Which method allows for the measurement of impedance directly in eddy current testing?

In eddy current testing, the impedance method is particularly significant because it directly measures changes in impedance as the eddy current probe interacts with the test material. This interaction leads to variations in the inductance of the coil due to changes in both conductivity and permeability of the material, which are crucial for assessing flaws or material properties. The impedance measurement provides a comprehensive view, allowing for the detection of defects and evaluation of material characteristics by analyzing the resistive and reactive components of the impedance.

The other methods focus on different principles or analyses. Modulation analysis, for instance, examines changes in frequency or amplitude of the eddy currents rather than directly measuring impedance. Phase analysis evaluates the phase shift in the signal induced by the eddy currents, which informs about the material properties but does not measure impedance directly. The linear time base method pertains to how signals are represented over time rather than focusing on the inherent impedance characteristics. Thus, the impedance method uniquely allows for a direct measurement that is foundational in the application of eddy current testing.