The Yarn Inspection System YIS 200 generates online real time feedback about the most decisive characteristics of filament yarn. Monitored yarn properties include interlace, diameter and evenness. Detected defects include thin- and thick places, evenness, broken filaments, fluff and yarn breaks. The ultra-fast line scan camera scans the illuminated yarn online in different processes such as filament spinning, texturing, twisting, etc. The generated raw signals are evaluated by means of intelligent algorithms. Each time a defect e.g. broken filament, fluff, thin or thick place or a diameter change is detected, an image of the defect is generated. This allows for detailed analysis and troubleshooting. It also offers offline analysis based on stored real time data.