At 03:27 AM 8/4/2011, Bill Hawkins wrote:
What that means is, that if the two locations representing the
red and green traces are on the same grid then there should be
less than one cycle difference between them at all times.
That's what I was expecting.
NTP can't be causing the jumps because the difference increases
with time. You would see the displayed time difference change
as well.
Agreed. Both machines are running Munin, which makes pretty graphs
of ntp data. tock shows ntp kernel estimated error of (avg/min/max)
1.72ms / 538us / 6.43ms over the last week. sparc is 1.37ms / 493us / 3.18ms.
I should copy the Munin data to the webserver tonight...it's also
doing live plots of the 60Hz error and frequency (1s, 60s, 600s, and
3600s moving averages).
Since that is not the result that you have, it is time to
calibrate your equipment. I'd start with the line frequency sensor
looking for dropped cycles.
tock might have dirty power--the embedded device shut down a couple
of times last month until I put a batt on it. Then again, someone
may have turned it off for me. sparc and its front end are on a
consumer grade UPS, tock and its front end are not. Now there is a
big old Sola line conditioner that I could add to tock at lunch.
It's possible that different computers running different other
programs could drop different numbers of points. What are they
doing when the steep drops in difference occur?
I doubt that the computers could be at fault. The front-end device
is counting cycles and transmitting it to the computer serial port
("+0123456789\r"), and then the computer timestamps the start char
("+") and reads the cycle count.
My new $10 webcam isn't setup yet (at sparc's location), so I don't
have my backup timelapse clock photo data source available.
I'm considering mods to the embedded hardware to increase noise
rejection--wait for 60 hz edge, start timer for (say) 15 ms, don't
look for next edge until timer expires.
--
newell N5TNL
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