## PSN-L Email List Message

Subject: Re: earth tide tables
From: ChrisAtUpw@.......
Date: Fri, 24 Jun 2005 23:43:09 EDT

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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.

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
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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=
t=20
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=
le=20
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.....

The NAWCC science chapter 161 http://www.ubr.com/clo=
cks/nawcc/hsc/hsc.html has=20
a lot of worthwhile articles in their archives.