描述

1C31194G03 空間的輻射電磁場(chǎng)（EMI）主要是由電力網(wǎng)絡(luò)

空間的輻射電磁場(chǎng)（EMI）主要是由電力網(wǎng)絡(luò)、電氣設(shè)備的暫態(tài)過(guò)程、雷電、無(wú)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(chǎng)內(nèi)，就回收到輻射干擾，其影響主要通過(guò)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)的輻射，由通信線路的感應(yīng)引入干擾。輻射干擾與現(xiàn)場(chǎng)設(shè)備布置及設(shè)備所產(chǎn)生的電磁場(chǎng)大小，特別是頻率有關(guān)，一般通過(guò)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)。

2.2.2來(lái)自系統(tǒng)外引線的干擾

　　主要通過(guò)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(guó)工業(yè)現(xiàn)場(chǎng)較嚴(yán)重。

　　（1）來(lái)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(guò)，后更換隔離性能更高的PLC電源，問(wèn)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(guò)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。

　?。?/span>2）來(lái)自信號(hào)線引入的干擾

　　與PLC控制系統(tǒng)連接的各類信號(hào)傳輸線，除了傳輸有效的各類信息之外，總會(huì)有外部干擾信號(hào)侵入。此干擾主要有兩種途徑：一是通過(guò)變送器供電電源或共用信號(hào)儀表的供電電源串入的電網(wǎng)干擾，這往往被忽視；二是信號(hào)線受空間電磁輻射感應(yīng)的干擾，即信號(hào)線上的外部感應(yīng)干擾，這是很嚴(yán)重的。由信號(hào)引入干擾會(huì)引起I/O信號(hào)工作異常和測(cè)量精度大大降低，嚴(yán)重時(shí)將引起元器件損傷。對(duì)于隔離性能差的系統(tǒng)，還將導(dǎo)致信號(hào)間互相干擾，引起共地系統(tǒng)總線回流，造成邏輯數(shù)據(jù)變化、誤動(dòng)和死機(jī)。PLC控制系統(tǒng)因信號(hào)引入干擾造成I/O模件損壞數(shù)相當(dāng)嚴(yán)重，由此引起系統(tǒng)故障的情況也很多。

1C31194G03 空間的輻射電磁場(chǎng)（EMI）主要是由電力網(wǎng)絡(luò)

The radiation electromagnetic 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, etc., usually called radiation interference, and its distribution is extremely complex. If the PLC system is placed in the RF field, the radiation interference is recovered, and its impact is mainly through two paths: one is the direct radiation inside the PLC, which is interfered by the circuit induction; It is the radiation to the network within the PLC communication, and interference is introduced 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.

2.2.2 Interference from external leads of 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.

(1) Interference from the power supply

Practice has proved that the interference caused by the power supply caused a lot of PLC control system failure, the author encountered in a project debugging, after replacing the PLC power supply with higher isolation performance, the problem was 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 induced voltage and circuit 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.

(2) Interference introduced from signal lines

All kinds of signal transmission lines connected with the PLC control system, in addition to the effective transmission of all kinds of information, there will always be external interference signal intrusion. There are two main ways of this interference: one is through the transmitter power supply or the power supply of the shared signal instrument into the grid interference, which is often ignored; Second, the signal line is interfered by electromagnetic radiation induction in space, that is, the external induction interference on the signal line, which is very serious. The interference introduced by the signal will cause the abnormal work of the I/O signal and the measurement accuracy will be greatly reduced, and the components will be damaged in serious cases. For the system with poor isolation performance, the signals will interfere with each other, causing the bus backflow of the common ground system, resulting in logical data changes, misoperation and crash. PLC control system due to signal interference caused by I/O module damage is quite serious, resulting in a lot of system failures.

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Company Introduction:
Chengdu Sunshine Xihe Co., Ltd. specializes in one-stop procurement consulting for imported industrial spare parts, offering original equipment and professional discontinued parts services. We are committed to providing efficient and reliable automation solutions for our customers. Customer support fast responseThe network of partners spans all continentsGlobal partner networkAlways achieve more delivery, be it parts, service or speed



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