NPL has been working with the European Space Agency (ESA) to develop in-situ self-validation of thermocouples, up to 2300 °C.
The design that developed during the course of the research encompasses a miniature temperature fixed point around the measuring junction of a typical industrial thermocouple. Even though the dimensions of the device are small - only 14 mm x 30 mm - the melting and freezing of the metal-carbon eutectic alloys present is clearly identifiable: for cobalt-carbon (~1324 °C), platinum-carbon (~1738 °C), ruthenium-carbon (~1953 °C) and iridium-carbon (~2292 °C). This has led to a factor 10 improvement in the uncertainty of Type C (W-Re) thermocouples.
This device is ready for use in ESA facilities, and the design is also applicable to high temperature industrial processes - enabling the user to periodically check and adjust for decalibration of temperature sensors in-situ. Further research is ongoing to investigate additional fixed-points and to allow their use in a wider range of high-temperature environments.
More information about developing self-validating thermocouples with ESA
Find out more about NPL's Temperature and Humidity research
Contact: Claire Elliott