26.04.2015 Views

Electromagnetic Testing

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Alternating current field measurement has been developed from the<br />

alternating current potential drop ACPD technique. Alternating current<br />

potential drop uses current injection and contact potential drop probes. This<br />

technique required extensive surface preparation of the weld under<br />

examination. It could be used to produce crack depth measurements.<br />

Alternating current field measurement ACFM has its origins in alternating<br />

current potential drop but instead of using a contact type probe the current<br />

is induced in the test specimen. The contact probes previously used in<br />

alternating current potential drop have been changed to (noncontact)<br />

magnetic field sensitive coils. The models developed in alternating current<br />

potential drop for mapping surface magnetic fields and electric cmrents have<br />

been utilized in alternating current field measurement.<br />

Charlie Chong/ Fion Zhang

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