The Roles of the Mise en Pratique for the Definition of the Kelvin

Abstract

The mise en pratique (“practical realization”) for the definition of the kelvin (MeP-K) was created by the Consultative Committee for Thermometry (CCT) in 2006 to give practitioners of thermometry a guide to the realization of the kelvin, i.e., measurement of temperature in kelvins, in accord with the International System of Units. In this article, the present and the future content of the MeP-K, the relationship of the MeP-K to other documents relevant to thermometry, the categorization of thermometry techniques in the MeP-K, and the benefits of proposed additions to the 2006 version of the MeP-K are discussed. The three categories of measurements within the MeP-K are: (1) primary methods for measuring thermodynamic temperature T; (2) formal approximations to T, in particular, the International Temperature Scale of 1990 (ITS-90) and the Provisional Low Temperature Scale from 0.9 mK to 1 K (PLTS-2000); and (3) indirect approximation methods that are neither primary nor defined on a temperature scale, yet capable of exceptionally low uncertainties or increased reliability. By providing a framework for primary methods and indirect methods, the MeP-K will foster development and application of new methods, such as the use of absolute radiometry or high-temperature fixed points. The MeP-K provides the CCT with a mechanism to update and to expand the thermometric methods in common use, without imposing on industry the high costs of changing the International Temperature Scale.