On Oct 9, 2024, at 1:07 AM, doug emcesd.com <[email protected]> wrote:
I agree and was involved with the early development of emission standards
with with Don Heirman. But still, other areas of engineering are much more
accurate/have very low uncertainty than EMC.
It is sad that most everyone I knew from the early days of EMC are gone
now. Many of them, Heirman and Ott, for example, were friends. I hope to
continue to help engineers in the wider field of engineering and physics,
including EMC for another 25-30 years.
By the way, another of my interests is medicine, which I have studied on my
own for 50 years now and have successfully slowed the aging process and
successfully treated my spouse’s ovarian cancer (after the surgery to
remove two very large tumors) without an oncologist. Just another part of
science as EMC is.
Doug Smith
Sent from my iPhone
IPhone: 408-858-4528
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Website: http://dsmith.orgFrom: Brent DeWitt <[email protected]>
Sent: Tuesday, October 8, 2024 5:57:46 PM
To: doug emcesd.com <[email protected]>; [email protected]
<[email protected]>
Subject: Re: [PSES] technical musings
Doug,
Respectfully, I would not agree. I'm not sure what "other areas of
engineering" you're referring to. 🙂
First, if we are discussing commercial emissions standards, they are
ancient and date back to the days when Apple 2 PCs were interfering with
"rabbit ear" TV reception (1979) when Part 47 was drafted. The levels were
largely drawn from the VDE 0871 standard. I doubt anyone with knowledge of
the methodology has suggested that the overall process is deterministic.
The question of measurement uncertainty was championed by Don Heirman for
years and continues to be debated.
Regulations and standards have done a very good, if somewhat painful, job
of quantifying the uncertainty of the measurement process. The most
competent and well executed test laboratory cannot fully control a
customer's EUT or even have total control over the configuration. That is
an advantage for a manufacturer having their own in-house test facility.
All that said, I feel that the "state of EMC testing" has evolved to
produce very respectable results, given the real world constraints.
Best to all and 73 Jim!
Brent DeWitt, AB1LF
IEEE EMC Society Senior Life Member
Milford, MA
On 10/8/2024 7:07 PM, doug emcesd.com wrote:
Seems like the state of EMC testing is not good compared to other areas of
engineering!
Doug Smith
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IPhone: 408-858-4528
Office: 702-570-6108
Email: [email protected]
Website: http://dsmith.org
From: Jim Bacher, WB8VSU <[email protected]>
Sent: Tuesday, October 8, 2024 8:50:49 AM
To: [email protected] <[email protected]>
Subject: Re: [PSES] technical musings
Back in the 1980s I had a variation in system measurements between labs.
Management decided the lab I used wasn't any good. In the process of trying
to convince management variations were normal, I came to the conclusion
that measuring systems at different labs would likely have a +5 to -7 dB
variations.
None of our test equipment is perfectly flat. No one calibrates every Hz to
account for those imperfections. The frequency being measured is typically
not on any of the calibrated frequencies.
For testing a system, equipment and cable variations can impact their
emmisions significantly. I have seen over 20 dB of variation due to the
variations. How much effort was made to peak signals?
Then is the test equipment measurement operator an avid Ham DXer (chases
weak signals to talk to far away stations)? Reason is a Ham will likely do
a more accurate peaking of rotation and height of the search antennas.
I have had one government lab fail to compensate for a preamp when
reporting levels and said the product failed. I had the agent pull it back
for a few days, then take it back and it passed with no changes. So some
errors can be to using the wrong calibration factors when calculating the
levels.
Jim Bacher, WB8VSU
[email protected] or [email protected]
JBRC Consulting LLC
Product EMC & Regulatory Consultant
https://www.trc.guru/ email:[email protected]
IEEE Life Senior Member
On October 8, 2024 11:14:28 AM David Schaefer
<[email protected]> wrote:
Harry Hodes gave a presentation at the C63 meetings last week on
proficiency testing. He runs the ACIL PT program, and the data he shared
showed a ton of variance. Many labs were in I think +/-3-4 dB range, but
there were outliers – the worst cases being one lab reading 30-40 dB high,
another 30-40 dB low. If I recall correctly for one PT program 95 labs
participated and around 10 were outside the expected tolerance.
Doing a check of the measurement system prior to testing is critical. A
comb gen scan takes only a few minutes but should catch these egregious errors.
<image404476.jpg>
David Schaefer
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Element Materials Technology
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From: doug emcesd.com <[email protected]>
Sent: Monday, October 7, 2024 6:08 PM
To: [email protected]
Subject: [PSES] technical musings
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I have seen differences of 9 dB on the same measurement on an EUT and comb
generator by different accredited labs!
Doug
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