Eddy current displacement sensors (ECDSs) are widely used for the noncontact position measurement of small displacements (lift-offs). Challenges arise with larger displacements as the sensitivity of the ECDSs decreases. This leads to a more pronounced impact of temperature variations on the inductance and, consequently, an increased position error. Design solutions often rely on multiple coils, suitable coil carrier materials, and compensation measures to address the challenges. This study presents a single-coil ECDS for large displacement ranges in environments with high temperatures and temperature variations. The analysis is based on a sensor model derived from an equivalent circuit model (ECM). We propose design measures for both the sensing coil and the target, focusing on material selection to handle the impact of temperature variations. A key part of improving performance under varying temperatures includes model-based temperature compensation for the inductance of the sensing coil. We introduce a method to calibrate the sensor for large displacements, using a modified coupling coefficient based on field simulation data. Our analysis shows that this single-coil ECDS design maintains a position error of less than 0.2% full-scale for a temperature variation of 100 K for the sensing coil and 110 K for the target.

Linear variable differential transformers (LVDTs) are precise linear position sensors capable of measuring position over a wide range. The selection of the plunger material, whether magnetic or non-magnetic, becomes relevant in environments characterized by high temperatures and temperature variations. Especially for sensors with larger measurement ranges, the sensitivity with respect to temperature increases. In this work we present an LVDT design for large displacements which offers a significantly reduced sensitivity with respect to the temperature. Our design uses a plunger made from solid copper. The proposed sensor design has improved linearity and lower temperature drift with respect to existing designs e.g. sensors with ferrite based plungers. From simulations and experiments we demonstrate a temperature stability of - $28.5$ to $25.5 \,\mu \mathrm{m}\mathrm{/}\mathrm{K}$ , which is comparable to other LVDT designs, which use further temperature compensation techniques. We further study the benefit of our design even for non-uniform heat distributions.

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 (MLCSs) measure the stopper position approximately 1.5 m away from the stopper, introducing potential deviations due to lever arm 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 article 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, for example, 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 postprocessing. Remaining errors can be further minimized by model-based temperature compensation. Laboratory and field experiments show that the sensor achieves an uncertainty of 0.1 mm [ ${k}={2}$ , 95% confidence interval (CI)] for displacements up to 80 mm at a temperature of $300~^{\circ } $ 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.

Reliable and accurate position measurement in harsh, high-temperature environments remains a major challenge in industrial automation. Linear variable differential transformers (LVDTs) are highly sensitive and robust against environmental influences. However, temperature-dependent variations in magnetic permeability, electrical conductivity, and component geometry can cause significant position errors. Existing countermeasures, such as geometric modifications, compensation techniques, or high-grade materials, increase cost and complexity with limited success. This article presents a temperature-insensitive LVDT achieved through three complementary design measures: (1) a coil configuration where the sensing coils are placed outside the excitation coil to minimize the influence of temperature-induced magnetic-field redistributions on the sensing voltages; (2) high-frequency operation (up to 100 kHz) to reduce penetration depth and temperature sensitivity; and (3) a nonmagnetic ceramic coil carrier with negligible electrical conductivity that does not disturb the excitation field. Temperature experiments up to 180 °C show a 20-fold reduction in temperature-induced errors at 30 kHz and 100 kHz, compared to 1 kHz, even without compensation. Position errors are reduced to below 0.8% full-scale (FS) over ±70mm (30 kHz) and below 1% FS from −50mm to 70mm (100 kHz). Active compensation could further reduce errors. The proposed design uses off-the-shelf components that allow integration into standard LVDT constructions, enhancing reliability in high-temperature applications.