Anti-magnetic watches: Effective protection from magnetic fields

It is clear that magnets and mechanical watches are not a good combination. Nobody would think of holding a magnet to an automatic watch. Nevertheless, the fact is that magnetism is one of the most common reasons why an automatic watch runs too fast, runs slow or stops completely. One solution to this problem are so-called “anti-magnetic watches”, which, unlike conventional mechanical watches, are less sensitive to magnetic fields.

Before we get to the different types of anti-magnetic watches, however, let’s first take a look at what magnetic fields exist in everyday life and why magnetism can have a negative effect on the accuracy of watches. At the end of this article, we’ll look at how to tell if a watch is magnetized and what options are available to demagnetize the watch again.

Magnetic fields in everyday life

In addition to shocks, magnetic fields can also negatively affect the accuracy of watches. When you think of a magnetic field, the first thing that comes to mind is a magnet. But in addition to classic magnets such as those found in bag fasteners or refrigerator magnets, electrical devices such as hand mixers, cordless vacuum cleaners, tower PCs, sound bars and loudspeakers also cause magnetic fields. Therefore, a non-antimagnetic automatic watch that has been placed on a soundbar for several hours out of ignorance, for example, can subsequently run very imprecisely or even stop. Because the fact that this soundbar is operated by a magnet, causing (even in standby mode!) a magnetic field, which in turn affects the accuracy of the watch, is known to very few people.

But why do magnets or magnetic fields have such a strong effect on mechanical watches?

The influence of magnetic fields on watches

To understand why magnets have such a strong effect on mechanical watches, we will briefly go into the functioning of these watches. Particularly important here is the wafer-thin hairspring, which, together with the balance, forms the “heart” of the watch and ensures that a mechanical watch ticks correctly. If the movement is now exposed to a magnetic field and the hairspring is made of a ferromagnetic material such as iron or nickel, the balance spring is magnetized. Depending on the strength of the magnetic field, this then has smaller or larger effects on the accuracy of a watch. The spectrum here ranges from deviations of several minutes to several hours per day! With particularly strong magnetic fields, a watch can even stop completely. This is due to the fact that a magnetized balance spring can become “stuck” and thus no longer oscillates as “roundly” as a non-magnetized balance spring.

Before we get to watches that are insensitive to magnetic fields, let’s take a brief look at the history of the anti-magnetic watch.

The history of the anti-magnetic watch

The history of anti-magnetic watches began over 100 years ago. As early as 1915, the first watch of this type was developed. It was a pocket watch.

In fact, the development of anti-magnetic watches was necessary at the beginning of the 20th century, because already then mechanical watches were negatively affected by magnetic fields. For example, the electric motors of locomotives or the magnetic deflection coils of radar screens in airplanes interfered with the accuracy of the watches.

The first wristwatch series with magnetic field protection was produced in 1930, and in the 1940s the first watch model came onto the market that protected the movement from magnetic fields by means of the principle of the so-called Faraday cage or soft iron cage.

Types of anti-magnetic watches

Nowadays, two types of magnetically insensitive watches have become established: antimagnetic watches with soft iron cages and, since about 2000, watches with hairsprings made of silicon or other amagnetic materials such as Glucydur.

Anti-magnetic watches with soft iron cage

In this type of watch, the entire movement is encased by a so-called soft iron cage to protect it from the influence of magnets. Soft iron consists of unalloyed iron of high purity and is characterized by the fact that it is very easy to magnetize, but not permanently magnetized. It absorbs magnetism and quickly releases it, thus reliably and permanently protecting the movement from the influence of magnets.

A soft iron cage for watches consists of the dial, a movement ring and the caseback. To ensure that the movement is completely enclosed, watches with soft iron cage typically have a screw-down crown and no date display.

The precise Sellita SW200-1 movement in the Elaboré version, which is installed in the Circula ProTrail Field Watch, is protected from magnetic fields of up to 80,000 A/m (or almost 100,000 microtesla μT, or 1,000 gauss) by the soft iron cage. By comparison, a commercially available soundbar emanates around 5,000 μT. The case is also scratch resistant up to 1,200 Vickers.

These special features make the Circula ProTrail a robust companion for everyday use and outdoor activities!

Watches with hairsprings made of amagnetic materials

In antimagnetic watches of this type, the materials of the hairsprings contain as few ferromagnetic components as possible and are thus insensitive to magnetic influences. A frequently used material is silicon, which is not only amagnetic but also corrosion-resistant. However, since silicon reacts strongly to temperature fluctuations, silicon hairsprings are often coated with an extremely thin layer of silicon oxide.

Another amagnetic material used for hairsprings is Glucydur. The alloy of copper, beryllium and iron is anti-magnetic, corrosion-resistant, very hard and also resistant to temperature fluctuations.

How to find out if a watch is magnetized

Since not all movements are protected by soft iron cages or have an amagnetic hairspring, it is of course important to find out whether a watch with accuracy problems has simply been magnetized (by mistake) or whether other problems are the cause.

The easiest way to find out if a watch has been magnetized is to place a compass next to the watch. If the compass needle is deflected, then that is a sign that the watch is magnetized.

A watchmaker can also check if the watch is magnetized. If the unusually high rate deviation has another cause, then the watch is also directly in the best hands at the watchmaker.

Demagnetize a watch

If the watchmaker has determined that the watch is magnetized, then he can quickly demagnetize the watch.

Another method is to purchase a (watch) demagnetizer yourself. These devices are available in different price ranges.

And if you would like to have a watch whose movement is protected from magnetic fields of up to 80,000 A/m, then be sure to check out the Circula ProTrail!