Patent ID: 7275438

Claim:
A method for detecting a tear-off strip ( 11 ) or a tear-off thread on a material web ( 12 ) with the aid of sensors comprising an ultrasonic transmitter and an ultrasonic receiver, said method comprising the steps of: a) positioning the ultrasonic transmitter ( 18 ) and the ultrasonic receiver ( 19 ) on opposite sides, respectively, of the material web ( 12 ), b) positioning the ultrasonic transmitter ( 18 ) and the ultrasonic receiver ( 19 ) such that the material web ( 12 ) conveyed between the ultrasonic transmitter ( 18 ) and the ultrasonic receiver ( 19 ) is registered by ultrasonic waves substantially exclusively in a region of the tear-off strip ( 11 ) or tear-off thread, c) constructing the ultrasonic transmitter ( 18 ) in such a way that a response curve generated by the ultrasonic transmitter corresponds approximately to a width of the tear-off strip ( 11 ) or thread, and d) connecting the ultrasonic receiver ( 19 ) to an evaluation unit which reacts to changes in the intensity of the waves picked up the ultrasonic receiver.