Eddy currents

[ResidualStressMan]

What exactly is the eddy current technique for crack detection?
How does it work? (obviously passing eddy currents would be involved )

[david]

An electrical defect testing device for a non-magnetic test object, for example crack detection on hot continuously cast billets, is provided with means for detecting and suppressing the influence of disturbing magnetic regions of the object (e.g. regions of cold oxide scale). The device comprises at least one sensing transducer for harmful faults which is adapted to move relative to the test object. At least one detector is associated with the transducer for identifying the presence of magnetic material, and a blocking circuit is provided which, directly or indirectly, is controlled by the magnetic detector and is used for suppressing signals originating from a fault vector, for example a signal indicating a harmful fault. The presence of magnetic material can be detected using an eddy current technique.