Eddy current testing relies on the scientific principle of electromagnetic induction. Within an eddy current probe, an alternating current traverses a coiled wire, producing a fluctuating magnetic field. When the probe and its magnetic field approach a conductive material, like a metal test object, a circular motion of electrons, comparable to swirling water in a river, initiates within the metal. This phenomenon, known as an eddy current, circulates through the metal. Consequently, this eddy current generates a magnetic field in the metal, which then engages with the coil and its associated field via mutual inductance. Any changes in metal properties, such as microstructure, hardness, or material grade, change the amplitude and phase of the eddy current and the resulting magnetic field. This, in turn, affects the electrical impedance of the coil. These signals are processed by the software in the instrument & plotted as impedance amplitude and phase angle. Changes, if any, are indicated on the screen & on an Andon system.