What role does the frequency of the AC signal play in Eddy Current Testing?

In Eddy Current Testing (ECT), the frequency of the alternating current (AC) signal is crucial as it influences both the sensitivity and the depth of testing. Higher frequencies tend to produce eddy currents that penetrate less deeply into the conductive material, making them more sensitive to surface and near-surface defects. Conversely, lower frequencies allow for deeper penetration of the eddy currents, which can be beneficial for detecting flaws that are located further below the surface.

The sensitivity of the test is affected because different defects may respond differently at varying frequencies. By selecting the appropriate frequency for a specific application, testers can enhance their ability to identify and characterize flaws, ensuring more reliable results.

The other choices do not accurately reflect the relationship between frequency and its impact on Eddy Current Testing. While probe size may be related to other factors, it is not directly determined by the signal frequency. Calibration is also affected by frequency, but it is only one of many factors in machine tuning, making it a narrower focus than what the question queries. Additionally, the notion that frequency is unrelated to the testing process is incorrect, as it is a fundamental aspect of determining the effectiveness of ECT.