You all are ignoring the by far the most salient point that I made last year. The poster said he measured cm and dm with a current probe, and this did not compare well with the LISN measurements, which are line-to-ground. Had he made line-to-ground measurements with a current probe, or cm and dm measurements off the LISN, there would have been much more agreement. Not complete, because of impedance differences with and without a LISN, but the degree of agreement would have been much greater than what would be achieved controlling line impedance alone.
And it is an absorbing clamp. Not an EM clamp: the EM clamp is designed for injection. -- Ken Javor Ph: (256) 650-5261 From: Brent DeWitt <bdew...@ix.netcom.com> Reply-To: Brent DeWitt <bdew...@ix.netcom.com> Date: Thursday, January 2, 2025 at 8:57 AM To: <EMC-PSTC@LISTSERV.IEEE.ORG> Subject: Re: [PSES] Conducted emission - LISN vs. current clamp Good point James. The EM clamp is well behaved and understood. My comment was only meant to address a simple device like an FCC F-33 used on a cord plugged into the wall mains. Thanks for the clarification! - Brent On 1/2/2025 3:50 AM, James Pawson (U3C) wrote: Following up on Brent’s reply, the CM current measured by the probe will be partially determined by the CM termination impedance which is 150 ohms in the CISPR setups. You can use an IEC 61000-4-6 EM clamp to approximate this with reasonably good results. All the best James James Pawson Managing Director & EMC Problem Solver Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy www.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 For inquiries, bookings, and testing updates please send us an email on he...@unit3compliance.co.uk or call 01274 911747. Our lead times for testing and consultancy are typically 4-5 weeks. From: Brent DeWitt <bdew...@ix.netcom.com> Sent: 17 December 2024 21:54 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Conducted emission - LISN vs. current clamp >From my experience, I would seldom expect the current probe and the LISN to >show the same answer. The big difference is that the current probe is looking >at a fairly random termination impedance compared to the "Line Impedance >Stabilization Network", which is reasonably stable in its design. An >interesting experiment is to use the CM/DM choke on a power cord plugged into >a LISN and examine the differences, On 12/17/2024 4:27 PM, Ken Wyatt wrote: We’ll need a lot more information on what you’re testing, the test setup configuration and how you’re measuring DM and CM. Can you share some photos or screen captures? Usually there will be a difference between DM and CM current spectral response. Now Line and Neutral from a LISN will like look the same typically. Kenneth Wyatt Windsor, CO On Dec 17, 2024, at 13:46, am...@westin-emission.no wrote: Clamp is ok for investigate DM and CM currents. LISN for formal testing at lab. Right now, the plots of CM and DM currents are almost equal over the whole spectrum (10k – 30MHz). Surprise? In the same setup, using a LISN, the spectrum is quite different regarding peaks and waveform. I know the information from this test is defective, but do you have a first thought anyway? BR Amund This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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