Nuts and Volts - January 2016

"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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