[time-nuts] Second FTS4060 shows Drift, is it me? Good Links
Brooke Clarke
brooke at pacific.net
Tue Feb 7 17:15:20 EST 2006
Hi Tom:
The plot with red and blue is the old data on s/n 1227 where the red
points are from LORAN-C and the blue points from GPS.
s/n 1227 = http://www.pacificsites.com/~brooke/pdf/Cs_Drift0429.pdf
from April 29, 2005.
This might be a clue to the problem I'm now having with s/n 1013.
http://www.pacificsites.com/~brooke/pdf/sn1013_850_Drift2.pdf s/n 1013
from yesterday.
It's my understanding the a properly working Cs standard probably has
it's frequency slightly off from perfect, but does NOT have any drift in
frequency.
So a Time Interval plot, like those in the links above, should be just a
straight line, i.e. it should not have a parabolic shape.
The slope of the TI plot is the first derivative of the equation of the
points and should have included two terms. The second derivative gives
the aging rate which should be zero for a Cs standard. When I recompute
based on the Excell equation coefficients the answer is off, so I think
that Excell is giving rough values. But in any case the second
derivative is just a single number whose units would be ns/day/day.
Don't have plots of s/n 1013 vs. s/n 1227. I just have one SR620 counter.
Is there a common way to check the TI counter, maybe based on a coax cable?
Thanks,
Brooke
Tom Van Baak wrote:
>Brooke,
>
>
>
>>For the last couple of weeks it has shown a parabolic plot like s/n
>>
>>
> > 1227, although this time the polarity is opposite that of s/n 1227 which
> > also showed drift, but that may be a setup difference. A plot of s/n
> > 1227 is at: file:///C:/Webdocs/pdf/Cs_Drift0429.pdf
>
>This plot has both blue and red dots; which is which?
>
>The red dots look like you should draw a line though
>them, not a parabola. The linear slope is approximately
>+700ns/21days = +4e-13, a perfectly reasonable value
>of the frequency error in a Cs standard.
>
>I see nothing wrong with the 3 weeks red dot data.
>Let it go another month or two and see if it shows
>parabolic behavior (frequency drift) rather than just
>linear (frequency offset).
>
>
>
>>The equation for s/n 1013 is:
>>y = 2.7943x2 - 302.64x + 8969.4 and the quality of fit is
>>R2 = 0.9088. The x-axis is in days and the y-axis is in ns.
>>The first derivative of the equation has a first term of 2 * 2.7943 * x
>>ns/day or +5.3E-14 seconds/seconds drift rate.
>>Today's plot is at: file:///C:/Webdocs/pdf/sn1013_850_Drift2.pdf
>>
>>
>
>I'm not sure I follow your math here; and frequency
>drift rates don't have units of "seconds/seconds".
>
>My eye tells me your frequency error (phase slope)
>the first few days is about -25ns/day (-3e-13). The
>last few days it is +25ns/day (+3e-13). The net change
>in frequency is 6e-13 over a 10 day span so your
>frequency drift is about 6e-14/day.
>
>This is odd. It's way too low to be free-running quartz
>(say 1e-9 to 1e-12 per day); it's even too low for Rb
>(about 1e-10 to 1e-11 per month). Yet it seems too
>high to be a correctly working Cs.
>
>Do you have simultaneous M12+ plots of both S/N
>1227 and 1013?
>
>/tvb
>http://www.LeapSecond.com
>
>
>
>
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