No, I meant the purpose of the whole thing. Why are you measuring power frequency? Not why are you using a PIC. How will the data be used, what is the question driving the measurement?
On Sat, Nov 16, 2013 at 11:23 AM, Bill Dailey <docdai...@gmail.com> wrote: > My purpose is to do it with a picpet. That's it. So, that eliminates a > bunch of the options. I can decouple the measurements from the pc clock > that way. > > Doc > > Sent from mobile > > > On Nov 16, 2013, at 11:26 AM, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > > > The signal is 120 volts. You hardly need to amplify it. Clip it with a > > diode to +- 9 volts so as not to blow up your serial port. But I'd use a > > transformer for safety. The zero crossing detectors are built into the > > RS232 interface. You take advantage of the RS232 spec which has a DCD > > pin input of about +-9 volts that is already set up to find a leading > edge > > of a pulse and cause a very low latency interrupt. The system software > > already will capture the time all inside a kernel level interrupt > handler. > > > > The jitter turns out to be on the order of a single digit microseconds. > > Good enough for measuring a 60Hz signal. > > > > I guess if you want to see transients depends on the purpose of the > > experiment. Are you looking at local AC power quality or wanting to > > measure the grid. The grid is well monitored, just use FNET and you get > > real-time data for all of North America. I think the reason for > measuring > > it yourself is to see local power quality and things load switching > inside > > your own building, that's transients. > > > > > > > > The other way to measure AC with zero added equipment is to treat it as > an > > audio signal and after reducing it to 1 volt run it into an audio > interface > > And then use FFT. This will let you see very small spikes and noise. > It > > depends again on your purpose for doing this. > > > > > > > > > > On Sat, Nov 16, 2013 at 1:18 AM, Magnus Danielson < > > mag...@rubidium.dyndns.org> wrote: > > > >>> On 11/16/2013 09:52 AM, Chris Albertson wrote: > >>> Your method tosses out a lot of data. You can't see transients. > Ideally > >>> rather then record a 1 second average you'd record the time of EVERY > zero > >>> crossing. It sounds like a lot of data but not really. You only > record > >>> 32 bits 60 times each second. That is 240 bytes per second. > >> But you want it filtered to avoid the transients. Those are really not > >> that interesting when you measure the grid. > >> > >> Also, if you use the event trigger method you probably want to use an > >> amplifier to increase the slew-rate such that noise does not convert > >> into time jitter. > >> > >> Cheers, > >> Magnus > >> _______________________________________________ > >> time-nuts mailing list -- time-nuts@febo.com > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > > > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > _______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
