[time-nuts] 60 Hz power glitch, US West coast (Silicon Valley)
jimmydburr at gmail.com
Wed Feb 5 20:14:12 EST 2014
Thanks for the info. I think I'm going to give it a go. At any rate it's a good excuse to buy another Raspberry pi :)
Thanks for the python source too. Looks useful.
> On Feb 5, 2014, at 11:39 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> jimmydburr at gmail.com 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.
> Linux has a back door to the PPS info. Things like
> /sys/class/pps/pps0/assert give text like this:
> 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.
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