<p>Investigating thermocouple inhomogeneity to unlock new calibration methods and devices</p>
Investigating thermocouple inhomogeneity to unlock new calibration methods and devices
The project
Thermocouple calibrations, commonly used in industrial manufacturing processes, currently require investigation of influence of the physical and chemical properties of each instrument on its calibration uncertainty, 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 are no standard traceable measurement methods to verify performance in-situ.
Completed EMPIR project Traceable measurement capabilities for monitoring thermocouple performance (18RPT03, MetForTC) has developed practical methods and devices traceable to the International Temperature Scale of 1990 to enable industrial thermocouple temperature drift to be checked in-situ. To determine thermocouple inhomogeneity, an easy-to-use thermocouple has been developed that integrates miniature fixed-point cells, a technology that realises liquid-solid equilibrium temperatures of high-purity metal elements without reference thermometers.
Through project collaboration on the design and validation of new temperature measurement methods and equipment all the project participants gained new knowledge and experience. It can be concluded that the project has helped to promote greater consistency in temperature metrology at the European level by enhancing the capabilities of European NMIs with emerging needs in the field of temperature measurement, improving their readiness for active participation in the future research projects.
The project outcomes will improve knowledge of uncertainty parameters due to the homogeneity and drift for at least a quarter up to maximum 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. This level of improved uncertainty could be significant in industrial laboratories.
Novel devices
Two novel devices for testing thermocouple inhomogeneity and drift were developed that utilise the Curie-point technique for maintaining the known and stable temperatures required for these tests. The Curie-point is a certain temperature at which a ferromagnetic material loses its magnetic properties. The devices measure temperature at a fixed temperature point where the material they are made of loses its magnetism. When a thermocouple is used in an industrial setting, the conductor wires can lose homogeneity through heat, chemical exposure, or mechanical damage.
These Curie-point devices are novel since they self-regulate the temperature inside their working zones, while achieving low temperature gradients and high temperature stability that can be maintained over long periods.
This work is described in the paper Determination of thermocouple inhomogeneity using miniature Curie-point furnace.
Benefits from the project
Thermocouples are used in industry at high temperatures up to 1100 °C and higher. For practical on-site measurements, usually thermocouples are replaced periodically to ensure continuity in maintaining process control at an optimal level. The efficiency of this replacement can be obtained by performing tests of inhomogeneity and drift.
Industrial processes that will benefit from the new facilities include:
- manufacture of building materials
- manufacture of furnaces
- manufacture of thermocouples
- manufacture of porcelain and glass
- metallurgical processes
- pharmaceutical industry
- rail transport
- automotive industry
- energy productions
This project developed novel methods and techniques, traceable to the ITS-90, that can significantly simplify and improve testing of thermocouple drift and inhomogeneity in calibration laboratories as well as in other measurement applications. These techniques are beneficial to users as they enable increase of confidence in results of thermocouple performances tests as well as decrease in the uncertainty of temperature measurement by thermocouples. As a result, the efficiency of industrial processes utilising thermocouples for temperature measurement and control can be increased.
Project coordinator Narcisa Arifovic from UME said
‘The MetForTC Project addressed the challenging task of developing novel practical methods and devices such as dual-type thermometers for monitoring thermocouple in-situ, drift performance, miniature fixed-point cells, and Curie-point furnace to determine the inhomogeneity of thermocouples for calibration laboratories. This will satisfy needs for these facilities within the thermometry metrology community.
Special attention was paid on easy-to-use methods to provide end users with information on related drift and homogeneity uncertainty parameters for accurate temperature measurements. Eventually this work will lead to decreasing the uncertainty of the measurement of temperature and, as a result, better positioning of the calibration and industrial laboratories.
The project provides the platform for joint work by the consortium where partners bring their expertise, and for networking and knowledge transfer between the leading and new emerging NMIs/DIs.
Within the joint work of the consortium of NMIs/DIs, the goal has been reached and the project developed, manufactured and tested the aforementioned novel tools, devices and methods for precise measurements of homogeneity and drift of thermocouples. The different approaches were studied, researched and shared with consortium and considerable knowledge and experience was gained through this team-work.
The benefits of this knowledge transfer enhanced the new emerging NMIs/DIs, strategically preparing them for new scientific cooperation that will last for a long time beyond the project lifetime.
Through the organisation of workshops, stakeholders gained knowledge on improving the performance of existing equipment and about developing novel ones.
It was great experience to work on and manage such a project.’
This EMPIR project was co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.
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