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.
-John ============ > 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 Electronics and computing are outdated in a few years and any 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 >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ >> time-nuts >> and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
