page  6/13
next page
previous page

electric clocks

 A history of the evolution of electric clocks

D. Reliability of contact making

The difficulties in devising consistent contact systems were well recognized and the causes of failure known. Gold and silver contacts were used to avoid failure but it only takes a speck of dust to make them inoperative with the light pressure available from the pendulum.

Charles Wheatstone devised a solution to this problem!

Charles Wheatstone
Similar to Steinheil's suggestion, Wheatstone used clock Wheatstone a large weight-driven clock with a light pendulum carrying a coil passing over two permanent magnets in 1870. The rapidly swinging coil induced electro-magnetic currents (Foucault or Eddy currents), reversing at each swing. These induced currents were used to drive secondary clocks without the need for contacts of any kind.

Wheatstone outlined his proposal to use these electro-magnetic currents as early as 1840 but it took until 1870 before this clock was actually built. However, the induced Foucault currents interfere ruthlessly with the freedom of the pendulum making it necessary to synchronize his clock every hour. His system was given a brief trial at the London University and the Royal-Society but was soon abandoned. His clock is now exhibited at the Science Museum of London.

The recoil escapement drawn here is not correct. In reality a more complicated escapement was used.

Martin Fischer (1867-1947)
In 1900 Martin Fischer of Zurich did manage to use this principle successfully. In his patent no. 19701 he used a master clock with a very high quality movement releasing each minute a weight-driven train, which in its turn rocked an armature of a generator within the poles of a powerful permanent magnet. The induced Foucault currents were used to drive his secondary clocks.           animation

His clocks became well known as Magneta clocks, later Inducta clocks.

Désiré (1847-1915) and Gustave van de Plancke
In 1885 the brothers Désiré and Gustave van de Plancke of Courtrai, Belgium, devised a system (Belgium patent no.67750) in which the contact making is not influenced by the wheelwork or its driving power.

The horizontal arm of a two-armed lever rests on a tooth of the wheel work of a spring-wound movement descending until it drops off this tooth onto a contact pin.               animation

The electro-magnet is now energized and attracts an armature, shaped like a hammer, adapted to hit a pin fixed to a weighted flywheel. The flywheel is kicked and forced to make a full revolution thereby storing energy in a spring.

At the same time a little finger attached to the flywheel makes contact with the other arm of the two-armed lever thereby throwing it up. Contact is broken by inertia and the lever will fall back on the next tooth of the wheel work.

Frank Hope-Jones (1867-1950) and George Bennett Bowell (1875-1942)
Ten years later in 1895, Hope-Jones and Bowell adopted the Van de Plancke system
for their version of a self-winding clock using a gravity arm as motive power. Hope-Jones

In their patent no.1587 a weighted lever turns the wheelwork, descending until the vertical arm touches a contact screw. The electro-magnet is energized and its armature resets the weighted lever by throwing it up. The breaking is caused by the inertia of the weighted lever.




This system disposed of the difficulties in obtaining a reliable contact without interfering with the timekeeping properties of the clock.

go to page 7
E. Synchronization

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
page   1.
page   2.
page   3
page   4
page   5
page   6
page   7
page   8
page   9
page 10
page 11.