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.
