Eddy-current testing

Eddy-current testing uses electromagnetic induction todetect aws in conductive materials. There are severallimitations, among them: only conductive materials canbe tested, the surface of the material must be accessible,the nish of the material may cause bad readings, thedepth of penetration into the material is limited by thematerials conductivity, and aws that lie parallel to theprobe may be undetectable.In a standard eddy current testing a circular coil carryingcurrent is placed in proximity to the test specimen (whichmust be electrically conductive).The alternating currentin the coil generates changing magnetic eld which inter-acts with test specimen and generates eddy current. Vari-ations in the phase and magnitude of these eddy currentscan be monitored using a second 'receiver' coil, or bymeasuring changes to the current owing in the primary'excitation' coil. Variations in the electrical conductivityor magnetic permeability of the test object, or the pres-ence of any aws, will cause a change in eddy current anda corresponding change in the phase and amplitude of themeasured current. This is the basis of standard (at coil)eddy current inspection, the most widely used eddy cur-rent technique.However, eddy-current testing can detect very smallcracks in or near the surface of the material, the sur-faces need minimal preparation, and physically complexgeometries can be investigated. It is also useful for mak-ing electrical conductivity and coating thickness measure-ments.The testing devices are portable, provide immediate feed-back, and do not need to contact the item in question. Re-cently tomographic notion of ECT has been explored seefor example:Another eddy-current testing technique is pulsed eddy-current testing. A major advantage of this type oftesting is that there is no need for direct contact withthe tested object. The measurement can be performedthrough coatings, weather sheetings, corrosion productsand insulation materials.[1] This way even high tempera-ture inspections are possible. Compared to the conven-tional eddy-current testing, pulsed eddy-current testingallows multi-frequency operation.[2]

1 See also Eddy current Nondestructive testing

Alternating current eld measurement Cover Meter Metal detector

2 References[1] Pulsed Eddy-Current Testing. Retrieved on July 18, 2012.

[2] Background on Pulsed Eddy Current. Retrieved on July18, 2012

3 External links An introduction to eddy current testing from theNDE/NDT resource center

Intro to Eddy Current Testing by JosephM. Buckley(pdf, 429 kB)

Eddy Current Testing at Level 2, InternationalAtomic Energy Agency, Vienna, 2011 (pdf 5.6MB).

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