Eddy Current Inspection
Eddy-Current Testing: Uses electromagnetic induction to detect flaws in materials
can be tested, the surface of the material must be accessible, the finish of the
material may cause bad readings, the depth of penetration into the material is
limited by the materials' conductivity, and flaws that lie parallel to the probe may be
undetectable. In a standard eddy current testing a circular coil carrying current is
placed in proximity to the test specimen (which must be electrically conductive).
The alternating current in the coil generates changing magnetic field which
interacts with test specimen and generates eddy current. Variations in the phase
and magnitude of these eddy currents can be monitored using a second 'receiver'
coil, or by measuring changes to the current flowing in the primary 'excitation' coil.
Variations in the electrical conductivity or magnetic permeability of the test object,
or the presence of any flaws, will cause a change in eddy current and a
corresponding change in the phase and amplitude of the measured current. This is
the basis of standard (flat coil) eddy current inspection, the most widely used eddy
current technique. However, eddy-current testing can detect very small cracks in or
near the surface of the material, the surfaces need minimal preparation, and
physically complex geometries can be investigated. It is also useful for making
electrical conductivity and coating thickness measurements.
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