I have seen digital systems with features that have been susceptible to radiated noise. One example was a system that had a capacitive touch power button. It failed initial radiated immunity testing at the frequency of the oscillator of the capacitive circuit. I see more and more digital systems with adaptive cooling that depends on some analog temperature measurement circuit. I'll admit that most digital systems I've worked on have passed radiated immunity without a problem, but not all. I suspect as we see an increasing number of touch screens and other interfaces, we will start to see radiated immunity issues with consumer computing products again.
I'm not arguing for or against the testing. I'm only stating that I have seen examples in the past few years of consumer computing products that do not pass radiated immunity testing on the first pass. Ted Eckert Compliance Engineer Microsoft Corporation [email protected]<mailto:[email protected]> The opinions expressed are my own and do not necessarily reflect those of my employer. From: Monrad Monsen [mailto:[email protected]] Sent: Wednesday, September 16, 2015 1:24 PM To: [email protected] Subject: Re: [PSES] RF Common Mode Immunity Test Question 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. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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