Re: [PSES] EMC Puzzle update
Good addition John, completely true I should have written "universal ground" Gert -Oorspronkelijk bericht- Van: John Woodgate [mailto:j...@jmwa.demon.co.uk] Verzonden: zondag 22 december 2013 23:19 Aan: EMC-PSTC@LISTSERV.IEEE.ORG Onderwerp: Re: [PSES] EMC Puzzle update In message , dated Sun, 22 Dec 2013, "ce-test, qualified testing bv - Gert Gremmen" writes: >Dirty planes do not exist, unless there is a reference to be compared >to, ideally universal ground. While most of what you say is true, there IS no 'universal ground', not even a conducting sheet, if it's bigger in any dimension than about 0.1 wavelengths, and, at lower frequencies, has a surface resistivity larger than that necessary to reduce the voltage between any two points to a negligible value. (What is negligible depends on signal levels, of course.) The case in this thread is that there was a separate 'chassis plane' in the stack. In terms of emissions, it's probably misleading to call it 'dirty', but for immunity, it certainly is dirty, because it introduces into the internal circuits stuff picked up from incident emissions. With seasonal greetings to all my readers. (;-) -- 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald: - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] EMC Puzzle update
In message , dated Sun, 22 Dec 2013, "ce-test, qualified testing bv - Gert Gremmen" writes: Dirty planes do not exist, unless there is a reference to be compared to, ideally universal ground. While most of what you say is true, there IS no 'universal ground', not even a conducting sheet, if it's bigger in any dimension than about 0.1 wavelengths, and, at lower frequencies, has a surface resistivity larger than that necessary to reduce the voltage between any two points to a negligible value. (What is negligible depends on signal levels, of course.) The case in this thread is that there was a separate 'chassis plane' in the stack. In terms of emissions, it's probably misleading to call it 'dirty', but for immunity, it certainly is dirty, because it introduces into the internal circuits stuff picked up from incident emissions. With seasonal greetings to all my readers. (;-) -- 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] EMC Puzzle update
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:j...@jmwa.demon.co.uk] Verzonden: donderdag 19 december 2013 23:46 Aan: EMC-PSTC@LISTSERV.IEEE.ORG Onderwerp: Re: [PSES] EMC Puzzle update In message , dated Thu, 19 Dec 2013, "McInturff, Gary" 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald: - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] EMC Puzzle update
In message , dated Thu, 19 Dec 2013, "McInturff, Gary" 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] EMC Puzzle update
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 Gary -Original Message- From: John Woodgate [mailto:j...@jmwa.demon.co.uk] Sent: Thursday, December 19, 2013 12:29 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] EMC Puzzle update In message <8d0cb0b733784c8-23b4-27...@webmailstg-m01.sysops.aol.com>, dated Thu, 19 Dec 2013, Derek Walton writes: >I am not a proponent of having all planes tied together, only ever seen >disasters that way. If you allow circuit currents to deliberately on >inadvertently flow in the chassis it becomes a nightmare to control >them. Planes that are intended to be at zero-voltage reference potential should meet at ONE point only. That way no unwanted sharing or stealing of currents occurs. Including in a stack a plane carrying stuff from the 'chassis' seems most unwise. -- 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald: - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] EMC Puzzle update
In message <8d0cb0b733784c8-23b4-27...@webmailstg-m01.sysops.aol.com>, dated Thu, 19 Dec 2013, Derek Walton writes: I am not a proponent of having all planes tied together, only ever seen disasters that way. If you allow circuit currents to deliberately on inadvertently flow in the chassis it becomes a nightmare to control them. Planes that are intended to be at zero-voltage reference potential should meet at ONE point only. That way no unwanted sharing or stealing of currents occurs. Including in a stack a plane carrying stuff from the 'chassis' seems most unwise. -- 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
Re: [PSES] EMC Puzzle update
HI James, This problem child isn't my design, just one that came in my lab for debugging and testing: my life revolves around fixing other peoples problems :-) I am not a proponent of having all planes tied together, only ever seen disasters that way. If you allow circuit currents to deliberately on inadvertently flow in the chassis it becomes a nightmare to control them. Much better to separate and segregate so you have control over outbound ( usually on a trace ) and return current ( usually on a plane ). This technique also allows you to keep outside threats like ESD and HIRF restricted to the connector and prevents them progressing into your ( metal ) box. If your box is plastic, you have to me more careful. Does this help? Cheers, Derek. L F Research -Original Message- From: Pawson, James To: EMC-PSTC Sent: Thu, Dec 19, 2013 11:00 am Subject: Re: [PSES] EMC Puzzle update Hi Derek, I’m glad you managed to find out what had been causing that problem. Why did you elect to have a separate “chassis plane” in the first place that (presumably) wasn’t tied into the PCB ground planes? My (limited) understanding is that it is better to have all ground planes connected together to provide a good quality RF return path and minimise the chance of traces crossing plane splits. Many thanks James From: Derek Walton [mailto:lfresea...