A few truths about EMC and grounding.... A conductive PLANE is the closest equivalent for RF of the SINGLE POINT grounding system John recommends. RF current at a certain point A will not travel to a single point S, so the single point comes to point A as a plane.
Dirty planes do not exist, unless there is a reference to be compared to, ideally universal ground. The biggest plane in a system automatically behaves as the CLEAN ground to the outside world, as it has the highest capacitance to the outside world thus the lowest interference potential. All measures on EMC should be referenced to the largest conductive surface in a system. If you have more than one, insulated from each other or not decently interconnected for RF, they will compete in RF potential to ground and none of them will do their job as clean ground. A wire is an impregnable obstacle for EMC problem currents. An RF conductor ideally should not be longer than wide. Gert -----Oorspronkelijk bericht----- Van: John Woodgate [mailto:[email protected]] Verzonden: donderdag 19 december 2013 23:46 Aan: [email protected] Onderwerp: Re: [PSES] EMC Puzzle update In message <d250d01e39356a4e9cc3b4b459d6655097e0e...@ms-cda-01.advanced-input.com>, dated Thu, 19 Dec 2013, "McInturff, Gary" <[email protected]> writes: >Not really practical above a few KHz or so. Above that parasitic >capacitance grounds at lots of points. For audio it works but for high >speed electronics not so much I'm talking about conductive connections, which are usually the source of this sort of EMI problem. If in the OP's case, the errant layer had not been connected to chassis, the emissions would not have occurred. I agree that consecutive layers in a stack have considerable capacitance between them and that is where the EMI gets from the 'dirty' plane to the 'clean' one. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
