Patent ID: 6346713
Filing Date: 2002-02-12
Classification: G01N

Abstract:
Method for inspecting an article (1) for defects (2), wherein the article (1) is scanned by means of a scanning light beam (3, 4, 5), the light scattered by the article (1) is collected and the collected light is converted into an electrical scanning response signal (6, 7, 8) which is fed to a processing unit (18) for processing the scanning response signals (6, 7, 8), a defect (2) in the article (1) giving rise to a pulse in the scanning response signal (6, 7, 8), characterised in that the light beam (3, 4, 5) has a wavelength such that the article (1) is transparent thereto, in that at least two scanning response signals (6, 7, 8) are obtained, each of which being associated with a focal point located in the direction of the light beam at a different depth in the article (1), and in that the location of the defect (2) in the direction of the light beam is determined from the steepness of the front and rear flanks of the pulses in the scanning response signals (6, 7, 8).