Hi My guess is that the “best design” would likely do a sample at some specific time of day. Just when would depend a bit on your local grid and how it is fed and loaded. There are definitely “it’s 6 PM and everybody just got home” issues with power line phase.
Next question wold be how long to run your sample. Is a few minutes good enough? Is an hour overkill? There would be more than a little trial and error involved. You likely get to some SNR floor long before the 10’s of minutes point, even at the “best time of day”. If you accept that you are getting 1x10^-4 sort of data, once a day gets you into the 1x10^-9 range. That’s not an unreasonable stability for a well warmed up OCXO for a few days to a few weeks. A sample a day may be quite adequate …. Of course this *assumes* an electronic approach. Given that it’s moving pretty slow and you only are looking at fractions of a millisecond, one *could* do an electro mechanical design …... Bob > On Dec 14, 2017, at 9:39 PM, Tom Van Baak <[email protected]> wrote: > > Jim, > >> You would want a filter time constant of several hours in the control loop >> to smooth out the variations in the 60 Hz. > > One can determine the appropriate time constant by looking at the ADEV of the > two clocks [1]. > > For GPS and OCXO the choice of time constant is fairly obvious. But the ADEV > for mains frequency isn't quite as pretty. So I'm not sure several hours > would work; maybe more like days or weeks? Here's a sample ADEV for power > line frequency: > > http://leapsecond.com/pic/mains-adev-mdev-gnuplot-g4.png > > I'd be curious if anyone has tried a mains disciplined oscillator and how > well it performed. Unlike a GPSDO, absolute phase can be lost (e.g., power > fail) so maybe use FLL instead of PLL. Shall we call it MFDO (mains frequency > disciplined oscillator)? > > Hal and I have months, even years, or mains zero crossing timestamps so if > someone wants to simulate how well a MFDO might work let us know. Maybe just > adapt the gpsdo simulator [2]. > > /tvb > > [1] some examples: > www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif > www.thinksrs.com/assets/instr/FS740/FS740_unlockedLG.gif > www.thinksrs.com/assets/instr/FS740/FS740_lockedLG.gif > www.leapsecond.com/pages/gpsdo > > [2] gpsdo simulator project > http://www.leapsecond.com/pages/gpsdo-sim/ > > <mains-adev-mdev-gnuplot-g4.png>_______________________________________________ > 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.
