[time-nuts] Regulating a pendulum clock
lists at rtty.us
Mon Aug 9 23:12:51 UTC 2010
Putting a computing device on a pendulum to compensate for "known effects"
is really no different than what you do with a analog or digital TCXO. I
suspect that the gravitational impact of the sun and moon can be calculated
with pretty good precision. The same would be true of secondary pressure
From: <bg at lysator.liu.se>
Sent: Monday, August 09, 2010 7:07 PM
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Subject: Re: [time-nuts] Regulating a pendulum clock
> Hi Ian,
>> Unfortunately Gravity is not constant. Pendulum clocks show cyclic errors
>> due to the influences of the Moon's and Sun's Gravitational fields. I
>> the amounts but it is in the region of parts in 10 to the 7, which is
>> This limits the compensations one can put into a pendulum clock.
> http://en.wikipedia.org/wiki/Tidal_force gives 1.1e-7g and 0.52e-7g for
> Moon and Sun acceleration at Earth.
> Hmmm that is ca 0.1 microg (ug).
> Leaving the pendulum clock line of thought... by instead measuring this
> change of apparent gravity and the models for Moon-Earth relative
> positions we have a source of time!
> Hmmm... spec sheet of my best accelerometer
> Temp stability <30 ug/degC
> 1 year bias stability <250 ug
> Threshold/resolution <1ug
> The accelerometer clearly needs to be ovenized, and hopefully the spec is
> is conservative and I need to have luck with a really good accel. You also
> need to mount it on a structure separate from where you walk. No nearby
> heavy vehicles and so on. Well we will need a stable sampling clock, so
> maybe the pendulum is back in the picture.
> As the sensing element in the acc is made of quartz, and adding an oven -
> there are quite a few similarities with an OCXO! Lesser models of these
> accelerometers are operated as temperature compensated or without any
> temperature compensations - compare with TCXOs and XOs...
> Sorry if this went off topic!
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