Hi Doug,
Thinking aloud here: This strikes me as more of a flicker/inrush current kind of problem, whereas conducted emissions would be more of a steady state problem. In the AC mains flicker test it's a "stiff" supply and a series impedance over which to measure the inrush current. In your case, the DC supply inrush probably won't be dictated by EMC standards but by system performance, acceptable dips in supply rails, decoupling, etc. Inductance/capacitance of the interconnecting supply lines will probably be less than that created by the LISN. Conducted emissions are always there when the equipment is running. To my knowledge tests aren't commonly carried out during power transitions, maybe for this very reason? If the power bus to the EUT isn't "primary" of "platform" power in the context of a military or automotive standard, or if the cables don't resemble an AC mains distribution network, where does the requirement to measure conducted emissions come from? If the power is only derived from the source unit that toggles the power to it, and if that source unit only powers this one device, then conducted emissions might be better measured on the input to the source device instead? Interesting issue. Anyway, hope this helps. James James Pawson The EMC Problem Solver Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy <http://www.unit3compliance.co.uk/> www.unit3compliance.co.uk | <mailto:ja...@unit3compliance.co.uk> ja...@unit3compliance.co.uk +44(0)1274 911747 | +44(0)7811 139957 2 Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and Wales # 10574298 From: doug emcesd.com <d...@emcesd.com> Sent: 10 December 2021 04:00 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] unusual conducted emissions question Not a car. The power to our EUT is cycled by a a device. To put it on the other side of the LISN would not mean much as we have no control of that device. And even if we did that, the continuous interruption of the DC current would still send the LISN into oscillation at each current edge. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: d...@dsmith.org <mailto:d...@dsmith.org> Website: http://dsmith.org _____ From: Ken Javor <ken.ja...@emccompliance.com <mailto:ken.ja...@emccompliance.com> > Sent: Thursday, December 9, 2021 7:55:05 PM To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> <EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> > Subject: Re: [PSES] unusual conducted emissions question The purpose of a LISN when testing for vehicular use is to simulate the common impedance between battery and fuse block. There should be no power cycling "behind" the LISN, because in the vehicle there is no switch between battery and fuse block other than the ignition switch itself. Therefore the power cycling device goes between the LISN output and the switched load. Ken Javor Phone: (256) 650-5261 _____ From: Douglas Smith <d...@emcesd.com <https://urldefense.proofpoint.com/v2/url?u=http-3A__doug-40emcesd.com&d=DwM FAw&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m =kavBu9H9umaS2l7Zwzp81cdwEgTt9UJa3f56hflvA8A&s=OVcQCPr1r2j4G99wMQoHdTA8Uh-Ec shq2eAiFJgY7Xc&e=> > Reply-To: Douglas Smith <d...@emcesd.com <https://urldefense.proofpoint.com/v2/url?u=http-3A__doug-40emcesd.com&d=DwM FAw&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m =kavBu9H9umaS2l7Zwzp81cdwEgTt9UJa3f56hflvA8A&s=OVcQCPr1r2j4G99wMQoHdTA8Uh-Ec shq2eAiFJgY7Xc&e=> > Date: Fri, 10 Dec 2021 00:16:51 +0000 To: <EMC-PSTC@LISTSERV.IEEE.ORG <https://urldefense.proofpoint.com/v2/url?u=http-3A__EMC-2DPSTC-40LISTSERV.I EEE.ORG&d=DwMFAw&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldr y-2pM9Bbuww&m=kavBu9H9umaS2l7Zwzp81cdwEgTt9UJa3f56hflvA8A&s=RMadKU3rlYA8dxMr L249JcSU5tJZbNiPKINvJSO5bwo&e=> > Subject: [PSES] unusual conducted emissions question Hi All, I have come across an unusual conducted emissions issue with a device where the impedance stabilization network for automotive testing itself causes a problem that will not let a class of equipment ever pass because of the network not the equipment itself. In this case, the power is cycled every second and the device that does that is behind the network as that is not being tested. The interrupted power goes through the network (12 Volts) and to the EUT. We got to the point where we replace the EUT with a DC load, 10 Ohm resistor in parallel with a 10 uF cap, to simulate the inrush current. That combination fails at the low end of the frequency spectrum a lot because the network, just a collection of L, C, and R is ringing at each power transition. Any thoughts? Seems like an artifact of the standard. The device cycling power is a lab circuit and not part of the test and so should be behind the network. Doug - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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