On 8/31/12 11:35 PM, Hal Murray wrote:
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
Interesting.. a 2-5 millisecond cutout.
And very sharp edged. That's what's weird.. if it were something in the
electrical distribution/transmission system, I don't know that it would
be that "clean" (after all, the power line is a moderately effective low
pass filter)
And it also doesn't look like switching from one source to another.
That is, the signal looks phase continuous.
Are the gaps 1/6 or 1/12th cycle long? (thinking here of an 3phase
inverter with an intermittent switching device)
I wonder if the line goes "open" or to "zero"?
_______________________________________________
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.
