Pulsed eddy current inspections and the calibration and display of

Abstract

A pulsed eddy current (PEC) instrument acquires PEC pulse responses from different locations on a structure being inspected. The difference between the acquired PEC pulse responses and a reference PEC response is determined to obtain time-domain difference signals having a time value and a magnitude value. The time and magnitude values are stored in memory with location information. An image display is provided that is determined from the stored magnitude values, although magnitude values for difference signals whose time values do not meet a defined time condition are filtered from the display. The time condition filters from the display known conditions such as the presence of fasteners, the presence of air-gaps between layers of the structure, and excessive PEC probe lift-off from the structure and filters the display so that only information from a particular layer or depth of the inspected structure is displayed. A quantified flaw measure can be determined by comparing the magnitude value to a calibration curve associated with a particular depth or layer of the structure. Also, Fourier transforms can be performed on the time-domain difference signal to obtain magnitude values at a multitude of frequencies which can be displayed in various formats, including an image display using a frequency condition for filtering.