An Eddy Current Method for Electromagnetic Property and Diameter Measurements of Metallic Rods Immune to Sensor Offset

Metallic rods are widely used in the aerospace, chemical, and construction industries, where long-term service can lead to problems such as wall thinning and fatigue damage. Accurate electrical conductivity and diameter measurements reflect the internal structural condition of the metallic rod, which can prevent accidents caused by material defects. In this article, an eddy current method for electromagnetic property and diameter measurements of metallic rods immune to sensor offset is investigated. The analytical solution regarding coil coaxial around metallic rod is established, and the features of the self-inductance variation curve can be extracted to invert the electromagnetic property and diameter. Considering small changes in the extracted features due to sensor offset can cause measurement errors. In order to solve the problem, the autoencoder is used to learn the offset features. Combining the theoretical features and offset features, the initial electromagnetic property, sensor offset and diameter can be estimated simultaneously by particle swarm optimization-extreme learning machines. Finally, by referring the initial estimated parameters, the electromagnetic property and diameters can be further accurately reconstructed based on the modified Newton–Raphson method. The experiments are conducted to evaluate the proposed method, and the average relative measurement error is only 1.5%.