Traceable measurement capabilities for monitoring thermocouple performance

Thermocouple calibrations currently require investigation of physical and chemical properties of each instrument, as thermocouple accuracy depends on the uniformity of these properties along the length of each thermo-element. Uniformity tends to degrade in use, also affecting thermocouple performance. Insufficient knowledge of these processes has hampered development of a standard method for measuring such ‘inhomogeneity’, and there’s no standard traceable measurement method to verify performance in-situ.

The project has developed practical methods and devices traceable to the International Temperature Scale of 1990 (such as dual-type thermometers and heater arrays) to enable thermocouple drift to be checked in-situ. To determine thermocouple inhomogeneity, an easy-to-use thermocouple has been developed integrating miniature fixed-point cells (a technology that realises liquid-solid equilibrium temperatures of high-purity metal elements without reference thermometers).

The outcome will be at least a doubling of the certainty of temperature measurement using thermocouples in the range 232 °C to 1100 °C, resulting in increased efficiency of industrial processes that require precise temperature measurement.