Uncertainty

[George, David L TR]

Rules are rules.  Because we let NVLAP into the situation we now have a more 
ridged and rigorous certification system in the US than in Europe for some 
applications.  If we are not careful how we implement the rules it will only 
get worse.  There are many people in the government who have not "been there 
and done that" who want to design a system by which we all must live. 
 Uncertainty is one of the issues.

Michael Barge is on the ball and he has a good perspective.  As I understand 
it most of you are applying Uncertainty too broadly.  The rules should be 
applied only as they pertain to the certification requirements.  For 
example, Europe has one application and the USA another.  For minimum impact 
they should not be mixed.

In the USA uncertainty only applies to calibration of test instruments and 
then only if you wish to become a NVLAP approved test lab.   If we easily 
accept it for the entire EMC test protocol, NVLAP will gladly apply it to 
the entire certification  procedure.  Before we go off and rant an rave over 
this net, we should read the rules, understand what they say and know what 
the limitations are.  Please read NIST Technical Note 1297 and note its 
applicability.

It seems only the test labs are preaching accreditation, certification and 
Uncertainty while most of the producing companies just quietly integrate the 
testing into the quality process and leave it at that.  I have news for the 
test labs.  Trying to create a closed association with licensing and other 
impedances to block competition only raises the price of service.  It does 
not improve quality of service and the competition will not be reduced.  Why 
make it hard on yourselves?

Dave George
Unisys Regulatory Compliance

Measurement Uncertainty

[emc-p...@ieee.org]

A quick question about calculating measurement uncertainty.
 
For example, if I am doing a conducted emission test, and I know the
calibration tolerance for each of the "modules" of my measurement system, how
do I calculate an overall uncertainty figure?
 
I have been under the assumption that, in the example I cite, that I have a
tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) and my analyzer
(+/- 1 dB). I have been using an "rms" calculation, where I square each of the
tolerances, sum them, and take the square root. Thus, square root of 1.6 dB
equals 1.26 dB uncertainty.
 
I recently had a customer say that this method implied that I was using
"rectangular" shape factors, and thus, I should be taking the cube root of the
sum.
 
Rectangular? Cube root?
 
 
Ed Price
ed.pr...@cubic.com mailto:ed.pr...@cubic.com>  WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA  USA
858-505-2780
Military & Avionics EMC Is Our Specialty
 
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uncertainty measurements

[Stuart Lopata]

Trying to interpret how to make uncertainty calculations for measurements using 
other measurement equipment, all with various uncertainties...

define: ( * ) ^ 2  as * squared.

So that,

Utotal ^ 2 = Urated ^ 2 + Ureading ^ 2 + Uresolution^2

Basically, the total uncertainty is a function of the rated,  reading, and 
resolution uncertainties of the measuring device applied to the DUT.  The 
reading uncertainty can be calculated by taking several measurements and 
calculating their standard deviation.  The resolution uncertainty is a measure 
of how well on can read some constant value.  The rated deviation can usually 
be found in the user's manual for most measurement equipment.   All deviations 
typically vary over the range of values (i.e.. frequencies).  A2LA 2000 has a 
paper that discusses uncertainty calculations titled, 'Approach, 
considerations, recommendations, and requirements determination...  In support 
of electrical testing assessments involving uncertainty of measurement'.  Their 
'basic uncertainty calculations' appear to be wrong (see eqn.. 1 & 2).  Eqn.. 2 
should have a summation of all samples (denoted by subscript k) before 
dividing. 

Stuart Lopata 

Measurement Uncertainty

[WOODS]

You may find the information on "Lab34" of use.

http://www.emctla.org/Seminars.htm  

Richard Woods

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Measurement Uncertainty

[khardin]

Dear All:

I am looking for the most accurate measuring device to determine the amplitude
of a RF sine wave with the lowest possible uncertainty .  For now lets
assume I am trying to measure a 80dBuV sine wave between 30MHz to 1GHz
from a 50 ohm source and other signal componets not at the intended frequency
is at least 80dB down.  The standard choices are spectrum analyzer with ~2dB
uncertainty, receiver with ~1dB uncertainty or watt meter with ~0.5dB
uncertainty.
All uncertainty's are assumed to be with an expanded uncertainty of K=2.

Does anyone know of a method or device that can do better than the watt meter?
Let's limit the discussion to a device that costs <$20K.

Thanks,
Keith Hardin
Lexmark International Inc.



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Measurement Uncertainty

[Jim Hulbert]

Can anyone recommend a good seminar on measurement uncertainty?  We are
particularly interested in the uncertainty of EMC measurements.

Thank you.

Jim Hulbert
Pitney Bowes



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Immunity Uncertainty

[Tudor, Allen]

This question is in regard to the radiated immunity test specified in
section 3.3 of GR-1089-CORE in which the test signal is 80% AM modulated
with a 1KHz tone.  In testing analog voiceband channels for idle channel
noise per section 3.5.3(c) of GR-1089-CORE, we have been using a
Transmission Impairment Measurement Set (TIMS).  It is my understanding,
that the TIMS input should be designed to see only the 1KHz demodulated
signal originating from the EUT.  It has become apparent that on more than
one occasion that the TIMS itself has demodulated the test signal and
displayed a reading that would indicate a failure.  This seems to be a
result of the modulated test signal coupling into the unshielded twisted
pair connected to the analog voiceband channels of the EUT.  Adding ferrites
to the analog voiceband twisted pair leads improves the situation.  I have
thought of using a shielded cable, but there isn't a good way to terminate
the shield at either end.
 
Has anyone seen a similar problem?  In summary it seems that in some cases,
we are testing the measuring instrument, not the EUT.  The TIMS seems to be
sensitive to the modulated test signal.
 
If this is the case, are some TIMS better than others?  If so, what
specification would indicate a TIMS immunity to the modulated test signal?
 
Is there a more reliable instrument than a TIMS?
 
Please feel free to call me if this would be easier.
 
Thanks in advance.
 
 -Original Message-
From: David Gelfand [mailto:gelf...@memotec.com]
Sent: Friday, September 08, 2000 11:07 AM
To: emc-p...@majordomo.ieee.org
Subject: 90 V gas-filled arrestors source?



Hello group,
 
Does anyone know who makes gas-filled arrestors called for in IEC 1000-4-5
coupling networks?  Would a MOV be ok?
 
Thanks,
 
David.
 
David Gelfand 
Regulatory Approvals 
Memotec Communications Inc.
Montreal Canada

Measurement Uncertainty

[Barge, Michael]

FROM:  michael_ba...@atk.com

Item Subject:  Measurement Uncertainty

Greeting Tregers;

There seems to be a requirement that, when giving a measured value, there 
must be an uncertainty associated with that value describing the confidence 
of that value.

(1) Do most labs report an uncertainty measurement in the test report, on 
the data sheet, on a certificate of compliance?
(2) How did you generate the measurement of uncertainty for emission 
tests? For immunity tests?

AND MOST IMPORTANTLY

(3) What do you tell the customer when he is below the limit by less than 
the measurement uncertainty? When he is above by less?

J Michael Barge
Alliant Techsystems
Annapolis, MD

Uncertainty calculations

[Peter Phillips]

I have recently started looking into the uncertainty associated with EMC
measurements, I have three documents published in the UK, NIS 80, 81 and
3003 which cover the topic, but I would like to see any other documents
or examples of calculations that are available.

Thanks in advance for your help

Peter.
-- 
***
Peter Phillips (p.phill...@ftel.co.uk)
Fujitsu Telecommunications Europe Limited
Birmingham B37 7YU
England
Telephone  +44 (0)121 717 6115
Fax +44 (0)121 717 6014/6018
***

Re: Uncertainty

[Gabriel Roy/HNS]

This is to voice my complete agreement with Dave George on the subject of 
measurement uncertainty. 

Gabriel Roy
Hughes Network Systems
MD
Just my peronal 2 cents worth. 

 snip --
Rules are rules.  Because we let NVLAP into the situation we now have a more 
ridged and rigorous certification system in the US than in Europe for some 
applications.  If we are not careful how we implement the rules it will only 
get worse.  There are many people in the government who have not "been there 
and done that" who want to design a system by which we all must live. 
 Uncertainty is one of the issues.

Michael Barge is on the ball and he has a good perspective.  As I understand 
it most of you are applying Uncertainty too broadly.  The rules should be 
applied only as they pertain to the certification requirements.  For 
example, Europe has one application and the USA another.  For minimum impact 
they should not be mixed.

In the USA uncertainty only applies to calibration of test instruments and 
then only if you wish to become a NVLAP approved test lab.   If we easily 
accept it for the entire EMC test protocol, NVLAP will gladly apply it to 
the entire certification  procedure.  Before we go off and rant an rave over 
this net, we should read the rules, understand what they say and know what 
the limitations are.  Please read NIST Technical Note 1297 and note its 
applicability.

It seems only the test labs are preaching accreditation, certification and 
Uncertainty while most of the producing companies just quietly integrate the 
testing into the quality process and leave it at that.  I have news for the 
test labs.  Trying to create a closed association with licensing and other 
impedances to block competition only raises the price of service.  It does 
not improve quality of service and the competition will not be reduced.  Why 
make it hard on yourselves?

Dave George
Unisys Regulatory Compliance
 

RE: Uncertainty

[Matejic, Mirko]

George,

IEC/ISO Guide 25 is the basis for ALL existing testing and calibration
laboratory accreditation programs in the world including NVLAP and A2LA
recognized by the FCC.

Need to express measurement accuracy was recognized long time ago. Many
experts are working together on national and international levels in
order to come up with reasonable and easy to implement document on
measurement uncertainty. Good starting point to learn more about ISO
Guide 25, its current draft Rev. 5, standards and accreditation contact
points could be URL: http://www.microserve.net/~iso25/

Your contributions and comments on ISO Guide 25 will be much appreciated
by US representative on the working group, James Cigler, tel: (301)
975-4171, email: james.cig...@nist.gov.

Mirko
 --
From: George, David L TR
To: pstc corespondence out
Cc: George, David L TR
Subject: Uncertainty
List-Post: emc-pstc@listserv.ieee.org
Date: Thursday, January 23, 1997 2:44PM

Rules are rules.  Because we let NVLAP into the situation we now have a
more ridged and rigorous certification system in the US than in Europe
for
some applications.  If we are not careful how we implement the rules it
will only get worse.  There are many people in the government who have
not
"been there and done that" who want to design a system by which we all
must
live.  Uncertainty is one of the issues.

Michael Barge is on the ball and he has a good perspective.  As I
understand it most of you are applying Uncertainty too broadly.  The
rules
should be applied only as they pertain to the certification
requirements.
For example, Europe has one application and the USA another.  For
minimum
impact they should not be mixed.

In the USA uncertainty only applies to calibration of test instruments
and
then only if you wish to become a NVLAP approved test lab.   If we
easily
accept it for the entire EMC test protocol, NVLAP will gladly apply it
to
the entire certification  procedure.  Before we go off and rant an rave
over this net, we should read the rules, understand what they say and
know
what the limitations are.  Please read NIST Technical Note 1297 and note
its applicability.

It seems only the test labs are preaching accreditation, certification
and
Uncertainty while most of the producing companies just quietly integrate
the testing into the quality process and leave it at that.  I have news
for
the test labs.  Trying to create a closed association with licensing and
other impedances to block competition only raises the price of service.
It
does not improve quality of service and the competition will not be
reduced.  Why make it hard on yourselves?

Dave George
Unisys Regulatory Compliance

Re: Measurement Uncertainty

[emc-p...@ieee.org]

Thanks John, I didn't qualify my contribution properly.  It's probably worth
adding that it is convention to regard a manufacturers stated tolerance from
an equipment specification sheet as a rectangular distribution.
 
Luke

>>> On 09/09/2009 at 11:00, in message <1pasr7ely3pkf...@jmwa.demon.co.uk>,
John Woodgate  wrote:

In message <4aa775df.6624.005...@trw.com>, dated Wed, 9 Sep 2009, Luke 
Turnbull  writes:

>As Derek said, UKAS document Lab 34 would be a good read for more 
>information:
> 
>http://www.ukas.com/library/Technical-Information/Pubs-Technical-Article
>s/Pubs-List/Lab34.pdf

Yes, this is quite helpful.
> 
>This document will (I think), tell you to divide each number by sqrt(3) 
>before adding them using root-sum-squares. 

Only if the probability distribution is rectangular (i.e. all values 
within the tolerance range are equally probable).

For Normally-distributed variation (I write 'N' to indicate that this is 
a special meaning), the variation is theoretically unbounded, so it has 
to be curtailed to something that has a high level of confidence - 
probability that it does not hide an error. The accepted confidence 
level is 95%, and for that the uncertainty value is divided by a 
constant k, whose value is 2. (95 % (0.95) is the fractional area under 
the Normal distribution curve between sigma = -1.96 and 1.96, 
approximated to +/-2. This isn't explained in Lab34, nor in CISPR 
16-4-2; it just 'appears'.)

For U-shaped distribution, the divisor is sqrt(2), and for triangular 
distribution it is sqrt(6).

But, as usual, nothing beats reading the document yourself.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Conekt is a trading division of TRW Limited 

Registered in England, No. 872948 

Registered Office Address: Stratford Road, Solihull B90 4AX 

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Re: Measurement Uncertainty

[emc-p...@ieee.org]

In message <4aa775df.6624.005...@trw.com>, dated Wed, 9 Sep 2009, Luke 
Turnbull  writes:

>As Derek said, UKAS document Lab 34 would be a good read for more 
>information:
> 
>http://www.ukas.com/library/Technical-Information/Pubs-Technical-Article
>s/Pubs-List/Lab34.pdf

Yes, this is quite helpful.
> 
>This document will (I think), tell you to divide each number by sqrt(3) 
>before adding them using root-sum-squares. 

Only if the probability distribution is rectangular (i.e. all values 
within the tolerance range are equally probable).

For Normally-distributed variation (I write 'N' to indicate that this is 
a special meaning), the variation is theoretically unbounded, so it has 
to be curtailed to something that has a high level of confidence - 
probability that it does not hide an error. The accepted confidence 
level is 95%, and for that the uncertainty value is divided by a 
constant k, whose value is 2. (95 % (0.95) is the fractional area under 
the Normal distribution curve between sigma = -1.96 and 1.96, 
approximated to +/-2. This isn't explained in Lab34, nor in CISPR 
16-4-2; it just 'appears'.)

For U-shaped distribution, the divisor is sqrt(2), and for triangular 
distribution it is sqrt(6).

But, as usual, nothing beats reading the document yourself.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: Measurement Uncertainty

[emc-p...@ieee.org]

Ed,
 
As Derek said, UKAS document Lab 34 would be a good read for more information:
 
http://www.ukas.com/library/Technical-I
formation/Pubs-Technical-Articles/Pubs-List/Lab34.pdf
 
This document will (I think), tell you to divide each number by sqrt(3) before
adding them using root-sum-squares.  (The reason is that to add uncertainty
contributions that have different distribution types e.g. rectangular,
triangular, normal; you calculate the width of a normal distribution that has
an equivalent spread to the e.g. rectangular distribution).  You will then
multiply this final number by 2 to get the uncertainty "for a confidence level
of 95%".
 
I hope this helps - it's not too easy to make sense of this in an email.
 
Luke Turnbull
 
 
 
 
Dr Luke Turnbull
EMC Technical Manager
TRW Conekt
Stratford Road
Solihull
West Midlands B90 4GW

Tel:+44 (0)121.627.3966

email:  luke.turnb...@trw.com
web: www.conekt.net <http://www.conekt.net/> 

>>> On 09/09/2009 at 00:16, in message 
9d04b979323dcd428297dda95108893e0287f...@bb-corp-ex2.corp.cubic.cub>, "Price,
Edward"  wrote:

A quick question about calculating measurement uncertainty.
 
For example, if I am doing a conducted emission test, and I know the
calibration tolerance for each of the "modules" of my measurement system, how
do I calculate an overall uncertainty figure?
 
I have been under the assumption that, in the example I cite, that I have a
tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) and my analyzer
(+/- 1 dB). I have been using an "rms" calculation, where I square each of the
tolerances, sum them, and take the square root. Thus, square root of 1.6 dB
equals 1.26 dB uncertainty.
 
I recently had a customer say that this method implied that I was using
"rectangular" shape factors, and thus, I should be taking the cube root of the
sum.
 
Rectangular? Cube root?
 
 
Ed Price
ed.pr...@cubic.com mailto:ed.pr...@cubic.com>  WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA  USA
858-505-2780
Military & Avionics EMC Is Our Specialty
 
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Conekt is a trading division of TRW Limited 

Registered in England, No. 872948 

Registered Office Address: Stratford Road, Solihull B90 4AX 

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Re: Measurement Uncertainty

[emc-p...@ieee.org]

In message , dated Tue, 8 
Sep 2009, Ken Javor  writes:

>Since dBs are logs of ratios, you cannot do sums of squares on them, 
>and take square roots. You would have to convert to numerics, do the 
>rss, and then convert back to dBs.

CISPR 16-4-2 does indeed (or certainly appears to: it's not very well 
written) add dB values as the square root of the sum of squares. As you 
say, adding dB values (NOT squared) and square-rooting is equivalent to 
calculating the geometric mean value.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: Measurement Uncertainty

[emc-p...@ieee.org]

In message 
<9d04b979323dcd428297dda95108893e0287f...@bb-corp-ex2.corp.cubic.cub>, 
dated Tue, 8 Sep 2009, "Price, Edward"  writes:

>I recently had a customer say that this method implied that I was using 
>"rectangular" shape factors, and thus, I should be taking the cube root 
>of the sum.
> 
>Rectangular? Cube root?

It's a subject with a lore of its own. There is extensive treatment in 
CISPR 16-4-1 to CISPR 16-4-5, but there are difficulties with these, 
mainly with certain inadequacies in CISPR 16-4-2. 16-4-3 to -5 are 
probably not relevant for your operations.

I don't see anything in 16-4-1 and -2 that permits a cube-root addition, 
but the statistical distributions of uncertainties is mentioned. Many 
quantities do have near-rectangular uncertainty distributions, but some 
do not.

Rather than rely on these standards as a source of understanding, it may 
be better to find a textbook, one that includes a reasonably full 
mathematical treatment. If that isn't there, some of the explanations 
are reduced to assertions, which may be counter-intuitive and thus hard 
to accept. I don't know a good textbook to recommend.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: Measurement Uncertainty

[emc-p...@ieee.org]

Since dBs are logs of ratios, you cannot do sums of squares on them, and take
square roots. You would have to convert to numerics, do the rss, and then
convert back to dBs.

Thus, given your example values:

probe: 0.5 dB is roughly 6% tolerance
cable: 0.1 dB is roughly 1.1% tolerance
analyzer: 1 dB is roughly 12% tolerance

RSS: = square root [ (0.06)^2 + (0.011)^2 + (0.12)^2 ] = 0.135 

That corresponds to about 1.3 dB overall tolerance.

Note that isn’t very far off from your 1.26 dB answer.  However, to get
that, you simply added the dB tolerances together (no rss) and then took a
square root of the sum of dBs.  When you add the dBs together, you are
multiplying the tolerances.  If you multiply the tolerances and take the cube
root, it is as if you are taking a geometric mean.  Geometric and arithmetic
means are pretty close as long as the factors going into the product don’t
vary much from each other. 

For instance, if the factors are identical, the geometric and arithmetic means
are identical. Of course, that is a degenerate case where the concept of mean
isn’t terribly useful.  If you had two factors, say one and ten, the
geometric mean would be 3.162, whereas the arithmetic mean would be 5.5. If
the two factors are one and one hundred, then the geometric mean is ten, and
the arithmetic mean is 50.5.  You can see where this is going.
 
Ken Javor

Phone: (256) 650-5261





From: "Price, Edward" 
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
Date: Tue, 8 Sep 2009 16:16:09 -0700
To: 
Conversation: Measurement Uncertainty
Subject: Measurement Uncertainty

A quick question about calculating measurement uncertainty.

For example, if I am doing a conducted emission test, and I know the
calibration tolerance for each of the "modules" of my measurement system, how
do I calculate an overall uncertainty figure?

I have been under the assumption that, in the example I cite, that I have a
tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) and my analyzer
(+/- 1 dB). I have been using an "rms" calculation, where I square each of the
tolerances, sum them, and take the square root. Thus, square root of 1.6 dB
equals 1.26 dB uncertainty.

I recently had a customer say that this method implied that I was using
"rectangular" shape factors, and thus, I should be taking the cube root of the
sum.

Rectangular? Cube root?

 
Ed Price
ed.pr...@cubic.com mailto:ed.pr...@cubic.com> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA  USA
858-505-2780
Military & Avionics EMC Is Our Specialty

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Measurement Uncertainty Contributors

[emc-p...@ieee.org]

I really want to understand how to properly determine my Measurement
Uncertainty (MU) for the tests our EMC lab performs starting with Radiated
Emissions.  

 

I understand how to do the math but I’m having a hard time nailing down the
Contributions and how to obtain, determine, or test for their proper values. 
I have been working with the UKAS Lab34 document which is very vague when it
comes to this information.  

