[PSES] Design by committee disasters!

[Doug Smith]

Hi All, Here are some thoughts of mine on two examples of design-by-committee in the EMC field which ended, in my opinion, a poor outcome: First, is the LISN (line impedance stabilization network), used in conducted emissions testing. I can’t believe that a design would be included in standards that can easily source a 1000 Volt transient out of an innocent looking BNC connector intended for connecting to a spectrum analyzer. But that is what happens and many people have burnt out the input of their spectrum analyzer by connecting it to a LISN. The LISN design should not rely on people realizing the BNC output cannot be connected to a spectrum analyzer and putting in various protecting circuits between the spectrum analyzer and LISN. Just on the surface, it seems the original LISN circuit was a concept proposal not a real design, or the designer was completely unfamiliar with the nature of the AC mains the LISN is used with, or both. Second, is the capacitive clamp used with IEC 61000-4-4, Electrical Fast Transients. By the way, EFT bursts as well as inductive kick are what causes the problems above with the LISN. The problem arises in that the capacitive clamp was poorly understood at the time it was included in the standard. It is quite directional and sends much more energy towards the auxiliary equipment than the equipment under test! In turns of peak current, the auxiliary equipment gets 30% to 100% more than the EUT, depending on the nature of how the common mode impedance of the auxiliary equipment interacts with the capacitive clamp. Not a good design! Does anyone else have examples like this? Doug -- University of Oxford Tutor Department for Continuing Education Oxford, Oxfordshire, United Kingdom -------------------------------------------------------------- ___ _ Doug Smith \ / ) P.O. Box 60941 ========= Boulder City, NV 89006-0941 _ / \ / \ _ TEL/FAX: 702-570-6108/570-6013 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: d...@dsmith.org \ _ / ] \ _ / Web: http://www.dsmith.org -------------------------------------------------------------- - ---------------------------------------------------------------- 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com>