Study and Comparison of Newly Developed ITS-90 Silver- and Copper-Point Cells

Abstract

For realization of the ITS-90, LNE-INM uses a series of Cu and Ag fixed-point blackbody cavities and a monochromator-based radiance comparator or linear pyrometers. As for the field of contact thermometry where, for every particular fixed point, the national reference is represented by a batch of fixed-point cells, the decision was made to construct multi-purpose Cu and Ag cells which can be implemented in various types of furnaces depending on their size. The cells are to be compared, on a semi-annual or annual basis, to detect any unexpected drift of one of the cells in order to discard it. In this study, the constructed cells, of different types and dimensions (three sizes for the Cu point and two sizes for the Ag point) have been extensively implemented and characterized in different furnaces of different temperature uniformity capabilities. The temperature differences between the cells, although small, are analyzed and the effects of the temperature drop as well as the emissivity are estimated. The uncertainty budget for the realization of these fixed points, as well as the effects on the extrapolation to the highest temperatures, is investigated. In this paper, a description of the cells and the furnaces used will be given and the results of the characterization of the cells and their comparison will be presented.