 

I have seen the MU reports from a couple other labs and I noticed the
Contributions and descriptions are not the same.  I would think for the MU to
have meaning, all labs would have to obtain the information the same way.  

 

So what document or documents describes the nuts-and-bolts to the
Contributions? Which ones do you consider and how do you determine their
value?  If testing is required, how is the test performed?  Is this
information in the CISPR 16-4-2 document? Do I also need sections 4-1 and 4-4?
What other sections do I need to get?

 

I’ll probably have more questions later, but for now I better get the proper
docs and do some more studying.

 

Thanks,

The Other Brian

 

 

 

 

 

_ 

LECO Corporation Notice: This communication may contain confidential
information intended for the named recipient(s) only. If you received this by
mistake, please destroy it and notify us of the error. Thank you. 
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EMC Measurement Uncertainty

[Spencer, David H]

Howdy all,

I hate to ask this loaded question.  But, I must.

For accredited EMC labs how are you addressing uncertainty?

I've read NIS 81, NIST TN 1297, a few papers published in the IEEE Symposium
Notes, and my  Statistics text book.

My basic question, is there an "easy", step-by-step method for doing this?

Let me take the radiated site as an example:

In general, radiated sites use the following devices for which we need to
determine uncertainty  (there are others such as 3dB pads and external
preamplifiers, but lets keep it simple):

EMI Receiver
Antenna(s)
Coaxial cables
Site  (NSA)

1)  The EMI RCVR has an uncertainty reported by the cal lab.
2)  The antenna(s) have an uncertainty reported (in our case) from by the
cal lab.
3)  The coaxial cable cal is performed in house using the above RCVR
4)  The NSA is performed using the RCVR and the in house cal'ed coaxial
cable.

Seems to me the RCVR uncertainty value is as reported by the cal lab.
Same is true for the antenna.  
However,  the coaxial cables uncertainty would a factor of the RCVR
uncertainty plus  (Root Sum Square),  of the variation of the coaxial cable
measurements  (several sets identical data  typically).
The NSA uncertainty, would be the RSS deviation from theoretical NSA,  the
coaxial, RCVR, and antenna  uncertainties.  This would be done for 3 and 10
meters and horizontal and vertical.

And finally the total radiated emissions uncertainty would be the RSS of all
uncertainties above 1-4.

I am determining uncertainty for each component  using the following method:

confidence of 95%   .05(SDEV) / (sqr N)  
That is,  confidence level of 95% times the standard deviation  "all over"
the square root of the number of measurements 


Any comments or direction would be greatly appreciated.


regards
David Spencer 

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Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

Good morning all group,

I am working with one of our local NCBs to get accredited as a CB Testing
Laboratory (CBTL) recognized in the CB Scheme to conduct testing and issue
CB test reports in-house under the responsibility of  this NCB (Testing at
the Manufacturing Premises)

An internal lab procedure for the test equipment measurement uncertainty is
required. I checked with our external calibration lab and the price of
getting the uncertainty stated in all test equipment Certificates of
Calibration will be very high. My intention is to buy the ISO test equipment
metrology standard called "ISO Guide to the expression of uncertainty in
measurements" for reference, but I am not quite sure if it is the most
helpful/handy document I can get.

Did anyone else get through this process of measurement uncertainty? Is any
software available for modeling the uncertainty equation for each test
equipment used in a test lab? Any inputs/comments will be appreciated.


Regards,
Carmen


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RE: Measurement Uncertainty

[HALL,KEN (HP-Roseville,ex1)]

Hello,

We use an agilent E4419B +/- 0.02dB log or 0.5% linear with an E4412A Mount
with an uncertainty of 1.3%.

See http://cp.literature.agilent.com/litweb/pdf/5965-6382E.pdf for
uncertainty.

Regards,

Ken Hall 

-Original Message-
From: khar...@lexmark.com [mailto:khar...@lexmark.com]
Sent: Friday, June 14, 2002 1:32 PM
To: emc-p...@majordomo.ieee.org
Subject: Measurement Uncertainty





Dear All:

I am looking for the most accurate measuring device to determine the
amplitude
of a RF sine wave with the lowest possible uncertainty .  For now lets
assume I am trying to measure a 80dBuV sine wave between 30MHz to 1GHz
from a 50 ohm source and other signal componets not at the intended
frequency
is at least 80dB down.  The standard choices are spectrum analyzer with ~2dB
uncertainty, receiver with ~1dB uncertainty or watt meter with ~0.5dB
uncertainty.
All uncertainty's are assumed to be with an expanded uncertainty of K=2.

Does anyone know of a method or device that can do better than the watt
meter?
Let's limit the discussion to a device that costs <$20K.

Thanks,
Keith Hardin
Lexmark International Inc.



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Re: Measurement Uncertainty

[Ken Javor]

How about reading the signal with another wattmeter of the same published 
uncertainty?  If the reading is the same on both meters, or more accurately
the two readings fall within a tighter tolerance than the published
uncertainty, the real uncertainty has to be much less than the published
uncertainty of each meter, right?  To make this more convincing, the two
meters should be of different make and calibrated at different places, so as
to minimize the expectation of systematic error.

Essentially this is what I did in my precompliance facility, and it's not
really limited to a specific kind of equipment or measurement.  In order to
convince myself my test equipment was functional, I would feed the output of
my rf signal source into my spectrum analyzer, and checked that the analyzer
read the same amplitude and frequency.  It's a real good bet that if the
readings are substantially the same (within manufacturer's tolerances), that
the calibration is still okay, because if you suppose that one of the
machines is out of tolerance, then the other machine has to also be out of
tolerance by exactly the same amount and in the same direction.  Application
of Occam's razor leads to the conclusion that both machines are operating
correctly.

--
>From: khar...@lexmark.com
>To: emc-p...@majordomo.ieee.org
>Subject: Measurement Uncertainty
>Date: Fri, Jun 14, 2002, 3:31 PM
>

>
>
>
> Dear All:
>
> I am looking for the most accurate measuring device to determine the amplitude
> of a RF sine wave with the lowest possible uncertainty .  For now lets
> assume I am trying to measure a 80dBuV sine wave between 30MHz to 1GHz
> from a 50 ohm source and other signal componets not at the intended frequency
> is at least 80dB down.  The standard choices are spectrum analyzer with ~2dB
> uncertainty, receiver with ~1dB uncertainty or watt meter with ~0.5dB
> uncertainty.
> All uncertainty's are assumed to be with an expanded uncertainty of K=2.
>
> Does anyone know of a method or device that can do better than the watt meter?
> Let's limit the discussion to a device that costs <$20K.
>
> Thanks,
> Keith Hardin
> Lexmark International Inc.
>
>
>
> ---
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Measurement Uncertainty Software

[reheller]

Does anyone know of any measurement uncertainty software that may be on the
market to
help in the determination of measurement uncertainty for the various EMC
test methods?

Thanks,
Bob Heller
3M Product Safety, 76-1-01
St. Paul, MN 55107-1208
Tel:  651- 778-6336
Fax:  651-778-6252


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Re: Measurement Uncertainty

[Lfresearch]

Jim,

I suggest that you get a hold of Daren Valentine at A2LA, they do a great 
course on Uncertainty.

I did attend the C63 course and was not impressed at all.

Derek Walton

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RE: Measurement Uncertainty

[Bronaugh, Edwin]

C63 has a seminar on EMC Measurement Uncertainty.  Contact D. N. Heirman at
d.heir...@worldnet.att.net.  I participate in that seminar.  I also have a
two-day course on EMC Measurement Uncertainty that I have given.  

Regards, EdB

-Original Message-
From: Jim Hulbert [mailto:hulbe...@pb.com]
Sent: Tuesday, October 17, 2000 8:33 AM
To: emc-p...@ieee.org
Subject: Measurement Uncertainty





Can anyone recommend a good seminar on measurement uncertainty?  We are
particularly interested in the uncertainty of EMC measurements.

Thank you.

Jim Hulbert
Pitney Bowes



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RE: Measurement Uncertainty

[WOODS]

The United States EMC Standards Corporation presents an excellent course.
Contact Don Heirman at d.heir...@worldnet.att.net
<mailto:d.heir...@worldnet.att.net> .

Richard Woods

--
From:  Jim Hulbert [SMTP:hulbe...@pb.com]
Sent:  Tuesday, October 17, 2000 9:33 AM
To:  emc-p...@ieee.org
Subject:  Measurement Uncertainty




Can anyone recommend a good seminar on measurement uncertainty?  We
are
particularly interested in the uncertainty of EMC measurements.

Thank you.

Jim Hulbert
Pitney Bowes



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Immunity measurement uncertainty

[Leslie Bai]

Hello, members,

Is there anyone who can direct me to somewhere I can
find the method to derive the Immunity Test
Uncertainties, e.g. ESD, RI, EFT/B, Surge, etc.

Thanks,
Leslie

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Yahoo! Mail - Free email you can access from anywhere!
http://mail.yahoo.com/

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??: Measurement of Uncertainty

[owner-emc-p...@ieee.org]

Dear Pryor,
 
As I know for EMC measurement uncertainty, below are the document can be used
for reference.
 
1. New CISPR 16-4
2. "Lab 34" publised by UKAS. ( Free download from internet )
3. A handy guide from Schaffner.com
 
But all of them just mentioned about radiated emission up to 1GHz Probably
you have read them.
 
What I am interested is why you put absorbing material between the EUT and the
Receiving anteanna, because for typical radiated emission measurement, we use
semi-anechoic chamber ( no absorber on the ground plane between EUT and the
antenna). We raised and lowered the antenna between 1-4m which is used for
obtaining the maximum reading including the reflected path from the ground
plane. There is absorber between EUT and antenna which is only in
fully-anechoic chamber which is used for radiated immunity test.
 
Regards,

Derek.
 
 
 


Pryor McGinnis  說：

Does anyone have a guideline for calculating
measurement of uncertainty above 1 GHz where absorbing
material is placed on grouond plane between EUT and
antenna per EN55011?

Pryor McGinnis


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Measurement of Uncertainty

[owner-emc-p...@ieee.org]

Does anyone have a guideline for calculating
measurement of uncertainty above 1 GHz where absorbing
material is placed on grouond plane between EUT and
antenna per EN55011?

Pryor McGinnis


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EMC Measurement Uncertainty

[emc-p...@ieee.org]

Hello Colleagues, 
 
I am currently revisiting the issue of Uncertainty Budgets in our lab. 
 
Primarily looking at radiated emissions on an OATS [both ANSI method and EN
substitution], radiated immunity, and transmitter ERP / spurious emissions on
an OATS. I imagine there are a lot of people out there who have been through
the exercise. 
 
Would anyone be willing to share some examples [on or offline] or have info on
useful guidance on EMC examples / application of the GUM method? I understand
tat SINGLAS may have some useful documents with good examples, but I couldn't
find them last night. 
 
I am sure that each lab will be different, but imagine the thought process is
similar. Just want to see the thought process and make sure I am on the right
track in deterring the right contributors, Error Type, and analysis. 
 
Best regards,
 
Mac
 
 
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Window of Uncertainty

[Dave Grant]

Hello all,

We have been doing development of our product here and have been testing
the conducted emissions with respect to CISPR 14.1.

There is a window of uncertainty of +/- 3dBuV with respect to this test?

The testing here that has taken place so far shows that the product fails
by 0.5 dBuV at a certain frequency.

My question is, is this an Assumed Pass as this fall within the Window of
Uncertainty?

or

Is any measurement above the limit irrespective of the uncertainty error a
fail?


This is with for the European, Australasian and American markets.

Cheers ...
Dave



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RE: Measurement Uncertainty

[Tony Fredriksson]

Michael,

The only such technique I know of to indicate uncertainty
is through a sampling test performed under CISPR 16.
A minimum of 3 samples can be used although the
test recommends 5 samples or more.

AT EACH EMISSION FREQUENCY each sample is measured and
the arithmetic mean and sample standard deviation of the sample
set is calculated.  The following calculation is then performed:

  X + kS <= L

Where: X = Arithmetic Mean
  S = Sample Standard Deviation
  k = a constant
  L = the measurement Limit in dB

The constant, k, is derived from a non-central "t" distribution and
is a function of the sample size, the desired confidence level and the
desired % of units that can be predicted to pass the limit based on that
confidence level.  The larger the sample set, the smaller is k.

As a result of this test, if the value is at or below the limit, the test
indicates that 80% of production would pass with an 80% level of
confidence.  If the sum is greater than the limit, L, then the "80/80
rule"  is broken so to speak.

It would seem that a similar experiment or test could be devised
to evaluate lab measurement uncertainty, but to my knowledge, nobody
does this.

The CISPR 16 test does shed some light on what is really expected
by the regulations:

1.   Statistically, it is impossible to guarantee that all shipped
 production measures below the legal limit because to
 guarantee that, 100% sampling would be required.  Cost
 to do this would be prohibitive.

2.   If 80% production can be predicted to pass the limit with
 an 80% confidence level, that is considered reasonable
 for practical considerations.

3.   You would need to do such a statistical test at regular
 intervals to ensure that product from your production
 process meets the 80/80 rule on an ongoing basis.

The factor, k, can be changed to yield other confidence and % pass
levels by referring to an applicable t-distribution table.  Therefore
you could fine-tune the test on your production to meet customer
specifications or your own internal corporate spec.

Finally, the VCCI in Japan uses the above test for their market sampling
test program in cases where a one-off production sample exceeds
emissions limits.

Good luck in getting a lab to statistically define and document its
measurement uncertainty!  Let us know if you find someone that has
done it.

Regards,
tony_fredriks...@netpower.com

 --
From: Michael_Barge
To: 'emc-p...@ieee.org'
Subject: Measurement Uncertainty
List-Post: emc-pstc@listserv.ieee.org
Date: Friday, January 10, 1997 3:33PM



FROM:  michael_ba...@atk.com

Item Subject:  Measurement Uncertainty

Greeting Tregers;

There seems to be a requirement that, when giving a measured value, there
must be an uncertainty associated with that value describing the confidence
of that value.

(1)  Do most labs report an uncertainty measurement in the test report,
on
the data sheet, on a certificate of compliance?
(2)  How did you generate the measurement of uncertainty for emission
tests? For immunity tests?
 
 AND MOST IMPORTANTLY
 
(3)  What do you tell the customer when he is below the limit by less
than
the measurement uncertainty? When he is above by less?

J Michael Barge
Alliant Techsystems
Annapolis, MD

Re: Measurement Uncertainty

[Paul V. Zahra]

Measurement Uncertainty is described in NAMAS NIS 81.  What
Tony is describing is a statistical method for a confidence
level over a certain sample allocation.  Measurement uncertainty 
takes in to account the errors associated with the Measurement you 
are making and through other statistical methods give use a factor 
to be added to the measured value ( Very basically described) for 
an even higher confidence level. 

Paul


At 03:33 PM 1/10/97 -0600, Barge, Michael wrote:
>
>
>FROM:  michael_ba...@atk.com
>
>Item Subject:  Measurement Uncertainty
>
>Greeting Tregers;
>
>There seems to be a requirement that, when giving a measured value, there 
>must be an uncertainty associated with that value describing the confidence 
>of that value.
>
>(1)Do most labs report an uncertainty measurement in the test report, on 
>the data sheet, on a certificate of compliance?
>(2)How did you generate the measurement of uncertainty for emission 
>tests? For immunity tests?
>   
>   AND MOST IMPORTANTLY
>   
>(3)What do you tell the customer when he is below the limit by less than 
>the measurement uncertainty? When he is above by less?
>
>J Michael Barge
>Alliant Techsystems
>Annapolis, MD
>
>
*   *   *   *   *   *   *   *   *   *   *   *   *   *   

 || |
Paul V, Zahra, NCE   |   :|:   :|:
Manager, EMC and Safety Laboratories | :|:   :|:
Corporate Compliance Engineering |   .:|||:.:|||:.
 |  c i s c o S y s t e m s


*   *   *   *   *   *   *   *   *   *   *   *   *   *   

Re: Measurement Uncertainty

[Tony Fredriksson]

Hi Paul,

Do you know of any commercial EMI test facilities that use
NAMAS NIS 81 to determine the measurement uncertainty
statistical factor and add it to their measured values?

Thx,
Tony

 --
From: Paul V. Zahra
To: Barge, Michael; 'emc-p...@ieee.org'
Subject: Re: Measurement Uncertainty
List-Post: emc-pstc@listserv.ieee.org
Date: Saturday, January 11, 1997 11:39AM

Measurement Uncertainty is described in NAMAS NIS 81.  What
Tony is describing is a statistical method for a confidence
level over a certain sample allocation.  Measurement uncertainty
takes in to account the errors associated with the Measurement you
are making and through other statistical methods give use a factor
to be added to the measured value ( Very basically described) for
an even higher confidence level.

Paul


At 03:33 PM 1/10/97 -0600, Barge, Michael wrote:
>
>
>FROM:  michael_ba...@atk.com
>
>Item Subject:  Measurement Uncertainty
>
>Greeting Tregers;
>
>There seems to be a requirement that, when giving a measured value, there
>must be an uncertainty associated with that value describing the confidence 

>of that value.
>
>(1)Do most labs report an uncertainty measurement in the test report, 
on
>the data sheet, on a certificate of compliance?
>(2)How did you generate the measurement of uncertainty for emission
>tests? For immunity tests?
>
>   AND MOST IMPORTANTLY
>
>(3)What do you tell the customer when he is below the limit by less 
than
>the measurement uncertainty? When he is above by less?
>
>J Michael Barge
>Alliant Techsystems
>Annapolis, MD
>
>
*   *   *   *   *   *   *   *   *   *   *   *   *   *

 || |
Paul V, Zahra, NCE   |   :|:   :|:
Manager, EMC and Safety Laboratories | :|:   :|:
Corporate Compliance Engineering |   .:|||:.:|||:.
 |  c i s c o S y s t e m s


*   *   *   *   *   *   *   *   *   *   *   *   *   *

Re: Measurement Uncertainty

[Steve Chin]

Michael, it is generally accepted for emissions purposes that if only one
sample were tested that it would be the best-case sample. It is also generally
accepted that due to site uncertainty and other factors, that if all of the
same construction principles and logic were applied to all manufactured items
identical to the sample tested that there may be a range of +6dB within all of
production.

This is the reason why most EMC consultants like to see a 6dB margin under the
limit on a single sample. I have heard that the VDE wants to see either a 6dB
margin for a single sample or at least five samples of a product tested to any
margin under the limit prior to issuing any CB reports (I don't know for
certain, since I have not gone the CB route with the VDE). See Tony
Fredriksson's earlier post about samples.

Steve Chin
StreamLogic Corp.
Menlo Park, CA, USA
sc...@sledgehammer.com

The contents of this message in no way intentionally represent the opininions
of any being other than myself, be they living, dead, or not of this Earth.

Re: Measurement Uncertainty

[George Alspaugh]

Steve Chin wrote:

>. I have heard that the VDE wants to see either a 6dB margin for a 
>single sample or at least five samples of a product tested to any
>margin under the limit prior to issuing any CB reports (I don't know for
>certain, since I have not gone the CB route with the VDE). See Tony
>Fredriksson's earlier post about samples.

Prior to EU Directives and CB Scheme, many European test agencies 
required both safety and EMC data to approve.  However, EU member 
states accept Declaration of Conformity (or other acceptable methods) 
for Safety and EMC conformity.

CB Scheme applies only to IEC 950, and has no provision to include
EMC requirements.  The rumored VDE position is logical, but cannot
apply to CB cert/report.  It may apply to Certificate of Conformity to 
harmonized EU EMC standards.  

George Alspaugh
Lexmark International

Re: Measurement Uncertainty

[WOODS, RICHARD]

ETSI limits assume a maximum level of uncertainty. For example,  I-ETS
300330, Short Range Devices 9kHz-25MHz, specifies that the uncertainty
for radiated emissions is to be no more than 2 dB with a 95% confidence
level when using the antenna substitution method. If the antenna
substitution method is not used, the uncertainty factor rises to 6 dB.
Using the latter method means that the measured emission level must be 4
dB below the limit due to the increased uncertainty.  The uncertainty of
the conducted emissions is to be no more than 3 dB.

Re: Measurement Uncertainty

[HANS_MELLBERG]

I take exception with the statement "passing is passing and failing is 
failing". CISPR 16 and 22(section 8.2.4) (maybe others too) require that 
during manufacturing sampling, the products pass the so called 80/80 rule. 
A minimum sampling of 3 units is required to perform this 80/80 calculation 
and products with minimal margin will discover that they fail the formula 
test! Go ahead and try a sample hypothetical test!


__ Reply Separator _
Subject: Re: Measurement Uncertainty
Author:  Non-HP-owner-emc-pstc (owner-emc-p...@majordomo.ieee.org) at 
HP-Boise,mimegw2
List-Post: emc-pstc@listserv.ieee.org
Date:01/13/97 05:14 AM


In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines 
for Evaluating and Expressing the Uncertainty of NIST measurement 
results."

