I've been busy last couple of days and only now seeing the additional convo around measurement uncertainty(MU). I like the comments. Most folks appear to be either agnostic or in support of MU for use as a quality and confidence builder. I notice there are no MU-deniers??
Ok, I'll break the ice..., I think MU is a waste. It wastes a labs (and engineers) most precious resource: time. I also cannot think of a single customer, internal or external, that was ever willing to pay for this metric. If your experience is different, hit reply-all with an anecdote. Here's an idea: If customers are willing to pay, then wouldn't they also be willing to pay for any upgrade? Would they pay for a better MU for their product test? Maybe a lab can offer two levels of MU service? Similar to a how a lab offers Data Report(lower cost) vs Accredited Formal Report(full cost)? Maybe call it... 'Certified GMO & MU-free test data'? Hmm, I should trademark that idea. Another thought... a two question survey for customers. This is for the P&L owner, the one that pays the invoice... #1) Ask if they are willing to pay 10% extra for each dB of uncertainty you remove. #2) Ask them if lab can ignore MU for their product and give them 10% discount. Drop the response here in the mail list. ... all in good fun! As always, I wish all the best for my friends in EMI world ! Patrick. On Wed, Jul 12, 2023, 13:53 John Woodgate <j...@woodjohn.uk> wrote: > Quite right. We don't need to add uncertainty to EMC measurements, because > they are uncertain enough already.đ > > ====================================================================================== > Best wishes John Woodgate OOO-Own Opinions Only > www.woodjohn.uk > Rayleigh, Essex UK > > I hear, and I forget. I see, and I remember. I do, and I understand. Xunzi > (340 - 245 BC) > > > On 2023-07-12 21:17, Elliott Martinson wrote: > > A fun thing to do if you have access to a semi-anechoic chamber is use > lots of duct tape to make sure *absolutely* *nothing* changes between > measurements other than a certain design change--one accepted long ago that > already went into production, which cost $$$ (cable ferrites, wrapping > cables multiple times through ferrites, various black > magic/witchcraft-based ideas)--and end up with evidence that a pass at a > compliance lab years ago was misattributed to an expensive design change > instead of a new test setup. Even all the duct tape in the world, however, > doesnât bring the uncertainty to 0. > > > > The standard almost addresses this as youâre supposed to (as best as I > can remember) adjust the EUTâs position on the turntable relative to the > cables, which are also to be individually adjusted (position/orientation) > to maximize emissions for each frequency âof interestâ (along with mast > height if I remember right). Try that with a console with 20+ cables at > even one frequency⊠with a simplifying assumption that a cable can either > be laid out in state âAâ or state âBâ, thatâs still over 1 million > combinations. Good thing for the lab techs (and whoever pays the labsâ > hourly rates) to have some âuncertaintyâ cushion > > > > -Elliott > > > > > > *From: *Brian Kunde <bkundew...@gmail.com> > *Reply-To: *Brian Kunde <bkundew...@gmail.com> > *Date: *Tuesday, July 11, 2023 at 9:31 AM > *To: *<EMC-PSTC@LISTSERV.IEEE.ORG> > *Subject: *Re: [PSES] FCC Part B questions > > > > If I may pile on late, keep in mind that measurement uncertainty is Plus > or Minus (±). Years ago when I was with a previous company, we had a > buy/sell piece of junk product that we were selling with our company's > brand/name on it. It was audited in Sweden as part of their > surveillance program and it failed by 2dB. The test lab said they could > not say it FAILED because 2dB was within their measurement uncertainty, so > we could continue to ship and sell this product in Sweden. > > > > Has anyone else ever experienced this? > > > > Thanks, > > The Other Brian > > > > > > On Sat, Jul 8, 2023 at 8:28âŻAM Brent DeWitt <bdew...@ix.netcom.com> wrote: > > Hi Brian. It's not entirely clear which measurement range you are asking > about, but I'll assume conducted emissions in the range of 150 kHz to 30 > MHz. > > Short answer: You can skip QP and Avg detection if the peak detection > level is below the Avg detection limit. > > No margin is "required" to pass any emissions limit. Zero dB margin is > still passing. That said, measurement uncertainty in that range is > generally 3-4 dB, so having a passing margin greater than that gives you > some confidence that a re-test at another time and lab will still pass. > > Hope that helps. > > respectfully, > > Brent DeWitt > Milford, MA > > On 7/8/2023 12:38 AM, Brian Gregory wrote: > > > > Hi there, > > > > A question came up that I can't answer w/o a copy of Part 47. > > Does the FCC report require Quasi-Peak (QP) data, or just Avg and Peak. > When do peak readings trigger the need to report QP? I'm pretty sure Part > 15 has AVG and QP limits listed. > > > > Next was what sort of margin is expected in order to pass CE emissions > requirements (CISPR 16 or 32)? Memory serves that one wants 3dB of margin, > but memories can be imperfect! > > > > "Colorado" Brian > 720-450-4933 > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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