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Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

Eddy Current Chapter 5 and 6

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5.1.5.8 Test procedure using other eddy current instruments<br />

If an impedance plane display instrument is being used to sort materials, liftoff<br />

signals should be obtained from suitable reference standards and the liftoff<br />

signals of the materials to be tested should be compared with these. For<br />

example, if it is required to sort material known to consist of two different<br />

known alloys or heat treatment conditions, lift-off signals should be obtained<br />

from a number of samples of each material. It is important to have enough<br />

samples to assure that the range of conductivities of the two materials do not<br />

overlap. The instrument is adjusted so that the lift-off signals from one<br />

material are located towards one edge of the screen, and the lift-off signals<br />

from the other material are located towards the other edge of the screen.<br />

Meter-indicating flaw detectors can be used for the same purpose, in this<br />

case adjusting the instrument so that the readings from one material lie<br />

towards one end of the scale, and the readings from the other material lie<br />

towards the other end of the scale.<br />

Charlie Chong/ Fion Zhang

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