Synchronous clock
A synchronous clock is a clock that uses the electrical alternating current network to drive its movement instead of an energy store ( clock weight or spring ) and an escapement ( pendulum or balance wheel ) and derives its time base from the network frequency instead of a classic mechanical escapement . Its name arises from the fact that it runs synchronously with this frequency. Due to this dependency, deviations in the network frequency from its nominal value lead to rate deviations , which in the interconnected network hardly exceed 20 seconds, even in the long term over years. In addition to a power failure, a long-term disruption in the European network can become a problem. In this case, too, the deviation is reduced again.
The heyday of mechanical synchronous clocks stretched from the 1960s to the early 1980s. With the introduction of electronic quartz clocks , mechanical synchronous clocks have lost more and more of their importance, but are still used in time switches , among other things . Synchronous clocks can be found as electronic devices in many radio alarm clocks or kitchen appliances such as ovens and microwave ovens .
Structure and special features
A drive source and an escapement are required for a mechanical movement . In the synchronous clockwork, these two components have been replaced by a single-phase synchronous motor . This drives the gear train of the clock and thus uses the mains frequency of the alternating current network of 50 Hz or 60 Hz as the time base . Pointers in front of a scale are preferably used to display the time . In some cases the time is also shown on a case sheet display .
The gear train of a synchronous clock mechanism is therefore similar to that of a fully mechanical clock: brass plates carry brass wheels with steel shafts; only the generation of vibrations is replaced. Since the first synchronous motors could not start by themselves, early synchronous clock movements often had a starting device in the form of a self-resetting lever. After connecting to the power grid and after a power failure, this lever had to be operated to start the synchronous motor.
Electronic network-synchronous watches often use number advertisements by means of liquid crystal displays (LCD) or light emitting diodes (LED). The built-in clock circuit essentially consists of a counter component that divides the mains frequency down to 1 Hz via frequency dividers and advances the time display in pulses. In order not to lose the time in the event of a power failure, some digital synchronous clocks are also equipped with a battery and a quartz movement.
Mauthe synchronous watch with power reserve
The fact that a synchronous clock movement stops in the event of a power failure and the synchronous clock slows down (possibly unnoticed), but in any case requires intervention to set it, led to the development of a synchronous movement with a power reserve.
This was achieved by using a conventional movement with a balance and spring mechanism . The elevator of the factory was done continuously by a synchronous motor. This simultaneously operated an eccentric (arrow A in the illustration) that was connected to the balance spring (arrow B in the illustration). As a result, the balance wheel was forced to oscillate and its frequency was permanently linked to the mains frequency.
In the event of a power failure, the balance wheel continued to swing in the conventional manner, driven by the escapement, and the watch had the accuracy of a conventional mechanical watch during this time.
This movement was able to bridge several hours of power failure without significant rate deviation and thus avoided a major disadvantage of synchronous clocks without foregoing the advantages of long-term accuracy and the elimination of winding. These clocks could thus be operated for years without any maintenance - an advantage especially in hard-to-reach (high) locations such as the wall of a large office or a production hall.
Advantages and disadvantages
Mechanical synchronous clock movements have a number of advantages over other mechanical clocks:
- More compact design
- Higher drive torque so that large pointers can also be mounted
- Operation possible in any position
- No need to wind up and readjust the clock
- Long-term high accuracy
- Before the introduction of summer time , i.e. in the heyday of synchronous clocks, operation without intervention possible for years (provided the power supply is never interrupted).
On the other hand, there are disadvantages:
- Necessity of a connection to the power grid, with costs and restrictions on the choice of place
- Safety aspects due to live elements inside, which make the assembly of the entire watch more expensive
- In the case of mechanical synchronous clocks, the energy required for the mechanical drive, since the motor in larger clocks is operated continuously with a power consumption of typically 2 to 3 W. For mechanical time switches with synchronous drive, the power requirement is less than 100 mW.
