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49-634: Flagstaff Tower is a one-room, castellated tower, built around 1828 as a signal tower , located in Kamla Nehru Ridge near the present-day North Campus of Delhi University in Delhi , India . It was here that many Europeans and their families sheltered on 11 May 1857, during the Siege of Delhi by the rebels at the beginning of the Indian rebellion of that year , waiting for help to arrive from nearby Meerut . Built by

98-425: A locking bed is constructed, consisting of steel bars forming a grid. The levers that operate switches , derails , signals or other appliances are connected to the bars running in one direction. The bars are constructed so that if the function controlled by a given lever conflicts with that controlled by another lever, mechanical interference is set up in the cross locking between the two bars, in turn preventing

147-648: A rail transport system, signalling control is the process by which control is exercised over train movements by way of railway signals and block systems to ensure that trains operate safely, over the correct route and to the proper timetable . Signalling control was originally exercised via a decentralised network of control points that were known by a variety of names including signal box (International and British), interlocking tower (North America) and signal cabin (some railways e.g., GCR ). Currently these decentralised systems are being consolidated into wide scale signalling centres or dispatch offices . Whatever

196-562: A common naming convention. In Central Europe, for example, signalling control points were all issued regionally unique location codes based roughly on the point's location and function, while the American state of Texas sequentially numbered all interlockings for regulatory purposes. As signaling control centers are consolidated it can become necessary to differentiate between older style boxes and newer train control centers, where signalmen may have different duties and responsibilities. Moreover,

245-432: A control lever may be moved into a position which would release other levers, a signal must be received from the field element that it has actually moved into the position requested. The locking bed shown is for a GRS power interlocking machine. Interlockings effected purely electrically (sometimes referred to as all-electric ) consist of complex circuitry made up of relays in an arrangement of relay logic that ascertain

294-505: A diagram of the track and signaling layout is mounted above the lever frame, showing the relevant lever numbers adjacent to the signals and points. Hand-powered interlockings were referred to as 'Armstrongs' and hand throws in the United States. Power frames have miniature levers and control the signals and points electrically. In some cases, the interlocking was still done mechanically, but in others, electric lever locks were used. In

343-422: A direct physical connection (or the space required by such connections). Power-operated switch points and signaling devices greatly expanded the territory that a single control point could operate from several hundred yards to several miles. As the technology of electric relay logic was developed, it no longer became necessary for signalmen to operate control devices with any sort of mechanical logic at all. With

392-529: A few cases, signals and points were operated pneumatically upon operation of the appropriate lever or slide. In a signal box with a control panel, the levers are replaced by buttons or switches, usually appropriately positioned directly onto the track diagram. These buttons or switches are interfaced with an electrical or electronic interlocking. In the UK, control panels are of the following types: Similar principles of operation as described above are applicable throughout

441-439: A mini fort but not that safe. In recent times some parts of the tower have been ruined due to people having scribbled on its wall. Before deforestation in the year 1910, the area where the tower was built was the point on the ridge and was mostly barren and covered with small-sized shrubs . 28°41′17″N 77°13′05″E  /  28.6881°N 77.2181°E  / 28.6881; 77.2181 Signal tower On

490-531: A municipality or neighborhood, a nearby road or geographic feature, local landmarks, and industry that may provide the railway with traffic or railway features like yards, sidings, or junctions. On systems where Morse code was in use it was common to assign control locations short identification codes to aid in efficient communication, although wherever signalling control locations are more numerous than mileposts, sequence numbers and codes are more likely to be employed. Entire rail systems or political areas may adopt

539-455: A total of 1,864 interlocking levers, were in use on 13 North American railroads. This type of system would remain one of two viable competing systems into the future, although it did have the disadvantage of needing extra single-use equipment and requiring high maintenance. Interlockings using electric motors for moving switches and signals became viable in 1894, when Siemens in Austria installed

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588-709: Is a safety measure designed to prevent signals and points/switches from being changed in an improper sequence. For example, interlocking would prevent a signal from being changed to indicate a diverging route, unless the corresponding points/switches had been changed first. In North America, the official railroad definition of interlocking is: " An arrangement of signals and signal appliances so interconnected that their movements must succeed each other in proper sequence ". A minimal interlocking consists of signals , but usually includes additional appliances such as points and Facing Point locks (US: switches) and derails , and may include crossings at grade and movable bridges. Some of

