Doc, I measure mains time & frequency with a picPET all the time. In fact that's one of the reasons I designed it. If you're having any trouble contact me by email.
/tvb (i5s) > On Nov 16, 2013, at 11:23 AM, Bill Dailey <[email protected]> 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 <[email protected]> >> 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 < >> [email protected]> 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 -- [email protected] >>> 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 -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
