Electromagnetic Testing

Multiparameter Techniques
It becomes obvious that the technician must have a good working knowledge
of current density and phase relationships to make intelligent frequency
choices. The frequency choice discussed to date deals with coil systems
driven by only one frequency. Test systems driven by more than one
frequency are called multifrequency or multi parameters systems. It is
common for a test coil to be driven with three or more frequencies. Although
several frequencies may be applied simultaneously or sequentially to a test
coil, each of the individual frequency techniques follows rule established by a
single frequency techniques. Signals generated at the various frequencies
are often combined or mixed in electronic circuits that algebraically add or
subtract signals to obtain the desired result.
Charlie Chong/ Fion Zhang