In the case of harmonics of clocks and other signals, these emissions will be related to the fundamental frequency and integral harmonics of these signals. The two major means by which these may be generated are harmonics of intentional signals or parasitic emissions, which can come from improperly terminated transmission lines and the lengths of these lines. Limits on the magnitude of these emissions are specified by regulatory bodies in many countries to protect licensed and unlicensed users of the radio spectrum from harmful interference.Įmissions from the product may be created by various means within the product. These emissions may be radiated from the product, typically as radio waves, or they may be conducted from the product via the power mains cable or other I/O cables connected to the product. Various functions within a product may contribute to the generation of emissions. What Causes Electromagnetic Emissions in the First Place? Countries that mandate immunity, on the other hand, require that products not suffer inference when tested to the levels called out in the applicable standards. In fact, the rules specifically state that a Part 15 device must accept any interference received. In the U.S., the FCC in Part 15 of its rules provides limits for emissions and does not mandate immunity for digital devices. In the commercial world, it depends on what product is being discussed, but for information technology equipment (ITE), broadcast receivers, and multimedia equipment, CISPR 32 provides limits for emissions and CISPR 35 provides tests and test levels for immunity.
Various tests and levels are called out for various services and products. In the aerospace and military world, a common standard for emissions and susceptibility is MIL-STD-461G. Emissions are regulated in the commercial world in various ways and immunity for commercial products is regulated in certain countries and not at all in many others. Susceptibility is a measure of how a device reacts to various items in the electromagnetic environment and immunity is simply a demonstration of its failure to react to certain levels of these phenomena. Susceptibility and immunity are pretty much the same things, just called by different terms. The two major parts of EMC are EMI and EMS (electromagnetic susceptibility) as it is called in the aerospace and military world and electromagnetic immunity (as it is called in the commercial world). EMI (electromagnetic interference) is just a part of EMC. You will see some people refer to EMC/EMI, but this is partially redundant. Go figure out what it is and how we must deal with it!” It will not be an all-encompassing treatment of the subject, but it will provide the reader with a start and some ideas of where to go for more information.ĮMC stands for electromagnetic compatibility. It is aimed at the people who have been told by their management, “You are now my EMC person. This article will serve as an introduction to the topic.
0 kommentar(er)
