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: A process and a device for detection of differences in yarn tension in a sheet of parallel yarn ends wherein the individual ends of the yarn sheet are deflected from a defined measuring plane, the extent of the deflection being measured.