[time-nuts] Physical Clocks - adjusting
Dr. David Kirkby
drkirkby at medphys.ucl.ac.uk
Thu Apr 28 07:01:16 EDT 2005
Mike S wrote:
> What got my interest in precision time started was adjusting clocks - especially wristwatches. I've tried to keep track of watch time vs. WWV and tweak adjusters to make them better, but it's a very long process, and I've not been particularly successful, probably due to lack of patience and diligence.
> So, with that interest, I thought to put together an electronic calibrator. My thought is to use a microphone or piezo disc somehow coupled to a watch to pick up the mechanical vibrations, amplify (filter?), and feed that into a TI counter. 3e-7 gets 1/sec/month, as much as can be expected with a normal wristwatch. That should be easily done, and allow adjustment in a matter of minutes. TVB's precision wristwatch isn't practical for my purposes. :-)
> A commercial unit is shown here: http://www.bmumford.com/microset.html
> They have a "simple watch sensor" ( http://www.bmumford.com/mset/access/watch.jpg ), which I guess to be a piezo sensor, fixed at one end with a brass post attached to the other, which in turn protrudes through the top of the case. Mechanical vibration in a watch in contact with the brass rod would generate the signal.
> Anyone with any experience with such a calibrator? My biggest concern is that there will be too much noise in the signal to get an accurate TI measurement.
I've not tried it with a watch, but did try it with my pendulum clock
using a microphone. When looked at on
scope, the signal was far from repeatable. Each oscillation was
different from the previous one, with no obvious correlations. I intend
hooking up an optical system, and are hoping the swing of the pendulum
is less erratic, otherwise my idea of locking this to quartz is not
going to work very easily.
I then tried the microphone on a cheap quartz clock, where the sound
from the second hand produced a nice clean signal on the scope, that
would be easy to trigger a counter on.
Dr. David Kirkby PhD CEng MIEE,
Senior Research Fellow,
Department of Medical Physics,
Mallet Place Engineering Building,
University College London,
London WC1E 6BT.
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