Electromechanical signal box

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An electromechanical interlocking or power interlocking (earlier name) is a railway system for setting points and signals (see also interlocking ). The name comes from the fact that these control elements are set electrically , but the dependencies of the control elements and routes in the signal box itself are partially created mechanically . Electromechanical interlockings were manufactured in numerous designs by various companies, such as Siemens & Halske , AEG or Orenstein & Koppel .

In Switzerland, the electromechanical interlockings are assigned to the switchgear . However, this term included both signal boxes with mechanical dependencies and those without mechanical dependencies. The latter are not considered in this article.

In Austria, as in Germany, the term electromechanical interlocking was used, in type designations also power interlocking .

Description and functionality

In the actuating range of an electromechanical interlocking, the actuating processes are carried out electrically. For this purpose, points, track barriers and form signals have an electric drive, whose electric motor is supplied with control current from the signal box via underground cables . In some cases, light signals are already used instead of the shape signals, so that the electrical drive of the signals is not necessary.

Lever mechanism with route signal levers, design S&H 1912 with colored disc monitoring

The electromechanical interlocking is operated with the help of rotary switches or with small control levers that are based on the control levers of the mechanical interlocking. In technical language, rotary switches are also called adjusting levers in Germany , while the term switch is used in Austria and Switzerland . The control levers are arranged in a switch mechanism. Connected to them is the locking register , which in its function corresponds to the route locking in the locking box of a mechanical interlocking. However, the individual components are much smaller here. The locking register creates mechanical dependencies, which, however, have been supplemented by electrical dependencies via relay circuits with signal relays or precursors. Mechanical dependencies on the route and station block, which correspond to the signal push rods in mechanical interlockings and thus mechanical block locks, do not exist in electromechanical interlockings. They are implemented purely electrically.

In the newer designs of the electromechanical interlocking, the signal levers have a double function. They act as route levers and as signal levers and are therefore called route signal levers . There are also turnout and track locking levers , locking signal levers and, in large stations with several signal boxes, command and approval levers . With the help of the command and consent levers, the dependencies between the interlockings are established. These control levers have the function of a route lever and at the same time the corresponding function of an approval or command output field of the station block in mechanical signal boxes . The functions of the receiving fields are implemented by receiving relays on the route (signal) levers in conjunction with the lever locks and the route setting fields are implemented by magnet systems with pendulums on the route and route signal levers. A special station block is therefore not necessary. A special feature is the fact that the dispatcher's command levers are kept free. In order to make the disposition easier for him, the fixing magnets of these levers are kept under tension after they have been turned into the 45 ° position as long as the guard concerned does not use the command. This means that a command that has been issued can be withdrawn up to the last possible moment without auxiliary operation and without hindrance to operation due to a repeated lock.

An adjusting lever designed as a handle and the device operated by it are in the basic position when the marking line on the adjusting lever is vertical. In order to initiate an actuation process, the switch attendant must pull the actuating lever a little bit out of its lock. Then he can turn it to the right or left. If he releases the control lever after turning it, it locks into place. If the control lever is designed as a small lever, it is the basic position

  • for levers with three positions (e.g. route levers) the vertical position;
  • in the case of levers with two positions (e.g. turnout and signal levers) the rear position is the case for most designs.

In contrast to the mechanical interlocking, the electromechanical interlocking lacks a fixed mechanical connection between the control lever and the on-site system. This is why an electrical monitoring device ensures that the lever position in the interlocking corresponds to the position of the outdoor system. A monitoring circuit that is independent of the control circuit , which usually uses the same cable cores and thus also checks their condition, reports the respective position to the interlocking via contacts in the drive. The status is displayed there with colored discs or indicator lamps. Because of the different display types, a distinction is made between electromechanical interlockings with colored discs and those with lamp monitoring.

electrical main signal drive of German design with integrated wing clutches

If the position of a control lever in the interlocking does not match the position of the outdoor system, the monitoring circuit is interrupted and the monitoring magnet is released. This is indicated acoustically in the signal box with an alarm clock and optically with a red colored disc or the lighting up of a red signal lamp. This condition occurs for a few seconds while a switch is being switched. The turnout alarm clock is also switched on when changing because there is usually no changeover time limit. If a switch does not reach the desired end position when switching, the lever must be reset. Otherwise the control current fuse will melt. If the monitoring device of a guideway element does not indicate an orderly position or the necessary approval has not been received, the route levers concerned are only accessible up to the mechanical lock (for systems with levers protruding forward, this is the 30 ° position, which corresponds to the auxiliary position of route levers in mechanical interlockings ) reversible. The first coupling current block cannot be overcome, the definition does not occur and the main signal cannot be set to drive.

