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Interference when the grounding system is chaotic:grounding is one of the effective means to improve the electromagnetic compatibility(EMC)of electronic equipment.Correct grounding can not only suppress the influence of electromagnetic interference,but also suppress the equipment’s external interference;and wrong grounding,but will introduce serious interference signals,so that the DCS system will not work properly.The ground wire of DCS control system includes:system ground,shield ground,AC ground and protection ground,etc.The disturbance of the grounding system to the DCS system is mainly due to the uneven potential distribution of each grounding point and the ground potential difference between different grounding points,which causes grounding 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 such as lightning strikes occurs,the ground wire current will be larger.In addition,the shielding layer,the ground wire and the ground may form a closed loop.Under the action of the changing magnetic field,there will be an induced current in the shielding layer,which will interfere with the signal loop through the coupling between the shielding layer and the core wire.If the system ground is confused with other grounds,the resulting ground circulation may produce unequal potential distribution on the ground wire,affecting the normal operation of the logic circuits and analog circuits in the DCS.The logic voltage interference tolerance of DCS work is low,and the distribution interference of the logic ground potential easily affects the logic operation and data storage of the DCS,resulting in data confusion,program runaway or crash.The distribution of the analog ground potential will lead to a decrease in the measurement accuracy,causing serious distortion and malfunction of the signal measurement and control.

来自接地系统混乱时的干扰：接地是提高电子设备电磁兼容性（EMC）的有效手段之一，正确的接地，既能抑制电磁干扰的影响，又能抑制设备向外发出干扰；而错误的接地，反而会引入严重的干扰信号，使DCS系统将无法正常工作。DCS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DCS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，引起接地环路电流，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，则有电流流过屏蔽层，当发生异常状态如雷击时，地线电流将更大。此外，屏蔽层、接地线和大地有可能构成闭合环路，在变化磁场的作用下，屏蔽层内有会出现感应电流，通过屏蔽层与芯线之间的耦合，干扰信号回路。若系统地与其他接地处理混乱，所产生的地环流就可能在地线上产生不等电位分布，影响DCS内逻辑电路和模拟电路的正常工作。DCS工作的逻辑电压干扰容限较低，逻辑地电位的分布干扰容易影响DCS的逻辑运算和数据存贮，造成数据混乱、程序跑飞或死机。模拟地电位的分布将导致测量精度下降，引起对信号测控的严重失真和误动作。