Hello Ken - I remember the setup and demo to Art Wall of the FCC during the 1999 EMC Symposium here in Denver. In spite of your best efforts it was clear that Art was not "persuaded" !!
The impact on the industry (as I recall) would be much cheaper filters...(if any). Best Regards Charles Grasso Compliance Engineer Echostar Communications (w) 303-706-5467 (c) 303-204-2974 (t) [email protected]<mailto:[email protected]> (e) [email protected]<mailto:[email protected]> (e2) [email protected]<mailto:[email protected]> From: Ken Javor [mailto:[email protected]] Sent: Tuesday, March 29, 2016 3:48 PM To: [email protected] Subject: Re: [PSES] Commom mode current vs. differential mode current and LISN 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 Doug's 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]<mailto:[email protected]>> Reply-To: <[email protected]<mailto:[email protected]>> Date: Tue, 29 Mar 2016 14:31:20 -0700 To: <[email protected]<mailto:[email protected]>>, Ken Javor <[email protected]<mailto:[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]<mailto:[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 can't 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 Nave's 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]<mailto:[email protected]>> Reply-To: Elliott Martinson <[email protected]<mailto:[email protected]>> Date: Tue, 29 Mar 2016 20:36:18 +0000 To: <[email protected]<mailto:[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 it's trying to say what I think it is. DM and CM each show up on L, but the same is true for N. It's a linear combination of both, so even if L and N are almost equal, you can't 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 energy's 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]<mailto:[email protected]> <[email protected]<mailto:[email protected]>> From: Amund Westin [mailto:[email protected]] <mailto:[email protected]%5D><mailto:[email protected]%5D> Sent: Tuesday, March 29, 2016 1:23 PM To: [email protected]<mailto:[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 can't say if noise is CM or DM. B.regards Amund - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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