Electronic railway signaling

In the early years, the industrial applications of electronics were made exclusively in the field of communication. It is interesting to note, that the very first application of electronics in industry, for purposes other than communication, was made by the railroads. Vacuum tubes enabled to use a circuit that prevents the coding relay contacts from closing or opening when current is flowing.

Electronic circuit require negligible amount of energy. A few microwatts are enough to convey information. Response to an input signal is obtained in a fraction of a microsecond. And such results are accomplished with no mechanical movement. Electronic equipment may be made very compact and lightweight. It is ideal for printed circuitry. With these advantages, the use of electronics will become ever more widespread in signaling practice.

The electronically operated system of signal interlocking is designed to perform the basic function of all railway signaling apparatus by controlling the interlocking of signals so that adequate distances are maintained between following trains and detecting the presence of railway vehicles at the rail circuit. Electronic interlocking monitor and control logic and safety-related facilities in line with the dependencies between signals, switches and vehicles. The input signals must be converted from an analogue signal to a digital representation by A/D converters and further processed by digital signal processing methods. Discrete Fourier transform, an iterative algorithm CORDIC and threshold was used for digital signal processing. The digital signal processing system was implemented in C language and then rewritten to the VHDL language to implement it in the FPGA (Field Programmable Gate Array) device.

It will do this by means of computer techniques using suitable arrangements of plug-in electronic "logic" units in which transistors and magnetic cores perform "logical" switching operations. To perform the movement of a train, the signalman simply turns a switch representing the point of entry to the required route, and pushes a button representing the exit of the route.

The main aim of the automation plan was to develop the signaling and train control system at the high-speed railways. The signaling functions managed by automated control systems prevent train collisions and maximize the rail network capacity and service. The train control manages the velocity of trains through each of the signal sections, obeying the signal status and, if required, additionally stopping the trains at station platforms. It also manages the switching of many points and crossings giving a choice of over 40 routes along the track system. Within the physical bounds of the track and signaling more than 16 trains can be simultaneously handled, quite comfortably, with the system minimizing conflicts and hence not delaying trains.

The operator or signalman is shown a graphical representation of the track network on the computer screen, depicting which track zones are occupied and by what. By clicking a mouse button the signalman can select any desired route, if available (no conflicting routes set).

If a route has been chosen the system controls the movement of the train through the route, switching all necessary points and also turns on animations such as model semaphore signals and level crossing gates. The first of the automatic running modes is known as automatic routing setting (ARS). When initiated, the ARS looks at position of each train, decides which routes are available and how close to capacity advance areas of the network are. The ARS system does not discriminate what type of train is in each position, its main control philosophy being only to avoid conflicts to keep as many trains as possible moving at any one time.

The latest electronic railway signaling technology differs from the old electromechanical relay system mainly in terms of safety and size. 
Modern electronic interlocking systems, which have been developed according to the highest safety requirements stipulated in
 European railway-related standards, operate on a fail-safe principle. 
It requires only limited space as the equipment and can be installed in compact cabinets. 
These cabinets can be erected in existing buildings or mobile containers.

 

Exercise 1