[time-nuts] I now have a clock accurate to 10E-6!!!

Jim Palfreyman jim77742 at gmail.com
Mon Aug 25 07:40:14 UTC 2008


Hi Folks,

Well I've had the best weekend since I've just acquired a pendulum clock
that used to be a telecommunication time standard in the 50s. It is a German
made Siemens pendulum master clock that is about 150cm high and has a
full-length seconds pendulum which is about a metre long. It is powered by
48V to automatically wind the weight up and will maintain time for about 8
hours without power.

The pendulum has an adjustment to raise and lower the 7.5kg weight to
calibrate the clock. One full turn of this knob will advance or retard the
clock by 40 seconds per day. It is graduated into 100 divisions enabling you
to adjust it within 0.4 seconds per day. Half way up the pendulum is a
little tray where you can deposit small weights for your final adjustment
(and most importantly without stopping the pendulum!)

Even though it's a master clock it is also designed to be synchronised to
another master clock and so there is an armature on the pendulum that can be
steered by a magnetic coil. I have no documentation on this bit, but when I
figure it out I naturally shall be driving it from a 1PPS reference. (See
photo.)

There are numerous contacts that are designed to open/shut at various times
including every second, every thirty seconds and minute. The photo shows the
mechanism behind the clock face.

By connecting the seconds contact up to my 5370B I tuned it quite quickly to
be accurate to about a second a day. Which is about 10 microseconds per
pendulum swing! I'm impressed a tick tock clock can do that. (Although it
pales into insignificance compared to what Harrison accomplished.)

It is beautifully constructed and now one of my prized possessions!

(I'll put some more photos in another post.)

Regards,

Jim
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