Re: Timing data for Synchronome # 2177


A vibrating pendulum rod is also oscillating the bob vertically.
Any bend shortens the rod. Which is the time standard now?
The oscillating shortened rod? Somewhere in between? Or the relaxed one?
Imagine "bending" a string on a guitar....


On 22/10/2019 23:56, Neville Michie via Groups.Io wrote:
Vibration of the pendulum rod should not be a problem if it has completely
died out by the time the pendulum is next impulsed.
A pendulum has one resonant frequency, the rate at which it beats.
You could apply energy at any other frequency, and unless there was a
non-linear process that could modulate the main resonance, the frequency of
the pendulum will not be affected.
However, interference at the same frequency, like another clock mounted on
the same wall, can add or remove energy from the pendulum.
The energy absorbed from a short impulse has many frequency components,
but only the frequency of the beat can be taken up by the pendulum.
If the pendulum is still shaking when next impulsed then the phase
of the impulse could be modified, this being a non-linear process there
could be interference with the pendulums frequency.
Neville Michie

On 22 Oct 2019, at 21:35, John Haine <> wrote:

Yes, my rod is actually CF tube. I suspect that it is no more rigid than invar. Actually I suspect that the vibration is not the rod bending, but rotating around the CG of the bob against the suspension spring - as Tom pointed out a while back it would be better to impulse through the centre of percussion of the pendulum to avoid this. I do see a bit of this movement especially when starting up but I don't think it's a big problem, the vibration frequency is well above 0.5 Hz.

I agree that the 'Nome is a very robust and reliable design, a great bit of "intermediate tech". That's not to say that it can't be improved with some modern techniques though.

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