P0400VP-CMP10 FOXBORO 通信处理器模块

P0400VP-CMP10 FOXBORO 通信处理器模块

第三类是来自接地系统混乱的干扰。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PLC系统无法正常工作。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。

此外，屏蔽层、接地线和大地可能构成闭合环路，在变化磁场的作用下，屏蔽层内会出现感应电流，通过屏蔽层与芯线之间的耦合，干扰信号回路。若系统地与其它接地处理混乱，所产生的地环流就可能在地线上产生不等电位分布，影响PLC内逻辑电路和模拟电路的正常工作。PLC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PLC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。

来自PLC系统内部的干扰。主要由系统内部元器件及电路间的相互电磁辐射产生，如逻辑电路相互辐射、模拟地与逻辑地的相互影响及元器件间的相互不匹配使用等。这都属于PLC制造厂家对系统内部进行电磁兼容设计的内容，比较复杂，作为应用部门无法改变，可不必过多考虑，但要选择具有较多应用实绩或经过考验的系统。

为了保证系统在工业电磁环境中免受或减少内外电磁干扰，必须从设计阶段开始便采取三个方面抑制措施：抑制干扰源、切断或衰减电磁干扰的传播途径、提高装置和系统的抗干扰能力。这三点就是抑制电磁干扰的基本原则。PLC控制系统的抗干扰是一个系统工程，要求制造单位设计生产出具有较强抗干扰能力的产品，且有赖于使用部门在工程设计、安装施工和运行维护中予以全面考虑，并结合具体情况进行综合设计，才能保证系统的电磁兼容性和运行可靠性。进行具体工程的抗干扰设计时，应主要注意以下两个方面。

The third type is interference from the ground system confusion. Grounding is one of the effective means to improve electromagnetic compatibility (EMC) of electronic equipment. Correct grounding can restrain the influence of electromagnetic interference and restrain the interference from the equipment. The wrong grounding will introduce serious interference signals, so that the PLC system can not work normally. The ground of the PLC control system includes the system ground, shielding ground, alternating ground and protection ground, etc. The disturbance of the grounding system to the PLC system is mainly the uneven distribution of the potential of each ground point, and the potential difference between different ground points causes the ground loop current, affecting the normal operation of the system. For example, the cable shield layer must be grounded at one point. If A and B at both ends of the cable shield layer are grounded, there is a ground potential difference and current flows through the shield layer. When an abnormal state, such as a lightning strike, occurs, the ground current will be larger.

In addition, the shielding layer, grounding wire and earth may form a closed loop, and under the action of changing magnetic fields, induced current will appear in the shielding layer, which interferes with the signal loop through the coupling between the shielding layer and the core wire. If the system is confused with other grounding, the resulting ground circulation may produce unequal potential distribution on the ground wire, affecting the normal operation of the logic circuit and analog circuit in the PLC. The logic voltage interference tolerance of PLC is low, and the distribution interference of the logic ground potential is easy to affect the logic operation and data storage of PLC, resulting in data confusion, program flying or crash. The distribution of simulated ground potential will lead to the decrease of measurement accuracy, and cause serious distortion and misoperation of signal measurement and control.

Interference from within the PLC system. It is mainly generated by the mutual electromagnetic radiation between the internal components and circuits of the system, such as the mutual radiation of logic circuits, the mutual influence of analog and logic, and the mutual mismatch between components. This all belong to the PLC manufacturer's electromagnetic compatibility design content inside the system, more complex, as an application department can not be changed, you do not have to think too much, but to choose a system with more application performance or tested.

In order to ensure that the system is protected from or reduced from internal and external electromagnetic interference in the industrial electromagnetic environment, three suppression measures must be taken from the design stage: suppressing the source of interference, cutting off or attenuating the transmission path of electromagnetic interference, and improving the anti-interference ability of the device and system. These three points are the basic principles of suppressing electromagnetic interference. The anti-interference of PLC control system is a system engineering, requiring manufacturing units to design and produce products with strong anti-interference ability, and depends on the use of the department in the engineering design, installation, construction and operation and maintenance to be fully considered, and combined with the specific situation of the comprehensive design, in order to ensure the electromagnetic compatibility and operational reliability of the system. In the anti-interference design of specific projects, the following two aspects should be paid attention to.