Analysis of Eddy Current Response to Lay Length of Wire Rope with Pancake Coil and Experimental Study

The lay length is one of the important parameters of the wire rope. The measurement of the lay length can indirectly reflect the stress state and the surface damage state of the wire rope. The imaging recognition method for measuring the lay length is limited by the external light and the attachment on the surface of the wire rope. The magnetic flux leakage method requires the wire rope to be magnetized. In view of the above problems, An eddy current method to detect the lay length using the double pancake coils differential bridge is proposed. Firstly, the governing formulations based on the Ar,V-Ar for the eddy current response analysis are established. Combing the formulations, the distribution of the eddy current in the single strand is simulated. It forms vortex on the strand surface just under the pancake coil. The distributions of the eddy current on the curved surfaces of the two sides of the strand are symmetrical. Secondly, the medium radius of the pancake coil is optimized. When the medium radius e