[time-nuts] Regulating a pendulum clock

[Didier Juges]

"This limits the compensations one can put into a pendulum clock" unless you actually build compensation for those effects too :)

I would think the timing of gravitational effects of the moon and the sun can be easily predicted. I am not sure the amplitude of these effects can be precisely modeled, but that would be an interesting part of the project. If you know the timing of a perturbation, you can measure the effect from the instrument itself (by checking it against a reference that is insensitive to that perturbation and applying the proper filtering algorithms) and determine the coefficients experimentally.

That is what the Thunderbolt does while it is locked to GPS, so that when it loses the signal, it can keep its OCXO in check. 

Didier


------------------------ 
Sent from my BlackBerry Wireless thingy while I do other things...

-----Original Message-----
From: "Ian Sheffield" <ian.sheffield1 at tesco.net>
Sender: time-nuts-bounces at febo.com
Date: Mon, 9 Aug 2010 18:34:40 
To: 'Discussion of precise time and frequency measurement'<time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: Re: [time-nuts] Regulating a pendulum clock

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.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of mike cook
Sent: 09 August 2010 18:21
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Regulating a pendulum clock



Le 09/08/2010 18:46, Bob Holmstrom a écrit :
>
> Food for thought.
>
> I find it interesting that no one has suggested alternatives to 
> improving the performance of a pendulum clock other than controlling 
> it with a higher performance clock.  If the goal is a better clock why 
> not attempt to understand the source of the errors and work on methods 
> to control or compensate for them?  Teddy Hall has been taken to task 
> for using a quartz controlled oscillator to measure the amplitude of a 
> pendulum in the control loop of his Littlemore clock.
>
> Tom Van Baak has developed techniques for analyzing the performance 
> and hence potential error sources of pendulum clocks - perhaps he will 
> share some of his work here.
>
> Horological history is full of many attempts at solutions to the 
> problem, but it would seem that the creativity of this group might 
> generate some new ideas that are more in the spirit of better 
> timekeeping than attaching the pendulum to a better oscillator.
>
> How about a wireless controlled device attached to the pendulum that 
> changes its position based on error sensor readings, not time errors, 
> but instead, temperature, barometric pressure, gravity, etc. that 
> would maintain a more constant pendulum period?

Yup. We have temperature and pressure ICs available , I think that 
gravity is pretty constant if the clock isn't being moved about. 
Humididty might also need logging aswell. So it should be easy enough to 
predict the pendulums response to changes given a reasonable time of 
observation.
  That said, clocks have always been adjusted against better 
references.. IIRC Harrison (and probably others) was using star transits 
to regulate his long case clocks.
>
> Bob Holmström
> Editor
> Horological Science Newsletter
> www.hsn161.com
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>
>


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