In the sense of the method of the invention, the term "fiber strands" is used to include both ordered and irregular strands of textile single fibers (slivers) and furthermore also webs.
It is known in the textile industry to use mechanical or capacitive sensors to monitor automatically mass fluctuations of continuously moving fiber strands or slivers for purposes of quality control. On the other hand, foreign particles and foreign fibers are measured manually by a lab technician who randomly pulls apart slivers on a luminous table and visually searches for foreign particles and counts them. The properties of the individual fibers cannot be measured at all, and therefore it is impossible to ascertain changes in parameters (for instance length, crimping) caused by processing conditions.