Microcontroller True RMS in Noisy Waveforms

Guys -

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?

Thanks!

Reply to
EnigmaPaul
Loading thread data ...

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.

Reply to
Hans-Bernhard Bröker

And if you are after calculating the power, you may also need to take the phase angle into account.

Reply to
Tom Gardner

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.

--
Tim Wescott 
Control system and signal processing consulting 
 Click to see the full signature
Reply to
Tim Wescott

Noted! I wanted to cross post but google groups has this capability disabled.

Reply to
<address_is

Noted. Google groups generally sucks, but fewer and fewer ISPs are providing newsgroup access in the package so you have to do something.

Fortunately, GigaNews is cheap.

--
Tim Wescott 
Wescott Design Services 
 Click to see the full signature
Reply to
Tim Wescott

I use Eternal September with slrn. It works ok for me.

See:

formatting link

Simon.

--
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP 
Microsoft: Bringing you 1980s technology to a 21st century world
Reply to
Simon Clubley

=

me=

z=

defi=

har=

=

Maybe you try windowing rather than zero-crossing detection?

--------------------------------------- Posted through

formatting link

Reply to
baranov

I'm a loyal customer of Individual.Net (

formatting link
)

10 Euros per year and very good spam filtering. Forte's Agent as a reader. (Must try slrn some day...)
--
Roberto Waltman 

[ Please reply to the group, 
 Click to see the full signature
Reply to
Roberto Waltman

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.

Dimiter

------------------------------------------------------ Dimiter Popoff Transgalactic Instruments

formatting link

------------------------------------------------------

formatting link

Reply to
dp

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.