The report on which the old 48 dBuV class B CE limit was based did develop that based on the conducted susceptibility of AM and shortwave radios, but it also noted that limit functioned as an adequate control for common mode noise that would radiate as per Doug¹s observation. Back in the late 90s I presented a detailed test report to TC77 showing that if instead of controlling conducted emissions at each LISN port, they instead controlled by modes, that dm could be relaxed 20 dB to 68 dBuV and the committee took an action item and back then said if that were implemented, it would save the power supply industry $35 million a year. The work I did was based on using the LISNMATE / LISNMARK technology as injection tools injecting pure cm and dm and showing that the susceptibility to dm was 20 dB less, because of bulk filter caps on the secondary of power supplies, whereas there were no Y-caps and no cm filtering. The reason this was missed back in 1977/78 when the report was written was they used a single LISN with neutral through the case. CM and DM flowed in the same path.
Ken Javor Ph. (256) 650-5261 From: Doug Smith <[email protected]> Reply-To: <[email protected]> Date: Tue, 29 Mar 2016 14:31:20 -0700 To: <[email protected]>, Ken Javor <[email protected]> Subject: Re: [PSES] Commom mode current vs. differential mode current and LISN Hi Ken and the group, I always thought that the FCC measures the wrong quantity for conducted emmissions. What shoud be measured is all conductors (two or three including phase/neutral/protective earth) together as common mode current as that is what radiates from the long power lines causing problems for shortwave receivers and Amateur Radio Operators. The old demonstration of conducted EMI into AM radios is not so useful, especially today. Below 30 MHz, most devices are not large enough to radiate efficiently, but the power wiring is long enough to radiate. I have a case of EMI in my house from two Feit Electric LED floodlights that meet conducted emissions, but I can't use a hand held, battery powered, shortwave receiver when the two are on except to walk quite a distance from that part of the house. The FCC test may catch this case, but apparently not for me, as there are only two wires but that is not the case for other devices. So phase+neutral could be noisy with respect to protective earth but as long as it is balanced by an opposite current on protective earth, radiation should be low. Any other Amateur Radio operators want to weigh in on this? Doug (K4OAP, since 1959) On Tue, 29 Mar 2016 16:13:58 -0500, Ken Javor <[email protected]> wrote: > > Re: [PSES] Commom mode current vs. differential mode current and LISN > Disagree. Westin had it right. A current probe can be used to isolate either > cm or dm current. If at any frequency the signal amplitude on individual line > and neutral conductors are very close, then all you can say is that at that > frequency either cm or dm predominates, but you can¹t say which. With a LISN, > a separate device must be used. Mark Nave of EMC Services designed a three > port device (connects to each LISN port and to the EMI receiver) trademarked > LISNMATE in the 1980s to isolate common mode, and sometime later he produced > LISNMARK, which isolated DM. Within the past decade, Ray Adams while at > Fischer Custom Communications packed both functions in one piece of equipment, > which if memory serves was named LISNUP. > > EMC Services, Mark Nave¹s company, is no longer producing his products, but I > believe the FCC product is still available. > > Ken Javor > Ph. (256) 650-5261 > > > > > From: Elliott Martinson <[email protected]> > Reply-To: Elliott Martinson <[email protected]> > Date: Tue, 29 Mar 2016 20:36:18 +0000 > To: <[email protected]> > Conversation: [PSES] Commom mode current vs. differential mode current and > LISN > Subject: Re: [PSES] Commom mode current vs. differential mode current and LISN > > http://www.hottconsultants.com/techtips/CM_vs_DM%20Conducted_Emission.html > This is a great resource for your question. > > Your second point kind of contradicts your first, if it¹s trying to say what > I think it is. DM and CM each show up on L, but the same is true for N. It¹s a > linear combination of both, so even if L and N are almost equal, you can¹t say > anything about the proportion of DM to CM currents. > > If they are not equal, then this implies current is travelling back via the > ground conductor and/or energy¹s being lost to radiated emissions. > > What you need is a physical circuit to do the adding/subtracting of the LISN > outputs. (otherwise your 3rd bullet point is correct) > > Your 4th bullet, well I refer you to the link above. > > > Elliott Martinson > Product Assurance Specialist I > Electronic Theatre Controls > 3031 N PLEASANT VIEW RD > MIDDLETON WI 53562-4809 > Work: 608.824.5696 / Cell: 608.209.9897 > [email protected] <[email protected]> > > > From: Amund Westin [mailto:[email protected]] > <mailto:[email protected]%5D> > Sent: Tuesday, March 29, 2016 1:23 PM > To: [email protected] > Subject: [PSES] Commom mode current vs. differential mode current and LISN > > Please correct me, if I am wrong (that happens quite often ): > > · Let one wire (L) pass through a current clamp, and you measure the > combination of current mode and differential mode currents > > · Do the same with wire N. If L and N are (almost) equal, you either > have major part of DM currents or major part of CM current > > · Let both wire (L and N) pass through a current clamp, and you measure > the only CM current (DM is canceled) > > · When doing conducted emission test by LISN, you actually get what > you get. LISN do not see the difference between CM or DM. From LISN > measurements, you can¹t say if noise is CM or DM. > > B.regards > > Amund > > > > > > > > > > > > > > - > ---------------------------------------------------------------- > 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) <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 <[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) <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 <[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) <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 <[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]>
