描述
与PLC控制系统连接的各类信号传输线，除了传输有效的各类信息之外，总会有外部干扰信号侵入。
此干扰主要有两种途径：一是通过变送器供电电源或共用信号仪表的供电电源串入的电网干扰，这往往被忽视；二是信号线受空间电磁辐射感应的干扰，即信号线上的外部感应干扰，这是很严重的。由信号引入干扰会引起I/O信号工作异常和测量精度大大降低，严重时将引起元器件损伤。对于隔离性能差的系统，还将导致信号间互相干扰，引起共地系统总线回流，造成逻辑数据变化、误动和死机。PLC控制系统因信号引入干扰造成I/O模件损坏数相当严重，由此引起系统故障的情况也很多。
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