Method and device for optically detecting impurities in horizontally moving thread

摘要

The method involves starting a learning phase, in which no impurities are evaluated. Light with a constant light intensity for a predetermined length of a yarn (1) is emitted in a direction of the yarn, and the intensity of a remitted light is measured. An average value of intensities of the remitted light are calculated, and another light intensity is determined depending on a value representing a yarn diameter such that the intensities of the remitted light corresponds to the calculated average value. An independent claim is also included for a device for optically detecting impurity i.e. foreign fiber, in longitudinally moved yarn.