Surface Inspection by Conventional Eddy Current
Eddy current testing is based on the physical phenomenon of electromagnetic induction. In an eddy current probe, an alternating current flows through a wire coil and generates an oscillating magnetic field. If the probe and its magnetic field are brought close to a conductive material, such as a metal test piece, a circular flow of electrons known as an eddy current begin to move through the metal like swirling water in a stream. That eddy current flowing through the metal in turn generates its own magnetic field, which interacts with the coil and its
field through mutual inductance.
Changes in metal thickness or defects, such as near-surface cracking, interrupt or alter the amplitude and pattern of the eddy current and the resulting magnetic field. This in turn affects the movement of electrons in the coil by varying the electrical impedance of the coil. The eddy current instrument plots changes in the impedance amplitude and phase angle, which can be used by a trained operator to identify changes in the test piece.