GB1323717A - Timing devices - Google Patents

Abstract

1323717 Electronic watches; controlling amplitude of mechanical oscillation JAEGER S A 1 Oct 1970 [2 Oct 1969 14 April 1970] 46788/70 Headings G3R and G3T In an electronic watch wherein a balance wheel oscillator is electro-magnetically maintained, the balance wheel comprises a pair of spaced discs 1, Fig. 1a, one disc carrying a pair of ferrite permanent magnets 2, 2'. The magnets co-operate with driving, control and regulating windings 3, 4, 5 respectively, co-axially disposed and fixed relative to the balance wheel as shown Fig. 1. The coils are connected in a drive circuit Fig. 4, in which a transistor 11 is switched ON by positive peaks of voltage induced in control winding 4 by movement of the magnets relative thereto, and passes current pulses to the drive winding 3. A cyclic voltage is induced in regulating winding 5 proportional to the amplitude of oscillation of the wheel and together with the induced voltage in winding 4 switches OFF a transistor 15 when the oscillation amplitude reaches a predetermined value, e.g. 220 degrees. This causes the mean voltage across a capacitor 13 and hence the bias of transistor 11 to vary in accordance with the amplitude of oscillation, the voltage increasing with decreased oscillation amplitude and vice versa. The result is that the greater the oscillation amplitude the smaller will be the drive current fed in each cycle to drive winding 3 and vice versa so that substantially constant amplitude is maintained. Alternative winding arrangements are described with reference to Figs. 5, 6, 7, 8 (not shown). In the arrangement Fig. 8 (not shown) for example the regulating winding 5 has a plurality of taps any one of which may be selected for connection to the base of transistor 15 thereby to determine the maximum amplitude of oscillation, e. g. in a range 200 degrees to 250 degrees. To reduce temperature dependent variations the magnets (ferrite) have negative temperature co-efficient and similar to that of the base/emitter junction of transistor 15 which is of silicon.