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空间的辐射电磁场（EMI）主要是由电力网络、电气设备的暂态过程、雷电、无线电广播、电视、雷达、高频感应加热设备等产生的，通常称为辐射干扰，其分布较为复杂。若PLC系统置于所射频场内，就回收到辐射干扰，其影响主要通过两条路径：一是直接对PLC内部的辐射，由电路感应产生干扰；而是对PLC通信内网络的辐射，由通信线路的感应引入干扰。辐射干扰与现场设备布置及设备所产生的电磁场大小，特别是频率有关，一般通过设置屏蔽电缆和PLC局部屏蔽及高压泄放元件进行保护。
2.2来自系统外引线的干扰
主要通过电源和信号线引入，通常称为传导干扰。这种干扰在我国工业现场较严重。
（1）来自电源的干扰
实践明，因电源引入的干扰造成PLC控制系统故障的情况很多，笔者在某工程调试中遇到过，后换隔离能高的PLC电源，问题才得到解决。
PLC系统的正常供电电源均由电网供电。由于电网覆盖范围广，它将受到所有空间电磁干扰而在线路上感应电压和电路。尤其是电网内部的变化，入开关操作浪涌、大型电力设备起停、交直流传动装置引起的谐波、电网短路暂态冲击等，都通过输电线路传到电源原边。PLC电源通常采用隔离电源，但其机构及制造工艺因素使其隔离并不理想。实际上，由于分布参数特别是分布电容的存在，隔离是不可能的。
（2）来自信号线引入的干扰
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。
（3）来自接地系统混乱时的干扰
MCPN750-1332A MCPN750-1342 MCPN750-1342A MCPN750-1352
MCPN750-1352A MCPN750-1362 MCPN750-1362A MCPN765-1271
MCPN765-2241 MCPN765-6171 MEMSD256-K MM-6260AD-32M
MPMC101 MPMC202 MPMC221 MPMC221
MPMC222 MPMC222 MPMC282-012 MPMC301-001
MTX604-004A MTX604-010A MTX604-010A Dual 300MHz MVIP302
MVIP303 MVIP341 MVIP530 MVME025
MVME101 MVME104 MVME105 MVME106
MVME110 MVME110-1 MVME110 MVME117 MVME117-3
MVME117-3F MVME123 MVME1301 MVME132DOF MVME132 DOF
MVME132XT MVME133 MVME133-1 MVME133A-20
MVME133SA-020A MVME133SA MVME133XT MVME134 MVME135A
MVME141-1 MVME142-012 MVME142-012A MVME143 MVME143-2
MVME147 MVME147-010 MVME147-010A MVME147-011 MVME147-11
MVME147-011A MVME147-11A MVME147-012 MVME147-012A MVME147-013
MVME147-013A MVME147-014 MVME147-022 MVME147-022A
MVME147-1 MVME147A MVME147S MVME147S-1
MVME147SA-1 MVME147SB-1 MVME147SB-2 MVME147SC-2
MVME147SRF MVME1600-001 MVME1600-011 MVME1600-024 MVME1600-001 MVME162-001 MVME162-01
MVME162-010 MVME162-010A MVME162-011 MVME162-11 MVME162-011A MVME162-11A
MVME162-012 MVME162-12 MVME162-012A MVME162-12A MVME162-013 MVME162-13 MVME162-013A MVME162-13A
MVME162-013A MVME162-13A MVME162-020 MVME162-20 MVME162-020A MVME162-02A MVME162-021 MVME162-21
MVME162-022 MVME162-22 MVME162-023 MVME162-23 MVME162-023A MVME162-23A MVME162-031 MVME162-31
MVME162-032 MVME162-32 MVME162-033 MVME162-33 MVME162-040 MVME162-40 MVME162-042 MVME162-42
MVME162-211 MVME162-212 MVME162-213 MVME162-215
MVME162-223 MVME162-253 MVME162-260 MVME162-262
MVME162-263 MVME162-270 MVME162-283 MVME162-410
MVME162-412 MVME162-412 MVME162-420 MVME162-423
MVME162-432 MVME162-433 MVME162-510 MVME162-510A
MVME162-512A MVME162-513 MVME162-513A MVME162-522A
MVME162-523 MVME162-523A MVME162-532 MVME162-532A
MVME162-533A MVME162-533A MVME162P-242E MVME162P-242L
MVME162P-242LE MVME162P-242LSE MVME162P-244LE MVME162P-252SE
MVME162P-344 MVME162P-344E MVME162PA-242LE MVME162PA-244L
MVME162PA-244LE MVME162PA-244LSE MVME162PA-344 MVME165
MVME165-01 MVME165-010 MVME166-11A MVME166-011A MVME166-12A MVME166-012A MVME166-13A MVME166-013A
MVME166-14A MVME166-014A MVME167 MVME167-005B MVME167-05B MVME167-006B MVME167-06B
MVME167-02A MVME167-002A MVME167-02B MVME167-002B MVME167-031A MVME167-31A MVME167-032B MVME167-32B
MVME167-033A MVME167-33A MVME167-033B MVME167-33B MVME167-034A MVME167-34A MVME167-034B MVME167-34B
MVME167-034B MVME167-34B MVME167-035B MVME167-35B MVME167-036B MVME167-36B MVME167-03B MVME167-003B
MVME167-04 MVME167-004 MVME167A MVME167B MVME167C