UT372b GKWN0007R1 ABB

The ground wire of PLC control system includes system ground,shield ground,AC ground and protection ground.The disturbance of the grounding system to the PLC system is mainly due to the uneven potential distribution of each grounding point,and the ground potential difference 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 will be a ground potential difference,and current will flow through the shielding layer.When abnormal conditions such as lightning strikes occur,the ground current will be larger.

PLC控制系统的地线包括系统地、屏蔽地、交流地和保护地等。接地系统混乱对PLC系统的干扰主要是各个接地点电位分布不均，不同接地点间存在地电位差，引起地环路电流，影响系统正常工作。例如电缆屏蔽层必须一点接地，如果电缆屏蔽层两端A、B都接地，就存在地电位差，有电流流过屏蔽层，当发生异常状态如雷击时，地线电流将更大。