Realising the redefined kelvin

Expected Impact


Temperature is one of the most measured control parameters in both industry and science. As such these developments will have significant impact in both these domains of human activity.

Temperatures <25 K

At low temperatures (<25 K) cryogenic equipment manufacturers will welcome the possibility of direct traceability to the redefined kelvin through a simplified calibration route.

Temperatures > 1300 K

At high temperatures, (>1300 K) these developments will impact a wide spectrum of industries, e.g. materials processing and aerospace/space. Current non-contact thermometry traceability is through recalibration of radiation thermometers. This entails costly down time, as well as recalibration costs. By replacing thermometers with known temperature HTFPs more reliable traceability will be established directly to thermodynamic temperature, with NMI-like uncertainties available.

Mid-temperature range

In the mid-temperature range, one early impact would potentially be the commercial exploitation of the mercury (Hg) fixed triple point replacement.

Life extension of ITS-90

More generally life extension of ITS-90 will be welcomed by industry. The introduction of ITS-90 caused significant costs through e.g. updating standards and recalibration of reference standards. If the ITS-90 life is extended and, as we expect, practical primary thermometry become more widespread, there will be less need for a new scale avoiding these costs.


Significant impact on the global temperature metrology community is envisaged through step changes in the SI system with respect to the quantity temperature, and in approaches to realisation and dissemination of the kelvin in the NMI/DI community. The key ones are:

  • Processes and equipment for temperature realisation and dissemination through the MeP-K, at temperatures >1300 K and <25 K are mature enough for wide adoption
    • For T>1300 K: When the current ITS-90 will be replaced, a significant number of NMIs have direct traceability to thermodynamic temperature through HTFPs.
    • For T<25 K: When replacement of this complex and difficult to realise region of the ITS-90 below 25 K will be underway through the primary thermometry methods demonstrated here, leading to a more robust traceability and dissemination route.
  • Life extension research for the ITS-90 will impact the NMI thermometry community by:
    • The reduction in uncertainties due to scale non-uniqueness effects, enabling all NMIs to improve their realisation of the ITS-90.
    • The identification of a viable replacement for the mercury triple point, ensuring the ITS-90 will be able to continue well into the 2020s. This will give sufficient time for alternative primary thermometry to be developed.

The NMI thermometry and wider scientific community will benefit from the “facilitating full range primary thermometry” activity. A reliable and comprehensive set of ab initio values of key thermophysical properties for thermometric gases (e.g. Ar, Ne, He), confirmed by experiment, will be available. These values will facilitate the use of primary thermometry for traceability in the middle part of the ITS-90 range.