Comparison Measurements for the Development of High-Temperature Platinum Resistance Scale

This paper describes measurements aimed to develop the high-temperature scale for high-temperature standard platinum resistance thermometers (HT-SPRTs). A furnace designed to facilitate comparison of a radiation thermometer with a HT-SPRT was developed for this work. The measurement uncertainty of the comparison is first reported, and then the comparison results for eight HT-SPRTs for temperatures from 660 °C up to 1040 °C are presented. Two different methods were adopted to analyze the comparison results. Upon discussion of the comparison results and adopting the second method to analyze the data, a correction term to the reference function of HT-SPRTs for temperatures above the current high-temperature limit, the Ag freezing point (961.78 °C), is suggested, as a preliminary result upon seeking the possibility to propose the extension of the platinum resistance thermometer scale. The two irregular cases for discussion of the criteria for interpolating HT-SPRTs of the current International Temperature Scale of 1990 (ITS-90) are also discussed.