@aol.com] Sent: 19 December 2013 16:24 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] EMC Puzzle update First off, many thanks to all who replied on and off list. Most of the replies we had already addressed, but here is an update. To re-cap, we had a sealed metal box with just a power cord, and that power cord had feed through type caps. In theory this should not radiate. To save the agony that we went through what was finally identified was on a 6 layer board, 6 traces left the sanctuary of a ground or power plane and were routed directly over a thin chassis plane that was incorporated to increase the number of chassis connections that we really needed on this board. Even though internal, we were able to break that connection and emissions reduced close to 30 dB. A board re-layout is needed to really fix this issue. As part of the debugging process, we also found that since the board chassis layer was "backfeeding" the Ethernet connector housing metal and the "grounding tabs" were just not adequate for bonding. The result was current on the outside of the case that cause the enclosure to radiate pretty much equally in all directions... Can I patent this? :-) The lesson here is that if you do bring chassis onto your PWB, and we do as a means to divert ESD and some RF current, that you keep it well away from internal high speed or sensitive traces and ideally confined to the region around where it's used. After our mods, we now have dropped from 20 dB over class A to about 13 dB under Class B. A big thank you once more to everyone that replied!!! Seasons Greatings to all. Sincerely, Derek. L F Research - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher David Heald - 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 <emc-p...@ieee.org> 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 <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - This message is from the IEEE Product Safety Engineering Society emc-pst
Re: [PSES] EMC Puzzle update
Hi Derek, I'm glad you managed to find out what had been causing that problem. Why did you elect to have a separate "chassis plane" in the first place that (presumably) wasn't tied into the PCB ground planes? My (limited) understanding is that it is better to have all ground planes connected together to provide a good quality RF return path and minimise the chance of traces crossing plane splits. Many thanks James From: Derek Walton [mailto:lfresea...@aol.com] Sent: 19 December 2013 16:24 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] EMC Puzzle update First off, many thanks to all who replied on and off list. Most of the replies we had already addressed, but here is an update. To re-cap, we had a sealed metal box with just a power cord, and that power cord had feed through type caps. In theory this should not radiate. To save the agony that we went through what was finally identified was on a 6 layer board, 6 traces left the sanctuary of a ground or power plane and were routed directly over a thin chassis plane that was incorporated to increase the number of chassis connections that we really needed on this board. Even though internal, we were able to break that connection and emissions reduced close to 30 dB. A board re-layout is needed to really fix this issue. As part of the debugging process, we also found that since the board chassis layer was "backfeeding" the Ethernet connector housing metal and the "grounding tabs" were just not adequate for bonding. The result was current on the outside of the case that cause the enclosure to radiate pretty much equally in all directions... Can I patent this? :-) The lesson here is that if you do bring chassis onto your PWB, and we do as a means to divert ESD and some RF current, that you keep it well away from internal high speed or sensitive traces and ideally confined to the region around where it's used. After our mods, we now have dropped from 20 dB over class A to about 13 dB under Class B. A big thank you once more to everyone that replied!!! Seasons Greatings to all. Sincerely, Derek. L F Research - 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 mailto:emc-p...@ieee.org>> 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)<http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas mailto:emcp...@radiusnorth.net>> Mike Cantwell mailto:mcantw...@ieee.org>> For policy questions, send mail to: Jim Bacher mailto:j.bac...@ieee.org>> David Heald mailto:dhe...@gmail.com>> - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
[PSES] EMC Puzzle update
First off, many thanks to all who replied on and off list. Most of the replies we had already addressed, but here is an update. To re-cap, we had a sealed metal box with just a power cord, and that power cord had feed through type caps. In theory this should not radiate. To save the agony that we went through what was finally identified was on a 6 layer board, 6 traces left the sanctuary of a ground or power plane and were routed directly over a thin chassis plane that was incorporated to increase the number of chassis connections that we really needed on this board. Even though internal, we were able to break that connection and emissions reduced close to 30 dB. A board re-layout is needed to really fix this issue. As part of the debugging process, we also found that since the board chassis layer was "backfeeding" the Ethernet connector housing metal and the "grounding tabs" were just not adequate for bonding. The result was current on the outside of the case that cause the enclosure to radiate pretty much equally in all directions... Can I patent this? :-) The lesson here is that if you do bring chassis onto your PWB, and we do as a means to divert ESD and some RF current, that you keep it well away from internal high speed or sensitive traces and ideally confined to the region around where it's used. After our mods, we now have dropped from 20 dB over class A to about 13 dB under Class B. A big thank you once more to everyone that replied!!! Seasons Greatings to all. Sincerely, Derek. L F Research - 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 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 Mike Cantwell For policy questions, send mail to: Jim Bacher: David Heald:
