Question

What are Eddy currents? Describe the ways in which they are used to advantage.

Answer 1

Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor, due to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.

The advantages of eddy current testing are:

Sensitivity to surface defects- Able to detect defects of 0.5mm in length under favourable conditions.

Can detect through several layers- The ability to detect defects in multi-layer structures (up to about 14 layers), without interference from the planar interfaces.

Can be automated- Relatively uniform parts can be inspected quickly and reliably using automated or semi-automated equipment, e.g. wheels, boiler tubes and aero-engine disks.

Little pre-cleaning required- Only major soils and loose or uneven surface coatings need to be removed, reducing preparation time.