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F Fixed coil system, contact controlled

System with a small piece of iron attached to the balance wheel, a fixed coil and mechanical contacts.

The first and most important watches of this kind were the Lip R 27 and the Elgin 722 and 725.

One piece of iron is attached to the balance wheel. When the balance wheel turns, a contact is closed exactly at the moment the iron on the balance starts to move towards the coil (stator), which is fixed on the full plate. As soon as the circuit is closed this way, the electrical current starts to pass the coil. The coil becomes an electromagnet and attracts the small piece of iron on the balance during the contact time. Thus, at the end of every oscillation, a forward impulse is given to the balance wheel, while the balance spring creates an impulse backwards, resulting in a forward and backward motion of the balance wheel.
However, when the contact opens, the fast changing reversed current causes an induction spark, which affects the contacts and diminishes their lifetime. If a diode is used, this reversed current is conducted through another closed circuit to earth. This way less harm is done to the contacts.

The following watches of this type were:

1Lip-electric R 27.
2Elgin-electric 722 and 725.
3Landeron L4750 and L 4751.
4Lip-electric R 148 and R 184.
5Lip-electric R 50.

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Copyright by Pieter Doensen

email: doensen@xs4all.nl

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