Abstract: For the detection of contaminants, a yarn or a thread is led through a zone of measurement, which is formed as a flat slit in an optically transparent body. This transparent body has outer surfaces for diffusely or non-diffusely reflecting light back into the body. Light is led into the body from several sources of light, such that the yarn is diffusely illuminated from all sides. The sources of light are arranged and adjusted such that the brightness of the yarn detected by a sensor is equal to the brightness of the yarn's background field. In this way, the measurement becomes independent of the yarn's thickness. Due to the use of a flat slit for receiving the yarn, the yarn can be inserted into the zone of measurement by the same procedures as they are used in conventional yarn cleaners.

Abstract: For detecting neps in a textile fiber fleece band transported along a transporting path through a carding machine a detecting device comprises a mechanism for illuminating the fiber fleece band on at least one area located on the transporting path. Imaging optics project an image of this illuminated area onto the surface of one of a plurality of photo sensor elements. The area projected onto each one of the photo sensor elements substantially corresponds to the size of the neps to be detected. The photo sensor elements are connected to evaluation circuits for evaluating light intensity variations caused by neps passing the illuminated area.