637-410: Is plainly labeled on the side of the signal box structure as an extra visual reminder to the train operators where they are. Moreover, wayside signals may also be equipped with identification plates that directly or indirectly indicate who controls that signal and that stretch of the line. For more information, see also Interlocking . The earliest signal boxes housed mechanical lever frames. The frame

686-600: Is still relatively common away from the busiest lines; in Europe, there is also a considerable amount in Germany, Poland, and the Czech Republic. Traditional signal boxes can be found on many heritage railways . The modern control centre has largely replaced widespread signal cabins. These centres, usually located near main railway stations , control the track network electrically or electronically. Interlocking Interlocking

735-549: The British Indian Army , the building was part of the British cantonment and was used as a signal tower. Before forestation started in 1910, the area where the tower was built was the highest point on the ridge and was mostly barren, covered with low-lying shrub. Today it is a memorial and "protected monument" under Archaeological Survey of India . The monument is still preserved and in very good condition. This cemetery , where

784-616: The Indian Rebellion of 1857 , when Delhi was captured by the rebellious East India Company forces . On the morning of 11 May 1857, when the sepoys started hunting for and killing European personnel and Christian Indians in the Cantonment, Civil Lines and the walled city of Delhi , the survivors started fleeing towards the Tower. A month later the Company army returned to capture Delhi , which

833-634: The London and North Western Railway alone. The first experiment with mechanical interlocking in the United States took place in 1875 by J. M. Toucey and William Buchanan at Spuyten Duyvil Junction in New York on the New York Central and Hudson River Railroad (NYC&HRR). At the time, Toucey was General Superintendent and Buchanan was Superintendent of Machinery on the NYC&;HRR. Toucey and Buchanan formed

882-421: The 1980s when solid state interlocking and control systems began to replace the older relay plants of all types. Modern interlockings (those installed since the late 1980s) are generally solid state , where the wired networks of relays are replaced by software logic running on special-purpose control hardware. The fact that the logic is implemented by software rather than hard-wired circuitry greatly facilitates

931-667: The Toucey and Buchanan Interlocking Switch and Signal Company in Harrisburg, Pennsylvania in 1878. The first important installations of their mechanism were on the switches and signals of the Manhattan Elevated Railroad Company and the New York Elevated Railroad Company in 1877–78. Compared to Saxby's design, Toucey and Buchanans' interlocking mechanism was more cumbersome and less sophisticated, and so

980-512: The ability to make modifications when needed by reprogramming rather than rewiring. In many implementations, this vital logic is stored as firmware or in ROM that cannot be easily altered to both resist unsafe modification and meet regulatory safety testing requirements. As display technology improved, the hard wired physical devices could be updated with visual display units (computer monitors), which allowed changes in field equipment be represented to

1029-445: The conflicting lever movement from being made. In purely mechanical plants, the levers operate the field devices, such as signals, directly via a mechanical rodding or wire connection. The levers are about shoulder height since they must supply a mechanical advantage for the operator. Cross locking of levers was effected such that the extra leverage could not defeat the locking (preliminary latch lock). The first mechanical interlocking

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1078-565: The design, and little saving of labour was achieved. The inventors of the hydro-pneumatic system moved forward to an electro-pneumatic system in 1891 and this system, best identified with the Union Switch & Signal Company, was first installed on the Chicago and Northern Pacific Railroad at its drawbridge across the Chicago River . By 1900, 54 electro-pneumatic interlocking plants, controlling

1127-420: The disparate parts of a rail line and linking them together to allow the safe passage of trains. The first signaling systems were made possible by technology like the telegraph and block instrument that allowed adjacent signal boxes to communicate the status of a section of track. Later, the telephone put centralized dispatchers in contact with distant signal boxes, and radio even allowed direct communication with

1176-478: The few British who fell during the uprising are buried with their leader, Brigadier John Nicholson , is now that well preserved that a Britain's High Commissioner , Mr. Michael Arthur, who once helped in the restoration and repairing of the cemetery thought that it surpassed many of the cemeteries in Britain , with its beautiful glimpse of the history of the year 1857. Flagstaff Tower played an important role during

1225-953: The first such interlocking at Přerov (now in the Czech Republic). Another interlocking of this type was installed in Westend near Berlin in 1896. In North America, the first installation of an interlocking plant using electric switch machines was at Eau Claire, Wisconsin on the Chicago, St. Paul, Minneapolis and Omaha Railway in 1901, by General Railway Signal Company (GRS, now a unit of Alstom , headquartered in Levallois-Perret , near Paris). By 1913, this type system had been installed on 83 railroads across 35 US states and Canadian provinces, in 440 interlocking plants using 21,370 levers. Interlockings can be categorized as mechanical, electrical (electro-mechanical or relay -based), or electronic/ computer-based . In mechanical interlocking plants,

