Re: question about logs of PPS

On 2007-05-15, Richard B. Gilbert <rgilbert88@xxxxxxxxxxx> wrote:

The Motorola M12+T is specified to deliver its Pulse Per Second output
with the leading edge within 50 nanoseconds of the top of the second.
Getting that into your computer is where the problem lies. Things like
cable length can be compensated for. Interrupt latency is more
difficult because it's difficult to determine exactly what value you
need to compensate for. Depending on interrupt priorities and what else
is going on, the latency may not even be constant.

I'd say that you are probably within one microsecond of the correct time
if you are using the Motorola M12+T as a reference clock.


So my offset is very bad, i have peaks of milliseconds. I have done
several graphics with gnuplot and i have put them available at:

http://bipt106.bi.ehu.es/~jtbpizac/ntp/loopstats.20070515.png
http://bipt106.bi.ehu.es/~jtbpizac/ntp/loopstats.20070516.png

At 15 i restarted several times the NTP daemon but today (16) i haven't
touch the server.

I think that the graphics are very bad and this could be by various
reasons:

1. The GPS aerial is in the roof inside a plastic water bottle to protect from
rain. I have seen that the bottle has too much adhesive tape that could
difficult the GPS to find satellites. I will remove the excess.

2. I don't know how my compains obtained the GPS coordinates. I will
run WinOncore during a week to check the latitude, longitude and height.
Could a bad value of these parameters produce a unstable GPS clock??

3. The Motorola M12 board is near other electronic components: wifi
access point, printer, PC, ... Could these components perturb the clock
quality??

Thanks for your comments and if i get a better behavior of the clock
signal i will post to the group,

--
Christian Pinedo Zamalloa
.

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