water, ice, and seawater need to be expressed in ITS-90, see Section 20.2.1. 

Saunders, P., 1990. The International Temperature Scale of 1990, ITS-90. Woce Newsletter 10. SCOR, 2006. Working groups reports. SCOR/IAPSO WG 127 on the Thermodynamics and Equation... 

Blackbody radiation is achieved in an isothermal enclosure or cavity under thermodynamic equilibrium, as shown in Figure 7.4a. A uniform and isotropic radiation field is formed inside the enclosure. The total or spectral irradiation on any surface inside the enclosure is diffuse and identical to that of the blackbody emissive power. The spectral intensity is the same in all directions and is a function of X and T given by Planck s law. If there is an aperture with an area much smaller compared with that of the cavity (see Figure 7.4b), X the radiation field may be assumed unchanged and the outgoing radiation approximates that of blackbody emission. All radiation incident on the aperture is completely absorbed as a consequence of reflection within the enclosure. Blackbody cavities are used for measurements of radiant power and radiative properties, and for calibration of radiation thermometers (RTs) traceable to the International Temperature Scale of 1990 (ITS-90) [5]. 

The standardized scale now used in temperature measurement is the International Temperature Scale of 1990 (ITS-90) [1-3]. ITS-90 has been designed to give values as close to the corresponding thermodynamic temperatures as practically possible. It covers the range of... 

A new temperature scale, the International Temperature Scale of 1990 (ITS-90), was officially adopted by the Comite International des Poids et Mesures (CIPM), meeting 26—28 September 1989 at the Bureau International des Poids et Mesures (BIPM). The ITS-90 was recommended to the CIPM for its adoption following the completion of the final details of the new scale by the Comite Consultatif de Thermometrie (CCT), meeting 12—14 September 1989 at the BIPM in its 17th Session. The ITS-90 became the official international temperature scale on 1 January 1990. The ITS-90 supersedes the present scales, the International Practical Temperature Scale of 1968 (IPTS-68) and the 1976 Provisional 0.5 to 30 K Temperature Scale (EPT-76). 

The first set of tables below lists, for each thermocouple type, the emf as a function of temperature on the International Temperature Scale of 1990 (ITS-90). The coefficients in the equation used to generate the table are also given. The second set of tables gives the inverse relationships, i.e., the coefficients in the polynomial equation which expresses the temperature as a function of thermocouple emf. The accuracy of these equations is also stated. 

Standard platinum resistance thermometers (SPRTs) are the most accurate and most delicate RTDs in existence. Their applications are largely limited to standard laboratories and other applications requiring temperature accuracies of 1 mK or better. SPRTs are the primary interpolation instrument in the very definition of temperature in the International Temperature Scale of 1990 (ITS-90) from 13.8033 K (the triple point of... 

Whenever necessary, values taken from the literature have been converted into SI units using the appropriate conversion factors. Temperatures are based on the International Temperature Scale of 1990 (ITS-90). The molar quantities are based on the 2005 table of the lUPAC Commission on Atomic Weights and Isotopic Abundances. The standard atomic weights apply to elements as they exist naturally on Earth (natural abundance of the stable nuclides) (06LID1). 

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