Development of Hot-Thermocouple System for Accurately Controlling Temperature with High Degrees of Freedom

Abstract

The high-temperature technique is fundamental but significant for a wide range of engineering and industrial fields, such as the development of functional materials, material manufacturing, and assessment. The hot-thermocouple technique is valuable because it enables us to perform in-situ observation of a high-temperature melt under rapid heating/cooling conditions of the sample. Despite its widespread use, this technique suffers from the maintenance and/or installation of new equipment because of its complexity in electrical circuits and configuration of the equipment. As of 2025, it is difficult to procure parts to maintain conventional hot-thermocouple equipment, and there are no manufacturers producing the equipment in Japan. The new system developed in this study overcomes this technical difficulty by employing LabVIEW, which is a graphical programming environment for measurement and control. The system allows us to control the temperature with high precision and a high degree of freedom. This device can be fabricated using only basic engineering knowledge by simplifying the electrical circuits of conventional hot-thermocouple devices. Test measurements demonstrated the reliability of temperature measurement using the developed system as well as its promising potential for temperature control of samples with complex patterns (e.g., sinusoidal wave with an amplitude of 50 ^°C and a period of 1 s). Furthermore, the production of a time-temperature-transformation diagram of the CaO–SiO₂–Li₂O system was demonstrated by in-situ observations of the sample melt using the developed system. By combining with image analysis, the timing of crystallization was determined quantitatively and mechanically, thus successfully eliminating the uncertainty caused by human analysis.