Tom, You sound like a guy who just might have experimented with different core materials for your transformer? Any suggestions for rolling your own?
I'd love to hear more about your pulse monitoring/measuring setup if it's something you can share. Thanks, Jimmy... N5SPE > On Feb 5, 2014, at 4:40 PM, Tom Harris <[email protected]> wrote: > > For your setup measuring mains there will be a large phase difference > across the transformer. This is due to very many physical properties of the > materials, the largest being the magnetic succeptability of the core. Now, > this does show a slight temperature dependance. So how do you know that you > are not getting a slow variation in the phase showing up as a frequency > shift, since you are measuring such tiny variations. I know that the > transformer is probably in thermal equilibrium with it's surroundings, so > is at a steady temperature, but this problem (of getting an accurate idea > of mains frequency & phase) has exercised me over the years. I currently > use an opto and voltage reference to get mains frequency, phase & and > voltage (computed by lookup table from pulse width) which I found was more > stable than a transformer. And cheaper as well, since this is for a > commercial product. > > I'm just surprised that you get such results with a cheap transformer. > > Just remembered, we got a tiny change in phase shift across a transformer > due to its orientation, we could turn it 90 Deg and get a tiny change (less > than a milliradian), we never got to the bottom of it, maybe the Earth's > magnetic field? > > > Tom Harris <[email protected]> > > >> On 6 February 2014 04:39, Hal Murray <[email protected]> wrote: >> >> >> [email protected] said: >>> Interesting.. I'm assuming the green graph is actual voltage and the red >>> graph is..? >> >> The green is the frequency as measured over the last 10 seconds. >> >> The red is the long term clock offset in cycles relative to what it would >> be >> if the frequency was exactly 60 Hz. It's the error you would see if you >> looked at a clock that was tracking the power line. The 0 point is >> arbitrary >> since I can't see the reference clock the power system is using. For those >> graphs, I used the start of the day/file as 0. >> >> >>> I've never done any mains monitoring/measuring and was wondering, what's >>> your equipment setup? >> >> It's simple. The hardware is an AC wall wart and a couple of resistors as >> a >> divider connected to a modem control pin. I forget which one. It's the >> one >> that ntpd expects to use with a PPS input. >> >> There was a discussion on that topic here a year or 3 ago. It's in the >> archives, but I couldn't find it with a quick look. >> >> The software is a simple python hack. It runs on Linux. >> http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/pps.py >> >> Linux has a back door to the PPS info. Things like >> /sys/class/pps/pps0/assert give text like this: >> 1391619268.999925084#1125070 >> The number left of the # is the time of the last PPS. The number to the >> right is the pulse count. The software above just waits 10 seconds, grabs >> another sample, and writes a line of text to a log file and switches to a >> new >> file every day. It's 1/2 megabyte per day. >> >> If you have FreeBSD or NetBSD rather than Linux, it shouldn't be too hard >> to >> use the same API as ntpd uses. I don't know how PPS works on Windows. >> >> Another approach would be to feed it into the audio input and scan for zero >> crossings. I captured the raw binary for a while when I was chasing some >> noise glitches. It's a lot of data. >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> _______________________________________________ >> 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.