1274-416: The form, signalling control provides an interface between the human signal operator and the lineside signalling equipment . The technical apparatus used to control switches (points), signals and block systems is called interlocking . Originally, all signaling was done by mechanical means . Points and signals were operated locally from individual levers or handles, requiring the signalman to walk between

1323-533: The fundamental principles of interlocking include: Railway interlocking is of British origin, where numerous patents were granted. In June 1856, John Saxby received the first patent for interlocking switches and signals. In 1868, Saxby (of Saxby & Farmer) was awarded a patent for what is known today in North America as “preliminary latch locking”. Preliminary latch locking became so successful that by 1873, 13,000 mechanical locking levers were employed on

1372-734: The interlocking plant. The first NX installation was in 1937 at Brunswick on the Cheshire Lines , UK. The first US installation was on the New York Central Railroad (NYCRR) at Girard Junction, Ohio in 1937. Another NYCRR installation was on the main line between Utica, New York and Rochester, New York , and this was quickly followed up by three installations on the New York City Subway 's IND Fulton Street Line in 1948. Other NX style systems were implemented by other railroad signal providers. For example, Union Route (UR)

1421-504: The jump to all electronic logic, physical presence was no longer needed and the individual control points could be consolidated to increase system efficiency. Another advancement made possible by the replacement of mechanical control by all-electric systems was that the signalman's user interface could be enhanced to further improve productivity. The smaller size of electric toggles and push buttons put more functionality within reach of an individual signalman. Route-setting technology automated

1470-445: The large mechanical levers of previous systems being replaced by buttons, switches or toggles on a panel or video interface. Such an interlocking may also be designed to operate without a human operator. These arrangements are termed automatic interlockings , and the approach of a train sets its own route automatically, provided no conflicting movements are in progress. GRS manufactured the first all-relay interlocking system in 1929. It

1519-513: The lineside signal box to niche or heritage applications. In any node -based control system, proper identification is critical to ensuring that messages are properly received by their intended recipients. As such, signaling control points are provided with names or identifiers that minimize the likelihood of confusion during communications. Popular naming techniques include using nearby geographic references, line milepost numbers, sequence numbers, and identification codes. Geographic names can refer to

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1568-406: The name of the signaling center itself may not be employed operationally in preference to the name of individual signaling workstations. This is especially true when signaling centers control large amounts of territory spanning many diverse lines and geographical regions. In most cases where the control locations are still in the field adjacent to railway tracks, the name or code of the control point

1617-403: The route manually. The NX system allowed an operator looking at the diagram of a complicated junction to simply push a button on the known entrance track and another button on the desired exit track. The logic circuitry handled all the necessary actions of commanding the underlying relay interlocking to set signals and throw switches in the proper sequence, as required to provide valid route through

1666-466: The setting of individual points and routes through busy junctions. Computerized video displays removed the physical interface altogether, replacing it with a point-and-click or touchscreen interface. Finally, the use of Automatic Route Setting removed the need for any human input at all as common train movements could be fully automated according to a schedule or other scripted logic. Signal boxes also served as important communications hubs, connecting

1715-643: The signal industry was achieving the same level of safety and reliability that was inherent to purely mechanical systems. An experimental hydro-pneumatic interlocking was installed at the Bound Brook, New Jersey junction of the Philadelphia and Reading Railroad and the Lehigh Valley Railroad in 1884. By 1891, there were 18 hydro-pneumatic plants, on six railroads, operating a total of 482 levers. The installations worked, but there were serious defects in

1764-780: The signaller without any hardware modifications. " Solid State Interlocking " (SSI) is the brand name in trade of work of the first generation microprocessor -based interlocking developed in the 1980s by British Rail , GEC-General Signal and Westinghouse Signals Ltd in the UK. Second generation processor-based interlockings are known by the term "Computer Based Interlocking" (CBI), of which VPI (trademark of General Railway Signal , now Alstom), MicroLok (trademark of Union Switch & Signal , now Hitachi Rail STS ), Westlock and Westrace (trademarks of Invensys Rail , now Siemens), and [Smartlock ] (trademark of Alstom ), and EBI Lock (trademark of Bombardier ) are examples. Interlockings allow trains to cross from one track to another using

