RTD™ eddy-current inspection

Eddy-current is a technique based on interaction of magnetic fields with the object under test to detect geometrical and structural flaws in conductive materials.

When inspecting, the disturbances to eddy-currents in objects are detected. This inspection technique can be used to detect cracks on or just below the surface of materials or deeper, dependent on the inspection parameters, thickness of the inspected material and for detecting corrosion under coating.


The disturbances of the current density in the object can be caused by surface roughness, corrosion, material inclusions, differences in hardness (partly through variations in the effects of heat treatment), differences in conductivity and magnetic permeability.

In fact, the measurement consists of tracing the alternating current resistance or impedance of the coil in combination with the material on an oscilloscope, to which a recorder (which can also be a computer) can be connected. The impedance is always dependent on the above-mentioned properties of the test object.

The two characteristic properties of the impedance as image vector on the screen, namely amplitude and phase angle (to be calculated from the x- and the y-coordinate of the vector), are the features which are recorded as flaw indication and which make it possible to compare the flaw against a reference.

RTD-branded approaches to eddy-current inspection include:




  • ACFM