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Implementing the new kelvin 2


Measurement of T – T90 over the temperature range from 430 K to 1358 K

The aim of this work package is to measure the difference between temperatures determined in terms of the International Temperature Scale of 1990, T90, and thermodynamic temperature, T, over the range from 430 K to 1358 K with a target standard uncertainty of 5 mK. The range is slightly extended beyond the limits specified in the selected research topic to link with the upper end of acoustic thermometry (430 K) measured in the InK‑1 project and to reach the highest reference fixed point defined on the ITS-90 and so link with the lowest temperature primary radiometry measurements carried out in InK-1.

The International Temperature Scale of 1990 (the ITS-90) is 25 years old and a new scale will eventually be needed. Measurements of the differences (T - T90) are required with the lowest achievable uncertainties to feed into the MeP-K and ultimately the possible new temperature scale, ITS202x. The first 'Implementing the new kelvin' (InK-1) project measured thermodynamic temperatures for fixed points ≥ 1358 K including a range of metal carbon eutectic cells and the freezing point of copper by primary radiometry. In addition primary acoustic thermometry to the In freezing point (430 K) was performed. Effort now needs to be focussed on measuring thermodynamic temperatures in the range from ~430 K to 1358 K. It should be noted that the target standard uncertainty of 5 mK is extremely challenging for any technique of primary thermometry but we believe it is possible to achieve this at least for the lower end of the acoustic thermometry range.

Primary radiometry between 505 K and 1358 K

The aim is to measure T – T90 over the temperature range from the Sn freezing point (505 K) to the Cu freezing point (1358 K) using primary radiometry techniques. The measurements will be performed using a range of radiation thermometers/radiometers, which will be adapted where necessary to enable measurements to be carried out over a number of different spectral wavelengths.


 Schematic of measurement of blackbody radiation by primary radiometry.

Acoustic Gas Thermometry

The aim is to extend our knowledge of T - T90 over the temperature range from 430 K to at least the aluminium freezing point (933 K), by exploiting the many years of experience gained in acoustic gas thermometry at lower temperatures.

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