Accutron model 214
phonefiddle by Stroh
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electric clocks

 A history of the evolution of electric clocks

E. Synchronization

Abraham Louis Breguet (1747-1823)
As early as 1793 the famous clock and watch maker Breguet devised a system to synchronize watches. Breguet

On placing a watch on his fully mechanical master clock, "La Pendule Sympathique", it not only winds the watch, sets its hands to the hour but also adjusts its rate of time. A remarkable achievement! Breguet neither wrote nor published any account of his work and his invention was probably unknown to anyone beyond his immediate circle. la pendule sympathique

In the watch a separate train is wound independently. The synchronization signal from the master clock lets the setting-train off doing what it has to do.
I do not know how things work in detail.

His grandson Louis Francois Clément Breguet (1804-1883) spent a great deal of his life investigating electricity and its applications. As watchmaker and scientist he set-up a system of electric clocks in Lyon as early as 1856.
In 1866 he built a remarkable mechanical clock in which a 25 cm high tuning fork (invented by the English musician John Shore in 1711) is used to control the release of the escape wheel.
The clock animated here is on display at the Musée International d'Horlogerie in La Chaux-de-Fonds, Switzerland.                               

The same principle would be used nearly a century later by the Swiss engineer Max Hetzel of the Bulova Watch Company to drive their Accutron watches.
In this watch a jewel fixed to one of the tines of a tuning fork, only 25 mm in length, engages an index wheel, 2.4 mm in diameter and carrying 320 teeth.
The tuning fork provides both the right frequency for time keeping and the power to drive the movement while an electronic circuit, powered by a battery, keeps the tuning fork vibrating.                                              

No one yet had succeeded in keeping a large number of mechanical clocks in absolute step. The rapid growth of the railways during the middle of the 19th century gave the stimulus to find means of ensuring that clocks did in fact indicate the same time.

R L Jones
A pioneer in synchronizing clocks was R L Jones, stationmaster of Chester. In his patent no.702 of 1857 Jones adopted Bain's system of sympathetic pendulums. A mechanical master clock provided the electric pulses to keep the pendulums of his ordinary key-wound clocks in step. The bob of these key-wound clocks consisted of a coil sliding over two permanent magnets. The electric pulses received from the master clock kept these secondary clocks in harmony with his master clock. He used the tower clock of Chester as master clock providing the electric pulses to control his secondary clocks.

Frederick James Ritchie (1828-1906)
In 1872 James Ritchie, a clockmaker from Edinburgh, also improved Bain's system of sympathetic pendulums (patent no.2078). On the right-hand side we see the pendulum of a secondary clock fitted with a coil passing over two permanent magnets. On the left-hand side is the pendulum of the mechanical master clock. By means of contacts, fitted to the pendulum of the master clock, the coil of the secondary pendulum is energized at each swing keeping it in absolute step with the master clock.

A reverse gravity escapement, connected to the pendulum of the secondary clock, drives the hands of its dial.                               animation

In 1878 Ritchie also devised a system of synchronization (patent no.333) relying on the use of a self-propelled secondary clock having a slight gaining rate.

A synchronizing current of 15 seconds duration, terminating exactly at the hour is received by the electro-magnet of the secondary clock. Its electro-magnet will pull down an armature holding-up the clock. However, the armature cannot move until the minute hand gets to the hour and the notch in a cam is able to receive the end of the armature. A pin fitted to the other end of the armature then holds-up the clock until the cessation of the current when the armature falls away.

John Alexander Lund
In 1876 Lund took out patent no.3924 for a forcible correction of the minute hand of key-wound secondary clocks.

Left dial: levers force the minute hand to the hour.
Right dial: a V-shaped cam slides upwards forcing the minute hand to the hour by means of a pin fixed to the back of the minute hand.

We have seen some systems in which the hands of secondary clocks are synchronized by a master clock. There were also systems devised that corrected the rate of time of the pendulum.

John Matthias Augustus Stroh (1828-1914)
In 1869 Augustus Stroh, a watchmaker from Furtwangen, Germany, who came to England in 1851and worked for Wheatstone, devised a system that synchronized the rate of time of a pendulum. Stroh would later become well know for his inventions related to musical instruments.
In his patent no.3028 a beam carries on the right a small subsidiary pendulum, counter-balanced by a weight on the left. The suspension spring of the little pendulum passes between fixed jaws and its bob is linked to the pendulum of the clock to be synchronized. A synchronizing signal pulls a feeler connected to the rocking beam over the point of a cam, mounted on the minute wheel of the clock, and so the feeler is pushed up or down dictated by the position of the cam. As a result, the beam is rocked and so the effective length of the subsidiary pendulum is altered.

The use of a short subsidiary pendulum linked to the main pendulum is only a convenient way of diluting the synchronizing effect.

Robert James Rudd (1844-1932)
Another synchronizer that corrects the rate of time of the pendulum (patent no.19337) was invented by Rudd in 1898.

On receiving the synchronizing signal, . the electro-magnet attracts its armature turning a Z-shaped lever. By means of a C-shaped spring a lever is now reset into whatever position may be dictated by a snail fitted to the second's hand. The Z-shaped lever also releases another lever provided with pins embracing the suspension spring of a subsidiary pendulum.
When this lever is raised or lowered it will alter the effective length of the subsidiary pendulum and so influence the rate of time of the pendulum.

go to page 8
F. Count-wheel and impulse



Electricity & Magnetism
Electricity & Horology
   A.Electrostatic clocks
   B.The first inventors
   C.Independency of battery
   D.Reliability of contact making
   F.Count-wheel and impulse
   G.The first free pendulum
   H.Shortt's free pendulum
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