Eddy Current Testing is an electromagnetic method for non-destructive testing of electrically conductive materials. Eddy Current Testing makes use of the fact that most impurities and damage in an electrically conductive material also have a different electrical conductivity or permeability than the actual material. The measurement signal depends on test parameters i.e. conductivity, permeability and the distance between the probe and the surface of the part. Therefore, Eddy Current Testing is typically used in the following areas of application: crack testing, layer thickness testing, material characterization and sorting.
During crack testing, the probe is moved above or through the test object. As long as there is no damage in the material, its electrical resistance is also homogeneous, and the eddy currents flow evenly in the material. For example, if there is an inclusion in the test part of a foreign material whose specific resistance is lower than that of the rest of the material, the electrical current density in that area will be greater than in the surrounding area. The opposite is the case for inclusions with higher specific resistance or for hairline cracks the current must flow around. In any case, the eddy current density changes in comparison to an undamaged component. The used probes are designed in way that small changes in material properties or the gap between the probe an the material surface are largely compensated.
When carrying out a sorting test, parts are tested for the material structure or sorted by their material identification .
Layer Thickness Measurement
By changing the frequency of the voltage, the penetration depth of the eddy current (skin effect) changes. In this way, the device can be adjusted to the test conditions. Different methods are used for layer thickness measurement depending on the material properties of the part to be tested, such as electrical conductivity and ferromagnetism: Magnetic inductive method, amplitude measurement, phase evaluation or a combination of these methods.
For material characterization, changes in conductivity or permeability are used to determine material states, hardness, heat treatment, detection of welds or for material identification.
Dipl.-Ing. Tobias Müller
Phone: + 49 (0) 681/9767153
Fax: + 49 (0) 681/9767158
suitable for automization
no particular preparation of the test surfaces required
clean test, no coupling agent required