Our NVLAP accreditation requires us to estimate uncertainties in our test 
reports.  Every Curtis-Straus EMC or Telco test report contains 
uncertainty
estimates.  As to the passing margin, passing is passing and failing is 
failing.  Before you take measurement uncertainty into the limit, first 
consider that technique has improved (and therefore unceratinty is lower) 
than it was when the limits were formulated.  Second consider that the 
regulators which accepted the limit were well aware that uncertainty 
exists and in all likelyhood accounted for it in their choice of the 
limit.

That said, I advise all clients who are within our uncertainty of the 
limit (but passing), that they should be aware that they may fail next 
time.
If they are at the prototype stage, or building a product which will 
become the platform for future development, it is advisable to seek a 
larger margin.

Jon D. Curtis, PE   

Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom 
527 Great Roadvoice (508) 486-8880 
Littleton, MA 01460   fax   (508) 486-8828 
http://world.std.com/~csweb
On Fri, 10 Jan 1997, Barge, Michael wrote:

> 
> 
> FROM:  michael_ba...@atk.com
> 
> Item Subject:  Measurement Uncertainty 
> 
> Greeting Tregers;
> 
> There seems to be a requirement that, when giving a measured value, there 
> must be an uncertainty associated with that value describing the confidence 
> of that value.
> 
> (1)   Do most labs report an uncertainty measurement in the test report, on 
> the data sheet, on a certificate of compliance?
> (2)   How did you generate the measurement of uncertainty for emission 
> tests? For immunity tests?
>   
>   AND MOST IMPORTANTLY
>   
> (3)   What do you tell the customer when he is below the limit by less than 
> the measurement uncertainty? When he is above by less?
> 
> J Michael Barge
> Alliant Techsystems
> Annapolis, MD
> 

MEASUREMENT UNCERTAINTY update

[Barge, Michael]

Jan 15, 1997.

FROM:  michael_ba...@atk.com

Item Subject:  Measurement Uncertainty Update

Greetings again Tregers;

Thank you all for responding to my questions on measurement uncertainty. I 
received more than 20 responses. This is what I have concluded:
(1) Some in the community are confusing measurement uncertainty with 
sampling uncertainty (80/80 rule).
(2) There is no consensus on the subject.

" If there is one fundamental proposition for the expression of 
uncertainties, it is: the information content of the statement of 
uncertainty determines, to a large extant, the worth of the result."

" Since two observers making measurements on the same EUT will not obtain 
the same results, it is important that the measurement uncertainties be 
understood by both observers and a consistent method of determining these 
uncertainties
be used. "  -TIA/EIA-603.

" In my opinion, the measurement uncertainty is unnecessary . . . 
measurement uncertainty is a lot of hog wash . . . .explain why his 
measurements at home were different than the measurements at the test site 
"

" passing is passing and failing is failing"

" If I were a customer I'd want to see statements of measurement 
uncertainty for all data."

After consulting NIS 82, The Treatment of Uncertainty in EMC Measurements 
published by NAMAS; Appendix B of TIA/EIA-603 Measurement Uncertainties 
April 95;  Determining and Reporting Measurement Uncertainties, 1994 by 
NCSL; and  Guide to the Expression of Uncertainty in Measurement, 1995, 
published by the IEC et al, our group has come up with a draft process for 
determining the measurement uncertainty, the measurement uncertainty number 
for the group, and the group policy for determining compliance, that is, 
how our group will use measurement uncertainty.

The uncertainty is base on both type A evaluation of uncertainty using a 
statistical analysis of a series of observations, and type B evaluation of 
uncertainty using values given in equipment spec sheets. This figure takes 
into account random variability of the measurement process and 
uncertainties of calibrated equipment. It can not be used to compensate for 
error in measurement procedures, transcription errors, or malfunctioning 
equipment.

The area our group needs help on is in immunity testing.

I have heard that there will be a session on measurement uncertainty at the 
EMC one day mini symposium scheduled  May1 somewhere in the DC area. I look 
forward to it.

It is my opinion that measurement uncertainty is more than "a lot of hog 
wash". And personal opinion aside, it is now, or soon will be a requirement 
for all EMC labs.

J Michael Barge
Alliant Techsystems
Annapolis, MD   Standard disclaimer statement.

Re: Uncertainty calculations

[Tom Bao]

Peter, it's one of my favourite topics.

Try ANSI C63.6-1988 Guide for the Computation of Errors in Open-Area Test 
Site Measurements, a couple of page standard, but it has some references 
as I remember. I would appreciate you share some of your findings, offline
if not many interested.

Best regards,
Tom
RCIC - http://www.rcic.com
Regulatory Compliance Information Center


At 05:04 PM 5/13/97 +0100, Peter Phillips wrote:
>I have recently started looking into the uncertainty associated with EMC
>measurements, I have three documents published in the UK, NIS 80, 81 and
>3003 which cover the topic, but I would like to see any other documents
>or examples of calculations that are available.
>

Re: Uncertainty calculations

[Robert F. Martin ITS/QS-Box]

NIST has also published a document on Measurement Uncertainty. This is
NIST Technical Note 1297, Guidelines for Evaluating and Expressing the
Uncertainty of NIST Measurement Results. There are a number of other
documents as well, including one published by CISPR, and another by
members of the  'CB scheme'.

NIST has had several conferences on Uncertainty, and another is planned
in August.

As for interest in the topic, I would say that everyone doing
measurements should be interested. It is becoming a major 'hot topic'
amongst accreditation agencies.


Bob Martin
EMC Department Manager
ITS-Boxborough
r...@itsqs.com

The views expressed are my own and not necessarily those of my employer.
 --
From: Tom Bao
To: Peter Phillips; emc-p...@ieee.org
Subject: Re: Uncertainty calculations
List-Post: emc-pstc@listserv.ieee.org
Date: Tuesday, May 13, 1997 10:27PM


Peter, it's one of my favourite topics.

Try ANSI C63.6-1988 Guide for the Computation of Errors in Open-Area
Test
Site Measurements, a couple of page standard, but it has some references
as I remember. I would appreciate you share some of your findings,
offline
if not many interested.

Best regards,
Tom
RCIC - http://www.rcic.com
Regulatory Compliance Information Center


At 05:04 PM 5/13/97 +0100, Peter Phillips wrote:
>I have recently started looking into the uncertainty associated with EMC
>measurements, I have three documents published in the UK, NIS 80, 81 and
>3003 which cover the topic, but I would like to see any other documents
>or examples of calculations that are available.
>

Re: Measurement Uncertainty

[Gabriel Roy/HNS]

Michael Barge asks: 

>(1)  Do most labs report an uncertainty measurement in the test report, on 
the data sheet, on a certificate of compliance?
>(2)  How did you generate the measurement of uncertainty for emission 
tests? For immunity tests?
 
> AND MOST IMPORTANTLY
 
>(3)  What do you tell the customer when he is below the limit by less than 
the measurement uncertainty? When he is above by less?

 

Well Michael, the lab that I do most of my business with does not report the 
measurement of uncertainty in my reports, and I am very satisfied that they do 
not. 

I certainly do not include a value in the declaration of conformity, nor do I 
intend to ever. It would be ludicrous for our declaration to  state that we are 
96% confident that we comply. Either we comply or we don't. 

In my opinion, the measurement uncertainty is unnecessary and its inclusion can 
only lead to stricter limits being enforced. Enforced by the unknowing in the 
beginning and eventually by decree "because that's the way it's done now".

I have delt with a lab that included the measurement of uncertainty in their 
report, it was 2 dB. And if we were closer than 2 dB to the limit they 
considered it a failure. Evidently, because their instrumentation was not 
sufficiently accurate to give them measurements that they could be confident 
in, our equiment suffered. I don't use that lab any more. 

My contention is that this measurement uncertainty is a lot of hog wash. The 
same as reporting frequencies to three decimal places and dB's to two decimal 
places. That's missing the original intent of the requirement, which was to not 
interfere with other's communications. The method used originally was a radio 
receiver, with front mounted rotary switches that dropped attennuation pads 
into the receive circuit (i.e. see the older Rhode & Schartz used by VDE).  The 
level was read as the amount of attennuation needed to bring the incoming 
signal to a null. Thus one either passed or failed, with no reguard to 
fractions of dBs. As far as the frequency was concerned, it was read off a log 
scale similar to a radio tuner (before digital readouts), and one was lucky to 
get the reading down to 10 MHz in the upper scale. 

It wasn't until the introduction of the spectrum analyzer by HP around 1979-80 
that we could get readings down to three decimal places. Why did HP pick three? 
If they had picked five, lab assistants and engineers would now be blindly 
writing values down to five decimal places. It doesn't make it more accurate, 
it only gives a feeling of being very scientific. One can get the diameter of a 
circle by using 3.14 for pie (?) just as well as using pie to 27 decimal 
places. 

Proponents of the measurement uncertainty practice should take a look at the 
way that the VDE engineers write down their measurements. They have a sheet of 
log paper and a pencil. They put the point of the pencil ot their best 
approximation of frequency and dB level on the log paper and make a large dot. 
They then pull down on the dot to make a tail, so that it will be easier to 
identify. Again, you either pass or you fail. The size of the pencil dot and 
the way the VDE engineer places the pencil on the paper greatly overshadows any 
measurement uncertainty there might have been in the system. 

One final comment, our instumentation has always been accurate, and we have 
always known how acurate it is. The accuracy is specified by the manufacturer 
and the instrumentation is kept within calibration. Also the regulatory bodies 
have been satisfied with that process. I have a hunch, and it is only a hunch, 
that this measurement uncertainty was developed by an EMI engineer who had no 
way of coming up with the reason for getting different measurements at 
different sites. The old "It passes at home by 2 dB and fails at the lab by 3 
dB" syndrome. So in an attemp to explain EMI in logical terms (!!!) to his 
boss, he lumpted the variations of all factors (cable losses, antenna factors, 
amplifiers, spectrum analyzer, preselector, attennuating pads, connector lo
sses, site attennuations, etc.) and came up with a fudge factor which he called 
"measurement uncertainty". Now he could go to his boss and explain why his 
measurements at home were different than the measurements at the test site. 

But I bet that he still had to fix his equipment. 

Enough ranting. 

Cheers, 

Gabriel Roy
Hughes Network Systems, MD

It's pretty obvious that the opinions are my own. Jim Eickler's invisible 
friend doesn't even talk to me any more. 

Re: Measurement Uncertainty

[Jon D Curtis]

In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
for Evaluating and Expressing the Uncertainty of NIST measurement
results."

Our NVLAP accreditation requires us to estimate uncertainties in our test
reports.  Every Curtis-Straus EMC or Telco test report contains
uncertainty
estimates.  As to the passing margin, passing is passing and failing is
failing.  Before you take measurement uncertainty into the limit, first
consider that technique has improved (and therefore unceratinty is lower)
than it was when the limits were formulated.  Second consider that the
regulators which accepted the limit were well aware that uncertainty
exists and in all likelyhood accounted for it in their choice of the
limit.

That said, I advise all clients who are within our uncertainty of the
limit (but passing), that they should be aware that they may fail next
time.
If they are at the prototype stage, or building a product which will
become the platform for future development, it is advisable to seek a
larger margin.

Jon D. Curtis, PE   
  
Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Fri, 10 Jan 1997, Barge, Michael wrote:

> 
> 
> FROM:  michael_ba...@atk.com
> 
> Item Subject:  Measurement Uncertainty
> 
> Greeting Tregers;
> 
> There seems to be a requirement that, when giving a measured value, there 
> must be an uncertainty associated with that value describing the confidence 
> of that value.
> 
> (1)   Do most labs report an uncertainty measurement in the test report, on 
> the data sheet, on a certificate of compliance?
> (2)   How did you generate the measurement of uncertainty for emission 
> tests? For immunity tests?
>   
>   AND MOST IMPORTANTLY
>   
> (3)   What do you tell the customer when he is below the limit by less than 
> the measurement uncertainty? When he is above by less?
> 
> J Michael Barge
> Alliant Techsystems
> Annapolis, MD
> 

Re: Measurement Uncertainty

[Tony Fredriksson]

Jon,

Thanks for the info on the NIST Technical Note.  Looks like I need
to get a copy and undertand it.

It is good to know that Curtis-Straus estimates uncertainty.
I am particularly interested in the EMC side of the discussion
and have a couple of questions:

1.  In the case of Immunity, I suppose the lab would only be able
 to estimate uncertainty of the disturbance from the test generator.
 Is that correct?  Wouldn't the loading of the signal source from
 EUT have a dramatic affect on the test result uncertainty?  If this
 is the case, how is it factored in such that uncertainty of the end
 result is quantified to any practical degree?

2.  In the case of EMI, what is the range of uncertainty that one of
 your tests can provide?  I would think it is a function of frequency.
 Does it attempt to take into account the uncertainty due to a change
 in cable or preripheral placement from one setup to the next of the
 exact same EUT?  If so, how was that uncertainty derived?

The reason that I am curious about this is that I have seen some cables
so hot (headphone on a CD ROM port for example) that moving them an
inch or two in either direction can vary emissions by 10dB or more.  That
would seem to be quite unpredicatable by statistical methods and would
seem to dwarf any uncertainties from other sources.  This even considers
test setup methods that have been designed to minimize test variation
(such as ANSI C63.4).

I can see that using the lab's stated uncertainty in combination with
a CISPR 16 style sampling test would be a significant improvement over
other procedures.

Thanks,
tony_fredriks...@netpower.com

 --
From: Jon D Curtis
To: Barge, Michael
Cc: 'emc-p...@ieee.org'
Subject: Re: Measurement Uncertainty
List-Post: emc-pstc@listserv.ieee.org
Date: Monday, January 13, 1997 9:14AM

In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
for Evaluating and Expressing the Uncertainty of NIST measurement
results."

Our NVLAP accreditation requires us to estimate uncertainties in our test
reports.  Every Curtis-Straus EMC or Telco test report contains
uncertainty
estimates.  As to the passing margin, passing is passing and failing is
failing.  Before you take measurement uncertainty into the limit, first
consider that technique has improved (and therefore unceratinty is lower)
than it was when the limits were formulated.  Second consider that the
regulators which accepted the limit were well aware that uncertainty
exists and in all likelyhood accounted for it in their choice of the
limit.

That said, I advise all clients who are within our uncertainty of the
limit (but passing), that they should be aware that they may fail next
time.
If they are at the prototype stage, or building a product which will
become the platform for future development, it is advisable to seek a
larger margin.

Jon D. Curtis, PE

Curtis-Straus LLC j...@world.std.com
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Fri, 10 Jan 1997, Barge, Michael wrote:

>
>
> FROM:  michael_ba...@atk.com
>
> Item Subject:  Measurement Uncertainty
>
> Greeting Tregers;
>
> There seems to be a requirement that, when giving a measured value, there
> must be an uncertainty associated with that value describing the 
confidence
> of that value.
>
> (1)   Do most labs report an uncertainty measurement in the test report, 
on
> the data sheet, on a certificate of compliance?
> (2)   How did you generate the measurement of uncertainty for emission
> tests? For immunity tests?
>
>   AND MOST IMPORTANTLY
>
> (3)   What do you tell the customer when he is below the limit by less 
than
> the measurement uncertainty? When he is above by less?
>
> J Michael Barge
> Alliant Techsystems
> Annapolis, MD
>

Re: Measurement Uncertainty

[Jon D Curtis]

Response to Tony Fredriksson's comments:  See below.

Jon D. Curtis, PE   
  
Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Mon, 13 Jan 1997, Tony Fredriksson wrote:

> 
> Jon,
> 
> Thanks for the info on the NIST Technical Note.  Looks like I need
> to get a copy and undertand it.
> 
> It is good to know that Curtis-Straus estimates uncertainty.
> I am particularly interested in the EMC side of the discussion
> and have a couple of questions:
> 
> 1.  In the case of Immunity, I suppose the lab would only be able
>  to estimate uncertainty of the disturbance from the test generator.
>  Is that correct?  Wouldn't the loading of the signal source from
>  EUT have a dramatic affect on the test result uncertainty?  If this
>  is the case, how is it factored in such that uncertainty of the end
>  result is quantified to any practical degree?
For radiated immunity, we do a Type B uncertainty evaluation on the test.
We only
consider the factors from the test equipment as we feel our uncertainty
results from the level of the field without the EUT.  The effects of the
EUT on the field will vary by EUT (size, dimensional resonances, etc.) but
between samples of individual EUTs these factors should be well behaved.
We do
ignore cable position as a factor, relying on the fact that we test 4
different sides in two polarities to give us some statistical protection
in this area.

The major contribution to uncertainty then becomes the leveling of the
field which is +-3dB.  Since this is a MUST be within 0dB to 6bB, we use
Uj as 3dB and divide it by square root of three assuming a rectangular
distribution.  See the NIST note.

> 
> 2.  In the case of EMI, what is the range of uncertainty that one of
>  your tests can provide?  I would think it is a function of frequency.
>  Does it attempt to take into account the uncertainty due to a change
>  in cable or preripheral placement from one setup to the next of the
>  exact same EUT?  If so, how was that uncertainty derived?
It could be a function of frequency.  Certainly antenna factors and site
anomalies are generally better behaved above 200MHz.  To date we use a
simple
uncertainty using estimated worst case results across the frequency
spectrum.  As factors we have: antenna factor: +-1dB, NSA: +-4dB (ours is
really max 2dB so we use +-4dB, but assume a traingular distribution on
this factor), Equipment factors: SA flatness 1.5dB, cable calibration:
.3dB, test method variance (cable manipulation: +-2dB, normal
distribution).  Add it up using Root-sum-of-squares=2.9dB uncertainty:
Note that there are additional factors based on the assumed distributions
of the uncertainties.

> 
> The reason that I am curious about this is that I have seen some cables
> so hot (headphone on a CD ROM port for example) that moving them an
> inch or two in either direction can vary emissions by 10dB or more.  That
> would seem to be quite unpredicatable by statistical methods and would
> seem to dwarf any uncertainties from other sources.  This even considers
> test setup methods that have been designed to minimize test variation
> (such as ANSI C63.4).
Yes, cable manipulation done properly is still the over-riding factor in
repeatibility.  I am able to obtain 2dB repeatibility with attention to
cable manipulation to maximize emissions at each frequency.  If you don't
maximize the cables you will see variances of at least 10dB between EUT
setups that appear identicle.

> 
> I can see that using the lab's stated uncertainty in combination with
> a CISPR 16 style sampling test would be a significant improvement over
> other procedures.
> 
> Thanks,
> tony_fredriks...@netpower.com
> 
>  --
> From: Jon D Curtis
> To: Barge, Michael
> Cc: 'emc-p...@ieee.org'
> Subject: Re: Measurement Uncertainty
> Date: Monday, January 13, 1997 9:14AM
> 
> In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
> for Evaluating and Expressing the Uncertainty of NIST measurement
> results."
> 
> Our NVLAP accreditation requires us to estimate uncertainties in our test
> reports.  Every Curtis-Straus EMC or Telco test report contains
> uncertainty
> estimates.  As to the passing margin, passing is passing and failing is
> failing.  Before you take measurement uncertainty into the limit, first
> consider that technique has improved (and therefore unceratinty is lower)
> than it was when the limits were formulated.  Second consider that the
> regulators which accepted the limit were well aware that uncertainty
> exists and in all likelyhood accounted f

Re: Measurement Uncertainty

[Jon D Curtis]

Dear Hans,

I know of no manufacturers actually engaged in series production audits.
So lets hear from them.  Please respond to this forum.

The companies I work with look to CISPR 22 8.2.1.1 and test one sample.
Some of them are happy with 0dB margin.  I advise a higher margin, but
they are responsible for signing the DoC.  To date it would appear to me
that the 80/80 rule only has a place in making it harder to take product
off the market.  You can go to market with only one sample tested, but if
someone wants to restrict your access they have to perform an 80/80 rule
statistical test to say you fail (CISPR 22 8.2.4).

As a test lab, I'd love the 80/80 rule if the market would support it
(three-five times the testing, yippee!).  The doctrine also seems to need
a bit of clarification: Xn is refered to as the value of the individual
item.  Is this the value of the one point closest to the limit?  Can you
change the frequency?  On a product do you evaluate more than one
frequency?  How many? - the six closest to the limit?  When doing more
than one test, are several 80/80 tests performed - one for radiated, one
for conducted?  The 80/80 test is a statistician's dream and a test
engineer's nightmare.

