Hi
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
effects.
Bob
--------------------------------------------------
From: <b...@lysator.liu.se>
Sent: Monday, August 09, 2010 7:07 PM
To: "Discussion of precise time and frequency measurement"
<time-nuts@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
forget
the amounts but it is in the region of parts in 10 to the 7, which is
easily
measurable.
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...
http://www.inertialsensor.com/
Sorry if this went off topic!
--
Björn
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