Greetings from Berkeley,
I an writing to ask if anyone might know if China CQC plans to issue a GB
standard based on CISPR 32 or EN 55032:2012?
Thank you,
Chuck McDowell
Compliance Specialist
Meyer Sound Laboratories Inc.
NOTICE: This email may contain confidential information. Please
Posit this to a North American lab that has a physical presence in PRC.
Mandarin speaker probably required.
Only thing know is that China sent people to sit in on the first committee
drafts.
Brian
From: Chuck McDowell [mailto:chu...@meyersound.com]
Sent: Monday, October 12, 2015 9:54 AM
To:
Hello EMCers,
I would like to ask...
Is there anyone out there that tests to stricter limits than the legal (CISPR,
IEC, etc.) limits? If so, what was the rationale behind selecting the stricter
limits? Our engineering teams are curious as to where the stricter recommended
limits come from,
Jerry,The "stricter" limits are not limits at all. Best practice says to always provide margin. While you may have a sample that passes with one or two dB of margin. This is usually accepted by most companies as
Margin. Pure and simple. Remember that there is inherent measurement
instrumentation uncertainty, not to mention uncertainty in the EUT set up
and measurement process. All this adds up to many dB. The last time I was
involved in suggesting a required, in-house, margin we settled on 6 dB for
1. measurement uncertainty
2. site variance (NOT part of #1)
3. customer spec
4. known (empirical) margin for intended end-use installation
5. because the Klingon Emperor so said
Brian
From: Itzenheiser, Jerry (GE Healthcare) [mailto:gerald.itzenhei...@med.ge.com]
Sent: Monday, October 12, 2015
In addition to the responses from Doug, Ghery and Brian, I will note that
margin protects you from unexpected or unknown changes from component
suppliers. To some extent, this falls under the manufacturing variance Doug
mentioned, but component changes is just another area that can be hard to
Ted,Very good points. If minimum passing margins are a result of âedge rates on transistors, diodes or ICs, then a second source or "upgrade" to a faster device can be counterproductive with regard to the
Patrick,In your story, what you did was a small statistical study. Multiple samples allow you to do this. It is similar to the problems of EMC. One possibility is to test multiple units and record the results as
Ahhh, our old friend: "Margin".
Margin is one of those timeless EMC topics.
IMHO- there is simply no evidence that margin is helpful.
In a practical sense we all know that a "single-measurement-plus-margin" is
not a confidence builder.
As an example, think about the last time you worked on your
Nobody seems to be asking _why_ margin is important or not. I expect no one
believes airliners are going to fall out of the sky or grandma’s pacemaker to
stop if a product is 10 dB over the FCC/CISPR Class B limits for radiated
emissions. So why? For emissions (not immunity, that’s a
The 80/80 rule in CISPR 22 is optional, not mandatory. Testing a single sample
and passing is acceptable under the standard. When did Intel use the 80/80
rule for PCs? I just retired from Intel in June and in the 20 years I worked
there I don’t remember us ever using the 80/80 rule.
5-6dB margin.
Bring two samples to the test lab, and make a quick check that sample no.2 also
is within 6dB (yes, additional test costs may apply)
Repeat testing (quick scanning) after 2 years to check compliance. More often
if modified in some way.
This is not a 100% good approach, but
Cispr 22 die, and maybe still does talk about statistical sampling during test
in lieu of pulling some off of the assembly line. I’ve seen the big kids (HP,
Intel etc. ) do this on complete personal computer systems. In fact I witnessed
in when I was in Europe working with HP when one of our
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