- When the power supply is interrupted, watches without a power reserve slow down.
scope of application
Synchronous clocks used to be used as advertising media. They were permanently installed in a suitable place in a shop or restaurant and were often provided with lighting behind the (with advertising) dial. The clocks did not need to be wound or readjusted. This made the synchronous large clocks attractive as an advertising medium at a time when very few people owned a reliable wrist or pocket watch.
Synchronous clocks can be combined with time switches because they have a high drive power or high torque. They are available as daily and weekly time switches with lower resolution and longer duration for a cycle. They often take the form of adapter plugs.
Other applications of the synchronous drive were mechanical switching mechanisms in washing machines, dishwashers and microwave ovens . The synchronous drive is used here because of its high drive torque and its constant speed, regardless of the load.
Accuracy
The high average accuracy is based on the fact that the time standard of the synchronous clock is the mains frequency and that this is kept stable in the European network by comparison with the coordinated universal time (UTC) on average at 50.00 Hz. There are constant fluctuations in the network frequency, so that the accuracy is not completely possible over short periods of time; However, over longer periods of time, deviations are compensated for using the quaternary regulation . This starts as soon as the deviation of the synchronous clocks in the network exceeds +20 or −20 seconds. The deviation is kept in this narrow range, even over the long term, by catching up a backlog due to a frequency that is temporarily too low by means of a frequency that is too high. This means that smaller rate deviations can be achieved with synchronous watches than with quartz watches, at least in the long term, since the deviation accumulates in quartz watches without external intervention. In the European grid, Swissgrid records the ongoing deviations in the grid frequency and coordinates the corrections to the nominal values as part of the Quaternary regulation. Only in the case of network overload with a long-term network frequency that is too low can a significant gear deviation accumulate, as in the first quarter of 2018 with 6 minutes as a result of disputes between individual network operators. This previously unrelated deviation in the grid time was then compensated for by the beginning of April 2018. The current network time deviation can be viewed at.
The synchronous clock is inferior to the radio clock only in view of the short-term inaccuracy (fluctuations in the sub-minute range) and the loss of information after a power failure . As far as electronic synchronous clocks change the winter / summer time themselves, they are equal to the radio clock in this respect.
If there was no quaternary regulation in the power grid, as was the case before 1991 in the GDR and in the entire Eastern Bloc , synchronous clocks showed considerable rate deviations so that they could hardly be used. This also meant that, for example, after the fall of the Wall, West Berlin synchronous clocks went wrong because the network was integrated into the supply system of East Berlin. It was not until the restructuring two years later that the average network frequency in Berlin and East Germany was stable at 50 Hz - all of Germany was now integrated into the Western European energy supply system.
End of synchronous clocks as wall clocks
From the beginning of the 1980s, quartz watches became increasingly cheaper. They also had a high rate of accuracy (relative frequency deviation typically <10 −5 ) and could operate battery-powered for years without maintenance. The lack of components carrying mains voltage made the structure inexpensive, the space for the clock could be freely chosen regardless of the connection to the power supply, installation work was eliminated, a nail in the wall was enough. In the event of a power failure, there was also no rate deviation; this could only be caused by empty batteries, which was quickly noticed by the stopped second hand.
The synchronous clock could no longer hold its own against these advantages even in the field of advertising clocks and disappeared more and more. Only where high drive forces are required for large hands are clockworks driven by a synchronous motor occasionally used.
The wall clock with synchronous motor can usually be identified by the fact that the second hand rotates continuously, i.e. without a jumping second . With wall clocks with clock quartz , this pointer is set step by step by the Lavet stepper motor .
Individual evidence
- ↑ Hans Dominik: The Eternal Heart . Wilhelm Limpert-Verlag, 1942
- ↑ Wissen.de: synchronous clock
- ↑ a b swissgrid on grid time deviation
- ↑ Grid frequency measurement - current information retrieved 2018-06-11
- ↑ Grid frequency measurement
Web links
- Gerrit Eckardt: Synchronous clocks