Highly Dynamic Eddy-Current-Based Sealed Magnetic Bearing Position Measurement With Temperature Drift Correction - “Seeing Through Conductive Walls”

This paper investigates the design of an Eddy Current Sensor (ECS) for position measurement of a moving conductive target located behind a fixed conductive shielding surface. Such a sensor can e.g. be used in completely sealed actuators with magnetically levitated rotor or mover for high purity applications. Starting from the analysis of the sensor’s operating principle, the design of the excitation coil, the achievable sensitivity and bandwidth as well as the temperature stability of the sensor are investigated. Subsequently, a suitable sensor interface, consisting of the driving and signal conditioning electronics, is selected. With this it is possible to distinguish between position and temperature variations, for which the optimal operational frequencies are identified. The results are finally verified with measurements on a hardware sensor prototype, showing that the ECS can achieve a sensitivity of 1 mV/µm, a position resolution of 1 µm, with a measurement bandwidth of 30 kHz and can hence be used to capture the mover’s position in an active magnetic bearing feedback control structure.