Abstract
Abstract
An electromotive force–temperature reference function for thermocouples made of platinum–20%rhodium versus platinum (Pt–20%Rh/Pt) was determined for the temperature range from 0 °C to 1100 °C. Three Pt–20%Rh/Pt thermocouples were constructed at the Physikalisch-Technische Bundesanstalt (PTB) and were compared with standard platinum resistance thermometers, an Au/Pt thermocouple and a Pt/Pd thermocouple, which were all calibrated at fixed points of the International Temperature Scale of 1990 (ITS-90). The comparison measurements were performed in stirred liquid baths in the range from 0 °C to 545 °C, in a sodium heat pipe from 560 °C to 980 °C, and in a five-zone furnace at temperatures between 1000 °C and 1100 °C. Furthermore, the Pt–20%Rh/Pt thermocouples were calibrated at fixed points of the ITS-90. The PTB reference function based on two of the three Pt–20%Rh/Pt thermocouples has an expanded measurement uncertainty of 0.25 K in the temperature range from 0 °C to 1100 °C.