Radiation Thermometry Toward the Triple Point of Water?

Abstract

The article describes and evaluates the possibility of using a high-temperature blackbody of accurately known thermodynamic temperature as a reference source for the determination of lower thermodynamic temperatures by spectral radiation thermometry. By applying various intermediate steps, this approach will allow spectral radiation thermometry to be used for the determination of the thermodynamic temperature of the triple point of water with a low uncertainty. The procedure for such an attempt is outlined, theoretical, and practical limits of the resulting uncertainty in thermodynamic temperature are given. The described experimental approach also provides a framework to calculate the uncertainties in determining the thermodynamic temperatures of the defining high-temperature fixed points of the International Temperature Scale of 1990 down to the triple point of water. The estimation of uncertainties is based on current and future values of the relevant contributing components. The uncertainty anticipated in determining the thermodynamic temperature of the triple point of water is 24 mK with current uncertainties and 1.9 mK in the future. Thus, the described approach yields uncertainties that are slightly higher, but comparable to, the tentative uncertainties of other methods—e.g., dielectric constant gas thermometry developed and applied within the framework of the new determination of the Boltzmann constant.