Jon D. Curtis, PE   
  
Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Mon, 13 Jan 1997 hans_mellb...@non-hp-santaclara-om4.om.hp.com wrote:

> 
> I take exception with the statement "passing is passing and failing is 
> failing". CISPR 16 and 22(section 8.2.4) (maybe others too) require that 
> during manufacturing sampling, the products pass the so called 80/80 rule. 
> A minimum sampling of 3 units is required to perform this 80/80 calculation 
> and products with minimal margin will discover that they fail the formula 
> test! Go ahead and try a sample hypothetical test!
> 
> 
> __ Reply Separator 
> _________
> Subject: Re: Measurement Uncertainty
> Author:  Non-HP-owner-emc-pstc (owner-emc-p...@majordomo.ieee.org) at 
> HP-Boise,mimegw2
> Date:01/13/97 05:14 AM
> 
> 
> In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines 
> for Evaluating and Expressing the Uncertainty of NIST measurement 
> results."
> 
> Our NVLAP accreditation requires us to estimate uncertainties in our test 
> reports.  Every Curtis-Straus EMC or Telco test report contains 
> uncertainty
> estimates.  As to the passing margin, passing is passing and failing is 
> failing.  Before you take measurement uncertainty into the limit, first 
> consider that technique has improved (and therefore unceratinty is lower) 
> than it was when the limits were formulated.  Second consider that the 
> regulators which accepted the limit were well aware that uncertainty 
> exists and in all likelyhood accounted for it in their choice of the 
> limit.
> 
> That said, I advise all clients who are within our uncertainty of the 
> limit (but passing), that they should be aware that they may fail next 
> time.
> If they are at the prototype stage, or building a product which will 
> become the platform for future development, it is advisable to seek a 
> larger margin.
> 
> Jon D. Curtis, PE   
> 
> Curtis-Straus LLC j...@world.std.com 
> One-Stop Laboratory for EMC, Product Safety and Telecom 
> 527 Great Roadvoice (508) 486-8880 
> Littleton, MA 01460   fax   (508) 486-8828 
> http://world.std.com/~csweb
> On Fri, 10 Jan 1997, Barge, Michael wrote:
> 
> > 
> > 
> > FROM:  michael_ba...@atk.com
> > 
> > Item Subject:  Measurement Uncertainty 
> > 
> > Greeting Tregers;
> > 
> > There seems to be a requirement that, when giving a measured value, there 
> > must be an uncertainty associated with that value describing the confidence 
> > of that value.
> > 
> > (1)   Do most labs report an uncertainty measurement in the test report, on 
> > the data sheet, on a certificate of compliance?
> > (2)   How did you generate the measurement of uncertainty for emission 
> > tests? For immunity tests?
> >   
> >   AND MOST IMPORTANTLY
> >   
> > (3)   What do you tell the customer when he is below the limit by less than 
> > the measurement uncertainty? When he is above by less?
> > 
> > J Michael Barge
> > Alliant Techsystems
> > Annapolis, MD
> > 
> 

Re: Measurement Uncertainty

[Tony Fredriksson]

Jon et al,

I helped to implement production audits per CISPR 16 @  Sun Microsystems
back in 1989.  When I left in 1995, they had discontinued doing the audits
for ongoing production, but were still doing 5 unit audits on pilot samples.
I am not sure if they do it any longer.  I felt that the program improved 
the
quality of their products and kept them out of trouble with the larger VARs
retesting their systems.

Regards,
tony_fredriks...@netpower.com

 --
From: Jon D Curtis
To: HANS_MELLBERG
Cc: emc-pstc; Michael_Barge
Subject: Re: Measurement Uncertainty
List-Post: emc-pstc@listserv.ieee.org
Date: Monday, January 13, 1997 5:09PM

Dear Hans,

I know of no manufacturers actually engaged in series production audits.
So lets hear from them.  Please respond to this forum.

The companies I work with look to CISPR 22 8.2.1.1 and test one sample.
Some of them are happy with 0dB margin.  I advise a higher margin, but
they are responsible for signing the DoC.  To date it would appear to me
that the 80/80 rule only has a place in making it harder to take product
off the market.  You can go to market with only one sample tested, but if
someone wants to restrict your access they have to perform an 80/80 rule
statistical test to say you fail (CISPR 22 8.2.4).

As a test lab, I'd love the 80/80 rule if the market would support it
(three-five times the testing, yippee!).  The doctrine also seems to need
a bit of clarification: Xn is refered to as the value of the individual
item.  Is this the value of the one point closest to the limit?  Can you
change the frequency?  On a product do you evaluate more than one
frequency?  How many? - the six closest to the limit?  When doing more
than one test, are several 80/80 tests performed - one for radiated, one
for conducted?  The 80/80 test is a statistician's dream and a test
engineer's nightmare.

Jon D. Curtis, PE

Curtis-Straus LLC j...@world.std.com
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Mon, 13 Jan 1997 hans_mellb...@non-hp-santaclara-om4.om.hp.com wrote:

>
> I take exception with the statement "passing is passing and failing is
> failing". CISPR 16 and 22(section 8.2.4) (maybe others too) require that
> during manufacturing sampling, the products pass the so called 80/80 rule. 

> A minimum sampling of 3 units is required to perform this 80/80 
calculation
> and products with minimal margin will discover that they fail the formula
> test! Go ahead and try a sample hypothetical test!
>
>
> __ Reply Separator
_____
> Subject: Re: Measurement Uncertainty
> Author:  Non-HP-owner-emc-pstc (owner-emc-p...@majordomo.ieee.org) at
> HP-Boise,mimegw2
> Date:01/13/97 05:14 AM
>
>
> In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
> for Evaluating and Expressing the Uncertainty of NIST measurement
> results."
>
> Our NVLAP accreditation requires us to estimate uncertainties in our test
> reports.  Every Curtis-Straus EMC or Telco test report contains
> uncertainty
> estimates.  As to the passing margin, passing is passing and failing is
> failing.  Before you take measurement uncertainty into the limit, first
> consider that technique has improved (and therefore unceratinty is lower)
> than it was when the limits were formulated.  Second consider that the
> regulators which accepted the limit were well aware that uncertainty
> exists and in all likelyhood accounted for it in their choice of the
> limit.
>
> That said, I advise all clients who are within our uncertainty of the
> limit (but passing), that they should be aware that they may fail next
> time.
> If they are at the prototype stage, or building a product which will
> become the platform for future development, it is advisable to seek a
> larger margin.
>
> Jon D. Curtis, PE
>
> Curtis-Straus LLC j...@world.std.com
> One-Stop Laboratory for EMC, Product Safety and Telecom
> 527 Great Roadvoice (508) 486-8880
> Littleton, MA 01460   fax   (508) 486-8828
> http://world.std.com/~csweb
> On Fri, 10 Jan 1997, Barge, Michael wrote:
>
> >
> >
> > FROM:  michael_ba...@atk.com
> >
> > Item Subject:  Measurement Uncertainty
> >
> > Greeting Tregers;
> >
> > There seems to be a requirement that, when giving a measured value, 
there
> > must be an uncertainty associated with that value describing the
confidence
> > of that value.
> >
> > (1)   Do most labs report an uncertainty measurement in the test report,
on
> > the data sheet, on a certificate of compliance?
> > (2)   How di

Re: Measurement Uncertainty

[Jerry Roberton]

  RE>>Measurement Uncertainty  13/1/97

The ADLNB group in Europe have published Guide Notes on the 'shared risk'
principle of intepreting test results for regulatory purposes.   These
guidelines are used except on interpretations where  limit/fail criteria  are
specially  written into particular Common Technical  Requirements.You should
refer to John Looyestijn of  Telefication in Holland .

Jerry Roberton
All opinions my own

--
List-Post: emc-pstc@listserv.ieee.org
Date: 13/1/97 8:16 am
To: Jerry Roberton
From: Jon D Curtis
In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines
for Evaluating and Expressing the Uncertainty of NIST measurement
results."

Our NVLAP accreditation requires us to estimate uncertainties in our test
reports.  Every Curtis-Straus EMC or Telco test report contains
uncertainty
estimates.  As to the passing margin, passing is passing and failing is
failing.  Before you take measurement uncertainty into the limit, first
consider that technique has improved (and therefore unceratinty is lower)
than it was when the limits were formulated.  Second consider that the
regulators which accepted the limit were well aware that uncertainty
exists and in all likelyhood accounted for it in their choice of the
limit.

That said, I advise all clients who are within our uncertainty of the
limit (but passing), that they should be aware that they may fail next
time.
If they are at the prototype stage, or building a product which will
become the platform for future development, it is advisable to seek a
larger margin.

Jon D. Curtis, PE   
  
Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Fri, 10 Jan 1997, Barge, Michael wrote:

> 
> 
> FROM:  michael_ba...@atk.com
> 
> Item Subject:  Measurement Uncertainty
> 
> Greeting Tregers;
> 
> There seems to be a requirement that, when giving a measured value, there 
> must be an uncertainty associated with that value describing the confidence 
> of that value.
> 
> (1)   Do most labs report an uncertainty measurement in the test report, on 
> the data sheet, on a certificate of compliance?
> (2)   How did you generate the measurement of uncertainty for emission 
> tests? For immunity tests?
>   
>   AND MOST IMPORTANTLY
>   
> (3)   What do you tell the customer when he is below the limit by less than 
> the measurement uncertainty? When he is above by less?
> 
> J Michael Barge
> Alliant Techsystems
> Annapolis, MD
> 


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Date: Mon, 13 Jan 1997 09:14:53 -0500 (EST)
From: Jon D Curtis 
To: "Barge, Michael" 
Cc: "'emc-p...@ieee.org'" 
Subject: Re: Measurement Uncertainty
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Re: Measurement Uncertainty

[HANS_MELLBERG]

When I worked for Wyse Technology we did perform audits of manufactured 
products. Each week we would audit one product. Statistical analysis was 
performed per the 80/80 rule. We only used the data points within 6 dB of the 
margin for the formula. Each frequency point within 6B was of the limit was 
treated as an entry. x-sub-n is is each entry point. This was done for conducted
emissions as well as radiated emissions. (remember to apply either qp or avg as 
applicable, do not use peak) You need a spread sheet program or you'll be 
calculating for days!

Best Regards

P.S., you need a minimum of three samples (the standard reccomends 5) to make it
meaningfull, i.e. you need a k value for one or two samples but those rise 
astronomically, so three is an acceptable minimum for statistical purposes.
__ Reply Separator _
Subject: Re: Measurement Uncertainty
Author:  Non-HP-Tony-Fredriksson (tony_fredriks...@netpower.com) at 
hp-boise,uugw2
List-Post: emc-pstc@listserv.ieee.org
Date:01/13/97 03:04 PM



Jon et al,

I helped to implement production audits per CISPR 16 @  Sun Microsystems 
back in 1989.  When I left in 1995, they had discontinued doing the audits 
for ongoing production, but were still doing 5 unit audits on pilot samples. 
I am not sure if they do it any longer.  I felt that the program improved 
the
quality of their products and kept them out of trouble with the larger VARs 
retesting their systems.

Regards,
tony_fredriks...@netpower.com

 --
From: Jon D Curtis
To: HANS_MELLBERG
Cc: emc-pstc; Michael_Barge
Subject: Re: Measurement Uncertainty 
List-Post: emc-pstc@listserv.ieee.org
Date: Monday, January 13, 1997 5:09PM

Dear Hans,

I know of no manufacturers actually engaged in series production audits. 
So lets hear from them.  Please respond to this forum.

The companies I work with look to CISPR 22 8.2.1.1 and test one sample. 
Some of them are happy with 0dB margin.  I advise a higher margin, but 
they are responsible for signing the DoC.  To date it would appear to me 
that the 80/80 rule only has a place in making it harder to take product 
off the market.  You can go to market with only one sample tested, but if 
someone wants to restrict your access they have to perform an 80/80 rule 
statistical test to say you fail (CISPR 22 8.2.4).

As a test lab, I'd love the 80/80 rule if the market would support it 
(three-five times the testing, yippee!).  The doctrine also seems to need 
a bit of clarification: Xn is refered to as the value of the individual 
item.  Is this the value of the one point closest to the limit?  Can you 
change the frequency?  On a product do you evaluate more than one 
frequency?  How many? - the six closest to the limit?  When doing more 
than one test, are several 80/80 tests performed - one for radiated, one 
for conducted?  The 80/80 test is a statistician's dream and a test 
engineer's nightmare.

Jon D. Curtis, PE

Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom 
527 Great Roadvoice (508) 486-8880 
Littleton, MA 01460   fax   (508) 486-8828 
http://world.std.com/~csweb
On Mon, 13 Jan 1997 hans_mellb...@non-hp-santaclara-om4.om.hp.com wrote:

>
> I take exception with the statement "passing is passing and failing is
> failing". CISPR 16 and 22(section 8.2.4) (maybe others too) require that
> during manufacturing sampling, the products pass the so called 80/80 rule. 

> A minimum sampling of 3 units is required to perform this 80/80 
calculation
> and products with minimal margin will discover that they fail the formula 
> test! Go ahead and try a sample hypothetical test!
>
>
> __ Reply Separator 
_____
> Subject: Re: Measurement Uncertainty
> Author:  Non-HP-owner-emc-pstc (owner-emc-p...@majordomo.ieee.org) at 
> HP-Boise,mimegw2
> Date:01/13/97 05:14 AM
>
>
> In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines 
> for Evaluating and Expressing the Uncertainty of NIST measurement
> results."
>
> Our NVLAP accreditation requires us to estimate uncertainties in our test 
> reports.  Every Curtis-Straus EMC or Telco test report contains
> uncertainty
> estimates.  As to the passing margin, passing is passing and failing is 
> failing.  Before you take measurement uncertainty into the limit, first
> consider that technique has improved (and therefore unceratinty is lower) 
> than it was when the limits were formulated.  Second consider that the
> regulators which accepted the limit were well aware that uncertainty 
> exists and in all likelyhood accounted for it in their choice of the 
> limit.
>
> That said, I advise all clients who are within our uncertainty of the 
> limit (but passing), 

Re: Measurement Uncertainty

[Steve Chin]

Well put, Jon. Let's not forget that all of that additional testing not only
costs the manufacturer time and test money, but there is the also additional
cost of at least two more sample units which may now no longer be sold as
"new" units (having been used). Some of the units my company manufactures
carry a list price in excess of $50,000 US. My accounting department would not
like to have me write off that much in equipment every time I test, and my
budget won't support that. In the end, it'd mean that the consumer would end
up paying even higher prices to purchase product from companies who are trying
to "do the right thing," or that the companies who are conscientious will go
out of business in favor of companies who either don't do testing (yes, they
exist!) and sell lots of stuff to consumers on the cheap, or those that do
minimal testing.

I'd love to be able to take up three OATS and test my equipment. I just can't
do that. Besides, my test lab doesn't have the site time available to run all
of those tests for al of their clients.

Steve Chin
StreamLogic Corp.
Menlo Park, CA, USA
sc...@sledgehammer.com

The views expressed in this communication belong only to their authors. They
do not necessarily reflect those of their employers or each others'.

--
List-Post: emc-pstc@listserv.ieee.org
Date: 1/13/97 7:04 PM
To: Steve Chin
From: Jon D Curtis
Dear Hans,

I know of no manufacturers actually engaged in series production audits.
So lets hear from them.  Please respond to this forum.

The companies I work with look to CISPR 22 8.2.1.1 and test one sample.
Some of them are happy with 0dB margin.  I advise a higher margin, but
they are responsible for signing the DoC.  To date it would appear to me
that the 80/80 rule only has a place in making it harder to take product
off the market.  You can go to market with only one sample tested, but if
someone wants to restrict your access they have to perform an 80/80 rule
statistical test to say you fail (CISPR 22 8.2.4).

As a test lab, I'd love the 80/80 rule if the market would support it
(three-five times the testing, yippee!).  The doctrine also seems to need
a bit of clarification: Xn is refered to as the value of the individual
item.  Is this the value of the one point closest to the limit?  Can you
change the frequency?  On a product do you evaluate more than one
frequency?  How many? - the six closest to the limit?  When doing more
than one test, are several 80/80 tests performed - one for radiated, one
for conducted?  The 80/80 test is a statistician's dream and a test
engineer's nightmare.

Jon D. Curtis, PE   
  
Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom
527 Great Roadvoice (508) 486-8880
Littleton, MA 01460   fax   (508) 486-8828
http://world.std.com/~csweb
On Mon, 13 Jan 1997 hans_mellb...@non-hp-santaclara-om4.om.hp.com wrote:

Re: Measurement Uncertainty

[Tony Fredriksson]

Hi Steve/Jon,

If you consider the test units as Work In Process (WIP), you
create an mfg inventory location for the test site, and consider this
an extension of the manufacturing process as Post Pack Audit, you
can consider the additional units as new and sell them as such.
Many companies have a post pack audit procedure under
which units are unboxed, tested, reboxed and sold as new after
performance testing is performed.  There is nothing wrong with this.
Actually, if I were a customer, I would want one
of the units subjected to the PPA test because I would know it
meets spec.

I do agree that this is impractical for very large units (although
we audited units up to the size of a large refrigerator weighing about
1000 lbs) or very fragile units.  It also adds cost for the occasional site 
time,
labor, and inventory management.  But if it is done right, there is
no good reason that the units need be sold as used instead of
new.

It is obviously also impractical for small companies and low volume
production environments.

WRT to Jon's specific questions, the CISPR 16 formula has the answers
when one thinks about the intent.

1.   Xn is the arithmetic mean of a data set.  It is meaningless in
 the context of the test to lump different frequency harmonics
 or sources into the same data set .  So

 a.   The data for the calculation is from at least 3 identically
  configured samples of the same model.

 b.   The data is for a given harmonic from the same source
  regardless of margin from the limit.  For example, the
  5th harmonic of a CPU clock will be considered the same
  frequency even though it is not EXACTLY the same due to
  variation in part tolerances.  The third and 5th harmonic
  would not be lumped in the same data set.

2.   There is no limit to how many frequencies are evaluated but common
 sense usually prevails.  For example, a frequency very close to the
 limit may have no problem if the standard deviation of the data set
 is 0 while a frequency with an Xn 10 dB below the limit may be a 
problem
 if the sample standard deviation of the data set is 8dB.  It is good to 
scan
 the first unit thoroughly, then spot check a second unit at the same
 frequencies.  If the data between the first two is very close (say, 
within
 2dB),  then check only frequencies within 6 dB or so from the limit for
 all remaining test samples.  If the data spread is larger, increase the 

 margin for the remaining samples to 10dB or whatever the data spread
 merits.  If you are testing 5 samples, and all frequencies pass by the
 test by the time the third sample is scanned, stop there and don't
 check the last two.  The constant, "k," in the equation takes the 
smaller
 sample set into account.

Typically, it would take about 16 hours of test time to do a 5 unit 
pre-production
audit and as I stated previously, about 30% - 50% of the products I saw had 
some
relatively minor problem (usually mechanical) that was corrected due to the
audit.  This worked well for high volume production environments where 
non-compliant product  was shipping by the 1000's of units.  It does not
make sense for huge products or low volume as stated above.

I did this for a couple of years so in this case, I comment from experience.
I am not a statistician by any means, but have seen real benefit from such
a program.

One final comment.  There is a farily sizable number of ITE products out 
there
shipping that do not comply with Class B EMI regs in typical configurations.
I see them all of the time.While I don't believe they
are bad enough to cause major EMI pollution, it makes it very difficult to
requalify this stuff as a VAR in end use configurations.  Wouldn't it be 
nice
if some of these vendors paid a little more attention to the EMC performance 

to these products?  Just wishful thinking!...

Ciao,
tony_fredriks...@netpower.com

 --
From: Steve Chin
To: HANS_MELLBERG@non-hp-santaclara; Jon D Curtis
Cc: emc-pstc; Michael_Barge
Subject: Re: Measurement Uncertainty
List-Post: emc-pstc@listserv.ieee.org
Date: Monday, January 13, 1997 7:27PM

Well put, Jon. Let's not forget that all of that additional testing not only
costs the manufacturer time and test money, but there is the also additional
cost of at least two more sample units which may now no longer be sold as
"new" units (having been used). Some of the units my company manufactures
carry a list price in excess of $50,000 US. My accounting department would 
not
like to have me write off that much in equipment every time I test, and my
budget won't support that. In the end, it'd mean that the consumer would end
up paying even higher prices to purchase product from companies who are 
trying
to "do the right thing," or that the companies who are conscientious will go
out of business in

Re: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

I would be careful about using the Uncertainty Calculator freeware tool.  It
was written in March 1997 prior to the release of CISPR16-4-2:2003 and
EN55016-4-2:2004.  Please note that these later standards have mandated extra
quantities to consider  in emissions testing that forces a different
measurement uncertainty for horizontal polarity versus vertical polarity
measurements.  

The math doesn't change for summing the squared uncertainties of each input
quantity, square rooting the sum, and then multiplying by 2 for an expanded
uncertainty.  Just be aware that you may need to add extra quantities and
create more expanded measurement uncertainty results.  Of course, that can
also be done on a simple spreadsheet.

The EN55016-4-2:2004 (CISPR16-4-2:2003) is pretty straight forward on the math
and the quantities to be included, but it is not very helpful on finding real
values for each of those quantities.  Section A.5 does attempt to give some
description on what the values of some quantities should be based on the type
of measurement equipment is used.  Still, I agree that it would be helpful if
a guide was created to help implement the standard including how to measure
some of the values as opposed to relying on the worst-case values listed in
the standard.. 


Monrad L. Monsen
Worldwide Compliance Officer
Sun Microsystems
monrad.mon...@sun.com
303.272.9612 Office


John Woodgate wrote on 9/9/2009 10:47 AM: 

In message 
<0ed66cd2c9bd0a459d54fb9119a605670107d...@mailserver.lecotc.com>
<mailto:0ed66cd2c9bd0a459d54fb9119a605670107d...@mailserver.lecotc.com> ,
dated Wed, 9 Sep 2009, "Kunde, Brian" 
<mailto:brian_ku...@lecotc.com>  writes: 




It should be simple.  



