Instruments used for RFT inspection are often dual
use eddy current / RFT instruments employing multi-frequency technology.
The excitation current from these instruments is passed on to
the probe that contains an exciter coil, sometimes referred to
as the driver coil. The receiving coil voltage is typically in
the microvolt range, so an amplifier is required to boost the signal
Certain systems will incorporate a probe excitation method known
as multiplexing. This utilizes an extreme high speed switching
method that excites the probe at more than one frequency in sequence.
Another method of coil excitation that may be used is simultaneous
injection. In this coil stimulation technique, the exciter coil
is excited with multiple frequencies at the same time while incorporating
filter schemes that subtract aspects of the acquired data. The
instrument monitors the pickup coils and passes the data to the
display section of the instrument. Some systems are capable of
recording the data to some type of storage device for later review.