"breathes" while oscillating back and
forth.
If any coils of the hairspring
touch each other, it effectively
shortens the length of the spiral and
radically increases the spring rate and
natural frequency of the oscillator.
Even small spurious magnetic fields
will cause the coils to stick together
when magnetized and make huge
increases in the rate of a watch.
It is not easy to demagnetize the
hairspring in an assembled watch, but
it can be done by immersing it in a
demagnetizer several times. Look at
the hairspring of a magnetized watch
while running and you will see the
coils sticking to each other and
destroying its spiral profile.
So, the answer to the first
question is that the oscillator is
isochronous and therefore immune
ANSWER #2. EDDY CURRENTS ARE
NOT IMPARTING ENERGY TO THE
MAINSPRING.
Eddy currents cannot impart
energy to the mainspring, and even if
they could, would not affect the rate
of the watch. Eddy currents act as a
mechanical brake and require relative
movement between a magnetic field
and a conductive — but not
necessarily magnetic — material.
If the balance wheel assembly
were highly magnetized, it could
generate a little eddy current braking,
resisting the oscillatory movement,
but isochronism would keep the rate
constant. You can make huge
changes to the mainspring of a good
watch and leave the rate relatively
constant.
ANSWER #3. MAGNETIZED
MOTORS DO NOT RUN MORE
EFFICIENTLY.
Magnetized motors may run less
efficiently because of the spurious
braking action of the unwanted eddy
currents. Note that motors that use
more non-conductive material like
plastic in their structure can improve
efficiency by minimizing eddy
current braking.
I was not as brief as I should
have been, but I wanted to
emphasize how hidden magnetic
fields can degrade mechanical
devices.
David Miller
Boulder City, NV
You've really considered the
questions posed in my editorial,
David. You apparently know your way
around a mechanical watch. It is
much appreciated.
As an aside, I've been reviewing
the various electro-mechanical
engines developed by Seiko over the
past few decades, including their
spring drive, which is part mechanical,
part quartz.
Bryan Bergeron
Spiraling Together
I love Bryan Bergeron’s column.
It's the first thing I read.
READER FEEDBACK Continued from page 7
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62 January 2016
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