The time-delay effect of multiple-network systems in NCS

Applications of the network control system (NCS) improve the efficiency, the flexibility, and the reliability of large-scale systems in modern industries. In the same time, applications of NCS for remote control and monitoring reduce the time and cost of installation, reconfiguration, and maintenance. This study integrates the Ethernet, the control area network (CAN) network, and the wireless 802.11b in the present NCS. The TCP/IP and the CAN protocols are adopted as the communication gateway in a remote control system for an AC 400 W servo motor. The time delay between the application layer of the client and the application layer of the remote control target has been measured and analyzed in this study. Experimental results indicate that different sampling rates and the environments will greatly affect the delayed time. Also, results indicate that the distance will not affect the delay time in wireless communication. However, as the sampling period reduces, the delay time of the network increases dramatically. In the wireless network, the delay time may change suddenly by the environment interferences. Finally, with a serious time delay, a Smith predictor has been successfully applied to control the servo motor from Kaohsiung which is in 300 km away to verify the feasibility of the proposed NCS.