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:
Re: [PSES] Adding more than one EUT 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 <johnmcb...@ieee.org>
*Reply-To: *John Mcbain <johnmcb...@ieee.org>
*Date: *Fri, 17 Feb 2023 14:22:44 -0800
*To: *<EMC-PSTC@LISTSERV.IEEE.ORG>
*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 IFadding 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)
<ja...@unit3compliance.co.uk> 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.
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