"Alternatively you can put mains through a 40-60 or 50-70 Hz bandpass filter to suppress anything but the fundamental"
The problem with any filtering is precisely that the phase shift through any filter is highly dependent on the actual signal frequency, so if your purpose is timing, the filter will probably do more damage than help. Tom's data shows that "no filter" works well at his location, which is probably typical, aside from the large number of precision time references in the basement :) I have some data about filtering the mains I am trying to put together in a web page. Will take a few days. That data was collected with regard to power factor correction, not timing, but it is within the scope of what has been discussed in this thread and it may be interesting to the curious mind. Didier KO4BB Poul-Henning Kamp <p...@phk.freebsd.dk> wrote: >In message <77A742979E2849FD9CA585192F2F5AFC@pc52>, "Tom Van Baak" >writes: > >>For tau 0.01 to 0.3 s it would take more work to quantify which pieces >are >>contributing to the instability pie. > >It doesn't really make sense to talk about taus less than approx >0.1s for Mains. > >It is not atypical to see 10% "harmonic distortion" on mains in a >household, most of it from switchmodes, but also single-phase >motors etc. Music amplifiers, in particular played at "teenagerockgod" >volumes add a very interesting challenge too. > >In theory harmonic distortion does not change your zero-crossings, >but it is not really "harmonic" in the Fourier sense, it's just >mostly centered around the overtones. > >Either you include the "harmonic" distortion, and then your measurement >applies only to that specific outlet, when the dish-washer is running >exactly 20 minutes into programme 3 and no kids listen to loud >music. > >Alternatively you can put mains through a 40-60 or 50-70 Hz >bandpassfilter to supress anything but the the fundamental, but >what exactly do you measure then ? > >Once you get below about 1Hz, the most interesting thing you can >do with mains is to sample it at ~4kHz, make a water-fall plot and >try to identify your house-hold appliances by their distortion >patterns :-) > >-- >Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 >p...@freebsd.org | TCP/IP since RFC 956 >FreeBSD committer | BSD since 4.3-tahoe >Never attribute to malice what can adequately be explained by >incompetence. >_______________________________________________ >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. -- Sent from my Motorola Droid Razr 4G LTE wireless tracker while I do other things. _______________________________________________ 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.
