[time-nuts] 60Hz line data
Hal Murray
hmurray at megapathdsl.net
Fri Jul 10 07:44:59 UTC 2015
My collection recently rolled over the year boundary:
http://www.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2014-2015.png
The grid is 4 weeks in the X direction. The start of the Y offset is
arbitrary. I picked the start of the data.
The pairs of colors are a month. Within a month, days alternate colors.
Here is May 2015:
http://www.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2015-May.png
There were a few interruptions. I lined things up by eye. They are probably
off by a few cycles. I don't think they are off by a second.
There are also occasional extra cycles. I assume they are caused by noise.
One of these days, I'll catch one. They add up to ballpark of a second.
Here is an old example:
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-10-a-pick.png
Here are the days before and after the leap second:
http://www.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2015-Jun-30-le
ap.png
Here is the same data zoomed in to 1 hour each side:
http://www.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2015-Jun-30-le
ap2.png
There is one frequency point way up high. (1 second out of 10 is huge on
that scale.) I set the Y2 scale manually in order to make the main section
interesting.
As you can see, I screwed up the leap second processing. I sure knew the
leap second was coming, but I don't remember considering what that program
(or any others I'm running) would do when one happened. I can't see a simple
way to fix it. I think I'd have to convert the program to use TAI, and then
find or write a package to convert normal/UTC time to TAI. That needs a
table lookup.
Google's smearing inserts a second over 20 hours: 1/72000 or 13.8 PPM.
If my collection system was playing the smear game, I think a 60 cycle shift
would be visible if you had a reference to compare to, but not significant
relative to all the other changes. (That pair of days has 500 cycles
peak-peak, so 60 is only 10%.) On the frequency scale, it's probably lost in
the noise.
--
These are my opinions. I hate spam.
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