[time-nuts] Weird TEC data
Scott Newell
newell at cei.net
Thu Aug 4 14:48:39 UTC 2011
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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