It's just for a few months now that CISPR/IEC are considering to implement measurement faults into the required margin. Several reports have been circulated for voting.
As far as my knowledge reaches, a margin for measurement errors in your equipment is officially not required, however silly that sounds. So you are allowed to go for the limit having measurement equipment with an accuracy of 10 dB as well as 1 dB, where the latter of course might be much more severe, depending on the polarity of the error. The only wise and required margin is that required by the 80/80 rule. I doubt however, that any of us can reliably prove it's measurement errors for radiated emissions are less then 6dB using a real life EUT. A recent survey of Goedbloed amongst accredited laboratories showed measurement differences of over 10 dB using a standard EUT, depending on frequency, OATS, SAR and FAR. This survey excluded variations in set up of the EUT, rotational variations and thoroughness of the test engineer in finding worst case ! EMI measurement is still a fuzzy discipline ! Gert Gremmen -----Original Message----- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of douglas_beckw...@mitel.com Sent: woensdag 19 december 2001 16:50 To: Stone, Richard A (Richard) Cc: 'Gary McInturff'; Doug McKean; EMC-PSTC Discussion Group Subject: RE: EMI guard bands From: Douglas Beckwith@MITEL on 12/19/2001 10:50 AM Legally you are not required to have any margin, but you measurement uncertainty is usually 3-4db, so you would set the margin to allow for at least your measurement uncertainty. In my previous company we specified 6dB margin to Class A and 3dB margin to Class B. If you specifiy greater than 3dB to class B, your development costs to achieve that rise exponentially. Regards Doug Beckwith Mitel Networks "Stone, Richard A (Richard)" <rsto...@lucent.com> on 12/19/2001 08:06:06 AM Please respond to "Stone, Richard A (Richard)" <rsto...@lucent.com> To: "'Gary McInturff'" <gary.mcintu...@worldwidepackets.com>, Doug McKean <dmck...@auspex.com>, EMC-PSTC Discussion Group <emc-p...@majordomo.ieee.org> cc: (bcc: Douglas Beckwith/Kan/Mitel) Subject: RE: EMI guard bands Does anyone make Class A AND Class B products? if so, do you allow for a much smaller margin on the B since its approx. 10 db quieter than A to start with. or do you treat them equally. Also Oats site to Oats site can differ as much as +/- 4 db do to many factors. any comments? Richard, -----Original Message----- From: Gary McInturff [mailto:gary.mcintu...@worldwidepackets.com] Sent: Tuesday, December 18, 2001 1:19 PM To: Doug McKean; EMC-PSTC Discussion Group Subject: RE: EMI guard bands I hold with the 3 db under class B, as well as A. The only effective argument, in my mind, is the uncertainty of measurement issue. Beyond that I find that if I have 3 db everywhere my measurements next time down with that product or with one off the shelf have also been compliant. So if pragmatic repeated measurements is telling me I'm in then I am not going to spend the time and money to make even more sure that I am in. The goal is to not interfere with communications not to be invisible at all costs. If it ain't broke I'm not fixing it. Obviously, others disagree. By the way if a customer requests it, they get what they want, if they want to pay for it, and I have never rejected products with a 3 db band - and they haven't bitten me yet either. My couple cents Gary -----Original Message----- From: Doug McKean [mailto:dmck...@auspex.com] Sent: Monday, December 17, 2001 3:15 PM To: EMC-PSTC Discussion Group Subject: Re: EMI guard bands "Tania Grant" wrote: > > Amund, > > My minimum criteria and recommendation has always been at least 6dB. > However, how many engineering managers, upon finding a 1.5 dB margin in > their favor, rule "ship it"! <nod> Although in some markets, there are customers who require -6dB under the Class A limit. Although if I had it my way, I'd make it about -10dB under the limit. - Doug McKean ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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