This is the 5th article . of our ”EMC awareness” series. At this point, before addressing the coupling path, occuring from (or to) the power mains, it was in order to review a solution that is widely involved in controlling Conducted, Radiated and Crosstalk EMI situations: the use of shielded conductors. The subject is not that simple and requires some insight. This article will explain as clearly as possible for the non-specialist how a cable shield works, how much EMI reduction can be expected, and why the choice of certain cables or installation practices will result in mediocre results.
Radiation Paths and cable-to-cable coupling . This is the 4th article of our EMC awareness series. The former articles, after a broad overview of the EMC subject, reviewed the principal Civilian and Military Norms and test methods, insisting on the legal inforcement of these verifications in Europe, where they are turned into mandatory, « must-comply » laws. Given that source/coupling path/victim concept is the basic approach to EMC, most of the time it is the coupling path between the culprit source and the victim equipment wich is the crux of the problem, hence of its solutions. The 5 essential coupling mechanisms were listed, by which EM Interference take place. Although any equipment can be alternately the victim, or the source, of an EMI problem, we focused on EM susceptibility as being the manifestation that appears first in the designer’s or field engineer’s worries.
Part 1: Conduction Paths . As briefly described in our introductory Article N°1 ( Issue #2-2015 of EE Magazine), ElectroMagnetic Interference is a Source/Coupling Paths/Victim situation, the basis for an overall understanding of EMI control in order to reach a satisfactory level of compatibility (EMC). We also said that reducing the interference at the source itself, or at the victim’s levels, were most of the time unpractical. Therefore, the only remaining area for action is in general the coupling path, which implies understanding the coupling mechanism.
Preamble . As briefly described.in our introductory Article N°1 (Issue #2-2015 of EE Magazine), ElectroMagnetic Compatibility is both a functional neccessity – equipments must operate in their intended environment without being disturbed nor causing disturbances to other devices- and a society requirement: interfering with radio/TV broadcast, radio-communications and other RF services is illegal and punishable by laws. Since consumers cannot be easily prosecuted as guilty for using an equipment that is causing interference, the most efficient way of controlling this EMC situation is to apply stringent limits to manufacturers, such as the products they put on market will ”never” (exceptional situations accounted) cause interference.
Michel Mardiguian . Electro Magnetic Interference (EMI) is the generic term describing a situation whereas an electrical disturbance generated by a certain electronic/electrical equipment is causing an undesirable response to another equipment. This undesirable effect may range from a mere nuisance to a catastrophic failure, with associated financial losses or eventually human casualties. The origin of the disturbance could also be a natural phenomena like lightning strokes or ElectroStatic Discharges (ESD). ElectroMagnetic Compatibility (EMC) is just the opposite: EMI being the disease, EMC is the cure, that is the discipline analyzing and preventing or fixing interference problems.