An eddy current proximity sensor independent of operation temperature based on the temperature invariant phenomenon

Proximity switches are widely applied in Internet of Things (IoT), akin to temperature sensors and accelerometers. The eddy current proximity sensor (ECPS) is a prevalent magnetic proximity sensor used extensively in industrial scenarios. However, the operating temperature significantly affects the output reliability, leading to misoperations from temperature drift. Therefore, it is urgent to design a novel eddy current proximity sensor intended for the operation temperature. In this paper, the temperature-invariant phenomenon found in our previous work is adopted to design an eddy current proximity sensor independent of the operation temperature. Due to the temperature-invariant point relative to the excitation frequency, and the structures of the coil probe, an optimisation function and strategy of the above parameters is put forward. According to the optimal parameters, an eddy current proximity sensor whose target distance is 10 mm is designed and its performance is verified by experiment. The experimental results indicate that the state of the ‘ON’ or ‘OFF’ is steady when the temperature changes in the range of −30℃ to 90℃. The proposed ECPS can be operated in different scenarios, such as to monitor the vibrations of the rotating machinery, and the expansion of the rail track.