Eddy current testers are based on the detection of variations in the electrical conductivity and magnetic permeability of a metal surface. It is commonly used in manufacturing to inspect thin metal for defects that translate to safety or quality problems. In addition to defect recognition in metal sheets and tubes, eddy current testers can be used to observe the results of heat treatment procedures and to find out the thickness of non-conductive layers over conductive materials.
Eddy current testing is confined to materials that conduct electricity and therefore cannot be applied to plastics. In some instances, eddy current and ultrasonic tests are used in tandem, with eddy current being a fast process for surface testing and ultrasonics being used to probe further below a surface.