Operating principle of the magnetic induction testing method
In magnetic induction testing, the part whose material properties are to be tested is led through a test coil with an exciter coil and a measuring coil. An impressed alternating current is applied to the exciter coil, and the resulting magnetic alternating field induces eddy currents in the testing material.
In the reception winding of the measuring coil, a voltage is generated depending on the conductivity of the tested material (electric parameter) as well as on the shape and size of the hysteresis curve (magnetic parameter). The evaluation of this voltage allows the testing of ferromagnetic and austenitic steels as well as non-ferric metals.
Since the hysteresis curve in particular is strongly influenced by technological parameters such as hardness, alloy components, and microstructures, these parameters can be determined especially well via the magnetic properties.
By varying the exciter field strength, it is possible to select the specific dynamic range of the hysteresis curve where the magnetic parameter is especially influenced by the desired technology parameter. The choice of exciter frequency also allows selective observation of the core and surface properties.