Abstract: The flanks of faults present in a surface produce abnormal reflection of a laser beam during linewise scanning of the surface by a laser beam. This apparatus deflects the angles of reflection from the surface, to indicate the presence of a flank, by a light conducting rod arranged parallel to the direction of linewise scanning for receiving reflected light on its surface and for conducting this light to its end face. The various light rays spread out transversely to the direction of scanning during their passage through the light conducting rod and are detected as they pass through a series of concentric annular apertures spaced from the end face of the light conducting rod. Each aperture is associated with a particular range of angles of incidence irrespective of the point on incidence along the surface of the rod and photoelectric detectors are used to sense the light passing through each aperture to provide the necessary indication of the presence or non-presence of a fault.

Abstract: A photo electric light detection device comprising an array of photodiodes is disposed at an end face of a light conducting rod in order to produce an output signal proportional to light incident on the surface of the rod and transmitted to the end face by total internal reflection. The array of photodiodes is subdivided into high and low pass frequency sub-arrays and the output signals from the sub-arrays are summed and processed to compensate for stray light. The device is useful in connection with a line scanner for detecting anomalies in a moving band.