Abstract: In a method for testing a continuously forward-moving strand a light beam which passes along a plane that extends approximately perpendicularly to the longitudinal axis of the strand is introduced into the strand. The brightness value is measured on a place of the strand exterior which is distal from the light incidence place by means of at least one photoelectronic element disposed directly on the strand exterior and the measured result is evaluated in a gating circuit which is electrically connected to the photoelectronic element.

Abstract: Faults in a composite filter rod being supplied to a sectioning device are detected optically by traversing the rod with a beam of light supplied along a first fiber bundle and taken up and delivered to photo-detector by a second fiber bundle. The ends of the cylindrical fiber bundles are held in the configuration of narrow homothetic rectangles transverse to the direction of feed of the rod, the width of the first bundle being approximately double that of the second bundle. The photo-detector controls elimination of faulty tips after sectioning; additional pairs of fiber bundles can be used to control synchronization of cutting with feed of the rod, and the correct succession of filter elements in the rod.