NPL has pioneered practical techniques to validate thermocouple readings in situ, or when the removal of a thermocouple for calibration is impossible or impractical. There are two methods and in both cases, the cell contains an ingot of metal (or eutectic metal-carbon alloy) which melts/freezes at a known temperature, chosen to be of particular relevance to the operational process in which the thermocouple is used. When the thermal environment of the thermocouple passes through this particular temperature, a hesitation (or plateau) in the thermocouple reading is observed. This enables a check to be made on the thermocouple performance.
Miniature fixed-point cells
This technology is a miniaturised version of the conventional calibration fixed-point cells. The new cell is a 3 cm x 1 cm cylinder which can be placed around the measuring junction of a 3 mm outer diameter thermocouple.
Integrated self-validation (inseva) design
This technology has a different, much smaller, design. The outer diameter is just 4 mm – enabling it to fit inside the sheath of a typical 7 mm outer diameter (alumina insulated) thermocouple.
This technology is licenced to CCPI Europe, and we continue to support the development of this technology, in partnership with CCPI Europe.
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