26.04.2015 Views

Electromagnetic Testing

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Modulation analysis testing depends on the test object passing<br />

through the test coil's magnetic field at a constant feed rate or speed. These<br />

systems act like a tuned circuit. The operating frequency of the tester is<br />

changed (modulated) as a discontinuity passes through the test coil's field.<br />

The amount of modulation is a function of the transit time of the discontinuity<br />

through the coil's field. The faster the transit time the greater the modulation.<br />

If a system is set up for one speed and then the parts are scanned at a much<br />

slower speed the discontinuities may not be detected.<br />

Charlie Chong/ Fion Zhang

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