Electromagnetic Testing - ECT Q&A
Electromagnetic Testing - ECT Q&A
Electromagnetic Testing - ECT Q&A
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More on Phase lag<br />
Phase lag is a parameter of the eddy current signal that makes it possible to<br />
obtain information about the depth of a defect within a material. Phase lag is<br />
the shift in time between the eddy current response from a disruption on the<br />
surface and a disruption at some distance below the surface. Phase lag can<br />
be calculated using the equations to the right. The second equation simply<br />
converts radians to degrees by multiplying by 180/p or 57.3.<br />
The phase lag calculated with these equations should be about 1/2 the phase<br />
rotation seen between the liftoff signal and a defect signal on an impedance<br />
plane instrument. Therefore, choosing a frequency that results in a standard<br />
depth of penetration of 1.25 times the expected depth of the defect will<br />
produce a phase lag of 45o and this should appear as a 90o separation<br />
between the liftoff and defect signals.<br />
Charlie Chong/ Fion Zhang<br />
https://www.nde-ed.org/GeneralResources/Formula/ECFormula/PhaseLag1/PhaseLag.htm
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