Detail ALTERNATINGCURRENT FIELD MEASUREMENT( ACFM)
ACFM is an electromagnetic technique for detecting and sizing
surface breaking defects in metals. ACFM is particularly suited
for inspecting painted and/ or welded structures. An ACFM
sensor probe is placed on the surface to be inspected and an
alternating current is induced into the surface. When no
defects are present the alternating current produces a uniform
magnetic field above the surface. Any defect present will
perturb the current forcing it to flow around and underneath
the defect; this causes the magnetic field to become non
uniform and sensors in the ACFM probe measure these field
variations.
Two components of this magnetic field are measured - one
provides information about the depth or aspect ratio of the
defect( s) , the other provides information on the positions of
the ends of each defect. The two signals are used together to
confirm the presence of a defect and, together with a sizing
algorithm, measure its length and depth.
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