[time-nuts] Non electrical time-nuttery

Brooke Clarke brooke at pacific.net
Tue Jan 12 14:42:32 UTC 2010


Hi Tom:

One problem with adjusting the rate of a pendulum clock is that you 
don't want to stop it to make fine adjustments.  That's why the tray for 
the micro weights.  In the case of the Western Union Self Winding Clocks 
you can slow down the pendulum by dropping candle wax on the bob.
http://www.prc68.com/I/SWCC.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com


Tom Van Baak wrote:
>> How does the pressure change the frequency?
>
> Assuming a fixed mechanical impulse, an increase in
> pressure will result in a slight decrease in amplitude
> due to the increased friction of the air. Then because
> of circular error this will result in a very slight change
> in period (by a few tens to hundreds of ppm). Thus
> you can use pressure as a fine-adjustment of rate.
>
> Equivalently, if one does not maintain the pressure to
> some level of stability, it will affect the stability of the
> amplitude which will affect the stability of the period
> which will affect the timekeeping performance of the
> clock. The exact numerical relationship among these
> factors depends on the design of the clock.
>
> So as you can imagine open-case pendulum clocks
> make good barometers as well as thermometers. And
> that's one reason why all the best pendulum clocks
> make use of a sealed, low pressure, chamber.
>
>> That does raise an interesting issue.  How would you fine tune a 
>> pendulum?
>
> Typically one adjusts the effective length by placing
> micro-weights to slightly move the center of gravity
> of the bob. Larger adjustments are made by raising
> or lowering the bob itself with the rating nut.
>
> These technique is also used for vacuum pendulum
> clocks but one does not want to do it more than once
> or twice.
>
> /tvb
>
>
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