This work focuses on use of particle swarm optimization (PSO) to identify the optimal PID controller gains in speed control of a conveyor system. The proposed method is implemented on Mitsubishi Q series-UDV PLC with a number of encoder sensors and a built-in Ethernet module to monitor the feedback. To verify the performance of the proposed technique, we apply the optimal gains, which are determined offline by PSO, to the simulator and actual model. The experimental results show that the proposed PSO based PID controller provides lower transient fluctuation and smaller steady-state error compared to other previous approaches.