I once tried to do a “worst case” analysis and decided that worst would be testing the HDMI output on the product we had designed at the highest resolution = highest frequency = biggest problem. I ran all our pre-compliance work at this frequency and neglected to check any other resolutions.
When we came close to lab time, prompted by my then manager, I checked other lower frequency, lower risk (surely?) resolutions and found that the second highest frequency was exciting an unintentional resonance in the product and the emissions were 6dB higher (just over the limit). However, in our experience of testing a lot of different products, 9 times out of 10 it is the more complex configuration that is more likely to have the problems, mostly because this has a bigger surface area for risk due to the variety of circuits. I like that phrase that “EMC is all about what isn’t on the schematics” i.e. the unintended performance. You really don’t know until you test. I would agree with the other voices on here to use pre-compliance testing to establish the actual worst case if in any doubt. All the best James James Pawson Managing Director & 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 Office hours: Every morning my full attention is on consultancy, testing, and troubleshooting activities for our customers’ projects. I’m available/contactable between 1300h to 1730h Mon/Tue/Thurs/Fri. For inquiries, bookings, and testing updates please send us an email on he...@unit3compliance.co.uk <mailto:he...@unit3compliance.co.uk> or call 01274 911747. Our lead times for testing and consultancy are typically 4-5 weeks. From: Gert Gremmen F4LDP <g.grem...@cetest.nl> Sent: Saturday, April 6, 2024 3:55 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] I would like to hear your thoughts please Dear All, Within the framework of the EMCD, all configurations shall be conform, so if you choose to actually test, all configurations shall be part of the test. The subject of worse case is a "miroir d'alouette"... how will you ever know which is worst case without carrying out the test ? A pre-scan is informative but the radiated emission test contains already a pre-scan (peak) for the final QP-measurement. We already require a EMC risk analysis which is a kind of pre-scan too. How many pre-pre-prescans will we need to be sure ? "to repeat some (which?) test to make sure nothing was broken".... it's another discipline, but that is how Boeing lost a door in flight. And that is not a unregulated sector without thorough quality scans (understatement), and still it happens. Imagine the costs and effort for Boeing to rebuild their reputation ? Didn't we all learned the exponential graph of EMC costs versus development time ? If you need proof (for authorities, or for yourself), nothing can replace the actual test. Gert Gremmen On 6-4-2024 0:47, Lfresearch wrote: Hi folks, I would like to advise a client at where to draw the line on what needs testing. I would like to solicit opinions besides my own. Otherwise it’s the fox urging the chicken coop… So a manufacturer that makes a product of which there will be several variants. All use the same board, but have different sections of circuits populated. This may require slightly different code to run on the same uP in each case. So.. The burning question is can we perform and analysis that postulates a worse case hardware/software combination and test just one configuration? Or, do we have to do every combination? Or, are there some guidelines about where we draw the line of what to test and what can be claimed as similarity? Off list responses are welcome too. Thanks, Derek Walton LFResearch/SSCLabs. - ---------------------------------------------------------------- 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-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/emc-pstc@listserv.ieee.org/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: msherma...@comcast.net <mailto:msherma...@comcast.net> Rick Linford at: linf...@ieee.org <mailto:linf...@ieee.org> For policy questions, send mail to: Jim Bacher: <mailto:j.bac...@ieee.org> <j.bac...@ieee.org> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC <https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1> &A=1 -- Independent Expert on CE marking EMC Consultant Electrical Safety Consultant _____ This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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