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
