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 strength.
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.