Thermocouples are the most widely used temperature sensor in industry. They are vital for monitoring high temperature processes, such as aerospace heat treatment, quartz manufacturing and many others.
Thermocouples consist of two metal wires joined at one end. A temperature difference between the hot end and the cold end gives rise to a voltage, which can be used to determine the temperature.
Over time – especially when used regularly at high temperatures – the composition of the wires is changed by contamination, oxidation, and other effects. This can affect how well they measure. To ensure thermocouples are measuring correctly, manufacturers – as well as National Metrology Institutes (NMI) and calibration labs that perform thermocouple calibrations – need to be able to check the wires are sufficiently ‘homogeneous’, i.e. free of these effects. Current approaches often involve large complex measurement systems at NMIs. These calibrations are high cost and operate at very high temperatures (600 °C +) which can degrade thermocouple materials during the test.
To provide a more practical solution, Isothermal Technology Ltd (Isotech) has developed the first ever commercially available homogeneity scanner, which operates at a more wire-friendly temperature of 100 °C. The design was first developed by the Measurement Standards Laboratory of New Zealand (MSL), from whom Isotech has an exclusive license from MSL to develop, manufacture and supply the scanner.
Isotech needed independent verification that its product worked as claimed, in order to confidently take it to their customers. M4R made it possible to carry out this important work, which would have otherwise been put on hold due to logistical challenges arising as a result of COVID-19.
Through the M4R engagement, NPL scientists compared the Isotech scanner, which operates at 100 °C, to their own homogeneity scanning equipment, which operates at 600 °C. Both scanners were used to measure the same two thermocouples which had
well-characterised pre-existing damage, and the results were compared.
The data showed that the Isotech scanner measurements were effective at characterising the damage at a level consistent with NPL’s scanner, and that scanning at 100 °C was sufficient to detect inhomogeneities.
The investigations provided an independent demonstration that the Isotech scanner yields results that are consistent with those from the NPL scanner.
This gives Isotech confidence in its product, and the data from NPL – an organisation well-known and trusted by its customers – can be used as an impartial verification that it is fit for purpose. This low temperature thermocouple calibration device does not otherwise exist commercially. Isotech anticipates that the initial market for the new product will be NMIs, with the study data providing confidence that they can rely on this commercially available device, rather than developing their own. Over time, Isotech will expand this market to commercial calibration labs.
These opportunities will help to safeguard the business, protect the future of its 50 employees and will help to maintain Isotech’s position as a world-leading temperature metrology equipment manufacturer.
The new device will ultimately offer NMIs, calibration laboratories and thermocouple manufacturers a practical, low temperature, low cost approach for properly characterising thermocouples and verifying their measurement uncertainties. This will increase options for measurement assurance and reduce calibration costs for customers.