Eddy Current Testing is an electromagnetic method for non-destructive testing of electrically conductive materials. In Eddy Current Testing, the effect is taken out 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 distance between the probe and the part surface. Therefore, Eddy Current Testing typically has 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 object to be tested. 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 the test part has a inclusion of a foreign material whose specific resistance is less than that of the rest of the material, the electrical current density in the area will be greater than in the environment. Conversely, the inclusion involves larger specific resistance or a hairline crack around the current has to flow around. In any case, the eddy current density changes compared to the undamaged component. The used probes are designed that small changes in the material properties or the distance of the probe from the material surface are largely compensated.
When carrying out a sorting test, parts are tested for the material structure or sorted for the material indentification.
Layer Thickness Measurement
By changing the frequency of the voltage, the penetration depth of the eddy current (skin effect) changes, which allows an adjustment to the test conditions. Different methods are used for the 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 the previous 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 necessary
clean test, no coupling agent required