Re: Safety Margins based on NSA premises
I read in !emc-pstc that Robert Wilson wrote
(in <3FF57405336C9B4C976A1819F860A2560F6929@xng_tirsys.TIRSYS.COM>)
about 'Safety Margins based on NSA premises', on Thu, 28 Feb 2002:
>A 10 dB margin? That's easy for the guy doing the test to say! Heck; why
>not 20dB?!
I think there's another way to look at this. 10 dB below the limit has
been a *target* in the context of radiated emissions for a very long
time; from before widespread control of emissions. 20 dB is too far off
to be even a target.
>For the designer who is sweating bullets trying to keep
>within cost and size requirements, however, this may be quite another
>matter.
Much of *radiated emission* control is about technique rather than cost-
and-size. Unfortunately, there are few circumstances where a synthetic
approach to emission control is available, so a solution has to be
sought analytically ('cut and try', if you like), and this takes time.
These days, time is costly.
>
>Considering the original specifications are somewhat arbitrarily derived
>in the first place, it seems to me a more pragmatic approach is
>warranted that meets the spirit of the regulations, rather than just
>overdesigning to meet ill-defined "worse case" scenarios that may or may
>not actually exist.
There is a need for balance. A product that appears to be 3 dB under the
limit *might* unfortunately be placed next to something sensitive that
gives rise to a complaint of interference. If subsequent tests show that
the emission is in fact 5 dB above the limit, this may result in
anything from temporary embarrassment of the manufacturer to a financial
disaster. It dends on which country is involved and the interpersonal
attitudes of the manufacturer's staff and that of the regulatory
authority: the latter is a particularly fraught and unpredictable
factor.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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RE: Safety Margins based on NSA premises
A 10 dB margin? That's easy for the guy doing the test to say! Heck; why not 20dB?! For the designer who is sweating bullets trying to keep within cost and size requirements, however, this may be quite another matter. Considering the original specifications are somewhat arbitrarily derived in the first place, it seems to me a more pragmatic approach is warranted that meets the spirit of the regulations, rather than just overdesigning to meet ill-defined "worse case" scenarios that may or may not actually exist. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: Greilich, Jeff [mailto:jeff.greil...@asl-tk.com] Sent: February 28, 2002 10:00 AM To: emc-p...@majordomo.ieee.org Subject: Safety Margins based on NSA premises Et Al: Another important point to consider on safety margins is how the site performed for Normalized Site Attenuation (NSA) when applicable. A +/-4dB variation is the maximum allowable for NSA based on the premise that 1.5 dB is attributable to the site uncertainty and 2.5 dB is attributable to instrumentation uncertainty. Considering these uncertainties, if a mere 3 dB of margin is considered as "safe", it is conceivable that the same EUT could be measured 8 dB different at another site (i.e. the FCC's Site). However, if a 10 dB margin is achievable, this automatically factors out site conjugate uncertainties and provides an additional 2 dB margin for a worst-case scenario. Regards, Jeffrey W. Greilich EMC Technical Manager Automotive System Laboratory, Inc. 27200 Haggerty Road, Suite B-12 Farmington Hills, MI 48331 (248) 848-2771 (Office) --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
Safety Margins based on NSA premises
Et Al: Another important point to consider on safety margins is how the site performed for Normalized Site Attenuation (NSA) when applicable. A +/-4dB variation is the maximum allowable for NSA based on the premise that 1.5 dB is attributable to the site uncertainty and 2.5 dB is attributable to instrumentation uncertainty. Considering these uncertainties, if a mere 3 dB of margin is considered as "safe", it is conceivable that the same EUT could be measured 8 dB different at another site (i.e. the FCC's Site). However, if a 10 dB margin is achievable, this automatically factors out site conjugate uncertainties and provides an additional 2 dB margin for a worst-case scenario. Regards, Jeffrey W. Greilich EMC Technical Manager Automotive System Laboratory, Inc. 27200 Haggerty Road, Suite B-12 Farmington Hills, MI 48331 (248) 848-2771 (Office) --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