1813-448: The signalman with a good view of the railway under his control. The first use of a signal box was by the London & Croydon Railway in 1843 to control the junction to Bricklayers Arms in London. With the practical development of electric power, the complexity of a signal box was no longer limited by the distance a mechanical lever could work a set of points or a semaphore signal via

1862-505: The state or position of each signal appliance. As appliances are operated, their change of position opens some circuits that lock out other appliances that would conflict with the new position. Similarly, other circuits are closed when the appliances they control become safe to operate. Equipment used for railroad signalling tends to be expensive because of its specialized nature and fail-safe design. Interlockings operated solely by electrical circuitry may be operated locally or remotely, with

1911-553: The trains themselves. The ultimate ability for data to be transmitted over long distances has proven the demise of most local control signal boxes. Signalmen next to the track are no longer needed to serve as the eyes and ears of the signaling system. Track circuits transmit train locations to distant control centers and data links allow direct manipulation of the points and signals. While some railway systems have more signal boxes than others, most future signaling projects will result in increasing amounts of centralized control relegating

1960-503: The various pieces of equipment to set them in the required position for each train that passed. Before long, it was realized that control should be concentrated into one building, which came to be known as a signal box. The signal box provided a dry, climate-controlled space for the complex interlocking mechanics and also the signalman. The raised design of most signal boxes (which gave rise to the term "tower" in North America) also provided

2009-544: The world. Modern signal boxes tend to be provided with VDU based, or similar, control systems. These systems are less expensive to build and easier to alter than a traditional panel. In the UK, large modern signal boxes are typical of the Integrated Electronic Control Centre type, or, more recently, of the Rail Operating Centre variety. Variations of these control systems are used throughout

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2058-400: The world. While rare, some traditional signal boxes can still be found. Some still control mechanical points and signals, although in many cases, the lever frame has been removed or is out of use, and a control panel or VDU has been installed. Most modern countries have little, if any, mechanical signalling remaining on the rail system. Both in the UK and Ireland, however, mechanical signalling

2107-430: Was condensed into a single large power signal box with a control panel in the operator's area and the equivalent of a telephone exchange in the floors below that combined the vital relay based interlocking logic and non-vital control logic in one place. Such advanced schemes would also include train describer and train tracking technologies. Away from complex terminals unit lever control systems remained popular until

2156-525: Was installed in Lincoln, Nebraska on the Chicago, Burlington and Quincy Railroad . Entrance-Exit Interlocking (NX) was the original brand name of the first generation relay-based centralized traffic control (CTC) interlocking system introduced in 1936 by GRS (represented in Europe by Metropolitan-Vickers ). The advent of all electric interlocking technology allowed for more automated route setting procedures as opposed to having an operator line each part of

2205-441: Was installed in 1843 at Bricklayers Arms Junction , England. Power interlockings may also use mechanical locking to ensure the proper sequencing of levers, but the levers are considerably smaller as they themselves do not directly control the field devices. If the lever is free to move based on the locking bed, contacts on the levers actuate the switches and signals which are operated electrically or electro- pneumatically . Before

2254-428: Was not implemented very widely. Union Switch & Signal bought their company in 1882. As technology advanced the railway signaling industry looked to incorporate these new technologies into interlockings to increase the speed of route setting, the number of appliances controlled from a single point and to expand the distance that those same appliances could be operated from the point of control. The challenge facing

2303-476: Was now with the sepoys. On 7 June, they faced stiff resistance from the sepoys at the Flagstaff Tower. A fierce battle followed which led to the killing and wounding of a great number of soldiers. However, by five in the evening the ridge had been recaptured and was now under British control. Inside the tower, which is locked, there is a circular room that can hold a crowd of up to a hundred people. It resembles

2352-408: Was the brand name of their Entrance-Exit system supplied by Union Switch & Signal Co. (US&S), and introduced in 1951. NX type systems and their costly pre-solid state control logic only tended to be installed in the busier or more complicated terminal areas where it could increase capacity and reduce staffing requirements. In a move that was popular in Europe, the signalling for an entire area

2401-548: Was usually mounted on a beam beneath the operating floor. Interlocking was attached to the levers, which ensured that signals showed the correct indication concerning the points and were operated in the right order. Wires or rods, connected at one end to the signals and points and the other to levers in the signal box, ran alongside the railway. In many countries, levers are painted according to their function, e.g. red for stop signals and black for points, and are usually numbered, from left to right, for identification. In most cases,

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