Back in a previous life when I worked on PCIe, VME, etc. boards that plugged into a chassis, we would frequently start adding cards until we saw no increase in emissions to satisfy compliance if a customer used multiples of our boards, which was often the case. These were components however and to me it seems a bit murkier if an end product that could function standalone is used with others, especially if each has its own power cord.
Even in my case with the PC cards, we didn’t test multiples of every combination of boards we sold, it would be impossible to do. Does the manufacturer of an LED light bulb need to test just one bulb or do they need to find the fixture that holds the most lightbulbs and test in that? I don’t think so much in the same way that a server manufacturer tests one server and doesn’t need to find the customer that puts the most servers in a rack or a computer room and test that number of servers. Perhaps if they are selling a rack of servers that uses a common power cord? Where does it stop? Dan From: John Mcbain [mailto:[email protected]] Sent: Saturday, February 18, 2023 2:20 PM To: [email protected] Subject: Re: [PSES] Adding more than one EUT Hi Brent - Yes, different testing certainly would be appropriate for different power distribution and connection methods, so knowing ALL the details is very important to decide how to test. However, one essential piece of knowledge may be overlooked. What exactly is the product being sold? Marketing plays a huge role in knowing what to test, and decisions made by Marketing AFTER the product is released can create non-compliant products without a single physical change being made. Common case - let's sell this new combination of equipment as a single product. And of course, since "no changes are being made to the product" (wrong!) why bother telling the compliance engineer? Been there! Best regards, John McBain On Sat, Feb 18, 2023 at 7:37 AM Brent DeWitt <[email protected] <mailto:[email protected]> > wrote: An unanswered, and critical, question is: Do the "daisy-chained" devices draw power produced by the initial item, or do they all have independent power supplies? - First case: Initial unit produces DC/AC for the additional units. - Second case: the initial unit is a simple, passive "power strip" for the additional units. In the first case, I would expect testing as a system, with all units attached In the second case, I would test a single unit. Another implication is for radiated emissions. What is the expected spacing between units in the typical users. with respect, Brent DeWitt Milford, MA On 2/17/2023 9:56 PM, Ken Javor wrote: I’m finding this an extremely interesting discussion. I don’t have anything definitive to offer, but I do have a question to help stir the pot. If the possibility that multiple items might be used together and that emissions will be additive in some fashion is a justification for testing multiple units at a time, what about ... light bulbs? Meaning CFLs or LEDs. My house is full of them. It is reasonable to assume that most homes/businesses are. Perhaps the emissions limits for these were based on this reasonably foreseeable outcome? Ken Javor Phone: (256) 650-5261 _____ From: John Mcbain < <http://[email protected]> [email protected]> Reply-To: John Mcbain < <http://[email protected]> [email protected]> Date: Fri, 17 Feb 2023 14:22:44 -0800 To: < <http://[email protected]> [email protected]> Subject: Re: [PSES] Adding more than one EUT Hi Derek - Typical requirement for a unit that may be sold and used in multiples (that is, all the units can be sold together as one product) is you can test just one IF adding the other units does not increase the emissions. Of course the most practical way to determine that is to assemble the multiple units to see what happens. If the test result for testing max. connected units compared to testing only one unit shows no significant difference, then you're good - but definitely archive those test results! If you can't pass the test with all units connected, then whatever you do, don't let Marketing create a multiple-unit product to sell. ;-) Similarly, the desktop PC system that James mentioned would have all power cords separately tested for conducted emissions as a fully connected system (monitor, printer, scanner, etc. attached) if it is a product sold as a complete all-included system. Best regards, John McBain On Fri, Feb 17, 2023 at 1:59 PM James Pawson (U3C) < <http://[email protected]> [email protected]> wrote: Hi Derek, Is the daisy chain connection the AC supply or some other power bus? How is 8 units daisy chained any different to 8 separate units all on the same power bus? We are looking for individual emission contributions from each connected unit. If measuring conducted emissions on a desktop pc (y'know, the big ones we had before everyone had laptops to work from home...) the you would just measure the PC, not the monitor and printer and scanner and modem and and and... Just thinking aloud All the best James ---- Lfresearch wrote ---- Hi folks, I’ve been asked to test a light fixture that has the ability to be daisy chained up to 8 units. When I run conducted emissions, I’m wondering if I need to insist on having 8 units plugged in at once i.e. fully populated, OR, can I just test one fixture at a time since that’s how the system is likely to be used also.. Is there a legal requirement or precedent on how this should be tested as I’m going round in circles arguing with myself here. Thanks, Derek. SSCLabs, Reno, NV. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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