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 Electronics and computing are outdated in a few years and any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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