From Wikipedia, the free encyclopedia
Anti-magnetic (non-magnetic) watches are those that are able to run with minimal deviation when exposed to a certain magnetic field. The International Organization for Standardization issued a standard for magnetic resistant watches, which many countries have adopted.
ISO 764 magnetic resistant watches standard
The international standard ISO 764 Horology—Magnetic resistant watches defines the resistance of watches to magnetic fields. According to ISO 764 or its equivalent DIN 8309 (Deutsche Industrie Norm - German Industry Norm) a watch must resist exposition to a direct current magnetic field of 4,800 A/m (Ampere per meter). The watch must keep its accuracy to +/- 30 seconds/day as measured before the test in order to be acknowledged as a magnetic resistant watch.Annex A of ISO 764 deals with watches designated as magnetic resistant with an additional indication of intensity of a magnetic field exceeding 4,800 A/m.
There are two ways of building an anti-magnetic watch:
- The first way consists in using different alloys, capable of withstanding magnetic fields. These alloys include Invar (iron - nickel - carbon - chromium alloy), Glucydur (beryllium - bronze alloy), Nivarox (iron - nickel - chromium - titanium - beryllium alloy) and Elinvar - an alloy similar to Invar, though less resistant to magnetism and more resistant to thermal influence. These alloys are preferred by different watchmakers due to their differing properties. Since the 1950s, Nivarox and Glucydur were extensively used by watchmakers[who?]. In the 1960s, almost all Swiss watches had Glucydur balance and Nivarox hairsprings. The anchors, escape wheels and other watch mechanisms were also made of non-magnetic metals or alloys.
- Another way of making a watch non-magnetic is to house the entire movement into a case made of a highly conductive (permeable) material. The movement is covered by an additional soft-iron clasp to prevent the forming of magnetic fields inside the watch itself. (See Faraday Cage.)
The first recorded experiments in anti-magnetic watch-making are in 1846. Watchmakers from Vacheron Constantin were among the first to experiment with anti-magnetic features of a watch. However, they succeeded in assembling the first antimagnetic watch only several decades later. That watch was able to withstand magnetic fields because some of its parts were made of non-magnetic metals: the palladium-made balance wheel, balance spring and the lever shaft.
In 1896 Charles Edouard Guillaume discovered the nickel based alloy Invar. Afterwards, in 1920, when he received the Nobel Prize in Physics, he developed another alloy - Elinvar. These alloys assisted in the assembly of anti-magnetic watches. Invar and Elinvar are able to resist magnetic fields, allowing the watch to continue to keep accurate time.
The first anti-magnetic pocket watch was assembled by Vacheron Constantin in 1915. Later, in 1929, Tissot assembled the first ever non-magnetic wristwatch. In 1954 Vacheron Constantin continued to innovate by producing the first anti-magnetic chronograph. In 1958 Jaeger-LeCoultre improved the chronograph's resistance to magnetic fields by doubling its anti-magnetic case.
Since their appearance, anti-magnetic watches have been favoured by people who deal with high magnetic fields. They are widespread among electronic engineers, and in other professions where magnetic fields are present.
After discovering the alloys for assembling anti-magnetic watches many watch-making brands use the materials in production and try to improve the performance of such timepieces.The most outstanding watches of this class were made by IWC: in 1989 IWC assembled the Ingenieur. It was able to withstand a huge magnetic field of 500,000 A/m. In 1993, when IWC celebrated its 125th birthday, the company substituted this model with a more conventional Ingeneur, resisting a magnetic field of 80,000 A/m. IWC Pilots' watches have the feature of showing accurate time under a moderate magnetic pressure too.
Almost all timepieces from Vacheron Constantin have this feature, especially those from the Overseas collection. These watches had an anti-magnetic screen in soft-iron for the protection of the movement.
The Olympic Games' timekeeper Omega also manufactures watches corresponding to ISO 764, which is based on the accidental exposure of the watch to a magnetic field of 4,800 A/m.Patek Philippe has also introduced a few innovations into this field: the engineers developed a non-metallic, silicon-based material for building parts of a watch's mechanism, thus making them fully non-magnetic.