[time-nuts] Regulating a pendulum clock

Bill Hawkins bill at iaxs.net
Mon Aug 9 20:53:47 UTC 2010


Note:
It would be easier to use separate clocks and masses for
the solar and lunar compensations.

Bruce suggests that the masses may be too massive.

If you mounted the compensated clock on vertical rails, how
long would the rails have to be to compensate by
accelerating the whole clock? How good would the
compensation be if the clocks controlling the acceleration
(with gears and ropes) were not themselves compensated?

Too bad I'm overworked, as usual (volunteered to edit 4 books)
because it poses an interesting problem that could be worked
out with a slide rule.

Anyway, it's a pleasant change from reading about micro-
controllers and de-spiking inductors (whatever happened to
RC snubbers? That's how telco got speed without sparks from
their relays).

Bill Hawkins

-----Original Message-----
From: Bill Hawkins [mailto:bill at iaxs.net] 
Sent: Monday, August 09, 2010 3:36 PM
To: 'Discussion of precise time and frequency measurement'
Subject: RE: [time-nuts] Regulating a pendulum clock

Ahhh, this is more like it! Large gears and thick ropes moving
heavy weights up and down. :)

Of course, you wouldn't want anything digital doing this. Just
a large pendulum clock driving a maze of gears that calculate
solar and lunar positions.

Bill Hawkins 

-----Original Message-----
From: J. L. Trantham, M. D.
Sent: Monday, August 09, 2010 3:10 PM

Personally, I would get out of the way.  : )

Joe

-----Original Message-----
From: Ian Sheffield
Sent: Monday, August 09, 2010 1:17 PM

What happens when the rope breaks?

-----Original Message-----
From: J. Forster
Sent: 09 August 2010 19:10

You could put a large mass of concrete or somehing above the clock and
crank it up and down, to balance out the computed gravity changes.

:)

-John

> 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: mike cook
> Sent: 09 August 2010 18:21
>
> On 09/08/2010 18:46, Bob Holmstrom has written:
>>
>> 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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