Why There is Still Plenty of EMI if All Equipment is EMC-Compliant?August 2021 Newsletter |
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Wouldn't EMC Compliance Assure Low EMI? Every commercial equipment must comply with electromagnetic compatibility (EMC) regulations. These government regulations control the maximum electromagnetic emission that a product can emit. Manufacturers spend inordinate amount of effort and money to make their equipment comply with these regulations. With such tight control over emission the world should be a much "quieter" place than it actually is. To understand why it isn't, we need to understand the regulations themselves. |
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Regulations: Missing the Point The signals that regulations regulate, and the way these regulations do it, have little to do with reality. EMC regulations were written for repeatability and compatibility with existing general test equipment and practices, not necessarily for relevance with actual product's use. Let's look at just a few examples. |
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Do We Measure Wrong Signals? EMC regulations favor continuous signals and largely ignore transients by using very slow so-called quasi-peak detector. But it is the transients, i.e. very short spikes, that are mostly present on actual power lines. As you can see, low-level continuous signal appears stronger than much bigger actual signal using such detector. A product can generate quite high level of transients and still be compliant with the regulations. |
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Important Frequencies Excluded Conducted (i.e. on wires) emission is regulated between 150kHz and 30MHz. Major EMI polluters - switched mode power supplies - operate between ~40kHz and 120 kHz. Shown here is the spectrum of a fully-compliant product generating very high level of EMI just below the lower limit of regulated spectrum. |
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A 50 Ohms Question EMC regulations call for very specific test conditions that are typical for laboratory-level RF measurements, among them the use of 50 Ohms terminations. We at OnFILTER have traveled the globe measuring EMI at factories and laboratories, and not once have encountered power line or ground with 50 Ohms impedance. The result of such mismatch is that a product can meet all the regulations' requirements in a test lab, but be a "gross polluter" of EMI in the field instead. |
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A Lawyer's Approach to EMC What if it is too expensive or too bothersome to reduce EMI for product compliance? Cheat, of course. Legally - there are even WIkipedia page, books, and patents on that. If EMI at your clock frequency is too high, why not sway this frequency a bit back-and-forth (i.e. spread) fast enough for the slow quasi-peak detector and for the sweep timing to misread its amplitude just enough to pass the requirements? Actual signal peak (the one that causes interference) doesn't change - only its perceived value does. As seen here, by moving clock frequency around by mere +/- 2% the perceived value drops by 17dB, or ~ 7 times. The product is still polluting just as it did before, but it is now in legal compliance. |
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Why This is Happening?Why there is such discrepancy between EMC regulations and real world? Standards are developed by the industry specialists - nothing wrong with this, except there are no organized technically-oriented groups of users affected by EMI to provide a different view point. We are skeptical that we will see any move in EMC regulations towards reality within our lifetime. |
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Wouldn't Common EMI Filters Help?If they did, you wouldn't have an EMI problem by now - your equipment already has at least one such filter, perhaps more. Most of EMI filters, being cost-sensitive, are narrowly tailored to fit EMC regulations, not to actually reduce EMI. Major misgiving of typical filters is their inability to adequately suppress the types of emission where it matters. OnFILTER' patented CleanSweep® AC EMI filters are designed for real-life requirements and real-life EMI signals. Read here for "why" and "how" our CleanSweep AC EMI filters work when common filters fail. |
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Are you planning to attend EOS/ESD Symposium in Tucson, AZ September 26-October 1? OnFILTER and Skyworks will be presenting a paper on practical steps in reducing EMI in IC handlers to comply with SEMI E.176 Standard. Also, OnFILTER will be doing a seminar on measurements of EMI on power lines and ground in manufacturing environment. To see the complete program and to register click on the button below | | |
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Should you have any questions on our filters, their applications, or any other aspect of EMI, call us at +1-831-824-4052 or drop us a line at info@onfilter.com |
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