In measuring True RMS voltage and current, waveforms from non-linear loads like rectifiers chop up the current and cause noise on the voltage. In me asuring with an A/D converter of a microcontroller, we need to figure out z ero crossing points in order to avoid truncation errors in the data to defi ne the start and stop of each cycle. That is challenging with a lot of har monics and noise that cause tons of false zero crossings.
Does anyone have any experience in doing something similar to this and how did you deal with the zero crossing noise?
That's your problem right there. Zero crossings are the wrong tool for that task, precisely because they're just too vulnerable to noise.
What you really need is a determination of the signal's base frequency based on the complete input data sequence, which allows most of the noise to cancel itself out. Auto-correlation or frequency-domain methods would apply.
I apologize for being a net cop. I don't do it much, and this is the only subject that I do it on (well, this an top-posting).
You have just multiple-posted. Multiple-posting is bad, although it's not as bad as not asking your question. It's bad because many people read more than one related newsgroup, and when you multiple-post you end up spawning a bunch of related but individual conversations, which makes it harder for helpful people (like me) to act out on their irrational compulsions to be nice.
Please get onto wikipedia and search on the term "cross-posting". Read the article. The one thing they say there that I disagree with is that you should set one follow-up newsgroup. I disagree with that because in the case of posts like this, you often get a very informative conversation between newsgroup denizens that would not occur if all the replies ended up in one newsgroup.
This subject, by the way, is an _excellent_ candidate to cross-post to comp.arch.embedded and to sci.electronics.design, precisely because it has one foot in embedded and another one in circuit design.
I don't know if you can cross-post from Google Groups, because I do not use Google Groups as my newsreader (I use Pan). If you ask on one of the more active technical groups (like either this one or sci.electronics.design), someone may know.
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Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Oh. The old google groups (went offline a month or two ago) did allow that. One step at a time, and they don't seem to take more time than it takes to make their next step into welcoming us to the brave new world they are apparently assigned to bring us to.
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