ET ASNT Level II Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

In the context of eddy current testing, variations in the test material can indeed be detected through changes in the impedance of the pickup coil. Eddy current testing relies on the principle of electromagnetic induction, where alternating currents are passed through a coil to create a magnetic field that induces eddy currents in conductive materials.

When the material's properties change, such as its conductivity or permeability, this directly affects the behavior of the eddy currents generated. As these properties change, the impedance of the pickup coil will vary accordingly. This is because the impedance reflects the opposition to the flow of alternating current, which is influenced by factors like material thickness, electrical conductivity, and the physical state of the material being tested.

In this way, the changes in waveform, amplitude, or phase of the signal received by the pickup coil manifest as variations in impedance, making it a critical parameter for detecting inconsistencies or flaws in the test material.