In this mode, PLC only monitors the operation and does not participate in the control process. The belt conveyor is manually operated locally by the post driver through the relay logic circuit in the control cabinet, and the belt conveyor is not interlocked; each protection device participates in the control. The start command signal sent by the start button of the local control box returns to the PLC control cabinet to complete the start function (eliminate the start difficulty caused by long-distance wiring and large voltage loss) through the photoelectric coupling and isolation relay which controls and commands the synchronous action.