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The roles of the mise en pratique for the definition of the kelvin.

Ripple, D C*; Davis, R*; Fellmuth, B*; Fischer, J*; Machin, G; Quinn, T*; Steur, P*; Tamura, O*; White, D R* (2010) The roles of the mise en pratique for the definition of the kelvin. Int. J. Thermophysics, 31 (8-9). pp. 1795-1808.

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As is well known, a new definition of the kelvin based on a fixed value for the Boltzmann constant is under discussion. One of the consequences of this will be the need for a formal document created and maintained by the Consultative Committee for Thermometry (CCT) giving definitive guidance for the practical realization of the kelvin in accordance with the International System of Units (SI). This will be called the Mise en pratique for the definition of the kelvin (MeP-K). In 2005, the CCT considered the possibility drawing up a new International Temperature Scale (ITS), to replace the present ITS-90 and its low-temperature counterpart, the Provisional Low Temperature Scale (PLTS-2000). However, the CCT decided not to do this because a new temperature scale imposes large burdens on industry, which has a large installed base of hardware and process algorithms specific to the ITS-90. Instead, the adoption of the MeP-K opens a new and flexible path for updating and expanding the thermometric methods in common use without changing the basis of the ITS-90. Future versions of the MeP-K, updating the initial 2006 version, will cover the following:
1. The new definition of the kelvin and its extension to primary realizations and the ITS; we emphasize that the MeP-K has great value independently of how the kelvin is defined.
2. Direct, primary methods for measuring thermodynamic temperature T; in particular, absolute radiometric methods, which have uncertainties significantly below realizations by ITS-90, especially at high temperatures.
3. The texts of the scales, a Technical Annex of essential additional information, and recommended differences, T90 ¿ T, along with the related uncertainty; note that the ITS provides formal approximations to T. Documentation of the known biases of the ITS-90 supports thermodynamically accurate measurements without mandating wholesale replacement of the ITS-90 in industry.
4. The realization of the kelvin by indirect methods in a new category of SI realizations giving the temperatures for selected fixed points and outlining interpolation or extrapolation methods. Realizations using high-temperature eutectic fixed points and radiometric interpolating equations are one example of a high quality, indirect method promising greater flexibility in the traceable temperature measurements.

Item Type: Article
Keywords: Mise en pratique, kelvin
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4816

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