Design and Testing of Robust High-Temperature Eddy Current Sensor for Stopper Position Measurement in Continuous Casting

In continuous casting (CC), the vertical position of the stopper controls the flow of liquid steel into the mold, which is essential for ensuring safety, process reliability, and continuous quality. Conventional mold level control systems (MLCS) measure the stopper position approximately 1.5m away from the stopper, introducing potential deviations due to leverarm effects. However, measuring near the stopper is challenging due to high temperatures, such as direct flame contact, as well as dust, and covering powder, that can lead to position errors. This paper presents a robust eddy current displacement sensor (ECDS) tailored to address these challenges and enable accurate stopper position measurement in CC. For the proposed sensor design, we carefully select materials, e.g., a temperature-resistant coil former, a highly conductive target, and a backside shield, that inherently reduce sensitivity to temperature variations, eliminating the need for additional complex post-processing. Remaining errors can be further minimized by model-based temperature compensation. Laboratory and field experiments show that the sensor achieves an uncertainty of 0.1mm (k = 2, 95% confidence interval) for displacements up to 80mm at a temperature of 300 °C. The ECDS matches the performance of the MLCS and can also measure short-term stopper dynamics. These capabilities improve CC reliability and have the potential for use in other high-temperature industrial applications.