New self-calibrating thermometry for high-temperature manufacturing

Hot steel bars on a conveyor belt inside a steel mill
Hot steel bars on a conveyor belt inside a steel mill

EMPIR project creates new integrated self-validation technique to ensure high-temperature thermometry remains accurate

Manufacturing contributes as much as 8 trillion euro to the global economy every year, with around 1.8 trillion euro of that total coming from the European Union. Manufacturing also accounts for around 25 % of the EU’s annual energy consumption. Thus, ensuring manufacturing processes are as energy and cost efficient as possible is of vital importance. The European Commission’s Energy Efficiency Plan has also outlined the importance of enhanced efficiency in increasing the European competitiveness in this area. Many manufacturing processes, such as fabricating parts for aerospace applications, can only maximise their efficiency when kept at very specific, very high temperatures, often in excess of 1000°C and with only a narrow tolerance. Therefore, in order to reduce the waste of energy and materials – as well as to ensure safety – the temperatures of these processes need to be carefully monitored.

Completed EMPIR project Enhancing process efficiency through improved temperatures measurement (14IND04, EMPRESS) has developed measurement and calibration methods for monitoring high-temperature industrial processes, including a new portable standard flame for traceable calibration of flame and combustion thermometry, and a number of other traceable thermometry techniques.

Self-calibrating probes

The most common instruments used to monitor temperature are thermocouples, electrical devices which produce a temperature-dependent voltage when heated. However, thermocouples are known to suffer from calibration drift, which produces unknown measurement errors. Because the thermocouples used to monitor high-temperature industrial processes are difficult, and often costly, to access for recalibration or replacement, an in-situ alternative is needed for some applications.

The project addressed this issue by creating a self-calibrating thermocouple using integrated miniature temperature fixed-point cells. The temperature fixed-point cells use an ingot of pure (~99.999 %) metal with a known melting point to calibrate the accompanying thermocouple in situ. In this new design, the metal ingot is shielded within a ceramic envelope within an argon atmosphere to reduce the risk of contamination. Usually, these kinds of cells are too large to be used outside of a laboratory, however, the EMPRESS project successfully miniaturised the technology, allowing these new self-calibrating devices to be integrated into existing industrial processes.

Project coordinator NPL and thermocouple manufacturer CCPI Europe Ltd have collaborated to produce commercial prototype self-validating thermocouples. The thermocouples have been tested successfully in industrial trials at high value heat treatment plants in France, Germany and the UK. In one trial, the devices successfully operated for over 200 freeze/melt cycles and endured temperatures over 1000 °C during a year of continuous operation, without failure, demonstrating the practical feasibility of the self-validating thermocouples.

Project coordinator Jonathan Pearce (NPL) has said on the project:

“Pan-European collaboration within the EMPRESS project was an absolutely key part of the successful early-stage development of self-validating thermocouples and provided a spring-board for subsequent elevation of the TRL and steps towards commercialisation, which is the main route for bringing assured traceable process control thermometry to industrial users.”

This project’s work has been built on by the EMPRESS2 (17IND04) follow-on project.

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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