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Electromagnetic Testing

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Projecting this examination, observe the phase lag for the entire part<br />

thickness. The standard depth of penetration is 1 mm, the part thickness is 5<br />

mm; therefore, the ratio x/δ equals to 5. This produces phase lag of 5 radians<br />

or about 287 degrees for the part thickness. Having a measurement capability<br />

of 1 degree increments, the part thickness could be divided into 287 parts<br />

each part representing 0.017mm. That would be considered excellent<br />

resolution.<br />

There is an obvious Iimitation. Refer to Figure 1.8 and observe the resultant<br />

relative current density with an x/δ ratio of 5. The relative current density is<br />

near 0. It should become apparent that the frequency can be adjusted to<br />

achieve optimum results for a particular variable. These and other variables<br />

will be discussed in Chapter 5 of this Study Guide.<br />

Charlie Chong/ Fion Zhang

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