Lever mechanism with a display board from the Breitenbachplatz underground station (S&H 1907 design), in the Berlin underground museum

In the electromechanical interlocking, the order display of the monitoring device is an essential prerequisite for the occurrence of signal dependency . The orderly position of the route elements is not only checked at the moment when routes are set, as is the case with mechanical interlockings, but is constantly checked. If the monitoring circuit of a guideway element involved is interrupted while a signal is in the driving position, then this automatically falls into the stop position. One consequence is that all drives for the main form signals and pre-signals are equipped with an integrated wing coupling.

Setting and securing a route in the electromechanical interlocking is basically the same as in the mechanical interlocking:

1. The signal box operator brings all equipment in the guideway and, if they serve as side protection , also in the neighboring tracks, into the correct position using the adjusting lever.

2. Then he throws the route signal lever. The dependent levers are mechanically locked from a position dependent on the design (e.g. 10 degrees). The 30 ° position, which can always be reached with the correct position of the switches and side protection devices, corresponds to the auxiliary detent of the route lever of mechanical and the route lock of relay and electronic interlockings. From this position, the route signal lever must be put back at any time; it is used in conjunction with an auxiliary lock for auxiliary routes.

3. At 30 ° the first coupling current block must be overcome. The lever lock magnet can only attract if all the guideway elements involved are properly monitored and an approval (or a command, both of which are practically identical in terms of circuitry) has been received. The lever lock magnet attracts a pendulum attached to the armature and enables further flipping.

4. If he turns or moves the route signal lever further (for designs with rotary handles by around 45 degrees), the anchor of the fixing magnet, which was previously mechanically supported, falls off. The incident pendulum locks the route lever against moving back, so that the route is determined. The determination switches on the operational dissolution devices. If the intended journey cannot take place, the specified route can only be released manually using an auxiliary operator that is subject to mandatory counting.

5. If he finally puts the route signal lever in the end position, the main signal comes on. The second coupling current block must be overcome at 68 °. This works like the first, it primarily checks the route block dependencies. For signal stop position in the event of danger, the route signal levers can be folded back up to 90 ° and can be moved back up to 45 ° at any time.

To establish the signal dependency, all four steps are run through, but steps 2, 3 and 4 only require an operator action. When using light signals, the route (signal) levers can usually only be turned up to 45 °, the signal travel position then takes place automatically after the route has been determined, provided that the route block criteria are also met. One consequence of this is that the feedback of the previous train must be obtained from an electromechanical interlocking with light signals and route levers that can only be turned up to 45 ° before allowing an exit to a substitute signal. The route resolution is preferably carried out by means of train action points, in some cases comparable with mechanical interlockings, especially at entrances, also manually.

Command and approval levers can only be turned up to 45 °. The collapse of the locking pendulum of the fixing magnet on the delivery interlocking causes the receiving relay on the corresponding lever in the receiving interlocking to pick up via the dependency circuit. The pick-up of this receiving relay is a prerequisite for overcoming the first coupling current block. In addition, this current path, the so-called "coupling circuit", enables a main signal that is in motion to be stopped by interrupting this coupling circuit from an approving signal box using an emergency button.

The size of the technically possible control range is significantly larger with electromechanical interlockings than with mechanical interlockings , since no friction in wire pulling or rod lines has to be overcome. The last types of such interlockings with track vacancy detection systems and the use of three-phase alternating current for switching points reach the same distance as relay interlockings , i.e. a few kilometers depending on the cables used (an example of such a system is still in Hadersdorf , Austria , whose control area also includes the train station about two kilometers away Etsdorf-Straß includes). However, as long as track vacancy detection systems were not used as standard, i.e. until around the beginning of the 1950s, the size of the control area was only comparable to the mechanical interlockings due to the route inspection by the guard. Another limit to the size of the system, however, is the increasing complexity of the operating devices.

The otherwise usual red illumination of occupied track sections cannot be used in the lever system, as red signal lamps are already used to report faults. For this reason, blue lamps are used for this. With color disc monitoring, a blue stripe is swiveled into the monitoring field.

