Speed Measurement Feasibility by Eddy Current Effect in the High-Speed MFL Testing

It is known that eddy current effect has a great influence on magnetic flux leakage testing (MFL). Usually, contact-type encoder wheels are used to measure MFL testing speed to evaluate the effect and further compensate testing signals. This speed measurement method is complicated, and inevitable abrasion and occasional slippage will reduce the measurement accuracy. In order to solve this problem, based on eddy current effect due to the relative movement, a speed measurement method is proposed, which is contactless and simple. In the high-speed MFL testing, eddy current induced in the specimen will cause an obvious modification to the applied field. This modified field, which is measured by Hall sensor, can be utilized to reflect the moving speed. Firstly, the measurement principle is illustrated based on Faraday’s law. Then, dynamic finite element simulations are conducted to investigate the modified magnetic field distribution. Finally, laboratory experiments are performed to validate the feasibility of the proposed method. The results show that B_mz(r₁) and B_mx(r₂) have a linear relation with moving speed, which could be used as an alternative measurement parameter.