Electromagnetic Testing Eddy Current in Brief
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A differential probe consists of two coils sens<strong>in</strong>g different areas of the<br />
material be<strong>in</strong>g tested, which are l<strong>in</strong>ked electrically <strong>in</strong> opposition. The circuit<br />
will become unbalanced when one of the coils encounters a change <strong>in</strong><br />
impedance. The response to this change <strong>in</strong> impedance creates what is known<br />
as a Lissajous figure. In general, the closer the element spac<strong>in</strong>g the wider the<br />
"loop" <strong>in</strong> the signal. Differential probes are relatively unaffected by lift-off as<br />
long as the elements are balanced, and are suited for detection of small<br />
defects.<br />
Keywords:<br />
Differential probes are relatively unaffected by lift-off as long as the elements<br />
are balanced<br />
Charlie Chong/ Fion Zhang
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