Characterization of High-Temperature Platinum Resistance Thermometers at Silver Point

Abstract

Thermal cycling tests have been conducted on various types of high-temperature standard platinum resistance thermometers (HTSPRTs) that are commercially available at present. The investigated HTSPRTs have nominal resistance values at the triple point of water (TPW) of 0.25 \(\Omega \), 0.6 \(\Omega \), 2.5 \(\Omega \), and 3 \(\Omega \). They vary in terms of the platinum wiring on their sensor supports (frames) and the support materials, their protective sheaths and their sealing materials. Ten HTSPRTs were evaluated with regard to their stability during use at silver-point temperature or above. This evaluation included a thermal cycling test following various setup patterns, which indicated that each HTSPRT has its own preferred pattern. The stability test results for eight of ten HTSPRTs during four silver-point realizations, based on this pattern, yielded a maximum discrepancy in the resistance ratio of within \(\pm 6\,\hbox {mK}\). The maximum resistance discrepancy at TPW was \(\pm 2.7\,\hbox {mK}\).