Thank you Gert! I was beginning to wonder if anyone would say it.
Gary Stuyvenberg
Sr. Electrical/EMC Engineer
thompsonconsultingservi...@yahoo.com
_______________________________________________
Note that for some frequencies and measurements taking 6 dB of margin will
bring you dangerously close to the system noise level (automotive, marine , GHz)
In addition, emission non-compliances, caused by components and build
(enclosure, mounting, wiring) changes
come more often the in the 10-12 dB range than within the 6 dB range.
Measurement errors of the test equipment are well in control nowadays,
and keeping a 4-6 dB margin for that makes sense, but the test set up is not
just
about the measurement equipment used. A much bigger test error (>20dB) is
easily obtained by varying (or not varying depending
on you test attitude), the operation modus of the test sample , EUT rotation
issues (degree step values?) and cable lay-out and -termination errors (both CM
and DM)
If for having peace of mind a margin is taken, than the 6 dB value is fully
arbitrary.
The definition of a meaningful margin requires statistical analysis of your
production samples, something we just wanted to avoid by defining a margin
;<(((((
Regards,
Ing. Gert Gremmen
Approvals manager
------------------------------------------------------------------------------------
+ ce marking of electrical/electronic equipment
+ Independent Consultancy Services
+ Compliance Testing and Design for CE marking
according to EC-directives:
- Electro Magnetic Compatibility 2004/108/EC
- Electrical Safety 2006/95/EC
- Medical Devices 93/42/EC
- Radio & Telecommunication Terminal Equipment 99/5/EC
+ Improvement of Product Quality and Reliability testing
+ Education
Web: www.cetest.nl (English)
Phone : +31 10 415 24 26
-------------------------------------------------------------------
This e-mail and any attachments thereto may contain information
that is confidential and/or protected by intellectual property rights
and are intended for the sole use of the recipient(s) named above.
Any use of the information contained herein (including, but not
limited to, total or partial reproduction, communication or
distribution in any form) by persons other than the designated
recipient(s) is prohibited. If you have received this e-mail in error,
please notify the sender either by telephone or by e-mail and
delete the material from any computer.
Thank you for your co-operation.
From: Amund Westin [mailto:am...@westin-emission.no]
Sent: Tuesday 13 October 2015 07:19
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] SV: [PSES] Stricter limits than legal (CISPR11, IEC, etc,)
Where?
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 in some way, you have some sort of
tracking the emission.
Best regards
Amund
Fra: Brent DeWitt [mailto:bdew...@ix.netcom.com]
Sendt: 13. oktober 2015 01:56
Til: EMC-PSTC@LISTSERV.IEEE.ORG
Emne: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where?
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 different question)
it’s probably so you can be guaranteed of legally selling the product in the
light of a third party audit or an internal whistle blower (just kidding). So
now the _probabilities_ start stacking up and your tolerance for risk comes
into play. All of the factors brought up by this list are valid for one
product scenario or another. Simply put, if you take the maximum measurement
uncertainty allowed for a lab under the law, multiply it by 1.414, add the
observed statistical variation of a large enough sample of your product that
the standard deviation from all causes starts settling down, and use that as
your required margin you should have a
guaranteed peaceful sleep. The bad news is that nobody really wants to design
for a number that huge (or should they?).
All that is a long winded way of saying “there is no universal right answer”.
Examine _your_ product, _your_ lab and _your_ anxiety level and act accordingly.
Respectfully,
Brent G DeWitt, AB1LF
Happily employed in the EMC thing since 1978
From: Douglas Powell [mailto:doug...@gmail.com]
Sent: Monday, October 12, 2015 7:23 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where?
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 a probability or simply
record the worst case. When dealing with large expensive equipment that can
take days to evaluate, it is far simpler to build confidence by simply adding,
pause for effect, margin.
Doug
Douglas E Powell
doug...@gmail.com
http://www.linkedin.com/in/dougp01
From: Patrick
Sent: Monday, October 12, 2015 5:13 PM
To: doug...@gmail.com
Cc: EMC-PSTC@listserv.ieee.org
Subject: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where?
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 home wiring.
How many times did you read that multi-meter before you touched the wires?
Did you read it just once? Then add some margin?
Nope- I'll bet you did like me: I read that meter, and double-read it.
Then I read it again.
One measurement is simply not enough to build confidence.
Next time someone asks you for "reasonable margin" ask them about their last
wiring project....
-Patrick
OOO.
On Mon, Oct 12, 2015 at 2:54 PM, Douglas Powell <doug...@gmail.com> wrote:
Ted,
Very good points. If minimum passing margins are a result of edge rates on
transistors, diodes or ICs, then a second source or "upgrade" to a faster
device can be counterproductive with regard to the emissions profile.
If such engineering changes or supplier changes have occurred, then a retest is
often the best policy. I was also aware that several cumulative engineering
changes over time can result in a non-compliance. Each change, when
evaluated by itself was inconsequential. But in aggregate, result was a
failure. This is often the reason I would require a retest after some number of
engineering changes had been applied to a product. Of course, keeping full
data test reports on each passing result is really the only way to do this
well.
Doug
Douglas E Powell
doug...@gmail.com
http://www.linkedin.com/in/dougp01
From: Ted Eckert
Sent: Monday, October 12, 2015 2:44 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Reply To: Ted Eckert
Subject: Re: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where?
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
control.
I’ve had IC vendors do a die shrink on a part resulting in sharper edge rates
on the outputs. At a previous employer, I was running emissions testing on a
number of samples where Motorola did a die shrink on the microcontroller we
were using. Some of my test samples had the old part and some had the new. It
took a long time to figure out why some samples were significantly worse than
others after controlling for all other variables. Having 6 dB margin to begin
with provides some protection against this type of change.
Ted Eckert
Compliance Engineer
Microsoft Corporation
ted.eck...@microsoft.com
The opinions expressed are my own and do not necessarily reflect those of my
employer.
From: Itzenheiser, Jerry (GE Healthcare) [mailto:gerald.itzenhei...@med.ge.com]
Sent: Monday, October 12, 2015 12:26 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Stricter limits than legal (CISPR11, IEC, etc,) Where?
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, such as the 6dB margin for emissions testing.
Thanks,
Jerry Itzenheiser Jr
EMC Technician - Waukesha
GE Healthcare
Global Engineering Technologies
EMC Laboratory Waukesha
T + 262-548-2217
M + 262-720-8846
gerald.itzenhei...@med.ge.com
www.ge.com
3000 N. Grandview Blvd.
Mail Code W618
Waukesha, WI 53188
-
-
----------------------------------------------------------------
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<emc-p...@ieee.org>
All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html
Attachments are not permitted but the IEEE PSES Online Communities site at
http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used
formats), large files, etc.
Website: http://www.ieee-pses.org/
Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Scott Douglas <sdoug...@ieee.org>
Mike Cantwell <mcantw...@ieee.org>
For policy questions, send mail to:
Jim Bacher: <j.bac...@ieee.org>
David Heald: <dhe...@gmail.com>
