| ??? 05/31/08 14:14 Modified: 05/31/08 14:35 Read: times |
#155328 - Have you ever been involved in CE testing? Responding to: ???'s previous message |
Jan said:
...that EMI sufficiently strong to throw the micro out of way, never occurs. Jan, CE standards are so demanding, that your product is immune against 99.9% of all strange effects. Jan said:
And how did you come to the conclusion that Alex's case is not due to unforeseeable situations? Because he talked about "lightning". And CE complying products are immune against lightning, as they are "surge" tested, which is a very harsh test by the way. If you design your power supply unit properly, lightning on mains is totally filtered out of your supply voltage. (I do not talk here about a direct hit, of course, but which is very very seldom.) He also talked about "unstable" power. When being designed properly, then only power downs and power up can be critical and these aren't cured by the help of a watchdog, but by a proper supervisory/reset controller. So, this all tells me, that Alex has an improper design which he wants to cure by the help of a watchdog. Jan, our products are designed in that way, that the watchdog never starves. We made long term tests and found that the watchdog not even once had to reset the micro. Jan said:
Ask the utility (electricity) provider. You cannot simply say "power dropouts shall not occur" if they DO occur in certain regions. You have a slightly different perspective: in Germany you have a substantially more stable and controlled utility grid than say here in Slovakia; and also it's less likely to have strong EMI injected into the grid by faulty devices. Jan, but that has nothing to do with the watchdog! What are you telling here? If you have mains dips or other fluctuations of mains voltage, then you still have the big electrolytic storage cap which filters much of the dips out. And the rest of fluctuations is handled by the help of your reset controller, just as simple power up and power down situations. The watchdog has never to bite in these cases. Even fast spikes on mains are no problem if you use proper filtering. Remember, your CE testing includes very demanding "burst" and "surge" testing. I have seen improper parts exploding during the surge testing... We use three pole mains filtering, PTCs from Epcos and transzorbs on secondary side of transformer, caps across the rectifier diodes, switchers as preregulators and 7805 for fine regulating. Each step with two pole lowpass filtering including ferrite beads from "Würth" and ceramic high caps from "Taiyo Yuden". Even behind the 7805 there's two pole low pass filtering on the boards, when using mixed analog/digital circuitry. Again, the watchdog did never bite. Kai |
