Hi Gert & John,
Gert gave some interesting examples of radiated immunity failures
(analogue measurement systems like thermocouples), but none of them
apply to computers (the products I usually work on). Also, Gert
mentioned some power supply design mistakes that have caused EFT
failures in the past. As mentioned, it is rare that computer
manufacturers design new power supplies as they go from CPU generation
to CPU generation, so there is really no need to redo the power related
immunity testing (especially benign EFT testing) for such changes
unrelated to the power supply. Hence, this testing is a waste of time
and money ... adding cost to the product development which is ultimately
passed to the customer.
John & others would point out that ... "In Europe, no testing is
mandatory." However, there is an expectation that some analysis be
documented for why a test was not run. It is not until a regulator
audits that one would know if the explanation is "good enough". Rather
than writing a doctoral thesis on why a test does not apply to the next
generation product, most resign themselves to running the uninteresting
test to "complete the record". Besides, South Korea does not give any
wiggle room for engineering judgment, so the test must be run for them
anyway.
The problem with government regulation is that politicians and
bureaucrats are not engineers. They certainly do not want to take the
time to analyze each product's design and create a product specific
regulation. Instead, regulators tend to lump all products together and
create a one-size-fits-all regulation for what is required to get their
approval. They also treat all manufacturers as equal ignoring a
manufacturer's design & performance history. As a result, government
regulations are inherently wasteful and should only be applied when
there are customer safety issues or excessive interference potential
neighbors.
John mentions the horror stories of 6dB differences in measured results
that are supposed to be solved by measurement uncertainty and
improvements on the non-conducting tables. However, the FCC limits
(similar limits were later adopted internationally) were set with a
margin to account for measurement issues. Years later today, most
communications are digital with error correction that which causes TV
reception to be crisp and other communications to be more fault
tolerant. As there are no interference complaints, then there is no
need to add extra site calibration days to a lab's accreditation
requirements or lab equipment costs. These costs get passed on to
manufacturers who must then pass them ultimately to their customers.
I note that even while some in the standards community are adding cost
in their efforts to systematically remove variation in measurements, no
one is then passing on the benefits of this improved measurement system
to manufacturers & their customers by accordingly raising the allowed
emissions limits. Wonder why???
Monrad
Note: All opinions expressed in this e-mail are my own and are not
necessarily those of any company I work for or have worked for.
<http://www.oracle.com>
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