It went off-topic so I moved it to chat.



The issue is, life is more complicated than black&white, as you present it here. And I believe you know it very well.

No matter how thick your metal box is, how perfect the inputs filters are, now much ferrite you used, how perfectly you welded down the lid and how thick the gold on it is, there are always circumstances which will throw your device off. I mentioned RF, but "curcumstances" are also mechanical influences (shocks, vibrations), heat/cold, humidity etc.

Every sensible designer designs to a certain set of requirements. Most often he is able to define a "typical" situation, maybe estimate likely deviations. Some of the requirements are set in standards, based on "normal" way of things.

But, sometimes, things get out of "standard", "normal", "typical". You can either moan, scream and complain, and eventually get out of business; you can make things in heavy metal and - being uncompetitive - get out of business; or you can make things as rugged as possible with as little effort/cost as possible and get a good reputation.

An example. Designing a PC mouse in pure metal, welded down and filled up with ferrite would indicate seriously damaged designer's sense. However, when one of my friends attempted to work with his laptop in the vicinity of a XX kW RF amplifier box, the cursor on the screen from time to time jumped wildly, opening and closing windows at random. He'd rather chose the mouse stay unresponding momentarily from time to time, I'd guess.

Another example. Your power supply is probably as perfect as possible (and you even provide your power supply, which is not always the case - e.g. in PCs). However, the electrolythics in it might suffer from a slow death, especially if subject to heat or similar (I know, there are higher-rated caps etc. but nobody can foresee how does it behave under xxxx current/voltage pulses suffering heat shocks etc.etc.). Consider one sopmewhere in feedback path, with randomly changing leak. The output of the power supply gets wild, emitting spikes and noise. The micro goes crazy and your display will display funny things, if the supervisor is too "bold".

JW