The variation in eddy current output as the distance from the probe coil to the test part changes is called what?

The variation in eddy current output due to changes in the distance from the probe coil to the test part is referred to as lift-off. Lift-off occurs when there is a gap between the coil and the surface being tested, which impacts the coupling of the eddy currents in the material and ultimately alters the signal received by the probe. As the distance increases, the strength of the eddy currents generated in the test material diminishes, leading to variations in the amplitude of the output signal. Understanding lift-off is crucial in eddy current testing, as it can significantly affect the accuracy of the measurements and the interpretation of the results.

Other terms like fill factor, phase differentiation, and edge effect do not accurately describe this change related to distance. The fill factor pertains to the efficiency of the coil's design in terms of how much of the coil's area is effectively used in producing eddy currents, while phase differentiation relates to the phase shift in the signal rather than the distance effect. Edge effect describes phenomena related to the presence of geometric edges in a material, which is separate from the concept of lift-off concerning distance from the probe.