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| International Temperature Scale | |
|---|---|
| Name | International Temperature Scale |
| Abbreviation | ITS |
| Established | 1927 |
| Jurisdiction | International Bureau of Weights and Measures (BIPM) |
| Related | International System of Units, Kelvin (unit), Celsius scale |
| Type | Calibration standard |
International Temperature Scale The International Temperature Scale is an agreed set of practical definitions for the measurement of temperature used to realize the Kelvin (unit), support thermometry, and calibrate instruments across national metrology institutes such as the National Institute of Standards and Technology, Physikalisch-Technische Bundesanstalt, and National Physical Laboratory (United Kingdom). It provides fixed points, interpolation methods, and procedures adopted by organizations including the International Committee for Weights and Measures and the Consultative Committee for Thermometry to ensure international uniformity among laboratories like the National Research Council (Canada) and the Bureau International des Poids et Mesures. The scale underpins scientific work in institutions such as the Max Planck Society, French National Centre for Scientific Research, and Japan National Institute of Advanced Industrial Science and Technology.
The development began with early 20th-century efforts linking practices at institutes such as the National Physical Laboratory (United Kingdom), Bureau International des Poids et Mesures, and the Physikalisch-Technische Reichsanstalt. The 1927 inaugural scale involved delegates from International Committee for Weights and Measures, Royal Society, and Académie des sciences (France), and subsequent revisions were influenced by research at laboratories like the National Bureau of Standards and the International Union of Pure and Applied Physics. Notable milestones involved collaborations with the International Organization for Standardization, meetings of the General Conference on Weights and Measures, and work by scientists affiliated with Imperial College London, Harvard University, Massachusetts Institute of Technology, and University of Cambridge.
The scale is built on fixed thermodynamic states associated with substances studied at places such as the Cavendish Laboratory, Ludwig Maximilian University of Munich, and Sorbonne University. It defines interpolation equations and measurement protocols used by metrology centers including CSIRO, Swiss Federal Institute of Metrology (METAS), and Korea Research Institute of Standards and Science. Key theoretical underpinnings were developed in the context of work at University of Oxford, ETH Zurich, and Princeton University and draw upon thermodynamic results from scholars affiliated with institutions such as École Normale Supérieure (Paris), Columbia University, and Stanford University.
Fixed points include triple points and phase transitions of substances maintained in reference cells at laboratories like the National Physical Laboratory (India), CSIC, and Australian National University. Historical and modern fixed points reference the triple point of water, gallium, indium, aluminium, and vapor-pressure points studied at facilities including the Rutherford Appleton Laboratory, Los Alamos National Laboratory, and Oak Ridge National Laboratory. Calibration chains involve comparisons coordinated by the Comité Consultatif de Thermométrie and international key comparisons organized by the BIPM and regional bodies such as the European Association of National Metrology Institutes.
Practical realizations use standard platinum resistance thermometers and radiation thermometers developed and evaluated at centers like the National Institute of Standards and Technology, Physikalisch-Technische Bundesanstalt, National Metrology Institute of Japan, Bureau National de Métrologie, and Swedish National Testing and Research Institute. Instrumentation includes devices traceable to artifacts maintained at Jet Propulsion Laboratory, Naval Research Laboratory, and university labs at University of Tokyo and University of California, Berkeley. Techniques originated from collaborations among groups at CERN, Los Alamos National Laboratory, and Lawrence Berkeley National Laboratory and are endorsed by committees such as the International Committee for Weights and Measures.
Major published versions include ITS-27, ITS-48, ITS-68, and ITS-90, each adopted following technical input from organizations like the International Union of Pure and Applied Physics, International Organization for Standardization, and national institutes including NPL, NIST, and PTB. These revisions reflect advances reported in journals where researchers from University of Chicago, University of Illinois Urbana-Champaign, University of Manchester, University of Sydney, and University of Toronto contributed. Implementation involved international comparisons coordinated by the BIPM and technical committees at IEEE conferences and meetings of the International Measurement Confederation.
The scale supports precision work in cryogenics at laboratories like Argonne National Laboratory, Kavli Institute for Theoretical Physics, and Max Planck Institute for Quantum Optics, high-temperature metallurgy research at Imperial College London and ETH Zurich, and climate science instrumentation developed by teams at Scripps Institution of Oceanography, NOAA, and Met Office. It underlies calibration services offered by organizations such as Underwriters Laboratories, Intertek, and national services including Measurement Canada and INMETRO (Brazil), enabling traceable measurements used in industries represented by Siemens, Boeing, and Airbus. The scale also facilitates international standards in projects involving European Space Agency, NASA, JAXA, and Roscosmos.
Limitations arise from realization uncertainties evaluated by interlaboratory comparisons involving BIPM, EURAMET, and APMP networks, and from material impurities studied at research centers such as Lawrence Livermore National Laboratory and Argonne National Laboratory. Sources of uncertainty include cell construction, thermometer self-heating, and radiometric calibration techniques developed at NPL, PTB, and NIST. Ongoing research at universities like University of Wisconsin–Madison, University of Maryland, and McGill University addresses discrepancies between ITS realizations and thermodynamic temperature determinations pursued at institutes including National Metrology Institute of Japan and NPL.