Magnetic sensors assessment in velocity induced eddy current testing

This paper presents an enhancement in the probes to be used on a new nondestructive testing method with eddy currents induced by velocity. In this method, a permanent magnet that is attached to a moving carriage creates eddy currents in the conductive material to be inspected. By measuring the opposing magnetic field generated by the eddy currents, it is possible to obtain information regarding the presence of defects. Different magnetic field sensors, such as, differential pick-up coils, giant magneto resistors (GMR) and Hall sensors have been used and compared. A permanent magnet moving above a plate was studied using a numerical model to allow further improvements to be made in the probe. Depending on each sensor's geometry, sensing axis and range, its position and orientation must be strategically chosen in order to increase defect sensitivity. The best probe's position is the one that guarantees the highest sensibility to the defects' presence.