电磁干扰或EMI是工业环境中生活中不幸的事实，因为近距离运行的设备和设备种类繁多。每台电动设备或电子设备都会产生可能干扰附近其他机械的信号，从而可能导致次优性能甚至总故障。尽管消除EMI的想法是一个崇高的目标，但更现实的途径是将这种干扰降低到可接受的水平。
EMI可以进行或辐射。通过执行的EMI，噪声通过电线和电缆从源传递到接收器或受害设备。电源线，尤其是交流线，是EMI的关键来源，这是由于连接到线路的所有设备（例如电动机和开关电源）产生的噪声。发电机，可变驱动器，电动机的软启动器，电弧焊接设备和灯泡镇流器是其他常见来源，我们不要忘记手机和WiFi网络。Subpar理由是进行EMI的另一个主要来源。相反，辐射的EMI无线发生，在无线信号传输过程中，噪声从源传播到受害者。这通常称为近场干扰，并在电缆内的各种电线中包括串扰。
管理EMI涉及采取有关发射和接收设备的不同方法。简单的修复涉及诸如在源设备和受害者之间创建更多空间，转动90°设备之一并重新布线电缆之类的动作。更复杂的解决方案涉及过滤，屏蔽和接地。例如，通常将过滤器添加到进入电路和电路线的线路上的电缆和连接器中。由于电缆倾向于充当天线并散发出大量嘈杂的信号，因此在EMI方面，它们是罪魁祸首，就像它们的连接器一样。使用屏蔽电缆将对最小化EMI有很大帮助。同轴电缆是仪表信号的理想选择，扭曲的对屏蔽电缆也是如此。扭曲有助于取消每条电线产生的磁场，同时还为EMI添加屏蔽层保护电缆，除了提供EMI电流到达地面的路径外。
The best shielding option, whether foil or a braided shield, will be determined by factors such as the operating environment, flexibility required, and cable strength. Foil shields are less expensive and use a thin layer of metal reinforced with a polymeric layer (often aluminum plus mylar composite tape) to ensure 100% shielding, although cable flexibility may be reduced. Braided shields made of woven wire mesh (using bare or tinned copper wires) provide roughly 95% coverage due to spaces in the braids, but offer better conductivity than foil options. Be sure to ground the shielded cable’s drain wire for it to function properly, as the shield’s role is to reflect signal interference as well as pick up noise and conduct it to ground.
Another important strategy for minimizing EMI is to route signal cables separately from power and motor cables. These different types of cables should be run in separate conduits or at least keep the following recommended distances: 4 in. between signal and power cables for drives below 20 A; 6 in. for 40-A drives; and 8 in. for 80-A drives. If instrument wiring must cross over power wiring, do so at a 90° angle and keep as much separation as possible. Finally, avoid creating loops in your wiring — cable should be run as straight as possible. Following a few simple tips will go a long way toward keeping EMI at a manageable level in your industrial cable layout, helping both wired and wireless equipment to function at its best.
Filed Under:Wire & Cable Tips
