A differential inductive linear displacement sensor against common-mode interference

Inductive displacement sensors offer robust interference resistance for harsh environments at the expense of reduced accuracy. This paper proposes an inductive sensor with a differential structure, which achieves precise displacement measurement through the eddy current effect between a planar coil and a metallic reflective conductor. The sensor incorporates a differential configuration, featuring two induction coils wound in opposite directions and connected in series, which effectively mitigates environmental common-mode interference. The sensor geometry was optimized through finite element simulation, employing a spatial phase shift of 1/6 cycle to eliminate third-harmonic distortion in the induced electromotive force. Experimental results indicate that the sensor achieves a resolution of 1 μm over a measurement range of 200 mm. To mitigate practical issues arising from installation errors, such as unequal signal amplitudes and non-orthogonal phase shifts, amplitude compensation and DC offset correction algorithms were applied. These measures substantially reduced the peak-to-peak error from 70 to 21 μm, resulting in a nonlinearity error of 0.014%. Because of the simple structure, cost-effectiveness, and proven reliability, the sensor is suitable for widespread industrial applications.