Estimating Probability of Detection Curves Related to Eddy Current Sender – Receiver Probes

Paper in proceeding, 2013

Sender – receiver probes are commonly used in eddy current procedures for crack detection. Such probes can give a non-linear signal response as a function of the crack size. Classical methods used for analysis in probability of detection (POD) assessments require that the signal response versus crack size can be predicted with a linear relation, which also must show a constant variance of the collected data points. One approach which can be used to overcome these limitations is to use a mathematical model of the eddy current probe – flaw interaction and use this to estimate the detection probability at specific crack sizes. This method is applied within this work, using the finite element method for the eddy current signal response predictions. In order to manage a large number of calculations at several crack sizes we propose the use of a meta-model approach. A linear meta-model is created at different crack sizes and then used for POD estimation. The number of signal responses above the detection level at specific crack sizes is then used to estimate the POD, a method which does not require any particular relation between signal response and crack size. The meta-model enables a large number of stochastic computations to be carried out in order to estimate the signal response distribution for a specific crack size. We conclude that modelling is a vital part of procedure capability estimations of eddy current procedures based on sender – receiver probe characteristics and can be used for procedure understanding, improvements and aid in experimental verifications.