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Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

Eddy Current Chapter 5 and 6

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(b) Gap or horseshoe probes<br />

Gap or horseshoe probes use a U-shaped ferromagnetic core to shape the<br />

magnetic field of the coil so that it is essentially parallel to the test surface, as<br />

shown in FIG. 5.9. This produces eddy currents loops in planes normal to the<br />

test surface. At the surface, the surface eddy currents flow at right angles to<br />

the line joining the two ends of the core. Consequently, the maximum<br />

sensitivity to surface flaws occurs if the flaw is parallel to this line, and, as the<br />

angle between the flaw and the line joining the ends of the core increases,<br />

the sensitivity decreases, reaching zero when the flaw is at 90° to this line.<br />

This type of probe is used for the detection of laminations in sheet material<br />

rather than for cracks or other flaws normal to the test surface.<br />

Keywords:<br />

This type of probe is used for the detection of laminations in sheet material<br />

rather than for cracks or other flaws normal to the test surface.<br />

Charlie Chong/ Fion Zhang

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