Hello Paul:
Your English is just fine. Your thread is getting some interesting replies,
I have enjoyed reading them. The following is MY PERSONAL SPIN on your
dilemma. I think we are stuck with rules but we can ENGINEER COMPLIANCE of
our products without a bunch of expensive compliance test equipment.
INTRODUCTION: Some years ago I designed an ESD gun for a European company
and in so doing made many-many-many tests to validate the energy shape and
level produced by their design as well as other ESD testing products. I
learned something (quite conclusively) while doing that project that I have
heard very little about over the years. I have passed this information on
to several of my customers and have received very positive feedback to the
effect that it works and saves a great deal of time and of course consequent
cost lowering. There are two major problems with what I am about to tell
you. a) Different manufacturers ESD testers produce quite different levels
of discharge and RF radiation, b) Application requires a good deal of skill
and judgment.
MY TEST RESULTS: We did several specific tests during the design and
validation stages of the ESD project. The first area of research was to put
a digital waveform sampler inside of a tem cell and connect it to an ESD
target on the outside wall. We walked over various carpet samples and
zapped the target with fingers or other items. Then we replaced the tem
cell and target with a PC set up and found a repeatable level of susceptance
using the same human body discharge. When we had ample data for modeled
human discharge and our ESD gun, we moved on to samples of several compliant
and noncompliant computers. We quickly discovered (here comes the secret)
that failing an ESD susceptibility of 1 to 2KV (relay) correlated to failing
the FCC A Radiated Emission Limit by several dB. Another area of our
research was to validate an ESD application level for a so called standard
industrial PC, in our case the failing level turned out to be 6 to 7KV
contact. That PC was under the FCC B Radiated Emission Limit by several dB.
DISCUSSION: So radiated emissions and ESD susceptibility seem to have a bit
of correlation depending on test operator application skills and result
interpretation. IF ESD testers are not licensed in Belgium, and IF you have
one, that may be a way to do some intelligent low cost pre-testing and
perhaps harden the emission and susceptance profiles of your product with a
minimum of equipment investment. The ESD application levels used are highly
product dependent and have little to do with the levels prescribed by the
standards.
WARNING: Many of the currently available ESD testers generate substantial
unnecessary RF fields (from the relay and wiring) which will color your
tests negatively, however once you tune in on the level correlation of your
particular gun you CAN determine the applied levels to produce a radiated
emission pass. BTW you can also simulate EFT testing with the ESD gun,
using conductive tape on the test lines. All this is highly general and is
meant only to help you accomplish some meaningful pre-testing with minimal
expense. Application will require a good deal of planning (design of
experiment) and scheming on your part. By all means work with a local test
lab to establish compliance for your product. This stuff and a bit of
clever engineering may help you show up at the test house with a compliant
product. Good luck.
Ben Bibb, EMC Engineer
LambdaMetrics, Inc.
ACIL IEEE NARTE NVLAP FCC ESDA
Cedar Park, Texas
(512) 219-8218
benb...@lambdametrics.com