As Einstein said, 'Things should be a simple as possible, but no 
simpler.'.
Uncertainty simply ISN'T simple, unless you will put up with
'worst-worst-worst' case approximations that may be very tough to handle. 



An example for Radiated Emissions, here are the contributors, 
here is how
you obtain those values, here are the factors for each, do some math on a
spreadsheet and DONE. 



Look at: 

    http://www.callabmag.com/freeware.html 

Uncertainty calculator 3.2 has been recommended to me by a REAL expert 
on the
subject. 


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RE: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

 





From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Kunde, 
Brian
Sent: Wednesday, September 09, 2009 8:49 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Measurement Uncertainty



What is needed is a simple document that describes for each EMC test 
that
requires a Measurement Uncertainty value a list of Contributors, how to obtain
those values, and a formula to plug them into to get your MU value. Simple.  

 

I don’t need to spend hundreds of hours reading, studying, and trying to
figure out if it is a rectangle, triangle, cube, square, star, whatever…… 
I’ll leave that up to all you super smart mathematicians to hash that out.  

 

It should be simple.  An example for Radiated Emissions, here are the
contributors, here is how you obtain those values, here are the factors for
each, do some math on a spreadsheet and DONE. 

 

Am I wrong?

 

Thanks for letting me rant. 

 

The Other Brian

 

 

Yes Brian, you are most emphatically wrong, absolutely wrong; wrong almost
beyond redemption. You are seeking the sensible and reasonable solution, and
do not see the opportunities to stretch your experience in statistics. 

 

Seriously, one I get this figured out, I think I'll post something like what
you are talking about. BTW, I am reading through UKAS LAB34 right now, and it
has a number of specific examples tailored to the various EMC tests that we
do. I also downloaded a measurement uncertainty calculator from Agilent, but I
can't install it in my computer because my IT departments protects me from
myself.

 

Ed Price
ed.pr...@cubic.com mailto:ed.pr...@cubic.com>  WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA  USA
858-505-2780
Military & Avionics EMC Is Our Specialty

 

 

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Re: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

In message 
<0ed66cd2c9bd0a459d54fb9119a605670107d...@mailserver.lecotc.com>, dated 
Wed, 9 Sep 2009, "Kunde, Brian"  writes:

>
>It should be simple. 

As Einstein said, 'Things should be a simple as possible, but no 
simpler.'. Uncertainty simply ISN'T simple, unless you will put up with 
'worst-worst-worst' case approximations that may be very tough to 
handle.

>An example for Radiated Emissions, here are the contributors, here is 
>how you obtain those values, here are the factors for each, do some 
>math on a spreadsheet and DONE.

Look at:

http://www.callabmag.com/freeware.html

Uncertainty calculator 3.2 has been recommended to me by a REAL expert 
on the subject.
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Re: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

In message 
, 
dated Wed, 9 Sep 2009, Alexandru Guidea  writes:

>CISPR 16-4

That's five documents (CISPR 16-4-1 to 16-4-5) and they give a lot of 
information, but I wouldn't say 'detailed instructions' for anything 
other than mass-produced products (16-4-3).
-- 
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
Things can always get better. But that's not the only option.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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RE: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

What is needed is a simple document that describes for each EMC test that
requires a Measurement Uncertainty value a list of Contributors, how to obtain
those values, and a formula to plug them into to get your MU value. Simple.  

 

I don’t need to spend hundreds of hours reading, studying, and trying to
figure out if it is a rectangle, triangle, cube, square, star, whatever…… 
I’ll leave that up to all you super smart mathematicians to hash that out.  

 

It should be simple.  An example for Radiated Emissions, here are the
contributors, here is how you obtain those values, here are the factors for
each, do some math on a spreadsheet and DONE. 

 

Am I wrong?

 

Thanks for letting me rant. 

 

The Other Brian

 

 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of
lfresea...@aol.com
Sent: Wednesday, September 09, 2009 11:31 AM
To: gui...@cae.com; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Measurement Uncertainty

 

I would suggest this, but it's costs big $$$.

LAB 34 is free

 

 


From: Alexandru Guidea 
To: EMC-PSTC@LISTSERV.IEEE.ORG 
Sent: Wed, Sep 9, 2009 10:13 am
Subject: RE: [PSES] Measurement Uncertainty

CISPR 16-4

 



From: emc-p...@ieee.org <mailto:emc-p...@ieee.org>  [mailto:emc-p...@ieee.org
<mailto:emc-p...@ieee.org?> ] On Behalf Of Grasso, Charles
Sent: Wednesday, September 09, 2009 10:58 AM
To: Brent G DeWitt; Ken Javor; EMC-PSTC@LISTSERV.IEEE.ORG
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> 
Subject: RE: [PSES] Measurement Uncertainty

Hello,

 

There is I believe a document that has detailed instructions on how to
calculate measurement uncertainty
for EMC type measurements. I do not have the document to hand. Does anyone
remember the number?

 

 

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_ 

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Re: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

I would suggest this, but it's costs big $$$.

LAB 34 is free




From: Alexandru Guidea 
To: EMC-PSTC@LISTSERV.IEEE.ORG 
Sent: Wed, Sep 9, 2009 10:13 am
Subject: RE: [PSES] Measurement Uncertainty


CISPR 16-4



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org <mailto:emc-p...@ieee.org?>
] On Behalf Of Grasso, Charles
Sent: Wednesday, September 09, 2009 10:58 AM
To: Brent G DeWitt; Ken Javor; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Measurement Uncertainty


Hello,
 
There is I believe a document that has detailed instructions on how to
calculate measurement uncertainty
for EMC type measurements. I do not have the document to hand. Does anyone
remember the number?
 
 
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RE: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

Here are three sources … there may be more recent editions of these documents

 

* NAMAS NIS81 document  “The Treatment of Uncertainty in EMC
Measurements” – Edition 1, May, 1994 

or

* UKAS LAB 34  - “The Expression of Uncertainty in EMC Testing” -
Edition 1, August, 2002, http://www.uka
.com/Library/downloads/publications/Lab34.pdf 

or

* CISPR 16-4 “Uncertainty in EMC measurements” –  First Edition
May, 2002. 

 

 

W. Richard Gartman, MS, CSP

Product Stewardship Manager

Texas Instruments, Education Technology

7800 Banner Drive, Dallas, Tx 75251

Office: 972-917-1636Email: rgart...@ti.com
<mailto:rgart...@ti.com> 

Fax: 972-917-0668 URL: www.education.ti.com
<http://www.education.ti.com/>  

  www.education.ti.com/us/productstewardship
<http://education.ti.com/us/productstewardship> 

  

  <http://education.ti.com/us/productstewardship> 

Please consider the environment before printing this email. There is only one
earth - don't waste it. <http://education.ti.com/us/productstewardship> 

Who is John Galt? <http://education.ti.com/us/productstewardship> 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Grasso, Charles
Sent: Wednesday, September 09, 2009 9:58 AM
To: Brent G DeWitt; Ken Javor; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Measurement Uncertainty

 

Hello,

 

There is I believe a document that has detailed instructions on how to
calculate measurement uncertainty
for EMC type measurements. I do not have the document to hand. Does anyone
remember the number?

 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Brent G DeWitt
Sent: Tuesday, September 08, 2009 9:16 PM
To: 'Ken Javor'; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Measurement Uncertainty

 

Well said Ken.  In addition I think it is worth explaining that not all
uncertainty contributions have the same weight, as Ed asked about.   This
results in a “k” factor that is applied to the contribution towards the
total uncertainty.  Check out the numerous on-line uncertainty calculators and
national guidelines for details.

 

Brent DeWitt

Westborough, MA

 

From: Ken Javor [mailto:ken.ja...@emccompliance.com] 
Sent: Tuesday, September 08, 2009 7:46 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Measurement Uncertainty

 

Since dBs are logs of ratios, you cannot do sums of squares on them, and take
square roots. You would have to convert to numerics, do the rss, and then
convert back to dBs.

Thus, given your example values:

probe: 0.5 dB is roughly 6% tolerance
cable: 0.1 dB is roughly 1.1% tolerance
analyzer: 1 dB is roughly 12% tolerance

RSS: = square root [ (0.06)^2 + (0.011)^2 + (0.12)^2 ] = 0.135 

That corresponds to about 1.3 dB overall tolerance.

Note that isn’t very far off from your 1.26 dB answer.  However, to get
that, you simply added the dB tolerances together (no rss) and then took a
square root of the sum of dBs.  When you add the dBs together, you are
multiplying the tolerances.  If you multiply the tolerances and take the cube
root, it is as if you are taking a geometric mean.  Geometric and arithmetic
means are pretty close as long as the factors going into the product don’t
vary much from each other. 

For instance, if the factors are identical, the geometric and arithmetic means
are identical. Of course, that is a degenerate case where the concept of mean
isn’t terribly useful.  If you had two factors, say one and ten, the
geometric mean would be 3.162, whereas the arithmetic mean would be 5.5. If
the two factors are one and one hundred, then the geometric mean is ten, and
the arithmetic mean is 50.5.  You can see where this is going.
 
Ken Javor

Phone: (256) 650-5261



From: "Price, Edward" 
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
Date: Tue, 8 Sep 2009 16:16:09 -0700
To: 
Conversation: Measurement Uncertainty
Subject: Measurement Uncertainty

A quick question about calculating measurement uncertainty.

For example, if I am doing a conducted emission test, and I know the
calibration tolerance for each of the "modules" of my measurement system, how
do I calculate an overall uncertainty figure?

I have been under the assumption that, in the example I cite, that I have a
tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) and my analyzer
(+/- 1 dB). I have been using an "rms" calculation, where I square each of the
tolerances, sum them, and take the square root. Thus, square root of 1.6 dB
equals 1.26 dB uncertainty.

I recently had a customer say that this method implied that I was using
"rectangular" shape factors, and thus, I should be taking the cube root of the
sum.

Rectangular? Cube root?

 
Ed Price
ed.pr...@cubic.com mailto:

RE: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

CISPR 16-4



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Grasso, Charles
Sent: Wednesday, September 09, 2009 10:58 AM
To: Brent G DeWitt; Ken Javor; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Measurement Uncertainty



Hello,

 

There is I believe a document that has detailed instructions on how to
calculate measurement uncertainty
for EMC type measurements. I do not have the document to hand. Does anyone
remember the number?

 

 
-

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


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List rules: http://www.ieee-pses.org/listrules.html 

For help, send mail to the list administrators:
Scott Douglas 
Mike Cantwell  

For policy questions, send mail to:
Jim Bacher 
David Heald  

RE: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

Hello,

 

There is I believe a document that has detailed instructions on how to
calculate measurement uncertainty
for EMC type measurements. I do not have the document to hand. Does anyone
remember the number?

 



From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Brent G DeWitt
Sent: Tuesday, September 08, 2009 9:16 PM
To: 'Ken Javor'; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Measurement Uncertainty

 

Well said Ken.  In addition I think it is worth explaining that not all
uncertainty contributions have the same weight, as Ed asked about.   This
results in a “k” factor that is applied to the contribution towards the
total uncertainty.  Check out the numerous on-line uncertainty calculators and
national guidelines for details.

 

Brent DeWitt

Westborough, MA

 

From: Ken Javor [mailto:ken.ja...@emccompliance.com] 
Sent: Tuesday, September 08, 2009 7:46 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Measurement Uncertainty

 

Since dBs are logs of ratios, you cannot do sums of squares on them, and take
square roots. You would have to convert to numerics, do the rss, and then
convert back to dBs.

Thus, given your example values:

probe: 0.5 dB is roughly 6% tolerance
cable: 0.1 dB is roughly 1.1% tolerance
analyzer: 1 dB is roughly 12% tolerance

RSS: = square root [ (0.06)^2 + (0.011)^2 + (0.12)^2 ] = 0.135 

That corresponds to about 1.3 dB overall tolerance.

Note that isn’t very far off from your 1.26 dB answer.  However, to get
that, you simply added the dB tolerances together (no rss) and then took a
square root of the sum of dBs.  When you add the dBs together, you are
multiplying the tolerances.  If you multiply the tolerances and take the cube
root, it is as if you are taking a geometric mean.  Geometric and arithmetic
means are pretty close as long as the factors going into the product don’t
vary much from each other. 

For instance, if the factors are identical, the geometric and arithmetic means
are identical. Of course, that is a degenerate case where the concept of mean
isn’t terribly useful.  If you had two factors, say one and ten, the
geometric mean would be 3.162, whereas the arithmetic mean would be 5.5. If
the two factors are one and one hundred, then the geometric mean is ten, and
the arithmetic mean is 50.5.  You can see where this is going.
 
Ken Javor

Phone: (256) 650-5261



From: "Price, Edward" 
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
Date: Tue, 8 Sep 2009 16:16:09 -0700
To: 
Conversation: Measurement Uncertainty
Subject: Measurement Uncertainty

A quick question about calculating measurement uncertainty.

For example, if I am doing a conducted emission test, and I know the
calibration tolerance for each of the "modules" of my measurement system, how
do I calculate an overall uncertainty figure?

I have been under the assumption that, in the example I cite, that I have a
tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) and my analyzer
(+/- 1 dB). I have been using an "rms" calculation, where I square each of the
tolerances, sum them, and take the square root. Thus, square root of 1.6 dB
equals 1.26 dB uncertainty.

I recently had a customer say that this method implied that I was using
"rectangular" shape factors, and thus, I should be taking the cube root of the
sum.

Rectangular? Cube root?

 
Ed Price
ed.pr...@cubic.com mailto:ed.pr...@cubic.com>
<mailto:ed.pr...@cubic.com%3e>  WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA  USA
858-505-2780
Military & Avionics EMC Is Our Specialty

-

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Re: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

Ed,

take a look at UKAS Lab 34. there is a nice write up in there about MU 
for many EMI tests.

Cheers,

Derek.
www.lfresearch.com
www.emclabservices.com


Brent G DeWitt wrote:
>
> Well said Ken. In addition I think it is worth explaining that not all 
> uncertainty contributions have the same weight, as Ed asked about. 
> This results in a “k” factor that is applied to the contribution 
> towards the total uncertainty. Check out the numerous on-line 
> uncertainty calculators and national guidelines for details.
>
> Brent DeWitt
>
> Westborough, MA
>
> *From:* Ken Javor [mailto:ken.ja...@emccompliance.com]
> *Sent:* Tuesday, September 08, 2009 7:46 PM
> *To:* EMC-PSTC@LISTSERV.IEEE.ORG
> *Subject:* Re: [PSES] Measurement Uncertainty
>
> Since dBs are logs of ratios, you cannot do sums of squares on them, 
> and take square roots. You would have to convert to numerics, do the 
> rss, and then convert back to dBs.
>
> Thus, given your example values:
>
> probe: 0.5 dB is roughly 6% tolerance
> cable: 0.1 dB is roughly 1.1% tolerance
> analyzer: 1 dB is roughly 12% tolerance
>
> RSS: = square root [ (0.06)^2 + (0.011)^2 + (0.12)^2 ] = 0.135
>
> That corresponds to about 1.3 dB overall tolerance.
>
> Note that isn’t very far off from your 1.26 dB answer. However, to get 
> that, you simply added the dB tolerances together (no rss) and then 
> took a square root of the sum of dBs. When you add the dBs together, 
> you are multiplying the tolerances. If you multiply the tolerances and 
> take the cube root, it is as if you are taking a geometric mean. 
> Geometric and arithmetic means are pretty close as long as the factors 
> going into the product don’t vary much from each other.
>
> For instance, if the factors are identical, the geometric and 
> arithmetic means are identical. Of course, that is a degenerate case 
> where the concept of mean isn’t terribly useful. If you had two 
> factors, say one and ten, the geometric mean would be 3.162, whereas 
> the arithmetic mean would be 5.5. If the two factors are one and one 
> hundred, then the geometric mean is ten, and the arithmetic mean is 
> 50.5. You can see where this is going.
>
> Ken Javor
>
> Phone: (256) 650-5261
>
> --------
>
> *From: *"Price, Edward" 
> *Date: *Tue, 8 Sep 2009 16:16:09 -0700
> *To: *
> *Conversation: *Measurement Uncertainty
> *Subject: *Measurement Uncertainty
>
> *A quick question about calculating measurement uncertainty.
> *
> *For example, if I am doing a conducted emission test, and I know the 
> calibration tolerance for each of the "modules" of my measurement 
> system, how do I calculate an overall uncertainty figure?
> *
> *I have been under the assumption that, in the example I cite, that I 
> have a tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) 
> and my analyzer (+/- 1 dB). I have been using an "rms" calculation, 
> where I square each of the tolerances, sum them, and take the square 
> root. Thus, square root of 1.6 dB equals 1.26 dB uncertainty.
> *
> *I recently had a customer say that this method implied that I was 
> using "rectangular" shape factors, and thus, I should be taking the 
> cube root of the sum.
> *
> *Rectangular? Cube root?
> *
>
> */Ed Price
> /**ed.pr...@cubic.com* mailto:ed.pr...@cubic.com> 
> <mailto:ed.pr...@cubic.com%3e> * WB6WSN
> **NARTE Certified EMC Engineer
> Electromagnetic Compatibility Lab
> Cubic Defense Applications
> San Diego, CA USA
> **858-505-2780
> **/Military & Avionics EMC Is Our Specialty
> /*
> -
> 
> 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 
>
> All emc-pstc postings are archived and searchable on the web at 
> http://www.ieeecommunities.org/emc-pstc
> Graphics (in well-used formats), large files, etc. can be posted to 
> that URL.
>
> Website: http://www.ieee-pses.org/
> Instructions: http://listserv.ieee.org/request/user-guide.html
> List rules: http://www.ieee-pses.org/listrules.html
>
> For help, send mail to the list administrators:
> Scott Douglas 
> Mike Cantwell 
>
> For policy questions, send mail to:
> Jim Bacher 
> David Heald 
>
> -
> 
> 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 mailto:emc-p...@ieee.org>>
>
> All emc-pstc post

RE: [PSES] Measurement Uncertainty

[emc-p...@ieee.org]

Well said Ken.  In addition I think it is worth explaining that not all
uncertainty contributions have the same weight, as Ed asked about.   This
results in a “k” factor that is applied to the contribution towards the
total uncertainty.  Check out the numerous on-line uncertainty calculators and
national guidelines for details.

 

Brent DeWitt

Westborough, MA

 

From: Ken Javor [mailto:ken.ja...@emccompliance.com] 
Sent: Tuesday, September 08, 2009 7:46 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Measurement Uncertainty

 

Since dBs are logs of ratios, you cannot do sums of squares on them, and take
square roots. You would have to convert to numerics, do the rss, and then
convert back to dBs.

Thus, given your example values:

probe: 0.5 dB is roughly 6% tolerance
cable: 0.1 dB is roughly 1.1% tolerance
analyzer: 1 dB is roughly 12% tolerance

RSS: = square root [ (0.06)^2 + (0.011)^2 + (0.12)^2 ] = 0.135 

That corresponds to about 1.3 dB overall tolerance.

Note that isn’t very far off from your 1.26 dB answer.  However, to get
that, you simply added the dB tolerances together (no rss) and then took a
square root of the sum of dBs.  When you add the dBs together, you are
multiplying the tolerances.  If you multiply the tolerances and take the cube
root, it is as if you are taking a geometric mean.  Geometric and arithmetic
means are pretty close as long as the factors going into the product don’t
vary much from each other. 

For instance, if the factors are identical, the geometric and arithmetic means
are identical. Of course, that is a degenerate case where the concept of mean
isn’t terribly useful.  If you had two factors, say one and ten, the
geometric mean would be 3.162, whereas the arithmetic mean would be 5.5. If
the two factors are one and one hundred, then the geometric mean is ten, and
the arithmetic mean is 50.5.  You can see where this is going.
 
Ken Javor

Phone: (256) 650-5261





From: "Price, Edward" 
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
List-Post: emc-pstc@listserv.ieee.org
Date: Tue, 8 Sep 2009 16:16:09 -0700
To: 
Conversation: Measurement Uncertainty
Subject: Measurement Uncertainty

A quick question about calculating measurement uncertainty.

For example, if I am doing a conducted emission test, and I know the
calibration tolerance for each of the "modules" of my measurement system, how
do I calculate an overall uncertainty figure?

I have been under the assumption that, in the example I cite, that I have a
tolerance for my probe (say +/- 0.5 dB), my cable (+/- 0.1 dB) and my analyzer
(+/- 1 dB). I have been using an "rms" calculation, where I square each of the
tolerances, sum them, and take the square root. Thus, square root of 1.6 dB
equals 1.26 dB uncertainty.

I recently had a customer say that this method implied that I was using
"rectangular" shape factors, and thus, I should be taking the cube root of the
sum.

Rectangular? Cube root?

 
Ed Price
ed.pr...@cubic.com mailto:ed.pr...@cubic.com>
<mailto:ed.pr...@cubic.com%3e>  WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA  USA
858-505-2780
Military & Avionics EMC Is Our Specialty

-

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Re: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

In article , Gordon,Ian 
writes
>The UKAS website includes information on uncertainty. Try the following
>2 links for general uncertainty and uncertainty in EMC in particular.

