5466-409 Woodward 控制器

5466-409 Woodward 控制器来自空间的辐射干干扰空间的射电磁场(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，其分布极为复杂·若PLC系统置于所射频场内，就回收到福射干扰，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通信内网络的福射，由通信线路的感应引入干扰。福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。

5466-409 Woodward 控制器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。
来自电源的干扰实践证明，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，后更换隔离性能更高的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性并不理想。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。

5466-409

5466-409 Woodward Controller Radiation from space Dry interference The radio magnetic field (EMI) in space is mainly generated by power networks, transient processes of electrical equipment, lightning, radio broadcasting, television, radar, high-frequency induction heating equipment, and so on, often called radiation interference. If the PLC system is placed in the RF field, it will recover the radiation interference, which is mainly affected by two paths: one is the radiation directly to the PLC inside, which is interfered by the circuit induction, but the radiation to the PLC communication network, which is interfered by the induction of the communication line. Radiation interference is related to the field equipment layout and the size of the electromagnetic field generated by the equipment, especially the frequency, and is generally protected by setting shielded cables and PLC local shielding and high voltage release elements.
5466-409 Woodward controller Interference from leads outside the system
It is mainly introduced through power and signal lines and is often referred to as conducted interference. This kind of interference is more serious in the industrial field of our country.
Interference from the power supply practice has proved that there are many cases of PLC control system failure caused by the interference introduced by the power supply, the author has encountered in a project debugging, after replacing the PLC power supply with higher isolation performance, the problem has been solved.
The normal power supply of the PLC system is powered by the power grid. Due to the wide coverage of the grid, it will be subject to all space electromagnetic interference and induction of electricity, voltage and circuits on the line. In particular, the changes in the power grid, the incoming switch operation surge, the start and stop of large power equipment, the harmonics caused by AC and DC transmission devices, the short-circuit transient impact of the power grid, etc., are transmitted to the original side of the power supply through the transmission line. PLC power supply usually uses isolated power supply, but its mechanism and manufacturing process factors make its isolation is not ideal. In practice, isolation is impossible due to the presence of distributed parameters, especially distributed capacitors.

5466-409