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Redefinition of Temperature

NML is acquiring an acoustic resonator system from National Physical Laboratory (NPL), U.K., for building a primary acoustic gas thermometer capability based on the NPL quasi-spherical acoustic resonator and cylindrical resonator. The first phase of the system installation has been completed in December 2018, and the whole equipment is expected to be completed by July 2020. In January 2019, Professor Graham Machin, Head of Temperature Standards and NPL Fellow at the NPL, was invited to have a technical exchange meeting with NML colleagues.

The discussion included how the international temperature community has approached the kelvin redefinition, including: the wording of the redefinition, coordinated effort in determining low uncertainty values for the Boltzmann constant and the extensive preparations underway for realization of the redefinition of the kelvin 2019 (MeP-K-19). Professor Machin introduced some of the leading contributions NPL has made to the kelvin redefinition including; one of the world’s lowest uncertainty determinations of the Boltzmann constant, the world’s lowest uncertainty values of T-T90 (for the MeP-K-19) and wider leadership through the Implementing the new kelvin InK-1 and 2 projects.

Professor Machin also presented NPL’s recent solutions to the challenges of industrial temperature measurement, especially those for harsh environments. The reliable measurement of temperature in hostile environments is problematic due to, for example, sensor degradation, limited access, unknown conditions. Typical contact thermometers can easily drift more than 10 ℃ over periods of hours, whilst drifts in non-contact thermometers and thermal imagers can be more than 50-100 ℃. Even at modest temperatures, unknown surface emissivity, window transmission, and reflected thermal radiation may also affect measurements. The improvements are, in some cases, facilitated through in-situ validation of the temperature measurement, assuring traceability.



  • Last Updated:2020/08/10
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