Yes, it does, but it takes a very extreme view about how uncertainty
should be allowed for in determining compliance. Other bodies have a
less stringent view. Even in Germany.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk


This message is from the IEEE Product Safety Engineering Society
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To post a message to the list, send your e-mail to emc-p...@ieee.org

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 Jim Bacher: j.bac...@ieee.org

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RE: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

Carmen
The UKAS website includes information on uncertainty. Try the following 2
links for general uncertainty and uncertainty in EMC in particular.
General:
http://www.ukas.com/Library/downloads/publications/M3003%20complete.pdf

EMC:
http://www.ukas.com/Library/downloads/publications/Lab34.pdf


Ian Gordon

> -Original Message-
> From: Carmen.Filimon [mailto:carmen.fili...@leitch.com]
> Sent: 19 August 2004 14:42
> To: 'emc-p...@ieee.org'
> Subject: Measurement uncertainty procedure
>
>
> Good morning all group,
>
> I am working with one of our local NCBs to get accredited as
> a CB Testing
> Laboratory (CBTL) recognized in the CB Scheme to conduct
> testing and issue
> CB test reports in-house under the responsibility of  this
> NCB (Testing at
> the Manufacturing Premises)
>
> An internal lab procedure for the test equipment measurement
> uncertainty is
> required. I checked with our external calibration lab and the price of
> getting the uncertainty stated in all test equipment Certificates of
> Calibration will be very high. My intention is to buy the ISO
> test equipment
> metrology standard called "ISO Guide to the expression of
> uncertainty in
> measurements" for reference, but I am not quite sure if it is the most
> helpful/handy document I can get.
>
> Did anyone else get through this process of measurement
> uncertainty? Is any
> software available for modeling the uncertainty equation for each test
> equipment used in a test lab? Any inputs/comments will be appreciated.
>
>
> Regards,
> Carmen
>

***
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RE: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

Thank you all for the feedback and helpful inputs.

Regards,
Carmen


From: owner-emc-p...@listserv.ieee.org
[mailto:owner-emc-p...@listserv.ieee.org]On Behalf Of bme...@lexmark.com
Sent: Friday, August 20, 2004 12:24 PM
To: emc-p...@ieee.org
Subject: RE: Measurement uncertainty procedure


Larry Gradin did a good paper on applicability of measurement uncertainty
to EMC laboratories at the 2003 EMC Symposium:

Kohler, J.L., Gradin, L.P., "Test laboratory position for expression of
uncertainty and confidence in measurement", Electromagnetic Compatibility,
2003 IEEE International Symposium on  ,Volume: 1 , 18-22 Aug. 2003,
Pages:292 - 297 vol.1

It should also be available upon request at:

http://www.integrity-solutions.org/useful.html

This is a good place to start to familiarize yourself with all (and I mean
all!) the standards involved with this type of work.  I will mention that
this paper also takes a much less stringent view than the UKAS, but since
Larry has been an A2LA auditor in the US, his conclusions should be well
supported in accredidation circles.

Bob.




  "Hall, Ken"
  To:   "John Woodgate"
, 
  Sent by: cc:
  owner-emc-pstc@LISTSESubject:  RE: Measurement
uncertainty procedure
  RV.IEEE.ORG


  08/19/2004 02:00 PM






Hello,

I find this URL: http://www.acemark.com/uncertaintyfrm.htm
the best.

Regards,

Ken Hall


From: owner-emc-p...@listserv.ieee.org
[mailto:owner-emc-p...@listserv.ieee.org]On Behalf Of John Woodgate
Sent: Thursday, August 19, 2004 7:59 AM
To: emc-p...@ieee.org
Subject: Re: Measurement uncertainty procedure


In article , Gordon,Ian 
writes
>The UKAS website includes information on uncertainty. Try the following
>2 links for general uncertainty and uncertainty in EMC in particular.

Yes, it does, but it takes a very extreme view about how uncertainty
should be allowed for in determining compliance. Other bodies have a
less stringent view. Even in Germany.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk


This message is from the IEEE Product Safety Engineering Society
emc-pstc discussion list.Website:  http://www.ieee-pses.org/

To post a message to the list, send your e-mail to emc-p...@ieee.org

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For help, send mail to the list administrators:

 Ron Pickard:  emc-p...@hypercom.com
 Dave Heald:   emc_p...@symbol.com

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 Jim Bacher: j.bac...@ieee.org

All emc-pstc postings are archived and searchable on the web at:

http://www.ieeecommunities.org/emc-pstc


This message is from the IEEE Product Safety Engineering Society
emc-pstc discussion list.Website:  http://www.ieee-pses.org/

To post a message to the list, send your e-mail to emc-p...@ieee.org

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For help, send mail to the list administrators:

 Ron Pickard:  emc-p...@hypercom.com
 Dave Heald:   emc_p...@symbol.com

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 Jim Bacher: j.bac...@ieee.org

All emc-pstc postings are archived and searchable on the web at:

http://www.ieeecommunities.org/emc-pstc

RE: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

Larry Gradin did a good paper on applicability of measurement uncertainty
to EMC laboratories at the 2003 EMC Symposium:

Kohler, J.L., Gradin, L.P., "Test laboratory position for expression of
uncertainty and confidence in measurement", Electromagnetic Compatibility,
2003 IEEE International Symposium on  ,Volume: 1 , 18-22 Aug. 2003,
Pages:292 - 297 vol.1

It should also be available upon request at:

http://www.integrity-solutions.org/useful.html

This is a good place to start to familiarize yourself with all (and I mean
all!) the standards involved with this type of work.  I will mention that
this paper also takes a much less stringent view than the UKAS, but since
Larry has been an A2LA auditor in the US, his conclusions should be well
supported in accredidation circles.

Bob.




  "Hall, Ken"
  To:   "John Woodgate"
, 
  Sent by: cc:
  owner-emc-pstc@LISTSESubject:  RE: Measurement
uncertainty procedure
  RV.IEEE.ORG


  08/19/2004 02:00 PM






Hello,

I find this URL: http://www.acemark.com/uncertaintyfrm.htm
the best.

Regards,

Ken Hall


From: owner-emc-p...@listserv.ieee.org
[mailto:owner-emc-p...@listserv.ieee.org]On Behalf Of John Woodgate
Sent: Thursday, August 19, 2004 7:59 AM
To: emc-p...@ieee.org
Subject: Re: Measurement uncertainty procedure


In article , Gordon,Ian 
writes
>The UKAS website includes information on uncertainty. Try the following
>2 links for general uncertainty and uncertainty in EMC in particular.

Yes, it does, but it takes a very extreme view about how uncertainty
should be allowed for in determining compliance. Other bodies have a
less stringent view. Even in Germany.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk


This message is from the IEEE Product Safety Engineering Society
emc-pstc discussion list.Website:  http://www.ieee-pses.org/

To post a message to the list, send your e-mail to emc-p...@ieee.org

Instructions:  http://listserv.ieee.org/listserv/request/user-guide.html

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For help, send mail to the list administrators:

 Ron Pickard:  emc-p...@hypercom.com
 Dave Heald:   emc_p...@symbol.com

For policy questions, send mail to:

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 Jim Bacher: j.bac...@ieee.org

All emc-pstc postings are archived and searchable on the web at:

http://www.ieeecommunities.org/emc-pstc

RE: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

I tend concur w/Mr Woodgate. Also, I have not had the pleasure of dealing with
an NCB auditor that understood the math required for uncertainty equations.

In any case, if the calibration lab is accredited, and if the instrument meets
mfr's specs, then the "base" uncertainty will "follow" directly from the mfr's
instrument spec. Additional uncertainty must be empiricaly derived, and tables
generated, that are based on the uncertainty of a formal procedure submitted
for each Type Test, for each authorized test location, and test set-up, for
each test location.

luck, 
Brian 

-Original Message- 
From: Hall, Ken [ mailto:ken_h...@hp.com] 
Sent: Thursday, August 19, 2004 11:00 AM 
To: John Woodgate; emc-p...@ieee.org 
Subject: RE: Measurement uncertainty procedure 


Hello, 

I find this URL: http://www.acemark.com/uncertaintyfrm.htm 
the best. 

Regards, 

Ken Hall 

-Original Message- 
From: owner-emc-p...@listserv.ieee.org 
[ mailto:owner-emc-p...@listserv.ieee.org]On Behalf Of John Woodgate 
Sent: Thursday, August 19, 2004 7:59 AM 
To: emc-p...@ieee.org 
Subject: Re: Measurement uncertainty procedure 


In article , Gordon,Ian  
writes 
>The UKAS website includes information on uncertainty. Try the following 
>2 links for general uncertainty and uncertainty in EMC in particular. 

Yes, it does, but it takes a very extreme view about how uncertainty 
should be allowed for in determining compliance. Other bodies have a 
less stringent view. Even in Germany. 
-- 
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory. 
The bad news is that everything is prohibited. 
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk 

 
This message is from the IEEE Product Safety Engineering Society 
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Re: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

In article , Hall, Ken  writes
>I find this URL: http://www.acemark.com/uncertaintyfrm.htm the best.

I have to say that my respected colleague is also a little militant on
uncertainty issues.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk


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RE: Measurement uncertainty procedure

[owner-emc-p...@listserv.ieee.org]

Hello,

I find this URL: http://www.acemark.com/uncertaintyfrm.htm
the best.

Regards,

Ken Hall


From: owner-emc-p...@listserv.ieee.org
[mailto:owner-emc-p...@listserv.ieee.org]On Behalf Of John Woodgate
Sent: Thursday, August 19, 2004 7:59 AM
To: emc-p...@ieee.org
Subject: Re: Measurement uncertainty procedure


In article , Gordon,Ian 
writes
>The UKAS website includes information on uncertainty. Try the following
>2 links for general uncertainty and uncertainty in EMC in particular.

Yes, it does, but it takes a very extreme view about how uncertainty
should be allowed for in determining compliance. Other bodies have a
less stringent view. Even in Germany.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk


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Re: Measurement Uncertainty Software

[Lfresearch]

Bob,

before you go round the houses on this, I suggest you talk to Trace at A2LA. 
He can tell you what a lab should really be doing IMHO, a spreadsheet is 
all you really need.

tmcintu...@a2la.org

Best regards,

Derek Walton

RE: Immunity measurement uncertainty

[Mike Hopkins]

Don't know about the others, but the ESD Association has done some work on
ESD uncertainties. I don't know if it's published yet (I don't think so) but
there is a meeting in Anaheim on Sunday the 23rd. I have some drafts, but
need to see if they are the final ones and if I can broadcast the info
yet..

Best Regards,

Mike Hopkins

-Original Message-
From: Leslie Bai [mailto:leslie_...@yahoo.com]
Sent: Thursday, September 14, 2000 4:24 PM
To: IEEE EMC-PSTC (E-mail)
Subject: Immunity measurement uncertainty 



Hello, members,

Is there anyone who can direct me to somewhere I can
find the method to derive the Immunity Test
Uncertainties, e.g. ESD, RI, EFT/B, Surge, etc.

Thanks,
Leslie

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Re: Immunity measurement uncertainty

[brent . dewitt]

You might try the IEEE EMC Symposium archives.  There have been lots of papers
over the years.  I co-authored a paper with Dan Hoolihan on radiated immunity
uncertainty for the 1997 symposium.

Regards,

Brent DeWitt
Datex-Ohmeda
Louisville, CO







Leslie Bai  on 09/14/2000 02:23:33 PM

Please respond to Leslie Bai 

To:   "IEEE EMC-PSTC \(E-mail\)" 
cc:(bcc: Brent Dewitt/US/D-O)

Subject:  Immunity measurement uncertainty





Hello, members,

Is there anyone who can direct me to somewhere I can
find the method to derive the Immunity Test
Uncertainties, e.g. ESD, RI, EFT/B, Surge, etc.

Thanks,
Leslie

__
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Re: ??? Measurement of Uncertainty

[owner-emc-p...@ieee.org]

I will hazard a pure guess.  Emphasize simply a guess based on experience. 
Below 1 GHz, the peaks and nulls occur relatively slowly as the antenna is
raised/lowered.  Above 1 GHz, you would need very precise positioning or a
slow enough travel that the spectrum analyzer/receiver could sweep all
frequencies in the span while the positioner was essentially motionless.  I
think the only way to accurately capture a peak well above 1 GHz would be to
have the antenna arm constantly moving up and down with the analyzer/receiver
in peak hold mode.   And recall that above 1 GHz people often use a relatively
high gain antenna, which means that the positioner not only has to move the
antenna up and down, but has to constantly aim the antenna main beam at the
EUT.  If you can't do all that continuously, it is better to eliminate the
reflections altogether.  



From: Y W Leung 
List-Post: emc-pstc@listserv.ieee.org
Date: Sat, 25 Jun 2005 00:50:10 +0800 (CST)
To: Pryor McGinnis , "'emc-p...@ieee.org'" 
Subject: ??? Measurement of Uncertainty




Dear Pryor,

As I know for EMC measurement uncertainty, below are the document can be used
for reference.

1. New CISPR 16-4
2. "Lab 34" publised by UKAS. ( Free download from internet )
3. A handy guide from Schaffner.com

But all of them just mentioned about radiated emission up to 1GHz Probably
you have read them.

What I am interested is why you put absorbing material between the EUT and the
Receiving anteanna, because for typical radiated emission measurement, we use
semi-anechoic chamber ( no absorber on the ground plane between EUT and the
antenna). We raised and lowered the antenna between 1-4m which is used for
obtaining the maximum reading including the reflected path from the ground
plane. There is absorber between EUT and antenna which is only in
fully-anechoic chamber which is used for radiated immunity test.

Regards,

Derek.





Pryor McGinnis  ??


Does anyone have a guideline for calculating
measurement of uncertainty above 1 GHz where absorbing
material is placed on grouond plane between EUT and
antenna per EN55011?

Pryor McGinnis


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RE: EMC Measurement Uncertainty

[emc-p...@ieee.org]

My many thanks to all who replied. I am currently taking the A2LA training and
all of your insight has been very much appreciated. 
 
Best regards, 
 
Mac

 

  _  

From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Elliott
Mac-FME001
Sent: 15 November 2005 12:33
To: emc-p...@ieee.org
Subject: EMC Measurement Uncertainty

 

Hello Colleagues, 

 

I am currently revisiting the issue of Uncertainty Budgets in our lab. 

 

Primarily looking at radiated emissions on an OATS [both ANSI method and EN
substitution], radiated immunity, and transmitter ERP / spurious emissions on
an OATS. I imagine there are a lot of people out there who have been through
the exercise. 

 

Would anyone be willing to share some examples [on or offline] or have info on
useful guidance on EMC examples / application of the GUM method? I understand
tat SINGLAS may have some useful documents with good examples, but I couldn't
find them last night. 

 

I am sure that each lab will be different, but imagine the thought process is
similar. Just want to see the thought process and make sure I am on the right
track in deterring the right contributors, Error Type, and analysis. 

 

Best regards,

 

Mac

 

 

-  This
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RE: EMC Measurement Uncertainty

[emc-p...@ieee.org]

Hi

 

Cispr A have just put out a document with a worked example for measurement
uncertainty on an OATS. I looked at it last week but do not have to hand at
present. You may have access to this through your national committee.

 

Best regards

 

John McAuley

Compliance Engineering Ireland Ltd

www.cei.ie

 

 

  _  

From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Elliott
Mac-FME001
Sent: 15 November 2005 12:33
To: emc-p...@ieee.org
Subject: EMC Measurement Uncertainty

 

Hello Colleagues, 

 

I am currently revisiting the issue of Uncertainty Budgets in our lab. 

 

Primarily looking at radiated emissions on an OATS [both ANSI method and EN
substitution], radiated immunity, and transmitter ERP / spurious emissions on
an OATS. I imagine there are a lot of people out there who have been through
the exercise. 

 

Would anyone be willing to share some examples [on or offline] or have info on
useful guidance on EMC examples / application of the GUM method? I understand
tat SINGLAS may have some useful documents with good examples, but I couldn't
find them last night. 

 

I am sure that each lab will be different, but imagine the thought process is
similar. Just want to see the thought process and make sure I am on the right
track in deterring the right contributors, Error Type, and analysis. 

 

Best regards,

 

Mac

 

 

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RE: EMC Measurement Uncertainty

[emc-p...@ieee.org]

Mac et al
Contact Phil Carter at Acemark http://www.acemark.com/uncertaintyfrm.htm.
You can purchase the XL spreadsheet that was used in UKAS document LAB 34. 

Ian Gordon




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RE: EMC Measurement Uncertainty

[emc-p...@ieee.org]

Try downloading the following uncertainty technical report form ETSI
TR102 273-4

The TR102 series has a number of specific uncertainty guides for differing
types of EMC But TR102 273-1, -2 and -4 are good for OATS
Thanks

Dennis Ward
Evaluation Engineer 
American TCB
Certification Resource for the Wireless Industry www.atcb.com 
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From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Derek Walton
Sent: Tuesday, November 22, 2005 9:31 AM
To: fme...@motorola.com
Cc: emc-p...@ieee.org
Subject: Re: EMC Measurement Uncertainty

HI Mac,

take a look at UCAS LAB 34 you will find it a great resource.

Also, Schaffner have a fee book on Measurement uncertainty. You may want
to chase a Schaffner guy down for a free copy.

Cheers,

Derek Walton

fme...@motorola.com wrote:

> Hello Colleagues,
>  
> I am currently revisiting the issue of Uncertainty Budgets in our lab.
>  
> Primarily looking at radiated emissions on an OATS [both ANSI method 
> and EN substitution], radiated immunity, and transmitter ERP / 
> spurious emissions on an OATS. I imagine there are a lot of people out 
> there who have been through the exercise.
>  
> Would anyone be willing to share some examples [on or offline] or have 
> info on useful guidance on EMC examples / application of the GUM 
> method? I understand tat SINGLAS may have some useful documents with 
> good examples, but I couldn't find them last night.
>  
> I am sure that each lab will be different, but imagine the thought 
> process is similar. Just want to see the thought process and make sure 
> I am on the right track in deterring the right contributors, Error 
> Type, and analysis.
>  
> Best regards,
>  
> Mac
>  
>  
> -  
> This message is from the IEEE Product Safety Engineering Society 
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>
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Re: EMC Measurement Uncertainty

[emc-p...@ieee.org]

HI Mac,

take a look at UCAS LAB 34 you will find it a great resource.

Also, Schaffner have a fee book on Measurement uncertainty. You may want
to chase a Schaffner guy down for a free copy.

Cheers,

Derek Walton

fme...@motorola.com wrote:

> Hello Colleagues,
>  
> I am currently revisiting the issue of Uncertainty Budgets in our lab.
>  
> Primarily looking at radiated emissions on an OATS [both ANSI method 
> and EN substitution], radiated immunity, and transmitter ERP / 
> spurious emissions on an OATS. I imagine there are a lot of people out 
> there who have been through the exercise.
>  
> Would anyone be willing to share some examples [on or offline] or have 
> info on useful guidance on EMC examples / application of the GUM 
> method? I understand tat SINGLAS may have some useful documents with 
> good examples, but I couldn't find them last night.
>  
> I am sure that each lab will be different, but imagine the thought 
> process is similar. Just want to see the thought process and make sure 
> I am on the right track in deterring the right contributors, Error 
> Type, and analysis.
>  
> Best regards,
>  
> Mac
>  
>  
> -  
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troubleshooting and test uncertainty

[emc-p...@ieee.org]

Hi All,

I have been working again and have posted a couple of new podcasts 
(Internet broadcast audio files) on my podcast site 
http://emcesd-p.com/podcast .

The latest addition is a discussion titled "Controlling Test Variables 
During Troubleshooting." The broadcast is playable on most any 
computer just left click to play in your browser or right click on the 
link to save the mp3 file. Controlling test variables during 
troubleshooting so that only one thing at a time changes is very 
important. Methods of accomplishing this and what happens when you 
don't are discussed. The article is the one dated February 17th (at 
the top of the list) on http://emcesd-p.com/podcast .

Also recently posted is the podcast dated February 14th, "Podcasting 
Tips" for those of you who are thinking of getting into this new way 
of communicating information over the Internet. Tips such as how to 
avoid a US$30,000 bill for web hosting at the end of the month are 
discussed.

I have posted a total of 11 podcasts now on various topics, with more 
to come. Let me know what topics you would like to hear about. So far 
the most popular podcast has been the January 7th podcast titled "So 
You Want to be a Consultant - Part 1."

Doug
-- 

 ___  _   Doug Smith
  \  / )  P.O. Box 1457
   =  Los Gatos, CA 95031-1457
_ / \ / \ _   TEL/FAX: 408-356-4186/358-3799
  /  /\  \ ] /  /\  \ Mobile:  408-858-4528
|  q-( )  |  o  |Email:   d...@dsmith.org
  \ _ /]\ _ / Website: http://www.dsmith.org


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RE: Window of Uncertainty

[richwo...@tycoint.com]

This brings up the question of "How much margin is necessary to account for
manufacturing variations?" And I guess that depends upon if periodic
sampling is performed or not. So, how much margin would be considered to be
acceptable if no periodic sampling is performed?

