Tuning fork watch
Tuning fork watches (English tuning fork watches ) are electrical watches and which generate for their Uhrgang necessary vibrations with a tuning fork .
principle
In the 1950s, all wristwatches were still working mechanically, they had a balance wheel to generate vibrations that ran at 2.5 to 5 Hz . The rate deviation of the watch depended on the accuracy with which this frequency was maintained, with a high frequency leading to a smaller deviation.
Now the frequency of a balance could not be increased significantly, so that other systems were used. In tuning fork watches, a tiny tuning fork swung at 300 to 720 Hz.
functionality
Mechanical construction
The tuning fork is excited by means of small electromagnets , for which a transistor circuit generates electrical impulses. A pawl on the tuning fork transfers the movement to the gear train , which in turn turns the hands . Instead of the ticking of a conventional clock, with the tuning fork clock you can hear a buzzing audible on the ear at a tone frequency between f and f sharp. The ratchet wheel is made of beryllium copper , a material that is particularly suitable for milling the very small teeth required .
The lower level of wear is an advantage . If a normal automatic watch movement consists of 26 moving parts, a tuning fork movement only needs 12. In addition, there is no heavily stressed lever escapement , which makes repairs easier. The bearings of the gears are also subject to a lower load , as they are not subjected to any spring force .
Electrical circuit
Just as a mechanical watch is driven by a spiral spring , two drive coils in a tuning fork watch ensure that the watch does not stop. For this purpose, there is a permanent magnet on each of the two prongs of the tuning fork . The two drive coils are switched on by a phase measuring coil via a transistor. To do this , one of the two permanent magnets induces the control current in the phase measuring coil, which then switches the transistor.
This control also compensates for jolts on the clockwork : if the fork deflects more because of such a jolt, the control current is smaller and thus less energy is supplied to the tuning fork, whereupon its deflections decrease; conversely, if the fork deflection is too small, the energy supply is increased.
This means that there are two circuits , one generated by the battery and another by the tuning fork itself. The energy consumption is so low that the battery has a lifespan of around one year.
Accutron
Emergence
The first tuning fork watch was created by physicist Max Hetzel from Basel , born in 1921: he took a job at the watch manufacturer Bulova in 1951 and started the first movement ever on June 19, 1953; the first prototype of a wristwatch was completed in November 1954. At that time, both the required transistor and the required button cell battery were only just available. The first models entered the sales range on October 16, 1960. Their name "Accutron" is made up of Accuracy (English: Accuracy ) and Electronic , the cheapest version cost 175 dollars. The Accutron ran at 360 Hz and had an excellent rate deviation of only 60 seconds per month.
Space missions
The Accutron watches were of great importance for NASA's space missions . The capsules of the Gemini program contained Accutrons with a 24-hour dial , while the lunar module of the Apollo program contained an Accutron with a 60-hour dial.
distribution
Its use at NASA contributed significantly to the popularity of the Accutron, so that the four millionth watch could already be sold in 1973. The last Bulova Accutron of the original production was made in 1977. In 2011, for the 50th anniversary, there is a series of replicas of the first Accutron limited to 1000 pieces .
development
For a long time there were only hand- wound wristwatches in which the increasing relaxation of the spring influences the synchronization. This was remedied by watches with constant spring tension , which could be achieved by means of an automatic winding mechanism driven by hand movement or, in rare cases, an electric motor .
The tuning fork clocks and, after 1970, the quartz clocks with their even higher frequency brought further progress in the rate deviation . These completely replaced the tuning fork clocks, because the tuning fork is no longer directly responsible for the mechanical drive, but a separate electric motor that is driven by an interconnected electronics .
Trivia
The prominent Heinz Haber owned an Accutron Spaceview wristwatch and presented it in 1968 in the series “What is man looking for in space?” (Episode 12). In doing so, he paid particular attention to the functionality of the clock and made the quiet humming sound of the tuning fork audible for the audience.
literature
- Léopold Defossez: “Accutron”, the Bulova electric wristwatch. In: Swiss Watches and Jewelry Journal. 1961, pp. 79-86.
- Franz Schmidlin: Electric and electronic wristwatches. Lausanne 1970.
Web links
- The Accutron Watch Page (in English)
- Tuning fork clocks - technology page (in German)
Individual evidence
- ^ Bulova Accutron , Bulova GmbH, Frankfurt a. M., Friedensstr. 5, p. 8
- ↑ http://www.bulovaspaceview.com/en/limited-edition/