During eddy current testing, what signifies the presence of defects in the test specimen?

In eddy current testing, the presence of defects in the test specimen is primarily indicated by changes in impedance. This is because eddy current testing operates on the principle of generating eddy currents within the conductive material being tested. When there is a defect such as a crack, void, or change in material properties, it affects the flow of these currents, which in turn causes a change in the impedance of the testing coil.

Impedance encompasses both resistance and reactance, and variations in impedance can be detected by the eddy current testing instrument. These changes can manifest as variations in the measurement readings, allowing the technician to infer the presence and potentially the size of defects within the material.

Other factors, such as temperature fluctuations or variations in coil resistance, do not directly relate to the identification of defects in the same way. While changes in voltage could occur as a result of these other variations, it is the changes in impedance that directly correlate with the presence of defects in the material being tested.