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Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

Eddy Current Chapter 5 and 6

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5.1.5 Conductivity testing and material sorting<br />

5.1.5.1 Introduction<br />

<strong>Eddy</strong> current testing can be used for material sorting on the basis that<br />

different materials, and even the samples of the same material in different<br />

heat treatment conditions, have different values of electrical conductivity. The<br />

conductivity of a conductor can be measured using a dedicated eddy current<br />

conductivity meter. Alternatively, most modern impedance display instruments<br />

include a digital conductivity measurement facility when used with a probe<br />

designed for this purpose. Neither of these instruments will give a conductivity<br />

reading if a ferromagnetic material is tested. For material sorting, a<br />

comparison of the phase of the lift-off signals obtained from the unknown<br />

samples with signals from known reference materials may suffice: it may not<br />

be necessary to determine the actual conductivity value. This approach may<br />

be used with both non-ferromagnetic and ferromagnetic materials.<br />

Conductivity testing or sorting by conductivity comparison can also be used to<br />

determine the density of parts produced by powder metallurgy.<br />

Charlie Chong/ Fion Zhang

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