The vehicle area is different as well. Standards like EN ISO 14982 and ISO 
13766 have limits, then add 25% for immunity, or subtract 2 dB for emissions. 
That is intended to account for doing type testing. Whether that’s a valid 
method is up for debate.

E-marking also has a requirement for Conformity of Production. Manufacturers 
must ensure that their products are still under the limit(with a 4 dB 
relaxation), or not susceptible. That is usually interpreted as testing a 
production sample every 2-3 years.


David Schaefer
EMC Chief Technical Advisor
TÜV SÜD America Inc
Office: 651 638 0251
Cell: 612 578 6038
Fax: 651 638 0285


From: Patrick [mailto:conwa...@gmail.com]
Sent: Friday, September 01, 2017 10:21 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] God EMC practice

God and Compliance Margin...  two topics that generate a lot of preaching!
    I think everyone has a "tradition" of what worked for them, and what did 
not.

Here is my sermon on margin:

I don't consider myself a monk of the EMI Chamber...
    ...but over the years I have preached various margins.
    ...margins are always situational, always depending on the business, and 
the products.
    ...call it relativism?


On one end of the extreme, I've been in the aerospace industry.
    Here, a single unit is built, and flown successfully, with *zero dB* of 
margin.

On the other end, consumer products.
    Here, just one or two units comply during development.
    Then the factory produces a million units a month for a year.
    Yes, that is 12 million units based on a couple of passing samples!
    In this industry, initial margin can not predict performance of the 
500,00th unit.
    So, the industry performs on-going EMC audits.


In both those cases, the dogma of margin was irrelevant.
    For aerospace, what mattered was coexistence.
    For commercial, it required an ongoing liturgy of audits.


What really drives margin is the product, the market, and the target usage.
    Everything else is just "tradition" & "hearsay".
    Every company needs enlightened margin decisions based on their own 
circumstances.



Thanks for the bit of humor to end the week!

-Patrick

On Fri, Sep 1, 2017 at 7:01 AM, Kim Boll Jensen 
<k...@bolls.dk<mailto:k...@bolls.dk>> wrote:
Hi

One of our customers want to know if there are some good practice for emission 
compliance. I normally recommend 3 dB margin, but I don't have any reference to 
why this is OK.

I know that some companies have internal rules for 3 or even 6 dB margin to 
compensate for production deviations and for many years ago VDE did have some 
rules like that.

Does anyone have some good references on this subject?

Best regards,

Mr. Kim Boll Jensen
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