PSN-L Email List Message
Subject: Re: earth tide tables
From: ChrisAtUpw@.......
Date: Fri, 24 Jun 2005 23:43:09 EDT
In a message dated 25/06/2005, royb1@........... writes:
A friend has several high precision pendulum clocks (and has built 2
others).
He asked me to inquire of this list about where to get tables of
earth tide data so that he can compare changes in the local value of g
to daily variations of period which he sees in his clocks.
Hi Bob,
If my memory is correct, the tide effects are at the 0.1 ppm level and
below. 1 ppm is about 1 sec every 11.57 days. You don't say what level of
accuracy he is aiming at. Three serious problems are providing adequate thermal
compensation, removing the effects of variations in the angle of swing and
removing seismic / environmental motion changes - particularly the ocean
background. Dual coupled pendulums working in antiphase can be an advantage here.
The pendulums need to be in airtight casings to remove atmospheric density
changes. Providing a high vacuum will show greatly increased Qs, up to maybe a
million, mostly below 10^-3 torr. The ecitation and the relation of it to the
timing of the swing are critical. He needs to correlate drifts with daily
changes to remove solar heating, ground tilts, weather effects.....
The NAWCC science chapter 161
_http://www.ubr.com/clocks/nawcc/hsc/hsc.html_ (http://www.ubr.com/clocks/nawcc/hsc/hsc.html) has a lot of worthwhile
articles in their archives.
Regads,
Chris Chapman
In a message dated 25/06/2005, royb1@........... writes:
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friend has several high precision pendulum clocks (and has built 2=20
others).
He asked me to inquire of this list about whe=
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to get tables of
earth tide data so that he can compare changes in the=
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local value of g
to daily variations of period which he sees in his=20
clocks.
Hi Bob,
If my memory is correct, the tide effects are a=
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the 0.1 ppm level and below. 1 ppm is about 1 sec every 11.57 days. You don'=
t=20
say what level of accuracy he is aiming at. Three serious problems are provi=
ding=20
adequate thermal compensation, removing the effects of variations in the ang=
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of swing and removing seismic / environmental motion changes - particularly=20=
the=20
ocean background. Dual coupled pendulums working in antiphase can be an=20
advantage here. The pendulums need to be in airtight casings to remove=20
atmospheric density changes. Providing a high vacuum will show greatly incre=
ased=20
Qs, up to maybe a million, mostly below 10^-3 torr. The ecitation and the=20
relation of it to the timing of the swing are critical. He needs to=20
correlate drifts with daily changes to remove solar heating, ground tilts,=20
weather effects.....
Regads,
Chris Chapman
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