[linux-audio-dev] Setting the Beat of a Clock

capnlinux at handsonarabians.com capnlinux at handsonarabians.com
Tue Sep 27 10:04:30 EDT 2005


There was a question about what kind of accuracy would be required.  Well,
the more the better.  Without electronic assistance this was done by letting
the clock run for a day and measuring it against a known good time source,
adjusting the pendulum, repeat.  Running the clock for longer periods
between measurements obviously makes the adjustment more accurate.

 

With electronic assistance the same rules apply.  Running the clock longer
between measurements makes the adjustment more accurate.  Let's do some
math.  Assuming we use one pendulum cycle to measure the period and say that
this clock is geared for a one second pendulum cycle.  If we can measure
that one second with an accuracy of 100ths of a second, then our average
error will be half that or

0.005 sec / sec   or

0.3 sec / min   or

0.3 min / hr     or

7.2 min / day  or

216 minutes over 30 days

If this is a 31 day clock, over 3 hours off is not very good per winding.
If I can get millisecond accuracy, then I'm down to 21.6 minutes over 30
days which is still not very good.  Now if I increase my sample size to 10
pendulum cycles and still maintain millisecond accuracy, I can set the clock
within 2.16 minutes lost/gained in 30 days.  That would be a good start.  It
would only take me 10 seconds to decide to adjust the clock slower or faster
and I would eventually be correct to within .072 minutes per day when I
finished adjusting to the accuracy level of this instrument.

Further adjustments using longer sample times would then be able to increase
the accuracy to the desired level or at least to whatever level of accuracy
the clock works are capable of.

Returning to one of my original questions.  Does anyone have any suggestions for
useful libraries or example source code to study as a start for this project?

 


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