Principles of Temperature -ITS-90

Shortly after adoption of the International Practical Temperature Scale of 1968 (IPTS-68), it was realized the scale had many deficiencies and limitations. Consequently, the Comit Consultatif de Ther-mom trie (CCT) - one of eight specialized technical subcommittees of the Comit International des Poids et Mesures (CIPM) - undertook the development of a new scale. On 26-28 September 1989, the CCT recommended ITS-90 be adopted. Following approval by CIPM, ITS-90 became the official international temperature scale on 1 January 1990, when it also was implemented at the U.S. National Institute of Standards and Technology (NIST).

According to a detailed report by B.W. Mangum, of NIST's Center for Chemical Technology, National Measurement Laboratory, and NIST guest scientist G.T. Furukawa, ITS-90 - when compared to IPTS-68 - extends upward from 0.65 K. Also, temperatures on the newer scale are in much better agreement with thermodynamic values. In addition, ITS-90's continuity, non-uniqueness and reproducibility throughout its ranges are much improved over previous scales. The most complete and authoritative document on ITS-90 from NIST is Technical Note 1265 by Mangum and Furukawa. It is available as a pdf from NIST's web site:

http://www.cstl.nist.gov/div836/836.05/papers/magnum90ITS90guide.pdf