The Bulldog alignment and rip detection switch is an electro-mechanical
system designed to detect dangerous misalignment of the conveyor and
also detection of belt tear damage. The switch will detect horizontal
misalignment of belts when contact is made with the roller, the roller
arm will be forced to pivot by the belt activating a switch at 20º to
trigger an alarm, and 35º to trigger a shut down procedure of the
conveyor. The sensors are usually installed in pairs on opposite sides
of the belt.
A steel flexible wire is set below the running conveyor belt approx
20-30mm attached by a rare earth magnet at each end. If the belt is
ripped or damaged the wire is pulled away releasing the magnet
connection which in turn will activate a switch.