Tear detection system for determining break in paper web in continuous drier - used in rotary printing press with printing cylinders for printing forward running paper web arranged before continuous drier

摘要

A unit (11) for establishing a direction reversal of the paper web (1) is arranged between the printing cylinders and the continuous drier. The determining of a direction reversal of the paper web acts as an indication for the existence of a break in the paper web. The direction reversal detection unit (1) includes a first sensor (12) sensing the printed image of the forward running paper web (1). The output signal of the first sensor is fed into a shift register (13). A second sensor (14) sensing the printed image is provided behind the first sensor in the forward running direction. The output signal of the second sensor is compared with the signal output of the shift register. A deviation between these output signals delivers the indication for the direction reversal. ADVANTAGE - Break in paper web is quickly and reliably identified.