Eddy Current Imaging of Aircraft Using Real Time Image Signal Processing

Abstract

The increased incidence of aircraft component failures as motivated a reassessment of the NDE methods applied to assure fleet airworthiness. In the past, eddy current testing has been limited by the presence of spurious signals, operator error and the lack of permanent test results. An eddy current system using portable precision scanners and signal analysis techniques developed in the nuclear industry has been applied to aircraft inspections. Using custom designed probes, multifrequency mixing, and digital signal processing, the detection criteria of 10% loss of wall on the interior faying surface and cracks 60 mils (1.5 mm) in length have been accomplished. The subtle nature of these flaw conditions and the presence of interfering signals prompted the need for signal processing techniques. To achieve this objective, real time signal processing that requires a minimum of computation has been implemented in an eddy current C-scan imaging system. The signal processing produces spatial displays of amplitude (in phase or quadrature), magnitude, phase of spatial derivatives of these parameters. Permanent images that are more easily interpretable for flaw detection are thus produced.