I think one could postulate a worst case hardware/software combination, but it would have to be well defended in text along the lines of “no other configuration could be worst case because…” followed by a discussion of the physical aspects of the other configurations and what they imply, based on ‘first principles’, regarding emissions and susceptibility. Even then, if there are many configurations (e.g., more than 5?), it would be wise to test a one or two for which your written hypothesis might be less certain.
The EMCD guidelines (19 Dec 2018) seem to me to be accepting of this idea… * “The EMC assessment needs to take into account all normal intended operating conditions of the apparatus. In cases where the apparatus can take different configurations, the electromagnetic compatibility assessment must confirm that the apparatus meets the essential requirements, “in all possible configurations identified by the manufacturer as representative of its intended use”[quoting Annex II.2]”. * “Where apparatus can take different configurations, the EMC assessment shall confirm that the apparatus meets the essential requirements in all of the configurations foreseeable by the manufacturer as representative of normal use in intended applications. The manufacturer is responsible for identifying the possible configurations and the choice of the worst case(s). The use of the worst case approach needs to be documented in the technical documentation”[35]. [35]=” Within the immunity and emission phenomena to be covered, different worst case selections may occur (because of non-related phenomena). This may increase the number of cases to be investigated “ Note particularly - the guide highlights the obligation of deciding worst case is placed on the manufacturer. If you provide them some guidance but remind them the decision of testing fewer or more of the configurations rests with them, they may have a softer attitude towards more testing. Best regards, -Lauren Confidential – Limited Access and Use From: Bill Owsley <[email protected]> Sent: Friday, April 12, 2024 1:19 PM To: [email protected] Subject: Re: [PSES] I would like to hear your thoughts please External Email: Do NOT reply, click on links, or open attachments unless you recognize the sender and know the content is safe. If you believe this email may be unsafe, please click on the “Report Phishing” button on the top right of Outlook. The usual response is that it depends... More 'light' reading ! To start ! https://www.fcc.gov/sites/default/files/32-KDB-996369-Modules-TCB_Oct_2023.pdf On Wednesday, April 10, 2024, 5:22:12 PM EDT, Lfresearch <[email protected]<mailto:[email protected]>> wrote: Sorry for the late reply, but I did feel the need to express strong disagreement with some statements here. Lets take there first one: how will you know which is worst case if you don’t test. Seriously? I would answer this by saying that an EMC engineer with any proficiency can make an educated decision as to what would be the worst case, further, if one can’t do that you shouldn’t probably be in EMC Engineering. Is the old saying from school days “ You should have an idea of the answer before doing the problem “ no longer stressed in school! The back reference to Boeing is utter BS, sorry Gert, but as someone who contracts for Boeing I take a very strong exception to that ridiculous statement. There is absolutely NO correlation between a poor quality subcontractor and the EMC performance of an EUT. It may be true for airbus, but leave my Boeing alone please. Back to the problem at hand, and serious answers only please. At what point(s) does one draw the line eliminating the need for testing similar designs. Thanks in advance, Derek Walton. On Apr 6, 2024, at 7:55 AM, Gert Gremmen F4LDP <[email protected]<mailto:[email protected]>> wrote: 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. 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