Eddy Current Theory

Eddy current theory is based on the fundamentals of electromagnetism.  Faraday’s Law states that an electrical signal flowing in a wire creates a magnetic field.  Eddy current instruments contain an AC (Alternating Current) signal generator which drives an electrical signal into the eddy current coil.  The electrical signals flowing in the coil generate a magnetic field.

Faraday’s Law also stated that current will flow in an electrical conductor when it enters a magnetic field.  When the conductive material shown enters the magnetic field generated by the eddy current coil, an electrical signal – called an eddy current begins to flow.  These eddy currents flow differently in different alloys and materials with different heat treat properties.  They also flow around cracks and flaws in the material.

The eddy currents flowing in the conductive material generate their own magnetic field.  This field is detected by the same eddy current coil, turned into an electrical signal and sent back to the eddy current instrument.  The eddy current instrument analyzes this signal and compares it to a “known good component” or a "known good condition.”