[time-nuts] Hello
Neville Michie
namichie at gmail.com
Wed Mar 28 00:44:53 EDT 2007
>>> Yes, others working with pendulums have also discovered that they
>>> end
>>> up making crude thermometers, barometers, or seismometers instead
>>> of a
>>> good clock. Still, not a reason to give up. But you know you have a
>>> world-class pendulum clock when, after having solved every other
>>> perturbation, you can see the effects of lunar tides in your data
>>> (as
>>> your good pendulum clock demonstrates it is also a fair gravimeter).
>>
>> That seems like a neat threshold. Are current pendulum clocks
>> good enough to
>> notice tides? When was the first published paper? If not, how
>> close?
>
> Yes, it is a neat benchmark. Not a few modern clock makers
> have tried to reproduce or improve on the old masters. It turns
> out a pendulum clock needs to be accurate (stable) to 1e-7 or
> 1e-8 for tau from an hour to a day in order for it to "detect"
> tides. See this article I wrote a while back on the subject:
>
> Lunar/Solar Tides and Pendulum Clocks (part 1)
> http://www.leapsecond.com/hsn2006/ch1.htm
>
> Not sure what you mean by "current" pendulum clocks. I think
> modern commercial pendulum clocks are nowhere as accurate
> as the state-of-the-art pendulum clocks of the 1920's. Quartz
> clocks in the 30's and atomic clocks in the 50's put an end to
> the market for ultra precise pendulum clocks.
>
> /tvb
>
>
My work with a pendulum seems to point to the need to know the exact
phase and amplitude of the pendulum as being a sticking point.
The pendulum can be mounted firmly, with no yielding or flexing of
brackets on a masonry mount bedded well into the ground.
The pendulum can be made mechanically stable with accurately fitted
joints between shaft and bob, and shaft and suspension.
The pendulum can be excited with a minute magnet and an air cored
coil to drive it with a few nanowatts.
The pendulum can be shielded from air currents and vibrations.
However accurate signals for phase and amplitude measurement with
accuracy of microseconds for phase and microns for amplitude seem to
be the challenges that must be met, this information is necessary to
generate the pendulum drive so that the pendulum is the only
frequency determining element.
Compensation for temperature and barometric pressure are do-able,
although the legendary clocks were in a vacuum (more or less) and in
underground clock vaults kept at constant temperature.
I still have hopes of getting great performance from a room
temperature clock at ambient pressure.
See
http://ph.groups.yahoo.com/group/synchronome/photos/view/c1ba?b=1
cheers, Neville Michie
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