GB906998A - Improvements in or relating to electrically-maintained balances for use in timing devices - Google Patents

Abstract

906,998. Clocks and watches. SMITH & SONS (ENGLAND) Ltd., S. Jan. 8, 1959 [Jan. 8, 1958], No. 817/58. Class 139. In an electric timepiece a coil 3, Fig. 1, carried by the balance staff 2, oscillates in the gap between a soft iron member 13 and the polepieces 11, 12 of a permanent magnet 10. The maintaining circuit, Fig. 2, includes a transformer 24, a transistor 21, a rectifier 23 and a voltage source 20, 22. As the coil swings through the magnetic field a voltage is induced in it to cause a current to flow in the primary winding of transformer 24. When the base of the transistor is driven negative, as the balance swings in one direction, a collector current flows through coil 3 in opposition to the induced voltage and a maintaining impulse is imparted to the balance. The induced secondary transformer voltage drops to zero when the transformer core reaches saturation and the transistor returns to its quiescent condition. The balance springs 5, 6 are connected to the coil 3 by wires 16, 17, respectively. The circuit is such as to tend to keep the amplitude of balance oscillation constant. The coil may be of rectangular form, Fig. 3 (not shown), and supported from the periphery of the balance to co-operate with a short bar magnet secured between the limbs of a V-shaped soft iron member. Specifications 227,499 and 300,992 are referred to.