Novel Direct Digital Interface of Frequency-Modulated Eddy-Current Displacement Sensor (ECDS) for Real-Time Control of AMB

Renowned for its non-contact nature, high-resolution capabilities, and suitability for real-time control, ECDS (eddy current displacement sensor) operates on electromagnetic induction principles to detect even the minutest changes in the position of conductive targets. The interface between an ECDS and external instrumentation stands as a critical juncture influencing signal conditioning, noise reduction, compatibility with modern data acquisition systems, and adaptability to dynamic measurement environments. This paper presents a novel direct digital interface of frequency-modulated (FM) ECDS for real-time control of AMB. First, an FM eddy-current gap sensor is built, and its LC oscillation frequency variation is detected with the proposed direct digital interface. The direct digital interface has several distinct advantages such as simple configuration, noise immunity, and adaptability. In particular, both the DSP's internal SW (software) prescale and an external HW (hardware) prescale, such as a counter are used together to balance the static and dynamic performances, which offers moderate resolution and sufficient stability for real-time applications. Finally, both the static and dynamic performances of the FM eddy-current gap sensor are investigated by measuring the levitation jitter and closed-loop sensitivity function of the one-DOF AMB system.