Electromagnetic compatibility in maintenance phase

The business of electromagnetic compatibility (EMC) is a difficult one, as we've seen from our various articles on the subject. Among the various aspects of this profession, one also stands out for the great difficulty of tackling it: the maintenance of a system's EMC performance during its operational life. It is this subject that we address in this article, certainly not in an exhaustive way, but sufficiently covered, we hope, to give guidance to engineers who will be confronted with this delicate problem.

When a system's functionality is compromised, the user is often quick to notice, either through alerts linked to a critical function, or because the unavailability of the function is updated at the moment of use. On the other hand, a degradation or loss of performance in EMC, which does not call into question functionality, may not be discovered until very late: after a loss of function following an electromagnetic attack against which the system was no longer protected, or because the same system has itself caused a problem in the use of the electronics around it.

We'll look at the maintenance of filters, twists or shielding (cable management) required for compliance with conducted or radiated emissions, then at the maintenance of conducted or radiated immunity protection, after briefly reviewing the various protection techniques: filtering, clipping, twisting or shielding, microwave "stubs" and circulators, and software protection. The term "twisting" is trade jargon, and means twisting two electrical wires to reduce the coupling between the two wires and electromagnetic fields.

In each case, we identify the origins of potential performance drift during the life of the system, then consider whether maintenance is necessary and, if so, present various solutions for eliminating it or reducing it to its simplest form.

EMC maintenance is part of the Safety Of Functioning (SDF) work attached to the system developed. Maintenance means that the time required to maintain the performance of certain components is less than the lifetime of the system. A typical example is the filter that is replaced on motor vehicles before the car itself is ready for the scrap heap! EMC follows this approach, but differs from ordinary SDF in that two concepts are considered in EMC: disturbance and degradation. SDF usually considers loss of function, and unavailability – therefore the notion of degradation. Disturbance in the EMC sense, which remains very fleeting in duration, is not generally considered by SDF, at least not formally in the standard calculations performed. However, this disturbance is likely to cause the system to deviate from its mission. From an unavailability that cannot be measured at component level, we arrive at...