Grounding and Shielding Existing Equipment

How to effectively minimize EMI issues when best practices are not available

Grounding and Shielding is an often misunderstood process. It is common to hear quotes ranging from “it’s magic!” to “the rules change all the time!” and “there’s no way to understand it!” These emotional statements are repeated but not true. There is a process, it hasn’t changed, and the more one knows about coupling mechanisms the more one will see that it’s sound engineering principals. There's no illusion - sound mathematical and logical process can resolve or reduce electromagnetic interference (EMI) problems to achieve desired machine performance. Let’s review a few of these comments one at a time to dispel these misconceptions.

Undesired signals couple into signals via four coupling factors; magnetic (inductive) coupling, capacitive (high speed voltage changes (dV/dt)) coupling, direct coupling, and radiative (Rf) coupling. These factors have their basis in science. One may not be able to predict the exact path just as one cannot predict the exact path of lightning, but one knows how to limit the chances of getting struck. Lightning is nothing more than one of the most powerful of the EMI events.