[time-nuts] 60 Hz graphs

[Hal Murray]

Here is a typical 2 day view.
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-Jul11-12.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-Jul11-12-freq.png

Note that there are 3 interesting events visible on the frequency graph.  
More on those later.

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I think this is a generator dropping off-line, or something interesting at 
the main power production level.
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g11.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g11-freq.png

That happens at about 4 hours on the above pair of graphs.  On the offset 
graph, it's just a tiny glitch.  It's much easier to spot in the frequency 
graph.

Here is another similar event:
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g29a.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g29a-freq.png

It took 0.07 hours (4 minutes) for the frequency to get back to normal.
During that time, the system lost 13 cycles or over 0.2 seconds.

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Here is a typical extra cycle event.  This one is actually 2 cycles.
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g12.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g12-freq.png

It's about 16 hours on the above graphs.

Here is another extra cycle:
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g13.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g13-freq.png

This is about 27.5 hours on the above graphs.

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Here is a time step on the machine collecting the data.
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g14.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g14-freq.png

I was downloading a huge file.  That added a lot of queuing delay on my DSL 
link.  After a while, ntpd decided the delayed version was the correct time 
and shifted to it which produced a 1/4 second offset.  After another hour the 
download finished and ntpd shifted back to the correct time.

1/4 second at 60 Hz is 15 cycles.  1/4 second out of 10 seconds at 60 Hz is 
1.5 Hz.

[I have good time locally.  I left that laptop running off network time 
servers so I could see things like this and/or other glitches I didn't 
anticipate.]

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This looks like a glitch in the PPS data collection code.  I think it got the 
new time-stamp with the old count.
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g29.png
  http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-g29-freq.png

My guess would be a missing lock or disable interrupts.  I've only seen one 
of these over roughly 2 months.  The extra cycle events are more like 1 per 
day.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.