Conventional laboratory testing in filament yarn productions take place after 24 or even more hours after production. Atline testing concepts reduce this feedback delay down to 1-2 hours. Online testing directly at the running yarn line with immediate feedback is what the filament industry is looking at for many reasons. Lenzing Instruments Prompt real time online monitoring system for synthetic filament yarns and monofilaments such as PET, PA and PP - POY, FDY, LOY, DTY and BCF offers great possibilities when it comes to capabilities, reliability, experience and fast return on investments. There are three types of sensors available: - MFS multi function sensor (Fig. 1) - OLT tension sensor - OLF spin finish sensor.