tom, nice plots. how do you figure out what the contribution of variability vs noise? In other words there is a differential between the "ideal" and the actual a dev curves... is there a way to tease out how much nose contribute to that differential? It does seem to me that there should be far less short term variability (< 100s) than there appears to be. Clearly in the very short tau (< 0.1 s) the picPET can't tease that out but as the curves diverge, how much of that is noise? between say 0.1s and 100s? Being a power plant operator I would say quite a bit although I am rethinking that some due to the way the turbines push and pull each other. I can envision some fine whole grid oscillations due to that push and pull.
bill On Mon, Nov 18, 2013 at 4:15 PM, Tom Van Baak <t...@leapsecond.com> wrote: > Magnus, > > I'm going to push back a bit on your mains sampling claim. Mostly, I'd > like to see the results of the professional I-Q demodulated gear that you > mentioned. Can you post raw data, or a sample plot? > > I agree that looking at power line voltage with 16- or 24-bits at 1 Msps > is going to reveal interesting amplitude and phase noise information. But > see how well a $1 PIC can do. > > Attached is a plot made using TimeLab + picPET just now. The picPET is > fast enough to capture the zero-crossing of every 60 Hz cycle with 400 ns > resolution; the TimeLab plots have tau0 of 16.67 ms. > > -- The blue trace was simply plugging a 9 VAC wall-wart into the picPET > though a 10k resistor. > -- The pink trace was adding a 10 nF cap across the input. > -- The green trace was unplugging my laptop switching power supply from > the same outlet! > -- The red trace is replacing the mains wall-wart with a hp 33120A set to > 9VAC at 60 Hz, a tentative noise floor measurement of the picPET when used > this way. > > My conclusions are that at least here in the US, or at least at my house, > the short-term stability of mains hits about 5e-6, at about tau 0.2 > seconds. The attached short-term plot is also not-inconsistent with the > long-term plot at http://leapsecond.com/pages/mains/ > > My other conclusion is that the picPET (a simple PIC-based time-stamping > counter) is doing a pretty good job measuring this. Note, no software or > data filtering was used. This is just raw serial/USB data going into > TimeLab. > > /tvb > > _______________________________________________ > 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. > -- Doc Bill Dailey KXØO _______________________________________________ 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.