A.C. Field measurement system

摘要

An ac field measurement system and method for detecting defects are disclosed where the system comprises an arrangement 6 for inducing an ac field in a conductor 2 and a sensor, coil 8, responsive to the ac field to produce a signal indicative of the ac field. The system further comprises circuitry 18 configured to apply a phase shift to the measured signal by an amount suitable to reduce a liftoff component of the signal dependent on the distance of the sense coil 8 from the conductor 2. A further arrangement comprises circuitry configured to phase shift the measured signal across a range of phases for a specific location of the sensor relative to the conductor surface.