The Kelvin Redefinition and Practical Primary Thermometry

In May 2019 four of the seven base units of the International System of Units (the SI) were redefined and are now founded on defined values of fundamental physical constants. One of these was the kelvin which is no longer defined by the triple point of water but instead through a fixed value of the Boltzmann constant. In this paper the kelvin redefinition is introduced and the implications for temperature traceability and practical temperature sensing discussed. This will include outlining new approaches for temperature traceability, as well as discussing the rise of in process calibration through practical primary temperature sensing approaches (where, in principle, no sensor calibration is required). These forthcoming changes are likely to have significant impact on everyone in the temperature calibration chain, whilst the advent of in process temperature calibration should lead to step change improvements in process control, energy efficiency and product quality consistency and will help facilitate autonomous production.