Calibration Scheme of Coil Sensors for Eddy Current Inspection

The coil sensor measures dynamic magnetic fields based on electromagnetic induction. With simple craft and broad applicability, it is widely used in various eddy current inspection. The sensing accuracy mainly depends on the frequency bandwidth of the coil, which may restrict the tracking of the output signal to the induced electromotive force, and this signal distortion reduces the reliability of the measurement. Therefore, engineers are committed to finding a convenient and reliable calibration method. It should be noted that non-uniform permeability environments, such as urban streets, mines, and power grounding grids, require real-time calibration to correct the disturbance of magnetic media to the detected signal. Unfortunately, the tedious conventional calibration method cannot meet this demand. As a solution, this work demonstrates a passive calibration method without interruption of measurement, it implements time-domain analysis of the conventional coil response based on the idea of control variables, so that no external calibration source is needed. This source-free scheme integrates sensor calibration into the measurement process, thus realizing uninterrupted operation even in complex interference environments.