I concur with John, the grid doesn't do that. To me it looks like line noise
and/or a software issue is causing your setup to give false results. I have
seen a lot of instrumentation get fooled by line noise, especially around zero
crossings. Measuring the power line accurately in the presence of all the
variations and possible kinds of noise and phase shifts turns out to be more
difficult than it seems at first.
Peter
On 9/1/2012 9:30 AM, J. Forster wrote:
IMO, you have an instrumentation issue. I don't think the power grid can
do anything like that.
YMMV,
-John
===============
The context is using the 60 Hz line for timing.
I'm feeding 60 Hz from a wall wart transformer into a modem control signal
that the kernel PPS stuff watches. Mostly, it works as expected, but
occasionally, it picks or drops a cycle.
In order to understand what was going on, I fed the same signal into the
audio input and setup a job to capture the audio. Here is an example of a
pick:
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a-pick.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a1.png
OK, that somewhat makes sense.
Something happened several days ago. I used to get picks/drops rarely,
say
ballpark of 1 a month. Now I'm getting 10 or 20 per day. So I started
looking closer.
I'm now seeing stuff like this. I've got lots and lots of examples. I
added
a second PC with different hardware. It sees the same stuff.
Does anybody recognize this?
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-a0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-b0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-c0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-d0.png
http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Sep-01-e0.png
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