Hi Derek,
I read Ken Wyatt's e-mail plus Ghery Pettit's Blog link and find them
very informative with insightful tidbits of knowledge that could be
helpful to the reader who uses 3^rd party EMC test labs or even
in-house original equipment manufacturer (OEM) test labs.
Years ago when I worked for a major OEM, an engineering director
requested that I audit some of the EMC test labs being used by 3^rd
party hardware firms from which we procured hardware that was
integrated into a product system that the OEM marketed for sale. The
audits were initiated due to the quality of some of the test reports
we reviewed. The hardware supplier remained on the list of approved
hardware suppliers if the 3^rd party lab they used agreed to a
requested audit and passed (or deleted from the list if they declined
or failed). So Ghery's blog is very useful for the things to be aware
of when choosing a test lab or if you're a major OEM with clout, even
requesting a lab audit.
And the statements in Ken's e-mail are very important points to be
aware of for anyone using any EMC test lab or looking into choosing an
EMC test lab. Matter of fact, I personally have witnessed all of the
deficiencies Ken points out in his e-mail. I like what he wrote and
agree with it because I have seen it in the various labs I've worked
in or have visited over the years. And if I had any authority or
influence over the lab quality system of these labs, the deficiencies
I saw were eventually resolved. I believe most labs do a pretty good
job, but statistically there will always be deficiencies until an
auditor or a knowledgeable person speaks up.
You'll probably put me on the same side as Ken and Ghery.
But that's okay, I'll be glad to be there.
Manny Barron
*From:*DEREK WALTON
[mailto:[email protected]]
*Sent:* Wednesday, April 17, 2019 8:47 PM
*To:* [email protected]
*Subject:* Re: [PSES] Question re: Measuring a signal in a noisy
environment
Whoah Ed,
you just landed along side Ken and Ghery!
I have to strongly oppose some of your views on what the test lab
should or shouldn’t Know/do. Wow, have you any idea of the variety of
equipment that roles in the lab door, and the complexity of it? NO, it
is NOT the labs job to understand the EUT, other than how to interpret
the standard so it can be tested. It is totally unreasonable to expect
a test person to muse the subtleties of sub micron silicon one day
then the ramifications of 10,000 psi hydraulic pumps the next. I doubt
few could listening in.
Having had the luxury of “visiting" well over 350 labs around the
globe over the last 23 years I’ve gathered quite a bit of insight on
lab operations and their clients. I happen to have worked in one for
40 years and owned one or two for 30+ years. So much of the email
thread is huff and puff. IN the sales world it would be called FAD:
fear and disillusionment.
Lets set some records straight:
The majority of labs do a superb job with all the constraints they are
under.
An ISO 17025 assessment cannot prevent mistakes, but it does make
provisions for just about all foreseeable, and quite a few
unforeseeable problems.
Everyone can have a bad day: that includes test engineers/technicians.
Technology evolves, and what’s true at one point may not be true
sometime later. Unless everything is checked to the nth degree, EVERY
time, things will escape notice.
For all those calling out check after check, I bet under the same
breath they are complaining about the cost of testing!
And for the record, those critical of overseas test labs should go and
pay a visit: most times they are careful to incredible levels running
tests.
If a manufacture brings a device in for testing, no-one, that’s NO-ONE
knows it better than he does. He has a responsibility to understand
the testing his device will be subjected to and its behavior, heck,
he’s supposed to have designed the device to pass the test! That
includes support equipment too!
A lab should help someone who’s a novice in the EMI field to avoid
pitfalls, that’s professional curtesy. It’s also in the labs interest
as they don’t want someone packing up and leaving a few hours into the
day and leaving the rest of the day not generating revenue.
This topic is huge, and I hear so called experts spout contentious
opinions that are ill founded. It’s particularly distasteful
especially in a professional form such as this as it forms false
opinions in peoples minds, especially as some of these experts have a
high platform from which to pontificate. There isn’t a rampant problem
in the testing community, and many hardworking technicians, engineers,
managers, QA people, Assessors, assessing bodies and even test
witnesses would be very aggrieved to hear some of these statements.
Testing is a team mentality, not a glass wall mentality. And valid
data is the responsibility of BOTH parties. It requires capable people
who have a systematic work approach. So unless ALL the full details
are known spreading scuttlebutt or opinions of what could have/should
have, is NOT helpful.
My 10 cents as I have to go back and tend to a test I’ve been running
since 6am.
Shalom.
Derek.
On Apr 17, 2019, at 6:21 PM, Edward Price <[email protected]
<mailto:[email protected]>> wrote:
*Derek:*
**
*When a test lab is engaged to perform testing on a product, the test
lab owes the client, at the minimum, accurate test data. However, it
is not the “chamber” that delivers that assurance of quality
workmanship, rather it is the EMC Engineer in charge of that facility.
When the client walks in the door, he expects a knowledgeable testing
operation, not an environment that seems to be learning as they go.
Not recognizing Ambient noise polluting the Operational emission data
is a failure to deliver the expected professional level of competence.
