Dear Hans,
I know of no manufacturers actually engaged in series production audits.
So lets hear from them. Please respond to this forum.
The companies I work with look to CISPR 22 8.2.1.1 and test one sample.
Some of them are happy with 0dB margin. I advise a higher margin, but
they are responsible for signing the DoC. To date it would appear to me
that the 80/80 rule only has a place in making it harder to take product
off the market. You can go to market with only one sample tested, but if
someone wants to restrict your access they have to perform an 80/80 rule
statistical test to say you fail (CISPR 22 8.2.4).
As a test lab, I'd love the 80/80 rule if the market would support it
(three-five times the testing, yippee!). The doctrine also seems to need
a bit of clarification: Xn is refered to as the value of the individual
item. Is this the value of the one point closest to the limit? Can you
change the frequency? On a product do you evaluate more than one
frequency? How many? - the six closest to the limit? When doing more
than one test, are several 80/80 tests performed - one for radiated, one
for conducted? The 80/80 test is a statistician's dream and a test
engineer's nightmare.
Jon D. Curtis, PE
Curtis-Straus LLC j...@world.std.com
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Road voice (508) 486-8880
Littleton, MA 01460 fax (508) 486-8828
http://world.std.com/~csweb
On Mon, 13 Jan 1997 hans_mellb...@non-hp-santaclara-om4.om.hp.com wrote:
>
> I take exception with the statement "passing is passing and failing is
> failing". CISPR 16 and 22(section 8.2.4) (maybe others too) require that
> during manufacturing sampling, the products pass the so called 80/80 rule.
> A minimum sampling of 3 units is required to perform this 80/80 calculation
> and products with minimal margin will discover that they fail the formula
> test! Go ahead and try a sample hypothetical test!
>
>
> ______________________________ Reply Separator
> _________________________________
> Subject: Re: Measurement Uncertainty
> Author: Non-HP-owner-emc-pstc (owner-emc-p...@majordomo.ieee.org) at
> HP-Boise,mimegw2
> Date: 01/13/97 05:14 AM
>
>
> In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
> for Evaluating and Expressing the Uncertainty of NIST measurement
> results."
>
> Our NVLAP accreditation requires us to estimate uncertainties in our test
> reports. Every Curtis-Straus EMC or Telco test report contains
> uncertainty
> estimates. As to the passing margin, passing is passing and failing is
> failing. Before you take measurement uncertainty into the limit, first
> consider that technique has improved (and therefore unceratinty is lower)
> than it was when the limits were formulated. Second consider that the
> regulators which accepted the limit were well aware that uncertainty
> exists and in all likelyhood accounted for it in their choice of the
> limit.
>
> That said, I advise all clients who are within our uncertainty of the
> limit (but passing), that they should be aware that they may fail next
> time.
> If they are at the prototype stage, or building a product which will
> become the platform for future development, it is advisable to seek a
> larger margin.
>
> Jon D. Curtis, PE
>
> Curtis-Straus LLC j...@world.std.com
> One-Stop Laboratory for EMC, Product Safety and Telecom
> 527 Great Road voice (508) 486-8880
> Littleton, MA 01460 fax (508) 486-8828
> http://world.std.com/~csweb
> On Fri, 10 Jan 1997, Barge, Michael wrote:
>
> >
> >
> > FROM: michael_ba...@atk.com
> >
> > Item Subject: Measurement Uncertainty
> >
> > Greeting Tregers;
> >
> > There seems to be a requirement that, when giving a measured value, there
> > must be an uncertainty associated with that value describing the confidence
> > of that value.
> >
> > (1) Do most labs report an uncertainty measurement in the test report, on
> > the data sheet, on a certificate of compliance?
> > (2) How did you generate the measurement of uncertainty for emission
> > tests? For immunity tests?
> >
> > AND MOST IMPORTANTLY
> >
> > (3) What do you tell the customer when he is below the limit by less than
> > the measurement uncertainty? When he is above by less?
> >
> > J Michael Barge
> > Alliant Techsystems
> > Annapolis, MD
> >
>
