Abstract: An apparatus for optical monitoring of at least one thread for irregularities, in particular for filament breaks in multifilament yarns, with a radiation source, a radiation detector, and a ray beam transmitted by the radiation source and received by the radiation detector and directed past the thread perpendicular to and at a defined distance to it, whereby the radiation source and radiation detector are situated next to the thread, characterized in that the radiation source and radiation detector are situated on the same side of the thread and that on the opposite side of the thread means for displaced reflection of the ray beam are situated such that the transmitted ray beam is directed past the thread on one side and the displaced reflected ray beam is directed past the thread on the other side, whereby the transmitted ray beam and the displaced reflected ray beam are as equidistant as possible from the thread and are at least approximately parallel to one another is disclosed.

Abstract: Process for monitoring a moving yarn sheet by means of a light beam, photodetectors and an electronic analyzer, whereby the yarn sheet is guided via thread guide rods before and after the monitoring site and the shadowing of the light beam caused by an increase in thread thickness is directed perpendicularly to the direction of travel of the yarn sheet for detection by photodetectors, and evaluated and recorded by the electronic analyzer, characterized in that the intensity of a single light beam is detected by at least two photodetectors arranged in series in the direction of travel of the yarn sheet and in that the evaluation by the electronic analyzer is such that a recording only takes place when the shadowing is detected by one or more of said photodetectors following in the direction of travel of the yarn sheet with a time delay corresponding to the running speed of the yarn sheet is disclosed.