This Master clock was made by Gents of Leicester, England in 1955. It has a part glazed wooden case and can drive a large number of half minute slave dials connected in series in a loop, the dial in the case being the first of those. The impulse to the pendulum is given by a weighted arm falling onto a sloping face on the pendulum crutch. The impulse force is therefore constant and not subject to the weakening of a battery. The battery is required to reset the gravity arm on to its latch, and to impulse the slave dials.
The clock is very noisy in operation, and not really suited to a domestic
environment.
The one second pendulum is made of Invar with a substantial cast iron bob which is cased in steel decorated with an antique 'bronze' effect.
The two coils that reset the gravity arm can be seen on the left of the pendulum. As the gravity arm falls, an electrical contact is made that energizes the coils to reset the arm. Also in series with the resetting coils are all the slave dials, so the slaves only receive a pulse to advance them when the gravity arm is reset.
The variable resistor at the lower left is in series with the resetting coils and slave dials, and is used to set the current drawn by the whole system to 220mA, irrespective of the battery voltage or number of slaves.
The gravity arm is released every 30 seconds. A 15 tooth escape wheel is indexed round by one tooth each time the pendulum swings left to right, i.e. once every two seconds. There is one deep tooth, visible on the right of the escape wheel, which triggers the whole resetting and impulse action. The weighted gravity arm is caused to fall; the roller rides down the inclined plane on the pendulum crutch, and impulse is given; at the bottom of its fall, the electrical contacts are made, the arm is reset, and the slaves are pulsed.
This is the slave movement in the master clock. The electromagnet attracts its armature (on the right), which is pivoted at the lower end of the diagonal bar, and releases it after about 1/5 second (the duration of gravity arm resetting). As the armature is released, the indexing pawl at the top pushes the large 120 tooth wheel round by one tooth and thereby moves the minute hand by half a minute. The hour hand is driven by conventional motion work. The pawl at the top left stops the minute hand being driven backwards.