An absolute linear displacement sensor based on eddy current effect

To meet the requirements of modern industry to absolute measurement, an absolute linear displacement sensor based on eddy current effect is proposed in this paper. The sensor is composed of a stationary ruler with metal reflection conductors and a movable ruler with field coils and inductive coils and includes a Coarse Measurement Track (CMT) and a Fine Measurement Track (FMT). The metal reflection conductors below the movable ruler will generate eddy current and a radiative magnetic field will be produced when the high-frequency alternating current is applied to field coils. The variation of displacement depends on the inductive Electromotive Forces (EMFs) of inductive coils. The CMT is used for positioning the pitch number while the FMT is used for high-precision displacement calculation. The absolute displacement is obtained by the combination of the CMT and the FMT. In this paper, the working principle and structure of the sensor is firstly introduced. Then, the electromagnetic field simulation is conducted according to the sensor model to verify feasibility and rationality. Finally, the sensor prototype is fabricated by PCB technology for experimental validation. The experimental results manifest that the peak-to-peak value of measurement error is 13 μm in 4 mm pitch and the peak-to-peak value of measurement error is 49 μm in the full measurement range of 500 mm.