Swinging Field Magnetization
Related Entries: Multi-Directional Magnetization,
Special equipment allows two or more currents in different directions to be applied simultaneously. This permits locating discontinuities in more than one direction and shortens inspection time.
There's a great paper on this subject that can be found at
www.insight-ndt.com/papers/technical/t002.pdf. One note, the author often refers the swing field changing vector direction 50 times/sec. In the US, this would be 60 times/sec.
normally, we use two kinds of current simultaneously, one is AC and the other is DC. we use AC to generate the direction of the magnetic field which is changing all the time. thus, the swing field forms.