What does impedance monitoring involve in Eddy Current Testing?

Impedance monitoring in Eddy Current Testing (ET) fundamentally involves assessing changes in coil impedance due to the presence of eddy currents. When an alternating current flows through the probe coil, it generates a magnetic field that induces eddy currents in the conductive material being tested. The existence and characteristics of these eddy currents affect the impedance of the probe coil—this is primarily what ET relies on for defect detection and material characterization.

As the condition of the material changes (such as through the presence of cracks, corrosion, or other discontinuities), the eddy currents will be altered, leading to measurable changes in the impedance of the coil. By monitoring these impedance changes, inspectors can infer the presence and severity of defect conditions within the material. This principle is a key aspect of how ET provides valuable information regarding the integrity of components without requiring direct contact or damaging the part.

The other options, while they may involve aspects relevant to testing, do not accurately capture the main principle of impedance monitoring in Eddy Current Testing. The size of the probe coil, the distance to the surface, and the frequency of the test signal can have influence, but the central focus of the impedance monitoring technique is directly related to the changes in coil impedance caused by the eddy currents generated