The alternating current field measurement (ACFM) technique is an electromagnetic technique capable of both detecting and sizing (length and depth) surface-breaking cracks in metals. The basis of the technique is that an alternating constant current in a tangential solenoid, remote from the test surface, induces electric currents in the sample surface which are uni-directional and of uniform strength over a localised area under the solenoid. When no defects are present in this area, these electric currents will be undisturbed. If a crack is present, the uniform current is disturbed and the current flows around the ends and down the face of the crack.
A standard PC is used to control the equipment and display results. ACFM is
unique in the way data is displayed.