5466-409 Woodward 控制器來自空間的輻射干干擾空間的射電磁場(EMI)主要是由電力網(wǎng)絡(luò)、電氣設(shè)備的暫態(tài)過程、雷電、無線電廣播、電視、雷達(dá)、高頻感應(yīng)加熱設(shè)備等產(chǎn)生的，通常稱為輻射干擾，其分布極為復(fù)雜·若PLC系統(tǒng)置于所射頻場內(nèi)，就回收到福射干擾，其影響主要通過兩條路徑:一是直接對(duì)PLC內(nèi)部的輻射，由電路感應(yīng)產(chǎn)生干擾，而是對(duì)PLC通信內(nèi)網(wǎng)絡(luò)的福射，由通信線路的感應(yīng)引入干擾。福射干擾與現(xiàn)場設(shè)備布置及設(shè)備所產(chǎn)生的電磁場大小，特別是頻率有關(guān)，一般通過設(shè)置屏蔽電纜和PLC局部屏蔽及高壓泄放元件進(jìn)行保護(hù)。

5466-409 Woodward 控制器來自系統(tǒng)外引線的干擾
主要通過電源和信號(hào)線引入，通常稱為傳導(dǎo)干擾。這種干擾在我國工業(yè)現(xiàn)場較嚴(yán)重。
來自電源的干擾實(shí)踐證明，因電源引入的干擾造成PLC控制系統(tǒng)故障的情況很多，筆者在某工程調(diào)試中遇到過，后更換隔離性能更高的PLC電源，問題才得到解決。
PLC系統(tǒng)的正常供電電源均由電網(wǎng)供電。由于電網(wǎng)覆蓋范圍廣，它將受到所有空間電磁干擾而在線路上感應(yīng)電,壓和電路。尤其是電網(wǎng)內(nèi)部的變化，入開關(guān)操作浪涌、大型電力設(shè)備起停、交直流傳動(dòng)裝置引起的諧波、電網(wǎng)短路暫態(tài)沖擊等，都通過輸電線路傳到電源原邊。PLC電源通常采用隔離電源，但其機(jī)構(gòu)及制造工藝因素使其隔離性并不理想。實(shí)際上，由于分布參數(shù)特別是分布電容的存在，隔離是不可能的。

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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.

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