I decided to impulse the clock electromagnetically for a number of reasons. It was
a fairly simple system, I could control the amount of impulse easily and I could
use electromechanical logic in keeping with the precision clocks of the early 20th
Century. (I was always more comfortable using relay logic). Makers of precision
electromechanical clocks impulsed the pendulums in many ways. Fedchenko used electromagnetic
impulsing below the pendulum bob very successfully. In an early experiment, Shortt
also used under the bob mechanical impulsing but never achieved acceptable results.
The later Shortt clocks mechanically impulsed the master clock more or less directly
against the pendulum rod. I thought Riefler had one of the best systems.
He impulsed the pendulum through the suspension spring - a very elegant solution.
I decided to do something similar by giving impulse to the pendulum directly to
the pendulum rod at the fulcrum of the suspension. I thought this would have the
least disturbing effect on the pendulum and was for me a very practical solution.
I mounted a small arm (the impulse arm) perpendicular to the pendulum rod at the
suspension. I fixed a small iron cobalt magnet at the end of the arm which moved
between two opposing coils. By reversing the current through these coils alternately
I was able to impulse the pendulum in both directions .There are three HE devices
in the clock. One of them senses the pendulum passing the center point of its excursion.
The other two sense the end of the swing at each side. As the pendulum passes the
center point, the HE device senses the small magnet fixed to the pendulum rod. It
turns on and causes the pair of impulse coils to give a short impulse to the magnet
fixed to the impulse arm. As the pendulum continues to the end of its excursion,
the HE device mounted to the side of the pendulum senses it and reverses the polarity
of the voltage supply going to the impulse coils. As the pendulum reverses itself
and again passes the center HE device, the impulse coils turn on again and give impulse
in the other direction completing the cycle. The HE device at the center of the swing
is mounted on a two axis micrometer adjustment that permits centering the HE device
as well as moving it closer to or away from the pendulum rod permitting adjustment
of the length of the impulse. It was a relatively simple business to design the logic
to keep the pendulum running. I used small mercury relays on the logic board because
of the very large number of operating cycles. The relays I used here made by CP Clare
will run for approximately 90+ years operating at 1 cps.
(ABOVE) Q1 on the test stand showing the relationship between the impulse coils
and the pendulum rod. The glass bulb on the left is a capillary style sensitive
vacuum gauge vernier.
(BELOW) A closeup of the experimental setup used to test the strength of the impulse
given to the pendulum assembly. The field of the coils is reversed alternately.
(BELOW) The finished clock impulse mechanism showing the adjustable beat plate and
adjustable impulse coils.
Q1 showing the impulse arm attached to the trunion holding the pendulum rod. A counterweight
is fitted to the side opposite the impulse arm.