Abstract: A web of moving material is successively scanned by a light source, such as a laser beam, and changes of intensity of the transmitted, reflected or scattered light from the material is detected to provide an indication for discerning flaws in the web. A once per scan line digital signal from the scanner controls a voltage controlled oscillator connected in a phased locked loop which is used for controlling the generation of a precision ramp analog voltage that follows the angular scan position of the light source on the material. The light signal from the web is applied to a comparator for providing a digital pedestal signal in which the first light passing the comparator is the leading edge of the web while the last light passing during a scan line is the trailing edge or the end of the web. If no pedestal signal is present indicative of a break in the web, a synthetic maximum width pedestal signal is substituted to enable the inspection system to continue to function.

Abstract: An alignment means is provided for aligning a light collector rod with a scanning light beam in a flaw detection system. The light collector rod means, having a diffusing or reflective stripe thereon, is positioned to receive light from a material being examined which is being scanned by a light beam. In order to align the light collector rod with the scanning light beam, an alignment light source is positioned on the side opposite to the stripe on which light is received from the material, and the alignment light source is selectively actuated to project a dark stripe or line from the light collector rod means on the material being examined so that the scanning light beam can be aligned with the line projected thereon.