[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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