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This chapter was translated from German into English by Steve Rickaby, Wordmongers Ltd, Treen, Cornwall, England.
Electrical horology systems consist of the following four fundamental components
- A master clock
- One or more secondary clocks
- Electric cables
- A power source.
The master clock has its own mechanism and supplies electric pulses to secondary clocks via electrical cabling. The trigger pulses increment all secondary clocks by one step at a time, usually in minutes. The power source can be taken from the mains supply using a transformer and rectifier, from an accumulator, from an inductor activated mechanically or some combination of these.
The most interesting part of this fascinating field is definitely the master clock. This chapter gives prominence to this component, and only discusses master clocks that use a pendulum as their time keeper. Master clocks with synchronous motor drives, balance or quartz work, radio clocks and so on may be handled later in their own chapters.
Pendulum-controlled master clocks can be subdivided as follows:
- Pure mechanical clocks with a weight or spring drive. In this type the impulses are passed from a passive contact system, by means of an external electrical supply, to the secondary clocks. (e.g. clocks from Hermann Moos & Co. of Zurich).
- Mechanical pendulum clocks with electrical winding. This group can be subdivided into clocks with an electrical motor for winding the drive weights (e.g. Inducta) or the main spring (e.g. Moser-Baer), and clocks in which the weight or the main spring is wound by means of a pawl-drive mechanism that is activated by the trigger pulse for the external dials. (e.g. Siemens & Halske, also Moser-Baer).
- Mechanical pendulum clocks with direct electric drive of the pendulum. ( e.g. FAVAG, Synchronome, Brillié, Bulle).
Purely mechanical clocks are not discussed here.
Older mechanical pendulum clocks with electrical winding mechanisms were derived from mantel clock movements in which the striking train was modified to generate the trigger pulses for the external dials. (e.g. "Alte Hauptuhr" by Siemens & Halske). The going work and the control mechanism are driven by a single weight using a differential gear. This design was also used later in more modern designs (Moser-Baer, Inducta). The control mechanism has the task of momentarily activating a contact once a minute (for a duration of several milliseconds up to a second) to send a positive and negative impulse to the secondary clocks. This is discussed further under secondary clocks. The contacts may consist of a conventional contact block or a mercury switch. As this category of electric pendulum clocks are weight or spring driven, the problem of a power reserve for running the master clock is solved - during a power failure the clock is driven by the power reserve provided by the main spring or the drive weight. However, the secondary clocks cannot be driven because the electrical power is removed. More ingenious designs store the time at which a power failure occured by means of cam disks. When the power is restored these cams are driven by motors to supply the missing pulses to the secondary clocks, so that they are automatically resynchronised with the master clock. If the hands of the master clock are turned backwards (which strictly speaking should not be done) the same mechanism guarantees that updating pulses are sent only if required.
The problem posed by the loss of drive pulses during a power failure is overcome in the case of master clocks that use an inductor. In these types (e.g. Magneta, Inducta) an inductor is driven mechanically by the control mechanism every minute to generate the positive and negative-going pulses for the secondary clocks. Mechanical power for driving the inductor is also (or mainly) provided by the drive weight. The master clock therefore generates the electrical energy required by the secondary clocks itself. Mains power is only used in this case for winding the drive weights. In the event of a power failure such clocks can be wound manually, so that the entire clock system continues to run correctly. The first master clocks that used inductors, invented by Martin Fischer in 1900 in Zurich and built by the Magneta company, were of the manually wound type.
Two main drive principles can be distinguished in mechanical pendulum clocks with direct drive of the pendulum: those in which an impulse is applied on each pendulum swing, and those in which an impulse is applied only if the amplitude of the pendulum swing falls below a certain value. The principle in which an impulse is applied on each swing is used by Brillié and Bulle, principally in table clocks with a short pendulum (see the chapter on electrical clocks). The latter type of drive, originated by Hipp, is applied by FAVAG clocks and also by other master clock manufacturers. I find this drive principle so brilliant that a closer description is worthwhile.
The entire system is represented schematically in the left picture. The pendulum carries a soft iron plate below it that is designed to act as a magnetic yoke. If a current passes through the coil the pendulum is attracted and thereby receives an impulse. Notice that in the animated picture to the right the contact is normally open. If the amplitude of the pendulum is large enough, the suspended hinged blade glides over the M-shaped prism. As pendulum amplitude decreases the time comes when the blade can no longer clear the groove in the prism. The blade lodges in the groove and during the pendulum's backswing it is lifted. This closes the contact, making the circuit and applying a fresh impulse to the pendulum to start the cycle again.
Driving the pendulum is one task, while signalling the time and advancing the secondary clocks is another. The pendulum activates a pawl wheel by means of a ratchet, which via a suitable gear activates both the clock's hands and the contact arrangement for advancing the secondary clocks. The hands of the master clock are often not activated mechanically, but instead the first secondary clock is used as its dial. It is therefore also driven by means of the trigger pulses once a minute. This pawl wheel principle recently made an important comeback in the Bulova Accutron tuning-fork watch.
The electrical power for supplying the drive and advancing the secondary clocks is taken most frequently from a 24V accumulator, which is trickle-charged from the public mains supply. This acts as a buffer battery to supply a power reserve in the case of mains failure.
A further enormous advantage of direct pendulum drive lies in power transmission. In a weight or spring-driven clock the whole movement, from the centre wheel to the escapement wheel, must be driven. For every pendulum half oscillation the escape wheel and the pendulum are driven through the whole gear train and stopped again. All journals are therefore always fully loaded. In the case of the direct pendulum drive only the hands and the contact system are activated by the pawl mechanism. Propulsion comes from the pendulum itself and is not transmitted through a gear train, so that virtually no bearing loads exist. The same applies to modern quartz crystal clocks of all sizes. These factors simplify the construction of such clocks, removing the need for expensive jewelled bearings and highly polished journals such as are required to withstand the loads caused by a mainspring drive.
