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PLC控制系統(tǒng)的地線包括系統(tǒng)地、屏蔽地、交流地和保護地等。接地系統(tǒng)混亂對PLC系統(tǒng)的干擾主要是各個接地點電位分布不均，不同接地點間存在地電位差，引起地環(huán)路電流，影響系統(tǒng)正常工作。例如電纜屏蔽層必須一點接地，如果電纜屏蔽層兩端A、B都接地，就存在地電位差，有電流流過屏蔽層，當發(fā)生異常狀態(tài)如雷擊時，地線電流將大。
此外，屏蔽層、接地線和大地有可能構成閉合環(huán)路，在變化磁場的作用下，屏蔽層內有會出現(xiàn)感應電流，通過屏蔽層與芯線之間的耦合，干擾信號回路。若系統(tǒng)地與其它接地處理混亂，所產生的地環(huán)流就可能在地線上產生不等電位分布，影響PLC內邏輯電路和模擬電路的正常工作。PLC工作的邏輯電壓干擾容限較低，邏輯地電位的分布干擾容易影響PLC的邏輯運算和數(shù)據(jù)存貯，造成數(shù)據(jù)混亂、程序跑飛或死機。模擬地電位的分布將導致測量精度下降，引起對信號測控的嚴重失真和誤動作。
The ground wire of the PLC control system includes system ground, shielding ground, AC ground, and protection ground. The interference of chaotic grounding system on PLC system is mainly due to uneven potential distribution at various grounding points, and the existence of ground potential differences between different grounding points, which causes ground loop current and affects the normal operation of the system. For example, the cable shielding layer must be grounded at one point. If both ends A and B of the cable shielding layer are grounded, there is a ground potential difference, and current flows through the shielding layer. When an abnormal state occurs, such as a lightning strike, the ground wire current will be high.
In addition, the shielding layer, grounding wire, and ground may form a closed loop. Under the action of changing magnetic fields, induced currents may appear inside the shielding layer, which can interfere with the signal loop through coupling between the shielding layer and the core wire. If the grounding of the system is chaotic with other grounding methods, the generated ground current may generate unequal potential distribution on the ground wire, affecting the normal operation of the logic and analog circuits in the PLC. The logic voltage interference tolerance of PLC operation is relatively low, and the distribution interference of logic ground potential can easily affect the logic operation and data storage of PLC, causing data confusion, program runaway or crash. Simulating the distribution of ground potential will lead to a decrease in measurement accuracy, causing serious distortion and misoperation of signal measurement and control.
