Eddy current testing is based on the scientific principle of electromagnetic induction. In this method, an alternating current flows through a coiled wire within an eddy current probe, creating a fluctuating magnetic field. As the probe, along with its magnetic field, approaches a conductive material such as a metal test object, it induces a circular motion of electrons in the metal, similar to swirling water in a river. This phenomenon, known as an eddy current, circulates through the metal. The eddy current, in turn, generates a magnetic field in the metal, which interacts with the coil and its associated field through mutual inductance. Changes in the metal properties, such as microstructure, hardness, or material grade, alter the amplitude and phase of the eddy current and the resulting magnetic field. These changes affect the electrical impedance of the coil. The signals generated are processed by the instrument's software and plotted as impedance amplitude and phase angle. Any alterations in the material properties are then indicated on the screen and, in some cases, on an Andon system, providing a visual alert.