[time-nuts] Mains frequency

[Chris Albertson]

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 <docdailey at 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.chris at 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 <
> > magnus at 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
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> >
> >
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
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-- 

Chris Albertson
Redondo Beach, California