Temperature measurement techniques are being developed that require reference only to primary constants, such as noise thermometry at very low temperatures and radiometry at high temperatures. Redefinition of the kelvin focuses attention on practical realisation of primary thermometry, expected to lead to a transformation in measurement certainties without need for recalibration. However, primary thermometers remain complicated to use, so scales derived from measurements of other quantities are still required but with revisions, particularly at extreme temperatures.
The project will test primary thermometry approaches at temperatures greater than 1300 K and less than 25 K to kick-start the process of making these methods competitive. It will also extend the life of the currently defined scale to allow time for primary methods to develop, and for thermal parameters of gases with potential for replacing mercury as a reference point to be determined. Easing the transition to primary thermometry in this way should enable in-situ traceability at lower cost, in applications such as remote monitoring in manufacturing and the nuclear power sector.