Richard Woods
Sensormatic Electronics
Tyco International



From: andy.wh...@nokia.com [mailto:andy.wh...@nokia.com]
Sent: Friday, October 31, 2003 11:37 AM
To: da...@alisonlabs.com; emc-p...@majordomo.ieee.org
Subject: RE: Window of Uncertainty



The FCC does not allow any units (sold on the marketplace) to be 'above' the
FCC limits. It is therefore prudent to ensure that 'all' finished production
units comply with the FCC limits taking in to account manufacturing build
tolerance/variability, product design tolerance/variability and final
laboratory measurement uncertainty. Which basically leads to ensuring that
your product has a designed in emissions 'margin' that will provide
compliance for units leaving the production floor.
In my experience during initial product development EMC
testing/qualification you have to pursue to attain as much 'margin' as
possible. To let a product through certification with a minimalist margin at
the beginning of marketing product launch will only make subsequent product
design changes/updates much more difficult to certify.

Andy

_
Andy White
EMC Engineer
Nokia Mobile Phones
San Diego, CA
Tel 858 831 4534
andy.wh...@nokia.com
_


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RE: Window of Uncertainty

[andy.wh...@nokia.com]

The FCC does not allow any units (sold on the marketplace) to be 'above' the
FCC limits. It is therefore prudent to ensure that 'all' finished production
units comply with the FCC limits taking in to account manufacturing build
tolerance/variability, product design tolerance/variability and final
laboratory measurement uncertainty. Which basically leads to ensuring that
your product has a designed in emissions 'margin' that will provide compliance
for units leaving the production floor.
In my experience during initial product development EMC testing/qualification
you have to pursue to attain as much 'margin' as possible. To let a product
through certification with a minimalist margin at the beginning of marketing
product launch will only make subsequent product design changes/updates much
more difficult to certify.

Andy

_
Andy White
EMC Engineer
Nokia Mobile Phones
San Diego, CA
Tel 858 831 4534
andy.wh...@nokia.com
_



From: owner-emc-p...@majordomo.ieee.org
[mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of ext Dave Grant
Sent: Thursday, October 30, 2003 5:02 PM
To: emc-p...@majordomo.ieee.org
Subject: Window of Uncertainty







Hello all,

We have been doing development of our product here and have been testing
the conducted emissions with respect to CISPR 14.1.

There is a window of uncertainty of +/- 3dBuV with respect to this test?

The testing here that has taken place so far shows that the product fails
by 0.5 dBuV at a certain frequency.

My question is, is this an Assumed Pass as this fall within the Window of
Uncertainty?

or

Is any measurement above the limit irrespective of the uncertainty error a
fail?


This is with for the European, Australasian and American markets.

Cheers ...
Dave



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Re: Window of Uncertainty

[John Woodgate]

I read in !emc-pstc that Gordon,Ian  wrote
(in ) about 'Window of Uncertainty' on Fri, 31
Oct 2003:
>Assuming you have determined an uncertainty budget for the measurement 
>then section 4 of the following UKAS document suggests what to do in 
>instances of 
>this nature.
>http://www.ukas.com/pdfs/Lab34.pdf

LAB34 is a very stringent document. It may well not be supported by
other regulatory authorities.
-- 
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk 
Interested in professional sound reinforcement and distribution? Then go to 
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!


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Re: Window of Uncertainty

[Luke Turnbull]

It would be very interesting to see what approach there is in different parts
of the world to this problem. 
 
UK laboratories have to coply with Guidance from the United Kindom
Accreditation Service, UKAS, where if the if the measurement is in the
"Uncertainty Window", we have to say "compliance cannot be determined".  See
pages 8-10 of their document "The expression of uncertainty in EMC testing"
http://www.ukas.com/pdfs/Lab34.pdf.  We essentially can only state a clear
pass when the emissions are, in the example below, 3dB below the limit, and
only state a clear fail when the emissions are 3dB above the limit.
 
Luke Turnbull

>>> Ken Javor  10/31/03 03:22am >>> 

Sorry for the pedantry, but a failure with respect to a logarithmic limit is 
given in dB, not dB with respect to the measurement unit. The failure is 
specified as a ratio relative to the limit. The measurement uncertainty is 
+/- 3 dB, not dBuV, and the outage is 0.5 dB above the limit, not 0.5 dBuV 
above the limit. If the outage really were 0.5 dBuV above the limit, that 
would TRULY be within the measurement tolerance of any rf equipment! 

IMO, if you are out, you are out. You cannot use measurement tolerances to 
rationalize an above limit condition. If you claim you are within 
measurement tolerances, I can postulate that your measurement system is 
measuring 2.9 dB low, so that a 0.5 dB above limit reading could actually be 
3.4 dB above the limit, putting you outside the tolerance band. 

Since you are very close, it would be nice to nail down just how accurate 
your measurement is. Depending on how good quality your measurement 
equipment is, I could see injecting a known signal at the spec level at the 
outage frequency into the LISN and seeing how your measurement system reads 
it. If it reads enough off that it affects your pass/fail status, then it 
is worthwhile to troubleshoot your test set up. MIL-STD-461E has detailed 
procedures for doing this. 

> From: Dave Grant < da...@alisonlabs.com> 
> Reply-To: Dave Grant < da...@alisonlabs.com> 
> Date: Fri, 31 Oct 2003 14:01:33 +1300 
> To: < emc-p...@majordomo.ieee.org> 
> Subject: Window of Uncertainty 
> 
> 
> 
> 
> 
> 
> Hello all, 
> 
> We have been doing development of our product here and have been testing 
> the conducted emissions with respect to CISPR 14.1.  <http://14.1.> 
> 
> There is a window of uncertainty of +/- 3dBuV with respect to this test? 
> 
> The testing here that has taken place so far shows that the product fails 
> by 0.5 dBuV at a certain frequency.  <http://frequency.> 
> 
> My question is, is this an Assumed Pass as this fall within the Window of 
> Uncertainty? 
> 
> or 
> 
> Is any measurement above the limit irrespective of the uncertainty error a 
> fail? 
> 
> 
> This is with for the European, Australasian and American markets. 
<http://markets.> 
> 
> Cheers ...   
> Dave 
> 
> 

RE: Window of Uncertainty

[Gordon,Ian]

Dave et al
Assuming you have determined an uncertainty budget for the measurement then
section 4 of the following UKAS document suggests what to do in instances of
this nature.
http://www.ukas.com/pdfs/Lab34.pdf
Also, if anyone is attempting to calculate an uncertainty budget for testing
the spreadsheet used in the document may be purchased from
http://www.acemark.com/uncertaintyfrm.htm
Another thing - does CISPR14 require sampling of production? If so you may
find that over time your clearance changes.


Ian Gordon
 

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Re: Window of Uncertainty

[Ken Javor]

Sorry for the pedantry, but a failure with respect to a logarithmic limit is
given in dB, not dB with respect to the measurement unit.  The failure is
specified as a ratio relative to the limit.  The measurement uncertainty is
+/- 3 dB, not dBuV, and the outage is 0.5 dB above the limit, not 0.5 dBuV
above the limit.  If the outage really were 0.5 dBuV above the limit, that
would TRULY be within the measurement tolerance of any rf equipment!

IMO, if you are out, you are out.  You cannot use measurement tolerances to
rationalize an above limit condition.  If you claim you are within
measurement tolerances, I can postulate that your measurement system is
measuring 2.9 dB low, so that a 0.5 dB above limit reading could actually be
3.4 dB above the limit, putting you outside the tolerance band.

Since you are very close, it would be nice to nail down just how accurate
your measurement is.  Depending on how good quality your measurement
equipment is, I could see injecting a known signal at the spec level at the
outage frequency into the LISN and seeing how your measurement system reads
it.  If it reads enough off that it affects your pass/fail status, then it
is worthwhile to troubleshoot your test set up.  MIL-STD-461E has detailed
procedures for doing this.

> From: Dave Grant 
> Reply-To: Dave Grant 
> Date: Fri, 31 Oct 2003 14:01:33 +1300
> To: 
> Subject: Window of Uncertainty
> 
> 
> 
> 
> 
> 
> Hello all,
> 
> We have been doing development of our product here and have been testing
> the conducted emissions with respect to CISPR 14.1.
> 
> There is a window of uncertainty of +/- 3dBuV with respect to this test?
> 
> The testing here that has taken place so far shows that the product fails
> by 0.5 dBuV at a certain frequency.
> 
> My question is, is this an Assumed Pass as this fall within the Window of
> Uncertainty?
> 
> or
> 
> Is any measurement above the limit irrespective of the uncertainty error a
> fail?
> 
> 
> This is with for the European, Australasian and American markets.
> 
> Cheers ...
> Dave
> 
> 
> ---
> This message is from the IEEE EMC Society Product Safety
> Technical Committee emc-pstc discussion list.
> 
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Re[2]: Measurement Uncertainty

[Cortland . Richmond-CC]

 Tony,
 
 Radiated immunity tests set up a situation where only the unloaded 
 field is known.  You're correct we cannot know for sure what is 
 actually getting into the EUT.  If we had to know what current was 
 actually entering the ports we would need to monitor it real-time.
 
 For radiated emissions, we maximize emissions -- within the allowable 
 configuration -- by movement of cables and peripherals.  This would 
 (if we did it properly) eliminate cable placement as an issue. We 
 would always end up with the maximum emission possible for a 
 configuration. However, that's' not so easy to forecast and results 
 depend on the person doing the test. It does NOT eliminate 
 site-to-site or lab-to-lab differences.  Using a different kind of 
 headphone cable may shift results 10 dB.  Can we call this 
 "measurement uncertainly"?  It's possible to keep this error down on a 
 given site by use of a uniform set of peripherals, but that does not 
 help those of us who need to compare our results against those 
 gathered elsewhere.
 
 Regards,
 
 Cortland
 
 The above does not reflect opinions or policies of my employer


__ Reply Separator _
Subject: Re: Measurement Uncertainty
Author:  Tony Fredriksson  at internet
List-Post: emc-pstc@listserv.ieee.org
Date:1/13/97 10:00


  
Jon,
  
Thanks for the info on the NIST Technical Note.  Looks like I need 
to get a copy and undertand it.
  
It is good to know that Curtis-Straus estimates uncertainty.
I am particularly interested in the EMC side of the discussion 
and have a couple of questions:
  
1.  In the case of Immunity, I suppose the lab would only be able
 to estimate uncertainty of the disturbance from the test generator. 
 Is that correct?  Wouldn't the loading of the signal source from 
 EUT have a dramatic affect on the test result uncertainty?  If this 
 is the case, how is it factored in such that uncertainty of the end 
 result is quantified to any practical degree?
  
2.  In the case of EMI, what is the range of uncertainty that one of
 your tests can provide?  I would think it is a function of frequency. 
 Does it attempt to take into account the uncertainty due to a change 
 in cable or preripheral placement from one setup to the next of the 
 exact same EUT?  If so, how was that uncertainty derived?
  
The reason that I am curious about this is that I have seen some cables 
so hot (headphone on a CD ROM port for example) that moving them an
inch or two in either direction can vary emissions by 10dB or more.  That 
would seem to be quite unpredicatable by statistical methods and would 
seem to dwarf any uncertainties from other sources.  This even considers 
test setup methods that have been designed to minimize test variation 
(such as ANSI C63.4).
  
I can see that using the lab's stated uncertainty in combination with 
a CISPR 16 style sampling test would be a significant improvement over 
other procedures.
  
Thanks,
tony_fredriks...@netpower.com
  
 --
From: Jon D Curtis
To: Barge, Michael
Cc: 'emc-p...@ieee.org'
Subject: Re: Measurement Uncertainty 
List-Post: emc-pstc@listserv.ieee.org
Date: Monday, January 13, 1997 9:14AM
  
In the USA, NIST has published Technical Note 1297 1994 ed. "Guidelines 
for Evaluating and Expressing the Uncertainty of NIST measurement 
results."
  
Our NVLAP accreditation requires us to estimate uncertainties in our test 
reports.  Every Curtis-Straus EMC or Telco test report contains 
uncertainty
estimates.  As to the passing margin, passing is passing and failing is 
failing.  Before you take measurement uncertainty into the limit, first 
consider that technique has improved (and therefore unceratinty is lower) 
than it was when the limits were formulated.  Second consider that the 
regulators which accepted the limit were well aware that uncertainty 
exists and in all likelyhood accounted for it in their choice of the 
limit.
  
That said, I advise all clients who are within our uncertainty of the 
limit (but passing), that they should be aware that they may fail next 
time.
If they are at the prototype stage, or building a product which will 
become the platform for future development, it is advisable to seek a 
larger margin.
  
Jon D. Curtis, PE
  
Curtis-Straus LLC j...@world.std.com 
One-Stop Laboratory for EMC, Product Safety and Telecom 
527 Great Roadvoice (508) 486-8880 
Littleton, MA 01460   fax   (508) 486-8828 
http://world.std.com/~csweb
On Fri, 10 Jan 1997, Barge, Michael wrote:
  
>
>
> FROM:  michael_ba...@atk.com
>
> Item Subject:  Measurement Uncertainty 
&g

Re[2]: Measurement Uncertainty

[Cortland . Richmond-CC]

 Nice post, Gabriel.  I really liked the reminder that what we call 
 precision doesn't necessarily mean something.  One dB is about 10 
 percent.  That's not really very good -- but for RF it's about what we 
 can get, generally.
 
 On the other hand, knowing the precise frequency -- down to KHz -- is 
 often helpful, especially where one must discrimina
 te from among several different sources close to each other
 .

Cheers,
 

 
Cortland
 


__
__
__
 Reply Separator _
Subject:
e: Measurement Uncertainty
Author:  Gabriel Roy/HNS  at internet
List-Post: emc-pstc@listserv.ieee.org
Date:1/13/97 13:18


Michael Barge asks: 
  
>(1)  Do most labs report an uncertainty measurement in the test report, on 
the data sheet, on a certificate of compliance?
>(2)  How did you generate the measurement of uncertainty for emission 
tests? For immunity tests?
  
> AND MOST IMPORTANTLY
  
>(3)  What do you tell the customer when he is below the limit by less than 
the measurement uncertainty? When he is above by less?
  
 
  
Well Michael, the lab that I do most of my business with does not report the 
measurement of uncertainty in my reports, and I am very satisfied that they do 
not. 
  
I certainly do not include a value in the declaration of conformity, nor do I 
intend to ever. It would be ludicrous for our declaration to  state that we are 
96% confident that we comply. Either we comply or we don't. 
  
In my opinion, the measurement uncertainty is unnecessary and its inclusion can 
only lead to stricter limits being enforced. Enforced by the unknowing in the 
beginning and eventually by decree "because that's the way it's done now".
  
I have delt with a lab that included the measurement of uncertainty in their 
report, it was 2 dB. And if we were closer than 2 dB to the limit they 
considered it a failure. Evidently, because their instrumentation was not 
sufficiently accurate to give them measurements that they could be confident 
in, our equiment suffered. I don't use that lab any more. 
  
My contention is that this measurement uncertainty is a lot of hog wash. The 
same as reporting frequencies to three decimal places and dB's to two decimal 
places. That's missing the original intent of the requirement, which was to not 
interfere with other's communications. The method used originally was a radio 
receiver, with front mounted rotary switches that dropped attennuation pads 
into the receive circuit (i.e. see the older Rhode & Schartz used by VDE).  The 
level was read as the amount of attennuation needed to bring the incoming 
signal to a null. Thus one either passed or failed, with no reguard to 
fractions of dBs. As far as the frequency was concerned, it was read off a log 
scale similar to a radio tuner (before digital readouts), and one was lucky to 
get the reading down to 10 MHz in the upper scale. 
  
It wasn't until the introduction of the spectrum analyzer by HP around 1979-80 
that we could get readings down to three decimal places. Why did HP pick three? 
If they had picked five, lab assistants and engineers would now be blindly 
writing values down to five decimal places. It doesn't make it more accurate, 
it only gives a feeling of being very scientific. One can get the diameter of a 
circle by using 3.14 for pie (?) just as well as using pie to 27 decimal 
places. 
  
Proponents of the measurement uncertainty practice should take a look at the way
that the VDE engineers write down their measurements. They have a sheet of log 
paper and a pencil. They put the point of the pencil ot their best approximation
of frequency and dB level on the log paper and make a large dot. They then pull 
down on the dot to make a tail, so that it will be easier to identify. Again, 
you either pass or you fail. The size of the pencil dot and the way the VDE 
engineer places the pencil on the paper greatly overshadows any measurement 
uncertainty there might have been in the system. 
  
One final comment, our instumentation has always been accurate, and we have 
always known how acurate it is. The accuracy is specified by the manufacturer 
and the instrumentation is kept within calibration. Also the regulatory bodies 
have been satisfied with that process. I have a hunch, and it is only a hunch, 
that this measurement uncertainty was developed by an EMI engineer who had no 
way of coming up with the reason for getting different measurements at 
different sites. The old "It passes at home by 2 dB and fails at the lab by 3 
dB" syndrome. So in an attemp to explain EMI in logical terms (!!!) to his 
boss, he lumpted the variations of all factors (cable losse

[PSES] Uncertainty in ESD testing

[Douglas Smith]

I recently replied to another post and mentioned uncertainty in ESD 
testing. I thought it would be good to post it separately to start a wider 
discussion, so here we go:
In ESD testing, the poor specification of the simulator in standards, like 
IEC 61000-4-2 [tel:61000-4-2] , leads to uncertainty (that one cannot 
calculate) that far exceeds any uncertainty calculation one could make on 
ESD testing. Until we fix the standards, uncertainty calculation for ESD 
testing is meaningless. What is needed is a maximum di/dt limit everywhere 
on the current waveform and a radiation spec on the simulator. And this is 
only for contact discharge. For air discharge, the large uncertainty of the 
discharge itself will likely dominate unless hundreds of discharges are 
used at each point to reach statistical significance.


Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 
Email: d...@dsmith.org Website: http://dsmith.org


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[PSES] LISN Calibration Measurement Uncertainty

[Mac Elliott]

All, 
We are interested in doing some in-house LISN calibrations (impedance 
verification only using network analyzer) and need to develop an uncertainty 
budget. 
Does anyone happen to have a budget you could share with us? We will go through 
the exercise of calculating ourself but if there is one out there would 
appreciate it if you could share.
Have a great day
Mac Elliott

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Heisenberg's uncertainty principle and circuits

[Douglas C. Smith]

Hi All,

Often, when making measurements, the loading on the signal by the
measurement is not taken into account. In addition to probe bandwidth,
its input impedance is just as important. Many high performance probes
on the market are useable to only a fraction of their stated bandwidth
because of very low input impedances, and this includes many FET probes.
That spec of less than a picofarad of input capacitance seems to imply
low circuit loading, but this is not always the case.

This month at http://www.dsmith.org the Technical Tidbit is on error
caused by probe loading. It is a real eye opener. But this is just the
"tip of the iceberg" on measurement limitations.

Doug
-- 
---
___  _   Doug Smith
 \  / )  P.O. Box 1457
  =  Los Gatos, CA 95031-1457
   _ / \ / \ _   TEL/FAX: 408-356-4186/358-3799
 /  /\  \ ] /  /\  \ Mobile:  408-858-4528
|  q-( )  |  o  |Email:   d...@dsmith.org
 \ _ /]\ _ / Website: http://www.dsmith.org
---

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RE: Radiated Emission Testing uncertainty

[owner-emc-p...@listserv.ieee.org]

Morning Geetha,

 

Although it certainly makes sense to measure the uncertainty of measurements
(?!?)

it remains the question what measurements are exactly evaluated.

 

The CISPR 16-4 evaluation is made using a standard EUT ( antenna used during

site attenuation measurements) , standard cable and standard equipment, which
on their

turn are regularly calibrated and of which uncertainty is known. A simple
addition (??)

is required to calculate the total uncertainty as you will find a very
detailed example

in CISPR 16-4.

 

You will also note that the Site attenuation (+/- 4dB)  is the dominant factor
in the calculation and

if your antenna is 2 dB off or your measurement receiver 1dB  out of CAL, will
NOT have

a major impact on the result ( unless you have a VERY smooth site)

 

So now you know that your lab can measure ONE type of EUT (send antenna)  with
the claimed

uncertainty. This says not much in how accurate YOUR EUT will be measured.

YOUR EUTand it’s cabling  is part of the test chain, and unlike a simple
voltmeter to a calibrator, the interface

>from EUT  to the emission test SET UP  is unknown, and at its best accurately
documented.

 

What you do know howver, is that any measurement error (can any emission
measurement 

 error actually be called an error ??) is not caused by the equipment and room
that the

 measurement was made in.

 

I will not disagree with any of you that recording measurement accuracy is a
relevant

parameter, but one needs to know it’s meaning and even more, the limitations
of such a figure.

 

I definitely disagree with you that measurement uncertainty is a key element
in 

emission measurements.  The arguments as delivered in this topic earlier

are of much more relevance to the final result as uncertainty.