The block system has been carried out in older systems as fields block. For this purpose, a special block mechanism is set up next to the lever system. The function of the mechanical block locks is simulated electrically (so-called »lockless block«). In the 1930s, the magnetic switch block was developed, which is operated with block levers. These are comparable to route levers and usually have a white handle with a nose and a red ring. They can be folded in both directions by up to 45 °, but do not lock into place in the folded position, but spring back. There are no dependencies on the mechanical locking register. In interlockings built later, the block levers were replaced by buttons in the lever system structure. The function of the actual section block fields is performed by block magnets, stepping mechanisms with polarized armature. This allows the magnetic switch block to work with Form C field blocks and compatible relay block types. The use of relay, carrier frequency and automatic section blocks is also possible; the corresponding relay groups are installed in the relay room of the interlocking.

So-called route adaptations serve as the interface between electromechanical and electronic interlockings . Dependencies between electromechanical and relay control units can be established in a relatively simple manner by means of relay circuits. Dependency circuits between electromechanical and mechanical interlockings using the typical facilities of both interlocking designs were developed as early as the early twentieth century. The best-known solution was named Wuppertal circuit after its first location .

Power supply

Due to the state of electrical engineering around 1900, the voltages used arose. DC voltages of 34 V for the monitoring and dependency circuits and 136 V as the control voltage were common. The comparatively out-of-round values ​​are in a ratio of 1: 4. The local networks were largely fed with non-transformable DC voltage. In order not to have to operate too many converters, it was operated with three lead batteries (with a cell voltage of 2 V). Each of the three batteries had 68 cells. The first was connected in series to supply the control circuits, the second in four parallel-connected groups of 17 cells each in series to supply the monitoring and dependency circuits, the third was charged. From time to time it was switched to the next group. With the spread of AC voltage networks and the introduction of dry rectifiers, it became possible to end the complex operation with three batteries. Since then, the setting and monitoring battery has been continuously buffered from the grid via transformers and rectifiers (combined as a device to form a »charging rectifier«). The interdependency of the voltages no longer exists, the introduction of components of the track diagram technology led, among other things, to the conversion of the monitoring voltage to the usual 60 volts. New systems were equipped in this way from the start. The AC power supply required for light signals and automatic track vacancy detection systems corresponds to that of track diagram signal boxes.


The development of the electromechanical interlockings meant a step forward, because they made use of electricity and thus made operation much easier. In addition, it cleared the way for the increasing realization of safety functions through electrical circuits, which finally culminated in the development of fully electric relay interlockings.

While setting the points in a mechanical interlocking can be physically very strenuous, the attendant in the electromechanical interlocking no longer needs a lot of physical strength to operate the systems. That alone was reason enough to start developing signal boxes with electric drive for the outdoor facilities. The first electromechanical signal box in Prerau in Moravia (now in the Czech Republic) was put into operation quite early, in 1894 . The first electromechanical signal box in Germany went into operation in Berlin Westend in 1896 .

As in the history of the development of mechanical interlockings, in the decades that followed there were a large number of sometimes quite different detailed solutions and designs from various manufacturers. It was essentially the same companies that also manufactured mechanical interlockings, such as AEG or Siemens & Halske.

Development in Germany

electromechanical lever mechanism type S&H 1907

In Germany, after the experimental design in 1896 and the forerunner designs in 1901 and 1907 (the latter becoming more widespread), the Siemens & Halske signal box was a widespread design in 1912. In the 1930s, this type of construction was further developed within the framework of the signal construction institutes, which were combined in the VES (United Railway Signal Works, Berlin), which resulted in the standard E43 (E43 = first year of construction 1943), which was built in larger numbers and is still in use. Other signal construction companies such as AEG, Orenstein & Koppel, Pintsch or Scheidt & Bachmann also developed their own designs for electromechanical signal boxes. No other manufacturer achieved a distribution comparable to that of S & H in 1912.

As early as the 1920s, light signals began to be installed as a replacement for the form signals that had previously been used exclusively in electromechanical interlockings, initially in urban high- speed railways and because of the obstruction of view from the catenary masts on electrified routes. The switching devices for the light signals were integrated into the dependency circuits at suitable points. After the Second World War, these efforts were continued, especially at the DR , the DB erected only a few such systems and instead immediately replaced the signal boxes with completely new track diagram signal boxes. The optimization work continued at the DR until 1990. The result was the E12 / 78 type, based on the 1912 or E43 type, with many components of the track diagram interlocking technology , especially the GS II type. One optimization goal was to reduce the number of cable cores required between the lever system and the relay room. A good distinguishing feature to type E43 are the generally used light signals with alternating voltage supply and in connection with this the usually green route lever, which can only be turned up to 45 °, the signal travel position takes place automatically after the route has been determined. With the exception of very small interlockings with simple conditions, an additional track diagram console was set up for monitoring the signals, crossing safety systems and the operation of additional equipment such as replacement and shunting signals and the relay block.

