Re: Clock or anemometer?


Andrew Nahum
 
Edited

Of course, the wind could also depressurise the house if any permeable areas are in the right ‘wind shadow’ zone. Few buildings are truly airtight - except bio security labs. 



On 4 Apr 2020, at 13:33, Andrew Nahum via groups.io <andrew.nahum@...> wrote:

The association with wind speed is fascinating. I wonder if the wind could in some way be pressurising your house?  Do you have a barograph actually next to your clock or is your pressure data that for  the Venice area taken from the public weather service?

The empty city must be quite wonderful in a way!  Andrew Nahum 


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

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