International Temperature Scale of 1990

International Temperature Scale of 1990
Marián Hubinský · CC BY-SA 4.0 · source
Name	International Temperature Scale of 1990
Abbreviation	ITS-90
Introduced	1990
Authority	International Committee for Weights and Measures
Superseded	International Practical Temperature Scale of 1968
Scope	Temperature metrology

International Temperature Scale of 1990

The International Temperature Scale of 1990 provides a practical, internationally agreed framework for assigning temperatures by reference to fixed points and interpolation instruments used by national laboratories, industry, and scientific organizations. It is intended to ensure comparability of temperature measurements across institutions such as the International Bureau of Weights and Measures, the National Institute of Standards and Technology, the Physikalisch-Technische Bundesanstalt, and the Bureau International des Poids et Mesures.

History and development

The development of the scale involved committees and conferences including the Consultative Committee for Thermometry, the General Conference on Weights and Measures, and working groups with participation from the International Organization for Standardization, the European Association of National Metrology Institutes, and national metrology institutes such as the National Physical Laboratory and the Laboratoire national de métrologie et d'essais. Influences on the 1990 scale trace to earlier practical scales like the International Practical Temperature Scale of 1968, discussions at the International Union of Pure and Applied Physics and the International Astronomical Union, and input from scientific figures affiliated with institutions such as the Royal Society and the American Physical Society. The design incorporated advances reported in journals reviewed by editors from the Journal of Chemical Physics, Metrologia, and Reviews of Modern Physics, and outcomes were presented at meetings alongside topics like thermodynamic temperature, the Kelvin redefinition debates involving committees of the International Committee for Weights and Measures and advisory panels linked to the Académie des sciences and the National Academy of Sciences.

Definitions and fixed points

The scale defines temperatures by reference to established fixed points including the triple point of water, the freezing or melting points of metals and alloys such as tin, zinc, aluminium, silver, and gold, and the triple points of gases like argon and neon. Fixed points derive from thermodynamic properties studied by laboratories including the Physikalisch-Technische Bundesanstalt, the National Institute of Standards and Technology, and the Laboratoire national de métrologie et d'essais, and are documented in publications associated with the International Bureau of Weights and Measures, the Consultative Committee for Thermometry, and the Comité International des Poids et Mesures. The ITS-90 specifies reference points tied to the international prototype standards and to phenomena originally investigated by researchers connected with institutions such as the Cavendish Laboratory, the École Normale Supérieure, and the Massachusetts Institute of Technology.

Realization methods and instruments

Realization of the scale employs primary thermometers and interpolation instruments including platinum resistance thermometers, standard platinum resistance thermometers maintained by national metrology institutes like the National Physical Laboratory and the National Institute of Standards and Technology, gas thermometers developed in laboratories associated with the Royal Institution, and radiation thermometers used in projects at organizations such as the European Space Agency and the National Aeronautics and Space Administration. Techniques rely on apparatus and methods refined in collaborations with universities including Cambridge University, Harvard University, Stanford University, and technical institutes such as the École Polytechnique and the Swiss Federal Institute of Technology. Instrument calibration and comparison campaigns have been coordinated through networks such as the International Bureau of Weights and Measures key comparisons program, regional metrology organizations including EURAMET and APMP, and projects funded by bodies like the European Commission and national science foundations.

Uncertainties and calibration practices

Estimates of uncertainty for ITS-90 realizations reference guidance from the International Organization for Standardization and protocols used by metrology institutes such as the Physikalisch-Technische Bundesanstalt, the National Institute of Standards and Technology, and the Laboratoire national de métrologie et d'essais, and incorporate statistical methods discussed by authors in journals like Metrologia and the Journal of Research of the National Institute of Standards and Technology. Calibration practices include intercomparisons conducted under auspices of the International Bureau of Weights and Measures, accredited laboratory procedures aligned with the Comité Européen de Normalisation, and traceability chains connecting industrial laboratories at Siemens, General Electric, and automotive test facilities to national standards. Uncertainty budgets reflect contributions evaluated using techniques originating from the Royal Society, the International Union of Pure and Applied Chemistry, and committees that have published guidance adopted by testing laboratories and calibration services.

Adoption, revisions, and successors

Adoption of the scale was formalized by the General Conference on Weights and Measures and implemented by national metrology institutes including the National Physical Laboratory, the National Institute of Standards and Technology, and the Physikalisch-Technische Bundesanstalt, with technical updates and guidance issued by the Consultative Committee for Thermometry and the International Bureau of Weights and Measures. Subsequent discussions about thermodynamic temperature and the redefinition of the kelvin involved stakeholders such as the International Committee for Weights and Measures, the International Union of Pure and Applied Physics, and the International Astronomical Union, leading to revisions in underlying constants considered by researchers at institutions including the National Research Council, the Max Planck Society, and the Royal Society. Successor frameworks and complementary conventions have been integrated into calibration infrastructures used by organizations such as the European Association of National Metrology Institutes, the Asia-Pacific Metrology Program, and the International Organization for Standardization.

Category:Temperature scales Category:Metrology Category:Standards