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Facilitating an effective redefinition of the kelvin

In this project, INK2, NPL's temperature team are working with partners to optimise the EU's primary thermometry capability.

The need

At the 16th General Conference of Weights and Measures (CGPM) in November 2018 it was agreed that the international system of units would be redefined in terms of defined values of fundamental constants. For the kelvin the redefinition will be in terms of a defined value of the Boltzmann constant.

To facilitate an effective redefinition it is essential that the required primary thermometry methods are in place. Through the development of reliable primary thermometry at the extremes of temperature (<25 K and >1300 K) it is envisaged that by the mid-2020s the current temperature scales (ITS-90 and PLTS-2000) will be superseded by practical primary thermometry.

The overall objective of this research project is to optimise the primary thermometry capability within the EU.  It exploits synergies between EU partners and ex-EU partners to ensure, as we approach and implement and realise the kelvin redefinition, the EU grows its scientific leadership position in this unit area.

This work is part of the EMPIR project INK2.

The impact

The kelvin redefinition is a once in a lifetime opportunity to fundamentally change the principles and practice of thermometry. This research is leading the international primary thermometry community, with input from many of the world leading NMIs and institutes.

The focus is on (a) performing thermodynamic temperature measurement in the difficult ranges as identified by the Consultative Committee of Thermometry (CCT) and (b) to support emerging primary thermometry techniques, which will improve our understanding of systematic uncertainties and hence lower the overall uncertainty in the estimates of thermodynamic temperature. It will also develop the background techniques necessary to supersede the defined scales, at least at the extremes of temperature, in the mid-2020s.

The project will lead to a more robust and stable data set for the mise en pratique for the definition of the kelvin (MeP-K) and to provide a firm foundation for the future developments in primary thermometry for realisation and dissemination of the redefined kelvin in the mid-2020’s and beyond. The project is laying the long-term foundation for improving the accuracy of temperature measurements throughout the world for all industries, sectors and disciplines.

Read more about primary thermometry.

kelvin (K)