[time-nuts] 60 Hz line quirks, anybody recognize this stuff?

[Jim Lux]

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"?