I
am collecting long-term clock data in this period and
looking at them occasionally I was bothered by noise bursts
I could not attribute to anything obvious. Since i live next
to a canal I was aware that boat traffic could account for
night/day noise differences, less intense during weekends.
But I was also getting random and large standard
deviations of the period measurements I couldn't explain
with instrumental or other effects. Here is an example, the
time trace is in hours:
The
clock period shown here is averaged over the 5 period
impulsing interval.
The
most common steady level is the one on the right of the
above chart, SD around 10 μs, as opposed to the 10 times
larger one at the center of the image.
The
clock is my magnetically impulsed synchronome described here, where the
pendulum is impulsed once every 5 periods.
I
don't get to go out too much during these quarantine days, a
centuries old tradition of Venice, my town, but I go for
groceries and some basking in the sun of the now almost
perfectly empty old town.
During
these outdoor activities I noticed that there was a good
relationship between wind strength and the standard
deviation of the period fluctuations.
The
following chart shows this for the above illustrated typical
case of March 23rd, where wind speed, in the 10 to 20 m/s at
the peaks and professionally monitored by a city weather
station, is superimposed to the fluctuations SD against time
in days.
The
relationship with atmospheric pressure is shown below:
I
am aware that these high frequency fluctuations are not very
relevant from the standpoint of the time measurement
accuracy, in the range where time accuracy is normally most
valued, but I find interesting that this effect is so large
for a clock which is bolted down to the internal foundations
of a building as sturdy and heavily built as mine, a former
army barrack from the Augsburg times. Wind turbulence is
doubly screened by tightly sealed apartment windows and the
clock case. Is this the effect of foundation vibrations or
of pressure fluctuations propagating indoor as inaudible
sub-hertz sound waves? Does anybody else see a similar
behavior? Any alternative explanation? I do have wind
direction measurements to help with the interpretation but I
didn't have time to check their correlation.
--
Bepi
