Operating principle of the eddy current testing method
Eddy current testing is a non-destructive method for testing metal surfaces for defects such as cracks or discontinuities. Such surface defects have high-frequency electromagnetic interactions that allow them to be detected manually or automatically, depending on the requirement, and evaluated.
Defect resolutions of up to 30 µm are possible under optimum conditions. The testing is normally contactless. For this reason, eddy current testing neither damages nor contaminates surfaces.
Modern sensors, electronics, and software solutions offer a variety of application and evaluation options for the metal-producing and metal-processing industry as well as for mobile use in maintenance testing.
The extremely low media consumption and maintenance expenses of eddy current testing have made it one of the most economical and environmentally friendly non-destructive testing methods, and it is therefore widespread in 100% testing in production processes as well. In addition, the high testing speeds and the testing automation mean that the production process is not interrupted.
Eddy current methods in semi-finished product and component testing
Eddy current testing in the field of semi-finished product and component testing covers a frequency range of up to 10 MHz and is used to test metals for surface defects. A wide variety of differential measurement coils are normally used for this. Standard sensors as well as customized adaptations are utilized.
Semi-finished products such as wires, rods, and tubes are inspected for transverse cracks and hole-like defects using the encircling coils, while the surface of semi-finished products are tested for longitudinal defects with rotating probes. Stationary probes can also be used to test critical points on components. The selection of the right sensor always depends on the testing task. This makes very high defect resolutions possible.
Eddy current methods for metal detection
In metal detection, eddy current testing is used to generate an electromagnetic field with one or two frequencies that can be used to detect even the smallest quantities of hidden metals (e.g., steel, Fe, Al, Cu, Au, Ag).
The detection sensor emits an electromagnetic field to detect metallic objects using active sensors. This produces eddy currents in the detection object that in turn generate a secondary electromagnetic field that is detected by the detection sensor and used for evaluation.