Figure 4-43. Phase Relationship Between Lift-Off and Crack
Response for Various Materials and Frequencies.
In performing manual eddy current inspection with a surface probe or pencil probe, it is usually impossible to maintain
the probe at the same angle, with respect to the inspection surface, as position is changed. In some instances, holders
may be fabricated to guide the probe and hold the angular relationship with the inspection surface. The angular change
between the probe and the inspection surface is termed probe wobble. Probe wobble results in changes in lift-off as