Hi Dennis,
we have common ground, and I'm in agreement, except for table size. If we have
to show it's not influencing the measurement, it's not a factor. If you want
to argue about height.... I'll pass on that. It's 80 cm.
Cheers,
Derek.
On 10/11/2011 2:14 PM, Dennis Ward wrote:
Heaven forbid we ever go back to the early 80’s when there was no
acceptable methods, no accepted procedures, no accepted setup and when the FCC
expected cable manipulation till the cows came home to find the maximum
emissions levels. Talk about a waste of time – days upon days moving every
cable into every likely position finding the ‘worse’ case. Then to find out
that the FCC or another lab found that one cable position that showed 10dB more
than the other lab measured. Everyone was right in their own eyes and most of
those eyes were blind except to their own erroneous methods and practices.
No, conformity of setup, table size, configuration, support equipment
etc, may not be the best, but it is infinitely better than 30, even 25 years
ago.
Dennis Ward
Director of Engineering
American Certification Body
Certification Resource for the Wireless Industry http://www.acbcert.com
703-847-4700 fax 703-847-6888
direct - 703-880-4841
From: [email protected] [mailto:[email protected]] On Behalf Of Ken
Javor
Sent: Tuesday, October 11, 2011 11:29 AM
To: 'EMC-PSTC'
Subject: Re: Table Size in Emissions test
Within his frame of reference, Ward is correct, which is why this
entire accreditation process is flawed and broken. We got along without it
before, and it is adding nothing but extra costs and bureaucracy, and negative
value to the process of controlling EMI.
Ken Javor
Phone: (256) 650-5261
________________________________
From: Dennis Ward <[email protected]> <mailto:[email protected]>
Reply-To: <[email protected]> <mailto:[email protected]>
Date: Tue, 11 Oct 2011 11:15:00 -0700
To: 'Derek Walton' <[email protected]> <mailto:[email protected]>
Cc: 'Grace Lin' <[email protected]> <mailto:[email protected]> ,
'WNya' <[email protected]> <mailto:[email protected]> , 'EMC-PSTC'
<[email protected]> <mailto:[email protected]>
Subject: RE: Table Size in Emissions test
HI Derek
The point of anything ‘nominal’ is that it starts with what is expected
and allows reasonable variations of sorts. And you hit the right words
“relating to a designated or theoretical size”. If you say you must follow the
standard, then follow it. The designated size of a table is 1m x 1.5m x 0.8m.
This then is the size generally expected. It is not a micrometer reading with
0.01m measurement uncertainty tolerances; it is a general designated and
expected size – a nominal size.
Now, and without going into uncertainties and its minutia, a 0.8m x
1.2m table, while not typically or generally expected, could be stretched to be
within a range of what could be considered within the nominal range. Likewise
a table 1.2m x 1.8m would or should still be considered within an expected or
nominal value. To the contrary, a table 0.2m x 0.2m, for many reasons, would
not be generally considered expected and thus not nominal, but abnormal in size
for the intent and purposes of the standard.
Remembering that there are three dimensions given (i.e. 1mx1.5mx0.8m),
if we take your ‘exception’, then I could place a device on the ground plane as
long as it was on a nonconducting surface. Yet I know of no lab nor auditor
that would accept this as a ‘nominal’ height condition for any of the standards
mentioned. I would not be able to reject or challenge their claim that my
table height was not 80cm by saying, nominal is “of, being, or relating to a
designated or theoretical size that may vary from the actual, and I don’t have
to have a table 80cm high.”
One might say, yes, but height matters. And they would be correct,
however, the dimensions are together in the same frame of reference in the same
sentence. So any exceptions to the dimensions would have to follow the same
process. The issue then is not uncertainty and its issues, but what is
generally expected and accepted as a reasonable table for the intent of the
standard.
Remembering that standards are produced as much to make something
consistent wherever used, then the nominal would be that which is generally
consistent within the population that uses the standard.
As to ‘bigger fish to fry’, this would be a good size fish for a lab
that was seeking accreditation. Yes there are allowable variations, equipment
considerations, etc that can be discussed with the accrediting organization.
