[time-nuts] Regulating a pendulum clock

J. Forster jfor at quik.com
Mon Aug 9 23:22:28 UTC 2010

In principle, there is no real reason a Rb, Cs, ot atomic fountain could
not be made to last a very, very long time in a lab. It would certainly be
possible to design a source that is either continuously fed from the
outside or a pair of sources that can be changed to maintain continuous
operation. Ditto for the vacuum system, and detector assembly. It'd be a
christmas tree of SS and Conflat. Not small but do-able. Electronics can
be designed to be hot-swapped at the functional block level.



> There are many pieces of technology developed in the 20th century
> that have not been applied to pendulum clocks.
> My take on much of the technology is that it is too volatile to be of
> use in making a better clock. The task is not to keep better time,
> that has already been done with non-mechanical clocks by atomic
> clocks. But atomic clocks only work a few years before they
> fail. Electronics and computing are outdated in a few years and any
> use of these technologies in a clock fails due to lack of
> spare parts and closure of the plant that made the components. What
> we need is a clock that can continue for 400 years with
> the skills and technology that will be available over that time span.
> Even in mechanical clocks, technology may fail through lack of
> understanding. I was once a fan of an escapement devised by
> Reid, later LeRoy, that used no crutch on the pendulum. Then I read
> of clocks with this escapement being convert back to a Graham
> escapement by clock repairers who did not understand the superior
> escapement.
> So progress in mechanical clocks should be for a clock that is simple
> to maintain and more precise than alternate clocks.
> To do this the known defects of traditional clocks need to be
> overcome. In the 20th century the big step was a "free" pendulum, this
> usually required a secondary pendulum to "clock" (using electronic
> terms) the system so that the free pendulum would be impulsed
> at the correct time. These clocks removed much of what was known as
> escapement error.
> Circular error is another defect, the frequency of a pendulum is
> slightly dependent on amplitude. Either really accurate control of
> amplitude is required (in some ways equivalent of an oven on a
> crystal) or a method is required to null the circular error.
> Barometric error is another defect. Buoyancy error can be eliminated
> in a compound pendulum of suitable design, but the error
> due to inertial effects of displaced air by the pendulum require a
> vaccuum (which is very inconvenient) or perhaps an idea I am
> working on of a container around the pendulum oscillating in the same
> phase and amplitude to move the air with the pendulum.
> This container could be the second pendulum which is phase-locked to
> the free pendulum and whose minor timing problems
> would not be significant.
> There is a geometric solution to circular error, a bit similar to the
> tempco turn-over in crystals, where locally the defect has zero
> amplitude.
> The remaining problem is to incorporate these ideas into a design
> that is entertaining to behold, simple to fix and durable enough to last
> long enough to make it worth maintaining.
> As for technology, electromagnets are robust, we have some great new
> materials, rare earth magnets and some great methods of construction.
> I look forward to a clock that, compared to an atomic clock, is
> really just an accurate gravity meter.
> cheers, Neville Michie
> On 10/08/2010, at 2:46 AM, Bob Holmstrom wrote:
>> 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?
>> Bob Holmström
>> Editor
>> Horological Science Newsletter
>> www.hsn161.com
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