Re: Magnetic vs gravity impulsing

Harvey Moseley

Hi Bepi,

Very impressive and interesting results!  These results raise a question; why is the mechanical impulse noisy?  I was trying to make a list of possible error sources:  1) dissipation in the mechanical impulse system 2) chaotic behavior due to nonlinearity in the impulse (bouncing, etc)  3)  timing errors in the fall of the gravity arm. 
The third (perhaps combined with the first) could be tested using your sensor to release the gravity arm rather than the gathering wheel.  Anyway, this is all very interesting. I look forward to seeing the results of your autocorrelation measurements.

Best Regards,

On Mon, Jan 13, 2020 at 7:04 AM Bepi <pepicima@...> wrote:

The old dear synchronome seems to be much better at measuring time than I was expecting.

When I say measuring time I mean intrinsically, with reference to its own internally produced noise. Then there are all those nasty potentials which depend explicitly from time like temperature, pressure, lunar attractions, etc, we'll take care of them later, here I am only concerned with the internally manufactured noise. Correct me if I am wrong.

The ones who have looked at my previous post might have noticed that I added to the clock a magnetic impulsing system which seems to be working really well, if somebody is interested I could describe it in detail in a following post.

It works really well especially in the sense that I could practically reduce the impulse irregular period to the level of any other period by carefully centering it in the sense of Airy's tangent rule. The average power is somewhat reduced too, I got rid of the clock losses linked to the timing wheel operation, and I am always referring to stationary states at constant amplitude of when the clock tiks normally, I should say ticked.

In the following I will show data where the amplitude stays the same within a few thousands of a degree for hours, corresponding to a fraction of a microsecond of circular error.

With the following graphs I'll compare two runs, one with the magnetic impulsing and the other with the old gravity escapement of a classic synchronome. The clock is always the same, I can switch from one impulsing scheme to the other in a matter of minutes on the same clock, the one I purchased a few months ago on Ebay for 280 pounds.

First set of plots refer to the classic escapement:

the second set of plots to the MI (magnetic impulsing) case:

Compare the second graph of both set first: the average period over the impulsing cycle vs time in hours. The average is different because the data were taken months apart and the calibration had been changed in the meantime, but we are not interested in the average, we are interested in the regularity of the clock. The y scale to contain all the measurements is roughly twice as big for the MI data, in fact over the experimental run the SD (standard deviation) of the MI data is 4.14 μs while for the gravity arm case the SD is 1.82 μs. The impulsing cycles are different, the MI cycle consists of 5 clock periods, the synchronome of 15, but the MI data have been averaged over the same number of periods, 15, before taking the SD, so the comparison is fair.

The circular error variation calculated from the amplitude (green points third graph) is shown in the red trace. In both cases is negligible, less than 1 μs.

The real surprise is in the detail of a cycle, first trace. The data show typical individual period amplitudes during the run. Those specific ones occurred at the end of the blue trace just below the second graph, in hours from the beginning of the run.

Pay attention to the y scale in those graphs, always in s, the mechanical escapement induces ms size fluctuations around the power impulse while the magnetic impulse induces a variation in the order of tens of μs, if any. The MI impulse was not optimized carefully but its amplitude deviations are nevertheless not bigger than the following free pendulum ones.

The regularity of a clock, even this fast scale regularity, is not just a matter of size of the fluctuations but also of their correlation properties, I'll test the autocorrelation function when I have time, but the fluctuations themselves are a prerequisite for errors and in the mechanical case they are almost 2 orders of magnitude larger. Since the SD we are talking about is the one of the averages over the whole cycle what just said means that those large deviations of impulse duration occurring at and around impulsing are just as regular and reproducible as all the others.

I find this surprising and I would like to share it with those people that fell speechless in front of these data too.


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