Bf Leipzig Hbf, Stw 3. The rooms in the cantilevered parts of the building below the control room contained the contacts and magnet systems of the four-row lever mechanism

In large train stations, single-row lever systems quickly reach a length that makes them confusing. In order to improve the clarity again and to shorten the distances for the staff, two-row and then four-row lever mechanisms were developed in the 1920s to 1940s. The operating device was relocated to the top of a table or desk surface. For reasons of space, the mechanical locking register is usually covered at floor level behind the operating table, and the contact and magnet systems belonging to the levers are under the operating room. A four-row lever mechanism already known for its size was the B3 signal box, built in 1940 on the Prussian side of the Leipzig Hbf train station. However, it was demolished in 2005.

Deutsche Bahn puts the service life of electromechanical interlockings, in which operation is worthwhile from a technical and economic point of view, at 60 years. At the beginning of 2006, the company operated 680 electromechanical interlockings with 21,300 actuating units. In 2017, 329 electromechanical interlockings were still in operation.

As a consequence of the railway accident in Aichach , the DB announced the project Technical Monitoring Track (Tüfa) to retrofit hundreds of mechanical and electromechanical signal boxes with electronic warning systems. A track vacancy detection system is planned to prevent a dispatcher from allowing a train ride into an occupied track. The main tracks of the stations are equipped with axle counters for the technical monitoring of the route . This monitors whether the track is occupied by a train. If you try to allow a journey into an occupied track, the signal lever is blocked and an acoustic signal sounds.

A total of around 600 of the 1178 mechanical and electromechanical interlockings of DB Netz are to be retrofitted accordingly without a track vacancy detection system. Installation should begin in January 2019 and be completed in 2024. Investments of 90 million euros are planned.

Development in Austria

Signal box Wien-Meidling 1981, type 42733

The world's first operational electromechanical interlockings were developed in Austria. After individual switches in Vienna West in 1892, as mentioned above, Siemens & Halske built such a system in Prerau in Moravia (today in the Czech Republic) in 1894 , which was in operation for 40 years. In the subsequent types in 1898 and 1901, the mechanical components were closely related to the mechanical type 5007, also developed by Siemens. The next type was the interlocking 42733, which was based closely on the switchgear of the Berlin light rail system : There the switch axes were not led out at the front to foldable handles, but small upright levers were used. The internal structure of the 42733 was practically identical to the German type Siemens 1912. After various individual pieces of German types (two and four-row signal boxes), after the Second World War, the types K46 and K47 (K for power signal box) were finally replaced by the type Siemens 1912 and the last 1954 version derived from the EM55 (EM for electro-mechanical ). With these types of construction, the turnout dependencies were for the most part only designed electrically, the mechanical dependencies only existed between the route switches.

Development in Switzerland

In Switzerland, electromechanical signal boxes were built by Siemens, AEG and Orenstein & Koppel. The switch mechanisms of the Swiss company Integra were not electromechanical interlockings, even if their operating elements ( switches ) were not arranged in a track diagram, but in a row. However, they had purely electrical dependencies and are therefore to be classified as predecessor types of relay interlockings. According to Oehler, the electromechanical types Siemens 1912 (from 1915), an AEG type (1922), an O&K type (from 1929) and some four-row signal boxes of the VES (from 1936) were built in Switzerland.

Development worldwide

The first electromechanical signal boxes were built in North America around 1906.

See also


  • Karl Oehler: Railway Safety Technology in Switzerland - The Development of Electrical Equipment , Birkhäuser Verlag, Basel, Boston, Stuttgart 1981, pp. 16-23, ISBN 3-7643-1233-5

Web links

Individual evidence

  1. Function tests for a route adjustment between an electronic interlocking and an electromechanical interlocking. Technical University of Dresden , accessed on May 27, 2016 .
  2. Lexicon of all technology , entry "Signal boxes"
  3. Berlin signal boxes . Retrieved November 24, 2012.
  4. Jörg Bormet: Requirements of the operator on the life cycle in route safety technology . In: signal + wire . tape 99 , no. 1 + 2 , 2007, ISSN  0037-4997 , p. 6-16 .
  5. Digital and good? In: DB World . No. 5 , May 2017, p. 4 f .
  6. Technical monitoring of the track (TüFa), a support for signal boxes without track vacancy detection. (PDF, 2.8MiB) In: BahnPraxisB, July / August 2019. Retrieved on May 3, 2020 .
  7. Bahn wants to retrofit signal boxes . In: Der Spiegel . No. 28 , 2018, p. 10 ( online ).