Methodologies and uncertainty estimates for T − T₉₀ measurements over the temperature range from 430 K to 1358 K under the auspices of the EMPIR InK2 project

We report new developments in instrumentation and techniques for both acoustic (speed of sound) and radiometric primary thermometry methods. These include both new cylindrical resonators for extending acoustic gas thermometry to higher temperatures and absolute radiation thermometers incorporating InGaAs detectors to extend primary radiometry to lower temperatures than can be achieved using Si-detector based instruments. These new approaches have been established in order to determine the difference between thermodynamic temperature, T, and the International Temperature Scale of 1990 (the ITS-90), T ₉₀, over the temperature range from 430 K to 1358 K as part of the three-year EMPIR project 'Implementing the new kelvin 2' (InK2). This paper describes the facilities and measurement methodologies for measuring T—T ₉₀ at each of the different institutes, along with an assessment of the target uncertainties. The work is ongoing, but we anticipate that the results of these measurements will ultimately be pooled to provide consensus values of T—T ₉₀ with associated estimated uncertainties. These consensus values will initially feed into the technical annex of the mise en pratique for the definition of the kelvin (MeP-K-19) and, if required, will be used to help to provide a foundation for any future temperature scale. (paper)