Kgs6 type magnetic induction spring main pipe sensor switch is selected. Detect the speed of belt conveyor to realize low-speed slip protection. In case of conveyor failure or belt slipping, the magnetic control switch of the speed sensor installed on the passive part of the conveyor will not be closed or can not be closed at the normal speed, and the speed protection will take effect after the control system delays according to the inverse time characteristic. The detection range is 0-3hz, which should be installed on the roller with a slightly larger diameter.