Investigation of self-validating thermocouples with integrated fixed-point units

Thermocouples are often exposed to harsh conditions when used for high-temperature measurements in industry. They suffer commonly from unavoidable drift effects which influence the required process efficiency and control. A self-validation concept for thermocouples to monitor their performance in the temperature range between 1000 C and about 1800 C in oxidizing atmospheres by using integrated miniature fixed-point units of different designs was tested. Two different models of fixed-point crucibles filled with high purity palladium (1553.4 °C) and platinum (1769 °C) have been constructed and assembled with type B thermocouples to be used as traceable references. Furthermore, two innovative self-validation methods by using thick wires of high purity gold (1064.18 °C), nickel (1455 °C), and palladium in multi-bore insulators as fixed-point materials were developed and investigated by assembling them with type B thermocouples. The measurement results obtained have demonstrated the suitability of the integrated fixed-point units to provide long-term confidence in industrial high-temperature measurements within about (2−3) K.