Relating remote field eddy current signals to anomalous source models

摘要

The voltage plane polar plot analysis method used in remote field testing is based on radial field transmission and the percentage overlap between a defect and a detector coil. It is successful when inspecting small-bore tubes using probes with coaxial detector coils. The recent development of anomalous source models to describe the detailed responses of defects in electromagnetic testing is promising for predicting the remote field response of slit defects in larger-diameter tubes. A comparison is made between the anomalous source models used to describe defect interactions in electromagnetic testing and the voltage plane representation and normalisation procedure used for remote field eddy current signals. The normalisation procedure and the isolation of anomalous signals are compared in terms of background or defect-free phasors and phasors measured in the presence of a defect.