UNS0868B-P ABB

The transmission medium of the node bus is generally a coaxial cable,and some use the token signal transmission mode,and some use the multi-channel transmission with conflict detection to compete for the bus signal transmission mode.No matter which method is adopted,when the main line of the bus is interrupted anywhere,it will cause communication failure of all stations and their sub-devices on the bus.

At present,the general method to prevent such failures is to use dual redundant configuration to avoid the global impact due to the failure of one bus,but this cannot fundamentally avoid the occurrence of failures,and once a bus fails,processing It is very easy to cause another bus failure,and the consequences are very serious.An effective method should be to prevent poor bus contact or open circuit.More successful is the node bus arrangement of the system.The connection of the coaxial cable is not in front of the communication module,but at the back of the module,so that when the system is running to deal with the failure of the communication module,it can avoid accidentally touching the coaxial cable and causing the network cable to be disconnected.At the same time,the coaxial cable will not be touched at any time except for special inspection,which can prevent the coaxial cable from being loosened due to multiple plugs and pulls,which increases the possibility of its failure.In addition,a management system for inspection and replacement of coaxial cables should be formulated,and replacement or treatment should be carried out before the contact resistance increases to affect communication.

节点总线的传送介质一般为同轴电缆，有的采用令牌信号传送方式，有的采用带冲突检测的确良多路送取争用总线信号传送方式。不论采用哪种方式，当总线的干线任一处中断时，都会导致该总线上所有站及其子设备通讯故障。

目前，一般防止此类故障的方法是采用双路冗余配置的方式，避免因一路总线发生故障而影响全局，但这并不能从根本上避免故障的发生，并且一旦一根总线发生故障，处理时极易造成另一个总线故障，其后果是非常严重的。有效的方法应是从防止总线接触不良或开路入手。比较成功的是系统的节点总线布置方式。其同轴电缆的连接不是在通信模件的前面，而是在模件的后面，这样当系统运行中处理通信模件故障时，可避免误碰同轴电缆，造成网线断路。同时，其同轴电缆除专门进行检查，任何时候都不会去触动，可防止因多次插拔同轴电缆的插头造成松动，增加其故障的可能。另外，应制定同轴电缆检查与更换管理制度，在其接触电阻增大至影响通信之前，进行更换或处理。