Re: Clock or anemometer?


neil
 

Hi Bepi,
                Its good to hear from you again, and that you are well. My wife & I are also in lockdown, and staying home 24/7.
Fortunately i am abale to continue work on my clock. i received a 1m length of Quartz glass 10 days ago and have dismantled the clock, in preparation for replacing the invar pendulum with quartz galss, and a below the bob aluminum temperature compensator, as described in Matthys's book "the accurate pendulum".
At the moment I have a 14lb bob hanging on the glass, to test the means of attachment, which is not easy.  I was intending to drill a hole thru the rod and use a pin, but because of the lockdown, I am unable to access a diamond drill, so will probably use expoxy or epoxy/carbide dust as an adhesive. Not as good, but needs must.
neil 

On 4/04/2020 11:35 am, Bepi wrote:

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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