EC: Eddy Current can be used in two different manners, Firstly for finding surface and subsurface flaws, and Secondly for determining different metallurgical characteristics. Eddy current is based on the principle of measuring changes in the impedance of an electromagnetic coil as it is scanned over a surface of conductive material.
An alternating current in the coil produces a magnetic field that is induced in the material. To counter the coil's primary magnetic field, eddy currents are produced in the material. Eddy currents produce a secondary magnetic field H'B to oppose the coil's primary magnetic field HB. When the coil is scanned over a discontinuity, the secondary magnetic field is distorted, thereby changing the loading on the coil. Changes in coil loading directly affect the coil impedance, these changes are signified on the trace as a (possible) flaw
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