Eddy current testing with absolute sensors

Eddy current testing uses a coil that builds up an alternating magnetic field. Changes in the material, such as cracks or microstructural differences, disturb this field and alter the coil's impedance. You measure this with the testing device. You must guide the sensor cleanly and at the correct distance over the surface. The distance to the workpiece is the critical point – it must not vary, otherwise you'll get false indications. Edges and the material itself (e.g., ferritic or austenitic) also play a big role, you have to consider that when setting up.