Electric tablet system
The Electric Tablet System is a route block for single-track railway lines . It was developed by Edward Tyer (1830–1912) and patented in 1880. Since it significantly increased operational safety in rail traffic compared to its predecessor systems , the Tyer system was widespread after just a few years, especially in Great Britain and the colonies of that time . It was still in use in Sri Lanka in 2012 and still in use on the route to Badulla in 2018 . It is also still used today on single-track museum railway lines, such as theNorth Yorkshire Moors Railway in Northern England. The manufacture and worldwide distribution was carried out by the company Tyer & Co.
concept
The Electric Tablet System is a design of the Electric Token Block . As with other block systems, the route is divided into block sections. A train may only enter a block section if the driver is in possession of a token that gives him the driving license. In the Tyer system, tablets called disks take on this function. These disks are taken from an apparatus called a tablet instrument , one of which is set up at the beginning and one at the end of the block section. The devices are electrically connected to each other in such a way that only one tablet can be removed from one of the devices for each block section. Before a tablet can be pulled out, a release must be made on the device at the end of the block section, which blocks this device. When the tablet is removed, the device at the beginning of the block section is also locked. The next tablet can only be removed when the train has arrived at the end of the block section and the block has been released by returning the tablet.
Components
Tablet apparatus
A Tyer device consists of a closed box made of wood or metal with two slides for removing and returning the tablets. Communication with the operator of the other device takes place with the Bell button on the top of the box, which can be used to trigger the bell at the remote station. A second Switch button unlocks the removal slide on the other device or releases the removal slide on your own device. An ammeter indicates whether the electrical connection between the devices is intact. A window on the front of the box shows whether the block is free or occupied and for which direction the block is released. One tablet at a time can be pulled over the removal slide on the underside after it has been released by the counterpart. This will automatically lock the device. The tablet from the arriving train is returned via a second slider on the top, thus releasing the lock. The box has space for around 20 tablets, the number currently available can be seen through a viewing window on the front.
The devices were initially set up in the stationmaster's office, nowadays they are usually in the signal box . They may only be operated by the dispatcher . If several devices are set up in one room, the bells have a different sound for better recognition.
Tablet
Round brass disks with a diameter of approx. 10–12 cm are used as tablets. The route section for which it is valid and a serial number are printed or embossed on each tablet. After taking it out, it is put into a leather pouch attached to a brass ring with a diameter of approx. 60 cm. The ring makes it easier to hand over the tablet to a moving train. Tablets have a larger round, triangular or square hole in the middle, a smaller round hole near the edge and a semicircular, square or triangular notch on the edge. In order to avoid confusion, the tablets of the individual block sections differ in the shape and arrangement of the holes and notches. They can only be placed in the devices that belong to the same block section.
In later years there were also square tablets and those made of aluminum or plastic.
Connecting line
The two devices belonging to a block section are electrically connected to one another via the line telephone or telegraph line. This means that no special cabling is required for the section block. The change between the pad and the telephone is carried out by a specific bell signal.
handling
If there is no train on the line, the removal slides of both devices are half open, all tablets are in the devices and no tablet can be removed. Before a train is supposed to run, the station of departure requests clearance with the bell button. The request is acknowledged with the bell button. Then the removal slide is closed on both devices and the switch button is pressed on the device of the destination station, which triggers a locking of the removal slide and releases the removal slide in the departure station. By pressing the switch button on their own device, the station manager can now remove a tablet at the departure station. When the train is removed, the device is also locked at the departure station and no further tablets can be withdrawn until the train arrives.
The number of the tablet is noted in the train registration book and the station manager instructs the signalman to set the exit signal. The tablet is put in a leather case and given to the driver as a driver's license. This checks whether the tablet is valid for the next section of the route and the train continues its journey. At the destination station, the train driver hands the tablet to the station manager and receives the tablet for the next section.
The block is released by returning the tablet to the destination station via the slide on the top.
Development, designs and distribution
Two head-on collisions, the Thorpe railway accident in 1874 and a second at Radstock in 1876, had shown that the block telegraph system that had been in use up to that point was tainted with critical safety deficiencies. The development of the Electric Tablet System resulted from the endeavor to eliminate these deficiencies and to increase operational safety on single-track routes.
Over the years the system has been further developed and modified for special requirements. The No. 3 from 1890 . With the rare design No. 5 ( 1891 ) two trains following one another could run in one direction. Before the development of the No. 6 in 1892 , the block section could only be released by returning the tablet to the neighboring instrument. With the No. 6 the tablet could also be returned to the same instrument. In this way, trains could also be secured with the system that did not go to the end of the block section, but returned from en route. With the patenting of the design No. 7 In 1898, the development of the Electric Tablet System ended, and easier-to-use token key systems took over.
In later years the installed devices were retrofitted, the most important change was the coupling of the exit signals with the block devices and in many places the relocation of the devices from the station buildings to the signal boxes . In Great Britain, the Tyer system was largely superseded by the end of the 20th century. In countries that use British signaling technology , such as The Electric Tablet System was also used in New Zealand, Australia, Japan and Indonesia, for example. In Sri Lanka, parts of the network are still operated using the Electric Tablet System.
Advantages and disadvantages of the electric tablet system
The electric tablet system has the advantage over the older stick system that several trains can run one after the other without any effort, that reliable communication is guaranteed between the operating points and that no special cabling is necessary due to the use of the telegraph line. In contrast to the block telegraph used previously, the operating status can be read off the device at any time.
The biggest disadvantage, especially of the older designs, is the lack of dependency between the exit signals and the block apparatus. H. it was possible to set the exit signal to drive even though the block was occupied. As the railway accident at Abermule shows, the Electric Tablet System was no substitute for the care and discipline of the industrial railroaders .
Web links
- Website Roland Ziegler (Sri Lanka)
- Illustration and description of various block apparatus
- Illustration of different tablets
- Electric Token Block ( English ) Retrieved on July 14, 2013.
Individual evidence
- ^ Gyan Fernando: Rozelle: A quaint little Railway Station. In: Railway Journeys and other railway articles :. Retrieved May 24, 2016 .