The Faraday cage and the B-Uhr

Watch Angels
Watch Angels
Published in
3 min readMay 16, 2023

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In the early days of watchmaking it was rare to stumble upon magnets, however this changed during the 2nd Industrial Revolution when new power sources were invented and implementd.

Suddenly the new electric power sources were causing precsion problems to previously accurate timepieces. Magnetic radiation has affected mechanical watches ever since. Watches may gain or lose time because when exposed to a magnetic field.

In particular, mobile phones, television and PC speakers, magnetic necklaces, handbag clasps, hair-driers, electric razors, magnetic parts of refrigerators are all magnetic and can influence the precision of the movement. To make matters worse, a mechanical watch which has been affected by magnetism remains magnetised even after removing it from the magnetic source.

What happens when a watch movement becomes magnetised?

The many parts of a watch movement are purposely designed to run as freely as possible and to experience as little friction as possible. They are locat­ed within a very small area, where they have to co-exist and operate in close harmony and under extreme tolerances. When ferrous metal parts or parts that contain some iron are mag­netised they become attracted to one an­other and, rather than run smoothly, they attempt to stick together and this friction, of course, disrupts the precise running of the movement. In particular, it causes some of the essential running parts, like the balance wheel and hairspring, to stick together and influence timekeeping accuracy. In fact modern watch balance wheels are usually made of an alloy of beryllium, copper and iron, and in practite even brass contains some traces of iron.

The Watch Angels design type antimagnetic B-Uhr “Baumuster B”

When the main requirement of a watch is precision — like for a B-Uhr used by pilots to navigate in the air — magnetism is a very significant problem which has to be managed in order not to compromise the purpose of the watch and the mission.

Watches and the Faraday Cage

In 1836 English scientist Michael Faraday invented the Farday Cage which blocks electric fields by using conductive metallic materials to pass the force around the outside of the cage, protecting a delicate equipment within.

The Faraday cage protects what it encages because it distributes the effect of the magnetic field over the conducting material which absorbs the magnetic waves, cancelling the effect inside the cage where a magnetically sensible object, like a mechanical watch movement, is placed.

How a Faraday cage works

The softer a metal is, the greater its capacity to absorb magnetic waves. Therefore a Faraday cage is a normally made of soft iron, which is iron that has a low carbon content.

The Faraday cage of the B-Uhr

The B-Uhr Faraday Cage

The movement of the B-Uhr is shielded by a soft iron Faraday cage to keep it’s COSC chronometer tolerance protected from magnetic fields.

Interestingly, the military markings are engraved directly on the Faraday cage and can be seen behind the sapphire crystal display case-back.

The engraved Faraday cage of the B-Uhr behind the sapphire crystal
View the B-Uhr and the case-back in 360°

Learn more about the Watch Angels design type B-Uhr and reserve it here

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