 

 

 

 

Gert Gremmen

 

  _  

From: owner-emc-p...@listserv.ieee.org 
mailto:owner-emc-p...@listserv.ieee.org] On Behalf Of Taylor, Michael
Sent: woensdag 23 maart 2005 16:30
To: Geetha Balasubramanian; Grasso, Charles; Bob Richards ;
owner-emc-p...@listserv.ieee.org ; EMC-PSTC@LISTSERV.IEEE.ORG 
Subject: RE: Radiated Emission Testing uncertainty

 

I have watched this subject unfold with interest.  However it seems the one
key element at the heart of this interchange has been left out of the
discussion.  That being Uncertainty of measurement.  

We are assuming that the lab in question did perform signal maximization of
the cables and did set up the EUT correctly.

The purpose of CISPR 16-4 (2002) " Uncertainty in EMC Measurements",  was to
help bring the issue of measurement deviations between different measurement
sites into some kind of relational understanding.  In Paragraph 4.1 it states:

".. the expanded measurement uncertainty for the test lab shall be stated
in the test report"

This is the only way a customer has to evaluate whatever margin to limit
exists with that particular product.

To the best of my understanding most labs do not state their uncertainty of
measurement for reasons best known to them.

When I send out a product that I can't do in my lab I insist on adherence to
CISPR 16-4. If the uncertainty of measurement is not included in the report
its of little value to me.

 

If more customers insisted on this information (backed up by real numbers in
the calculations) these sort of problems would resolve themselves in short
order. 

 

Just one guys opinion.

Michael Taylor - NCE

Loveland, CO

 

  _  

From: owner-emc-p...@listserv.ieee.org 
mailto:owner-emc-p...@listserv.ieee.org] On Behalf Of Geetha Balasubramanian
Sent: Tuesday, March 22, 2005 8:52 AM
To: Grasso, Charles; 'Bob Richards '; 'owner-emc-p...@listserv.ieee.org ';
'EMC-PSTC@LISTSERV.IEEE.ORG '
Subject: RE: Radiated Emission Testing

Hi Gurus,

 

   As per the US lab report, the frequency at which the device had
minimum pass margin is 68 MHz. At 68 MHz in vertical polarisation the margin
is 4.7 dB & in horizontal polarisation the margin is 1.6 dB. Measurable
emissions were found only in 40 , 43, 52.38, 64 & 68 MHz.

  But as per the Taiwan lab report no measurable emission is found
>from the device at the above frequencies. The device failed in 122.61 MHz at
horizontal polarisation. 

  There are 2 clock sources in the device, one runs at 12 MHz and the
other runs at 4 MHz. Frequencies showing up in the US lab report are atleast
the harmonics of these 2 frequencies. But frequencies mentioned in the Taiwan
lab report are looking funny (111.27, 135.3, 285.69 MHz. etc.)

   US lab tested in OATS but the TAIWAN lab tested in a anechoic
chamber. I heard that chambers are not the correct way to measure ( always the
results will be wrong) that is why FCC never accepts chamber measurement. Is
it so? 

Thanking you all for the time & efforts spent on this.

 

Thanking you all in anticipation

 

Geetha

"Grasso, Charles"  wrot

RE: Radiated Emission Testing uncertainty

[owner-emc-p...@listserv.ieee.org]

I have watched this subject unfold with interest.  However it seems the one
key element at the heart of this interchange has been left out of the
discussion.  That being Uncertainty of measurement.  
We are assuming that the lab in question did perform signal maximization of
the cables and did set up the EUT correctly.
The purpose of CISPR 16-4 (2002) " Uncertainty in EMC Measurements",  was to
help bring the issue of measurement deviations between different measurement
sites into some kind of relational understanding.  In Paragraph 4.1 it states:
".. the expanded measurement uncertainty for the test lab shall be stated
in the test report"
This is the only way a customer has to evaluate whatever margin to limit
exists with that particular product.
To the best of my understanding most labs do not state their uncertainty of
measurement for reasons best known to them.
When I send out a product that I can't do in my lab I insist on adherence to
CISPR 16-4. If the uncertainty of measurement is not included in the report
its of little value to me.
 
If more customers insisted on this information (backed up by real numbers in
the calculations) these sort of problems would resolve themselves in short
order. 
 
Just one guys opinion.
Michael Taylor - NCE
Loveland, CO

  _  

From: owner-emc-p...@listserv.ieee.org 
mailto:owner-emc-p...@listserv.ieee.org] On Behalf Of Geetha Balasubramanian
Sent: Tuesday, March 22, 2005 8:52 AM
To: Grasso, Charles; 'Bob Richards '; 'owner-emc-p...@listserv.ieee.org ';
'EMC-PSTC@LISTSERV.IEEE.ORG '
Subject: RE: Radiated Emission Testing


Hi Gurus,
 
   As per the US lab report, the frequency at which the device had
minimum pass margin is 68 MHz. At 68 MHz in vertical polarisation the margin
is 4.7 dB & in horizontal polarisation the margin is 1.6 dB. Measurable
emissions were found only in 40 , 43, 52.38, 64 & 68 MHz.
  But as per the Taiwan lab report no measurable emission is found
>from the device at the above frequencies. The device failed in 122.61 MHz at
horizontal polarisation. 
  There are 2 clock sources in the device, one runs at 12 MHz and the
other runs at 4 MHz. Frequencies showing up in the US lab report are atleast
the harmonics of these 2 frequencies. But frequencies mentioned in the Taiwan
lab report are looking funny (111.27, 135.3, 285.69 MHz. etc.)
   US lab tested in OATS but the TAIWAN lab tested in a anechoic
chamber. I heard that chambers are not the correct way to measure ( always the
results will be wrong) that is why FCC never accepts chamber measurement. Is
it so? 
Thanking you all for the time & efforts spent on this.
 
Thanking you all in anticipation
 
Geetha

"Grasso, Charles"  wrote:

Hi Bob,

Don't you ALWAYS maximize cables. I found that
with cable maximization my test repeatabilty
improved dramatically.

HAs cable maximization fallen out of favour?



From: owner-emc-p...@listserv.ieee.org
To: EMC-PSTC@LISTSERV.IEEE.ORG
Sent: 3/22/2005 6:58 AM
Subject: Re: Radiated Emission Testing

It is not an unusual occurance. This is one good
reason why you want a good margin under the limit.
Most people like to see a margin of at least 6dB.

One variable is the site itself. A good OATS is the
best. Sites can have up to 4dB variation from
theoretical, and one chamber I've been involved with
had a problem in the 50-60MHz range, where it was
3.9dB out -- barely acceptable. You might want to ask
to see the site attenuation data from the labs
involved.

There can ! also be a big difference depending on the
measuring distance. Some standards allow extrapolation
to be done when measuring at some distance other than
the distance spelled out in the standard, but looking
at the difference in theoretical site attenuation
between a 3m and a 10m site will show that linear
extrapolation is not accurate through much of the
frequency range.

It is not unusual to get different results at the SAME
lab, depending on the person conducting the test. Like
it or not, some technicians are better or more
diligent when it comes to maximizing the emission by
playing with cable placement. When I worked at a
compliance test lab, I ticked off a few clients when
their product was passing by 2dB until I moved the
cables and rescanned only to fail them by 1dB.

Bob Richards
Square D.

--- Geetha Balasubramanian 
wrote:
> Dear Experts,
>
> One of our products had b! een tested by an
> accredited lab at US on May 2004 and found to be
> compliant with FCC, CE & VCCI. We started mass
> manufacturing the product and it is being sold in
> the US, Europe & Japan markets for the past 6
> months. Then came a requirement for that product in
> Taiwan market. Since the May 2004 testing at the US
> lab was not run in a BSMI approved system it became
> necessary for us to retest the same product. This
> time the product

NSA measurement and its uncertainty

[KC CHAN [PDD]]

Hi all

I just got a tough question from our auditor about NSA and uncertainty.  He 
asked if we will include the uncertainty into our Normalized Site Attenuation 
measurement or not.

If we include the uncertainty of NSA measurement, it is impossible for us to 
ensure it is within the +/- 4dB with 95% CL.

I would like to seek comment form the expertise if it is necessary to include 
the uncertainty when we do the NSA measurement.

Thank you
KC Chan


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[PSES] Uncertainty Measurement Calculations [General Use]

[Price, Andrew (Leonardo, UK)]

Hi all

Can anyone shed some light on working up the Uncertainty Measurement 
Calculations based on UKAS Lab34 for MIL-STD-461 CS115 and CS116.
I need to show the uncertainty values for these tests as follows:
Uncertainty in overall test level = 2.2dB, Uncertainty in time measurement = 
1.91%, Uncertainty in Amplitude measurement = 0.82%

MIL-STD-461 defines
4.3.1 Measurement tolerances.
Unless otherwise stated for a particular measurement, the tolerance shall be as 
follows:
a. Distance: ±5%
b. Frequency: ±2%
c. Amplitude, measurement receiver: ±2 dB
d. Amplitude, measurement system (includes measurement receivers, transducers, 
cables,
and so forth): ±3 dB
e. Time (waveforms): ±5%
f. Resistors: ±5%
g. Capacitors: ±20%

Also what equipment do I include, ie. DSO, Current Probes, Calibration Jig, 
Transient Generator, etc. and what do I exclude

I hope there are some group members that have already done this process and can 
help.

Regards
Andy


LEONARDO
 Land & Naval Division
 Andrew Price
 Land & Naval Defence Electronics Division
 Prinicpal Environmental Engineer (EMC)

 Leonardo MW Ltd
 Sigma House, Christopher Martin Rd, Basildon SS14 3EL, UK
 Tel  EMC LAB : +44 (0)1268 883308
 Mobile: +44 (0)7507 854888
 
andrew.p.pr...@leonardocompany.com<mailto:andrew.p.pr...@leonardocompany.com>
 leonardocomapany.com

HELICOPTERS / AERONAUTICS / ELECTRONICS, DEFENCE AND SECURITY SYSTEMS / SPACE

P Please consider the environment before printing this email.



Leonardo MW Ltd
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 
3EL
A company registered in England & Wales.  Company no. 02426132

This email and any attachments are confidential to the intended
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[PSES] Measurement Uncertainty Above 18 GHz

[Grace Lin]

Dear Members,

Is it reasonable to request measurement uncertainty (MU) above 18 GHz?
CISPR 16-4-2 Edition 2.1 seems only up to 18 GHz.

Is there any standard that addresses MU above 18 GHz?

Is it reasonable to claim that MU is not applicable for radiated
disturbance / emission measurement above 18 GHz as there is no site
validation standard available for frequency above 18 GHz?

Thank you very much and I look forward to hearing from you.

Best regards,
Grace Lin

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Re: [PSES] Uncertainty in ESD testing

[Ken Javor]

I made this point (in a less erudite manner) within the TSWG when we were
drafting MIL-STD-461G, but with a requirement such as RE102 already on the
books, we are all well acquainted with uncertainty and unafraid of it...

Ken Javor
Phone: (256) 650-5261



From: Douglas Smith 
Reply-To: Douglas Smith 
Date: Fri, 1 Sep 2017 09:37:45 -0700
To: 
Subject: [PSES] Uncertainty in ESD testing


I recently replied to another post and mentioned uncertainty in ESD testing.
I thought it would be good to post it separately to start a wider
discussion, so here we go:

In ESD testing, the poor specification of the simulator in standards, like
IEC 61000-4-2  , leads to uncertainty (that one cannot
calculate) that far exceeds any uncertainty calculation one could make on
ESD testing. Until we fix the standards, uncertainty calculation for ESD
testing is meaningless. What is needed is a maximum di/dt limit everywhere
on the current waveform and a radiation spec on the simulator. And this is
only for contact discharge. For air discharge, the large uncertainty of the
discharge itself will likely dominate unless hundreds of discharges are used
at each point to reach statistical significance.

Doug Smith
Sent from my iPhone
IPhone:  408-858-4528
Office:702-570-6108
Email: d...@dsmith.org
Website: http://dsmith.org

-


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Re: [PSES] Uncertainty in ESD testing

[John Woodgate]

As long as your lack of fear isn't because you are not aware of the
situation..
 
With best wishes John Woodgate
3 Bramfield Road East, RAYLEIGH Essex SS6 8RG UK OOO - Own Opinions Only
 <http://www.jmwa.demon.co.uk/> www.jmwa.demon.co.uk J M Woodgate and
Associates 
 
Beware averages! They hide or discard data, and may distort it (them?).
 
 
From: Ken Javor [mailto:ken.ja...@emccompliance.com] 
Sent: Friday, September 1, 2017 7:39 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Uncertainty in ESD testing
 
I made this point (in a less erudite manner) within the TSWG when we were
drafting MIL-STD-461G, but with a requirement such as RE102 already on the
books, we are all well acquainted with uncertainty and unafraid of it...

Ken Javor
Phone: (256) 650-5261


  _  

From: Douglas Smith mailto:d...@emcesd.com> >
Reply-To: Douglas Smith mailto:d...@emcesd.com> >
Date: Fri, 1 Sep 2017 09:37:45 -0700
To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG> >
Subject: [PSES] Uncertainty in ESD testing


I recently replied to another post and mentioned uncertainty in ESD testing.
I thought it would be good to post it separately to start a wider
discussion, so here we go:

In ESD testing, the poor specification of the simulator in standards, like
IEC 61000-4-2  , leads to uncertainty (that one cannot
calculate) that far exceeds any uncertainty calculation one could make on
ESD testing. Until we fix the standards, uncertainty calculation for ESD
testing is meaningless. What is needed is a maximum di/dt limit everywhere
on the current waveform and a radiation spec on the simulator. And this is
only for contact discharge. For air discharge, the large uncertainty of the
discharge itself will likely dominate unless hundreds of discharges are used
at each point to reach statistical significance.

Doug Smith
Sent from my iPhone
IPhone:  408-858-4528
Office:702-570-6108
Email: d...@dsmith.org <mailto:d...@dsmith.org> 
Website: http://dsmith.org

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Re: [PSES] Uncertainty in ESD testing

[Patrick]

@Ken.Javor - I had to look this up...  "erudite".The act of looking it
up showed that I am not!  Ha!

Thanks again for the Friday humor!
-Patrick

On Fri, Sep 1, 2017 at 12:39 PM, Ken Javor 
wrote:

> I made this point (in a less erudite manner) within the TSWG when we were
> drafting MIL-STD-461G, but with a requirement such as RE102 already on the
> books, we are all well acquainted with uncertainty and unafraid of it...
>
> Ken Javor
> Phone: (256) 650-5261
>
>
> --
> *From: *Douglas Smith 
> *Reply-To: *Douglas Smith 
> *Date: *Fri, 1 Sep 2017 09:37:45 -0700
> *To: *
> *Subject: *[PSES] Uncertainty in ESD testing
>
>
> I recently replied to another post and mentioned uncertainty in ESD
> testing. I thought it would be good to post it separately to start a wider
> discussion, so here we go:
>
> In ESD testing, the poor specification of the simulator in standards, like
> IEC 61000-4-2  , leads to uncertainty (that one cannot
> calculate) that far exceeds any uncertainty calculation one could make on
> ESD testing. Until we fix the standards, uncertainty calculation for ESD
> testing is meaningless. What is needed is a maximum di/dt limit everywhere
> on the current waveform and a radiation spec on the simulator. And this is
> only for contact discharge. For air discharge, the large uncertainty of the
> discharge itself will likely dominate unless hundreds of discharges are
> used at each point to reach statistical significance.
>
> Doug Smith
> Sent from my iPhone
> IPhone:  408-858-4528 <(408)%20858-4528>
> Office:702-570-6108 <(702)%20570-6108>
> Email: d...@dsmith.org
> Website: http://dsmith.org
>
> -
> 
>
> 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) <http://www.ieee-pses.org/list.html>
> <http://www.ieee-pses.org/list.html>
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>
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> Scott Douglas 
> Mike Cantwell 
>
> For policy questions, send mail to:
> Jim Bacher  
> David Heald 
>
> -
> 
>
> 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) <http://www.ieee-pses.org/list.html>
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> Jim Bacher <j.bac...@ieee.org>
> David Heald <dhe...@gmail.com>
>



-- 
//
Patrick

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Re: [PSES] Uncertainty in ESD testing

[John Woodgate]

I once kidded someone that it was a mineral, a sort of orange-blue colour, and 
nearly as hard as diamond.
 
With best wishes John Woodgate
3 Bramfield Road East, RAYLEIGH Essex SS6 8RG UK OOO – Own Opinions Only
 <http://www.jmwa.demon.co.uk/> www.jmwa.demon.co.uk J M Woodgate and 
Associates 
 
Beware averages! They hide or discard data, and may distort it (them?).
 
 
From: Patrick [mailto:conwa...@gmail.com] 
Sent: Friday, September 1, 2017 8:25 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Uncertainty in ESD testing
 
@Ken.Javor - I had to look this up...  "erudite".The act of looking it up 
showed that I am not!  Ha! 
 
Thanks again for the Friday humor!
-Patrick
 
On Fri, Sep 1, 2017 at 12:39 PM, Ken Javor mailto:ken.ja...@emccompliance.com> > wrote:
I made this point (in a less erudite manner) within the TSWG when we were 
drafting MIL-STD-461G, but with a requirement such as RE102 already on the 
books, we are all well acquainted with uncertainty and unafraid of it...

Ken Javor
Phone: (256) 650-5261  



  _  

From: Douglas Smith mailto:d...@emcesd.com> >
Reply-To: Douglas Smith mailto:d...@emcesd.com> >
Date: Fri, 1 Sep 2017 09:37:45 -0700
To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG> >
Subject: [PSES] Uncertainty in ESD testing


I recently replied to another post and mentioned uncertainty in ESD testing. I 
thought it would be good to post it separately to start a wider discussion, so 
here we go:

In ESD testing, the poor specification of the simulator in standards, like IEC 
61000-4-2  , leads to uncertainty (that one cannot calculate) 
that far exceeds any uncertainty calculation one could make on ESD testing. 
Until we fix the standards, uncertainty calculation for ESD testing is 
meaningless. What is needed is a maximum di/dt limit everywhere on the current 
waveform and a radiation spec on the simulator. And this is only for contact 
discharge. For air discharge, the large uncertainty of the discharge itself 
will likely dominate unless hundreds of discharges are used at each point to 
reach statistical significance.

Doug Smith
Sent from my iPhone
IPhone:  408-858-4528  
Office:702-570-6108  
Email: d...@dsmith.org <mailto:d...@dsmith.org> 
Website: http://dsmith.org

-


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<emc-p...@ieee.org <mailto:emc-p...@ieee.org> >
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-- 
//
Patrick
-

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Re: [PSES] Uncertainty in ESD testing

[Ken Javor]

I neglected to say in my previous post the obvious: we were discussing
implementation of CS118, the new ESD requirement.  Regarding charging in
where angels fear to tread, MIL-STD-461 has since 1993 imposed measurement
system integrity checks, wherein a known stimulus is applied to the
transducer and the response at the EMI receiver is verified to be within +/-
3 dB, or the measurement system needs adjustment.

For RE102, the radiated electric field requirement, that injection is always
less the actual transducer, i.e., the antenna. The antenna is disconnected
and the injection is made where the antenna would connect.

This approach obeys a fundamental rule of life: ³If you can¹t stand the
answer, don¹t ask the question.²

Ken Javor
Phone: (256) 650-5261



From: John Woodgate 
Reply-To: John Woodgate 
Date: Fri, 1 Sep 2017 19:47:18 +0100
To: 
Subject: Re: [PSES] Uncertainty in ESD testing

As long as your lack of fear isn't because you are not aware of the
situationŠ.
 

With best wishes John Woodgate
3 Bramfield Road East, RAYLEIGH Essex SS6 8RG UK OOO ­ Own Opinions Only
www.jmwa.demon.co.uk <http://www.jmwa.demon.co.uk/>  J M Woodgate and
Associates 
 
Beware averages! They hide or discard data, and may distort it (them?).
 
 

From: Ken Javor [mailto:ken.ja...@emccompliance.com]
Sent: Friday, September 1, 2017 7:39 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Uncertainty in ESD testing
 
I made this point (in a less erudite manner) within the TSWG when we were
drafting MIL-STD-461G, but with a requirement such as RE102 already on the
books, we are all well acquainted with uncertainty and unafraid of it...

Ken Javor
Phone: (256) 650-5261


From: Douglas Smith 
Reply-To: Douglas Smith 
Date: Fri, 1 Sep 2017 09:37:45 -0700
To: 
Subject: [PSES] Uncertainty in ESD testing


I recently replied to another post and mentioned uncertainty in ESD testing.
I thought it would be good to post it separately to start a wider
discussion, so here we go:

In ESD testing, the poor specification of the simulator in standards, like
IEC 61000-4-2  , leads to uncertainty (that one cannot
calculate) that far exceeds any uncertainty calculation one could make on
ESD testing. Until we fix the standards, uncertainty calculation for ESD
testing is meaningless. What is needed is a maximum di/dt limit everywhere
on the current waveform and a radiation spec on the simulator. And this is
only for contact discharge. For air discharge, the large uncertainty of the
discharge itself will likely dominate unless hundreds of discharges are used
at each point to reach statistical significance.

Doug Smith
Sent from my iPhone
IPhone:  408-858-4528
Office:702-570-6108
Email: d...@dsmith.org
Website: http://dsmith.org

-


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