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An electric watch, which commonly means any watch that is powered by electricity, has become a generic term for the first generation of electrically powered watches which appeared starting in 1957, before the invention of quartz watches in the 1970s. Their timekeeping element was either a traditional balance wheel or a tuning fork, driven electromagnetically by a solenoid powered by a battery. The hands were driven mechanically through a wheel train. They were superseded by quartz watches, which had greater accuracy and durability due to their lower parts count. Recent automatic quartz watches, which combine mechanical technology with quartz timekeeping, are not included in this classification.
A weak point in early balance wheel electric watches was the switch contacts on the balance wheel, which turned the solenoid on briefly to provide the impulse to keep the wheel oscillating. These wore out and did not operate reliably. Later designs used electromagnetic sensing, with a transistor in the circuit to turn the solenoid on.
Types of electric watches
- Moving coil system, contact controlled: refers to watches with a balance wheel with integrated coil, fixed magnets and mechanical contacts. Examples of this technology are Hamilton 500 (first electric watch), Epperlein 100, Champion (Ruhla / UMF), Slava 114ChN and Timex M40.
- Fixed coil system, contact controlled: watches with a piece of refined iron attached to the balance wheel, a fixed coil and mechanical contacts. In order to extend the life of the watch, some of these movements included a diode to minimize sparking on the contacts. Examples of this technology are Lip electronic R 27, LIP R 148, Elgin-electric 722 and Landeron (ESA - Ebauches S.A.) 4750.
- Transistorized watches with balance: had a balance wheel, a transistor acting as a switch and no mechanical contacts. Usually the coil was located in the base plate and the magnets are on the balance wheel. Watches using this technology include Timex M87/Laco 882, Citizen X-8 series and Seiko Electronic 31A. Another common example is ESA Dynotron cal. 9150.
- Tuning fork watches: Instead of a balance wheel, these watches used a tuning fork driven by a solenoid powered by a one-transistor oscillator circuit and no mechanical contacts. The tuning fork had an attached pawl and 'index wheel', which turned the gear train. The common frequencies used in watches were 300 Hz (ESA MOSABA cal. 9162, 9164 and 9210), 360 Hz (Bulova Accutron cal. 214 and 218), Slava Transistor, 480 Hz (Bulova Accutron cal. 2300) and 720 Hz (Omega Megasonic cal. 1220 and 1230). Omega F300Hz and Speedsonics series are common examples of ESA MOSABA based watches.