[time-nuts] 60Hz extra PPS: got one

Bill Hawkins bill at iaxs.net
Fri Aug 10 12:17:20 EDT 2012


Hal, do you have a resonant 60 Hz filter in the pickoff? The waveform
in Aug-09-a1 certainly had multiple zero crossings.

Remote-controlled tap changers can do things like that.

If I got the UTC offset right, that happened at about 2 PM local time,
when a big transformer tap could have been changed for more A/C load.

I expect you'd rather do things in software, but the mechanical
solution is to couple a synchronous motor to a flywheel marked with
60 Hz lines for photocell pickup. A precision 33 1/3 rpm turntable
with strobe markings would work very well.

Bill Hawkins


-----Original Message-----
From: Hal Murray
Sent: Friday, August 10, 2012 3:51 AM

Actually, there were 2 extra pulses.

Here is the PPS view:
  http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-a-pick.png
(Samples every 10 seconds.)

Here is the audio view:
  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
(16 bit audio, 8 KHz)

I noticed a couple of other fishy areas:
  http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-b0.png
  http://www.megapathdsl.net/~hmurray/time-nuts/line/2012-Aug-09-b1.png
They didn't confuse the PPS collector.

I'm probably overlooking lots of similar glitches.  I only noticed that pair

because the first one happened at the bottom of a cycle and that was big 
enough to stand out.  I noticed the second one because it was close enough
to 
the first one.

Anybody got software to emulate a PLL?  I'm looking for something that will 
track a sine wave and tell me when it finds noise.

I haven't seen any of the ground problems in the last day or so.  I don't 
know if that is just luck or if upgrading to Fedora 17 fixed something.  (Or

maybe I accidentally fixed something.)


-- 
These are my opinions.  I hate spam.




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