Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

(a) Probe wobble
Probe wobble appears as a variation in fill factor and so gives an approximately
horizontal signal either side of the operating point for all test frequencies, as
shown in FIG. 5.34. This signal is readily distinguishable from flaw signals, but
can add noise to other signals and so is undesirable.
High frequencies increase the relative
intensity of the inside surface eddy
currents and so cause greater probe
wobble signals. The signals can
therefore be reduced by decreasing the
test frequency. This may not be
acceptable because of decreased
sensitivity to the outside surface
conditions, so if probe wobble noise is a
problem, a slightly larger diameter probe
should be used. Alternatively, the probe
being used could be wrapped with
adhesive tape to reduce wobble.
Charlie Chong/ Fion Zhang