To me, it seems pretty clear that the testing lab is at fault. If the
problem was rapidly recognized by them, and a new set of data was
taken, then the problem is mainly one of embarrassment of the testing
lab’s people. However, if it goes on without recognition, if the lab
lets the client take his equipment home with the assumption that the
equipment has failed, then the longer it goes on, the greater the
testing lab’s error and financial responsibility becomes. Perhaps the
testing lab never noticed the problem on their own? That would have
been a pretty serious indication that the testing lab just wasn’t
ready to deliver professional quality testing services.*
**
*Another interesting comment was that there was difficulty in “setting
up” the test specimen and its support equipment. A good test lab will
know what a customer needs to supply long before the test date. Time
should be budgeted for the setup and trouble-shooting of ancillary
devices, and the customer should be warned that home-brew support
equipment may cause EMI issues all on their own. A good test lab will
make some suggestions about best practices, but alert the customer
that it may be necessary to ameliorate support equipment problems
before EUT testing can begin, and this may entail additional time and
materials needed to make the support equipment quiet or immune enough
to allow testing. Further, a good test lab should always expect some
set-up problems, and be ready to surmount these with a plentiful
junkbox of rolls of aluminum foil, conductive tape, bond straps,
shielded boxes, knitted wire mesh, capacitors, inductors, ferrite
beads, isolation transformers, sheet metal and a decent assortment of
common hand tools. In short, if your customer says his gadget needs an
external water chiller, the test lab should have already thought about
ground loops, how to get water in and out of the chamber, and have
considered what problems a water chiller might induce in the lab’s
electrical environment. The test lab’s customer should not feel that
the test lab was unprepared to receive him or that the test lab was
anything less than expert in integrating the test specimen and support
equipment into the test chamber.*
**
*It would appear that the selected test lab was just not ready for
prime time.*
**
**
*/Ed Price
/**WB6WSN**/
/**Chula Vista, CA USA*
**
*From:*DEREK WALTON
[mailto:[email protected]]
*Sent:*Wednesday, April 17, 2019 12:08 PM
*To:*[email protected] <mailto:[email protected]>
*Subject:*Re: [PSES] Question re: Measuring a signal in a noisy
environment
Interesting discussion, not surprising I have a little empathy, and a
whole slew of disagreement with both Ken and Ghery ( both Chaps I have
a lot of respect for ) on this one.
How best to respond is the question?
Cheers,
Derek Walton.
On Apr 17, 2019, at 1:12 PM, Bill Stumpf <[email protected]
<mailto:[email protected]>> wrote:
Absolutely agree with Ken.
Bill Stumpf
Lab/Technical Manager
D.L.S. Elecronic Systems, Inc.
*From:*Kenneth Wyatt [mailto:[email protected]]
*Sent:*Wednesday, April 17, 2019 12:21 PM
*To:*[email protected] <mailto:[email protected]>
*Subject:*Re: [PSES] Question re: Measuring a signal in a noisy
environment
Boy, I have heard all sorts of horror stories from clients with
knowledgeable EMC backgrounds who have witnessed sloppy, or just plain
wrong, procedures used in commercial EMC test labs. In a lot of cases,
the technicians operating these tests have limited background in EM
theory and poor knowledge of the actual tests they are running and
standards the tests are based on.
Just because a test lab is assessed per IEC 17025, doesn’t mean much
unless they show evidence the documented procedures are actually being
followed.
Many test labs fail to perform frequent verification tests to confirm
the measurement system is accurate and is repeatable from one day to
the next. When I worked for HP, we did a daily verification test using
an RF generator connected to the antenna cable to ensure the back-end
system measured the same as the day before. We also ran comb generator
tests frequently.
I always suggest to my clients to make their preferred test lab
measure a client-owned comb generator prior to any testing in order to
ensure the chamber continues to be reasonably consistent before real
measurements are taken.
It’s also very important to understand the test standards and EUT
configurations well enough to ensure the test technician is setting up
things correctly. I know of one case where the EUT cabling was
configured wrong and their client repeatedly had emissions failures
over weeks of retesting until the correct configuration was pointed
out in the standard.
Taking photos of the test setup is very important for day to day test
consistency. A difference in one cable position can completely throw
off repeatability and thus, mislead any troubleshooting efforts.
What about ESD simulators? When was it verified last? Does the test
lab even have the means to verify the correct tip voltage and pulse
characteristics?
Is all the measurement equipment calibrated and cal tags current?
I could go on…
My colleague, Ghery Pettit wrote a recent blog on the subject for
Interference Technology:
https://interferencetechnology.com/emc-laboratory-selection-audit-items/
Cheers, Ken
_______________________
I'm here to help you succeed! Feel free to call or email with any
questions related to EMC or EMI troubleshooting - at no obligation.
I'm always happy to help!
Kenneth Wyatt
Wyatt Technical Services LLC
56 Aspen Dr.
Woodland Park, CO 80863
Phone: (719) 310-5418
Web Site <http://www.emc-seminars.com/> | Blog <https://design-4-emc.com/>
The EMC Blog (EDN)
<https://www.edn.com/electronics-blogs/4376432/The-EMC-Blog>
Subscribe to Newsletter
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Connect with me on LinkedIn <https://www.linkedin.com/in/kennethwyatt/>
On Apr 17, 2019, at 10:46 AM, Grasso, Charles <[email protected]
<mailto:[email protected]>> wrote:
To those wondering what the background and conclusion to that question
was:
_Background_: Our testing was performed in a newly minted
chamber so proper
EMC installation of our product was challenging.
_Effect_: Ingress of high levels of external bb noise.
_Result_: Proper install eliminated the external
noise and now the system passed.
_Concern_: While I accept that proper installation and operation of
our system is our
responsibility, I had expected that the tester would point to the
excessive ambient
and indicate that our data may not be valid. An inexperienced customer
would
have left thinking that their product had failed.
Am I wrong?
Thanks!
Charles Grasso
W: 303-706-5467
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