To say that because ‘nominal’ is used and because ‘shall’ is not, I can do what
I want, is simply not the case if they want to become accredited. It is fairly
easy and cheap to construct a nominal table of dimensions in the standards.
There is probably more money, time and effort in trying to challenge or reject
the assessment than to simply hire a carpenter and build one.
But the choice is the labs and how they wish to relate to their
accreditation body.
Dennis Ward
Director of Engineering
American Certification Body
Certification Resource for the Wireless Industry http://www.acbcert.com
703-847-4700 fax 703-847-6888
direct - 703-880-4841
From: Derek Walton [mailto:[email protected]]
Sent: Tuesday, October 11, 2011 10:09 AM
To: Dennis Ward
Cc: 'Grace Lin'; 'WNya'; 'EMC-PSTC'
Subject: Re: Table Size in Emissions test
Sorry Dennis,
you are not correct. Nominal means:
b : of, being, or relating to a designated or theoretical size that may
vary from the actual.
This is from Websters.
As you indicate, there is NOTHING that says it has to be 1 by 1.5m
I'm sorry to be so anal about this, but it is happening too much where
assessors are assessing to opinions and personal agendas. We must follow the
standard. Usually there are MUCH bigger fish to fry than quibbling over
something like this
I repeat, again, that there is NOTHING that says the table SHALL be 1
by 1.5m. Only then could a deficiency be written.
Sincerely,
Derek.
On 10/11/2011 11:43 AM, Dennis Ward wrote:
Both ANSI C63.10 and ANSI C63.4, the typical standards for which
ISO17025 accreditation is used, contain the following statement, “Tabletop
devices shall be placed on a nonconducting platform, of nominal size 1 m by 1.5
m, raised 80 cm above the reference ground plane.
While a bit more open to variation due to size of equipment, CISPR 22
has the statement “Equipment intended for tabletop use shall be placed on a
non-conductive table. The size of the table will nominally be 1,5 m ◊ 1,0 m but
may ultimately be dependent on the horizontal dimensions of EUT.
So while you may challenge the accreditation organization, they are
correct, your table does not meet the ‘nominal’ size requirements for at least
the two standards ANSI C63.4 and C6310.
Other standards may also have the nominal size issue as well.
Thanks
Dennis Ward
Director of Engineering
American Certification Body
Certification Resource for the Wireless Industry http://www.acbcert.com
703-847-4700 fax 703-847-6888
direct - 703-880-4841
From: [email protected] [mailto:[email protected]] On Behalf Of Grace
Lin
Sent: Tuesday, October 11, 2011 4:16 AM
To: WNya
Cc: EMC-PSTC
Subject: Re: Table Size in Emissions test
Wendy,
When I look for an accredited ANSI C63.4 laboratory, I expect the
laboratory has the facility as stated in the standard, including a standard
size of the table as defined in the standard. For this reason, unless the
accreditation certificate bears a restriction note, I support the auditor's
comment.
From the other point of view, many manufacturers' laboratories are for
internal use only, including my employer's. For this reason, the auditor may
be willing to accept the smaller size of the table. The question is how to
determine if the laboratory is for internal use only (for testing certain type
of products). An example is Alcatel-Lucent's EMC laboratory in New Jersey,
USA. It opens to the general public.
With regards,
Grace
On Mon, Oct 10, 2011 at 7:54 PM, WNya <[email protected]>
<mailto:[email protected]> wrote:
Dear Experts,
Recently my company went through the first ISO17025 audit. We have a
table smaller than the standard requirement of 1.5m x 1m since our products are
small, typically 10cm x 10cm x 10cm. The height of our table was 0.8m. The
auditor wanted us to change the table size to follow the standard.
What does it matter since we never use the extra space on the table? I
do agree we must keep to the height requirement since the floor is a ground
plane and thus it sets a fixed capacitance to the EUT and also controls the
lengths of any attached cables.
Can we reject or challenge the auditor's request? Has anyone experience
the same situation?
Sent from Wendy.Nya iPhone
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