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2022 Update for the Differences Between Thermodynamic Temperature and ITS 90 Below 335 K



Christof Gaiser, Bernd Fellmuth, Roberto Maria Gavioso, Murat Kalemci, Vladimir Kytin, Tohru Nakano, Laurent Pitre, Anatoli Pokhodun, Patrick Rourke, Richard Rusby, Peter P.M. Steur, Weston L. Tew, Robin James Underwood, Rod White, Inseok Yang, Jintao Zhang


In 2011, a working group of the Consultative Committee for Thermometry published best estimates of the differences between thermodynamic temperature (T) and the International Temperature Scale ITS 90 (T90). But for temperatures below 335 K, it was stated that for the range from 35 K to 77 K, the available literature data do not allow to get estimates of sufficiently low uncertainty. In the meantime, the situation has improved essentially because of the primary-thermometry activities of different metrological institutes. This allows now to publish estimates, the uncertainty has been reduced up to one order of magnitude (at 70 K from formerly 1.9 mK to 0.18 mK). For comparison purposes, the updated estimates are given at the same temperatures as in the 2011 paper. Furthermore, an analytic function for the dependence of (T T90) on temperature T90 (power series of order 12) has been deduced by fitting the carefully selected data applying two different algorithms for checking purposes. This analytic function allows easy access to thermodynamic temperature values via the ITS 90, which is of great importance for practical purposes.
Journal of Physical and Chemical Reference Data


Thermodynamic temperature , primary thermometry , International Temperature Scale , ITS 90 , gas thermometry


Gaiser, C. , Fellmuth, B. , Gavioso, R. , Kalemci, M. , Kytin, V. , Nakano, T. , Pitre, L. , Pokhodun, A. , Rourke, P. , Rusby, R. , Steur, P. , Tew, W. , Underwood, R. , White, R. , Yang, I. and Zhang, J. (2022), 2022 Update for the Differences Between Thermodynamic Temperature and ITS 90 Below 335 K, Journal of Physical and Chemical Reference Data, [online],, (Accessed June 23, 2024)


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Created December 27, 2022, Updated January 30, 2023