The most precise and today sought-after master clocks have a 1 meter pendulum, giving a half-period of one second. Three-quarter-second pendulums with a length of around 60 cm are also customary, and for smaller clocks the half-second pendulum, which is approximately 25 cm long.
As you can see from this explanation, the field of master clocks and electric clocks is very diverse. For the interested clock enthusiast with a flair for electricity this is a broad and interesting area. Electric clocks of all kinds can be bought today at sensible prices. Unfortunately our wives and girlfriends are frequently not so interested in electric clocks in general, and master clocks in particular, so the installation of one or even several master clocks in the living room would not be readily accepted...
see also: Electrical Horology by Martin Ridout
Some examples of master clocks follow:
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Early purely mechanical time recorder with two-colour ribbon card mechanism.
Seller's signature on the dial:
Massive 8-day going, spring-driven lever escapement with heavy pendulum. The minute hand increments a whole minute at a time, driven by the card mechanism.
The clock has a passive contact system for driving external clocks and can therefore be considered as a master clock.
England, circa 1910, height: 86 cm
Interesting astronomical switch-clock with electrical minute winding system.
Signed: "Ernest Capt-Lecoultre, Fabricant-Inventeur, Orient-Vaud"
"Brevet Suisse 30807" from 1904
Lever escapement, pendulum,
"Alte Hauptuhr" by Siemens & Halske, type HU3.
Mechanical weight driven master clock with endless chain.
The weight is wound at the same time as a trigger pulse is sent to the external clocks. The weight therefore always remains in the same position, as shown.
Germany, circa 1915
INDUCTA master clock with inductor, type "UMI1".
Mechanical master clock with motor driven winding. The winding is activated every six hours. In the worst case it therefore has six hours of power reserve. The weight weighs 10 kg and drives both the movement and the inductor. The horseshoe-shaped magnet is almost visible on the left of the dial.
Switzerland (Landis & Gyr), 1940s,
Moser-Baer, Sumiswald master clock, type H71
Mechanical master clock with spring-driven lever escapement and electrical winding.
The upper (visible) dial is driven directly from the clock movement, and the contacts for generating the trigger pulses for the external clocks are located here. The lower dial is the first external clock, and drives a signalling arrangement to mark the start and end of work periods, for example in a factory. This removes the burden of signalling from the master clock.
FAVAG master clock.
Master clock with direct drive of the pendulum after Hipp (see detail)
The 24V accumulator for the power reserve has been removed.
Switzerland, circa 1960,
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Now for further discussion of secondary clocks.
Secondary clocks consist only of a step control mechanism for advancing the hands each minute. This control mechanism receives a phase-changed signal from the master clock each minute lasting approximately half a second. The two terminals "a" and "b" may be supplied with polarity-switched signals, positive to "a" and negative to "b", followed by negative to "a" and positive to "b" and so on. For the hands to advance the polarity must be continuously changed in this way. When compared to unipolar systems this principle has the advantage of immunity to poor impulse quality. If contact bounce at the master clock causes several pulses to arrive instead of only one incremented by several minutes is impossible. The trigger pulse for the secondary clocks is 12, 24 or 48V. 24V is usual in the case of more modern systems.
Here is a typical contact arrangement for generating the alternating trigger pulses. The operating cam usually moves a half turn each minute, activating the right and left contact blocks alternately, so that the current in the secondary clock moves from the right to the left (red arrows) and then from the left to the right (blue arrows).
Secondary clocks with contact control such as this are switched in parallel.
Master clocks that use inductors, such as Magneta and Inducta, demand a specific system for their secondary clocks. This is because their impulses are of larger amplitude but considerably shorter in duration than in the case of contact systems. If a secondary clock is marked "INDUCTA" on the dial it does not neccessarily mean that it can operate with an inductor, as Inducta also produced clock systems for external current drive. Secondary clocks with induction drive are switched in series.
A further well-known form of secondary clock is the railway station clock with creeping second hand. These are basically "normal" secondary clocks. The second hand is driven by a synchronous motor that runs slightly faster than 60 seconds per rotation, independent of the movement. As soon as the second hand reaches an entire minute the mechanism is blocked, and is then unlocked by the trigger pulse for the minute hand. This synchronises the second hand with the minute jump characteristic of railway station clocks.
Secondary clocks can only be operated through a master clock or an electromechanical or electronic appliance that provides suitable signals. To the disappointment of many clock friends, a secondary clock that turns up in a flea market can't be operated successfully without further work, even though it looks attractive. However, it is possible to obtain a suitable excitation device, allowing a system to be built for private use at low cost such as might be used to show the times in different capitals cities or countries, familiar from travel agencies, banks, airports and so on. This equipment should perhaps be considered suitable for the office or workshop rather than the parlor or living room, as in addition to its purely aesthetic aspects the incrementing of the minutes and electrical winding of the master clocks will not be very quiet. For clock enthusiasts something like a facade advertisement clock might make a very good bar.
The following are some examples of secondary clocks:
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Standard external dial.
A well-known design of external dial, in use since circa 1950
Diameters: 20 - 50 cm
Tensions: 12, 24 or 48V
Double-sided illuminated advertisement facade clock.
Dimensions: 90 x 90 x 30 cm
Drive: 24V, minute standard trigger pulses
Facade clock on a factory building.
Diameter: 60 - 150 cm
From a prospectus of 1954,
"INDUCTA" time central
The two master clocks are electromechanically synchronised. One is the master, the other the reserve clock. In case of failure the reserve clock becomes the master clock, forming what would today be called today a "hot standby". The six small dials indicate the time of the six secondary clock lines.
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