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Microcomputer Controlled Interlocking System Niels Siggaard and L. Norbert Sorensen into railway signalling attractive. The Danish company, Dansk Signal Industri A S. a member of the Ericsson Group, has developed a microcomputer controlled interlocking system. The Dansk Signal Industri A/S has de­ system was developed in collaboration with the Danish State Railways (DSB), and veloped a microcomputer controlled in­ the first system is now in operation on the Vejle-Holstebro line in Jutland. terlocking system, which was first com­ The authors outline the circumstances that have made it possible to use missioned in December 1980. Today the microcomputers in interlocking systems and describe the structure and functions system is in operation at 14 stations in of the system. They also describe briefly how it is possible to plan and test the Denmark ranging from 20 devices (sig­ system using a general purpose computer. nals, point machines etc.) to more than 170 per station. Development of the new interlocking system began in 1976, initiated by the UDK 656.25:681 31-181 4 Interlocking systems are used on rail­ need to modernize signalling on the line ways to ensure the safety of train move­ between Vejle and Holstebro in Jutland, ments. The primary aim is to prevent so as to obtain reliable track circuit collisions and derailments. Another detection from a new generation of purpose of the signalling systems, of lightweight trains introduced by the which the interlocking system forms Danish State Railways. part, is to ensure the traffic flow in ac­ cordance with the timetable and to per­ The interlocking function is computer mit easy operation at the lowest overall controlled and relays are only used to cost interface the track devices. The compu­ ter processes the interlocking functions For more than 40 years safety relays by means of two program systems have^een the predominant component which are independent of each other. in railway fail-safe systems. Many at­ The devices communicate continuously tempts have been made to replace the with the interlocking computer via con­ clumsy and expensive safety relay with centrator computers common to sever­ electronic components, but the cost al devices. has previously been too high. The in­ creasing use of microcomputers has led With the microcomputer interlocking, to a drastic price reduction as a result of most of the wired logic specific to one Fig. 1 installation is replaced by stored data. Local control of a station with the aid of a colour mass production. This has made the VDU and an alphanumeric keyboard introduction of solid state technology As manual preparation of these data would be as cumbersome as the plan­ ning and implementation of traditional installations, an off-line support pro­ gram has been developed. It is run on a general purpose computer to produce the engineering and interlocking data needed. The resulting outputs is data ready for direct loading into the compu­ ters of the interlocking installations, with printouts to be read as signal and route control tables. The dispatcher's control of the inter­ locking system at each station is carried out either locally or remotely (CTC) through microcomputerized interfaces. The eguipment for local control con­ sists of a colour video display unit (VDU) showing the track diagram with an indication of the actual status of all track devices, including track circuit oc­ cupancy and route setting. Provision has been made, especially at small sta­ tions, for the alternative use of a local control panel with keys and lamps. 153 NIELS SIGGAARD System JZSD 770 handles the exchange of commands be­ LNORBERTSORENSEN tween the the dispatcher's equipment Dansk Signal Industri A S Interlocking system JZSD 770 consists and the interlocking computer. CAPP of a number of subsystems, fig. 3: processes and stores commands from - A subsystem for local control consis­ the keyboard and transmits them to the ting of the VDU with keyboard and a interlocking computer, SID. computer CAPP - A subsystem for remote control con­ Status information from the devices is sisting of a computer FU transmitted continuously in the op­ - An interlocking computer SID posite direction, from SID to CAPP. This - A number of concentrators each con­ information is processed in CAPP and sisting of a concentrator computer then used for updating the information KC with associated relay equipment displayed on the screen. RS. Alarms received from the interlocking The track devices (signals, points, track computer, for example burn-out of a circuits etc.) are connected to the con­ filament in a signal lamp, and internal centrators. Transmission of data be­ alarms from CAPP are recorded and Fig. 2 tween the different subsystems takes stored for display on the screen and for Track-diagram, train routes, train movements etc. place via transmission links. The data are presented on the VDU later printout. All control commands messages are transmitted in serial form, and changes in the status of devices are and each message is supplemented also logged continuously, and the over­ with redundant information in order to all state of the system is logged at spe­ ensure faile-safe function. Fig. 3 cific time intervals. Printout of logged Block diagram of interlocking system JZSD 770 information is used in connection with Subsystem for local control investigation of accidents and for sys­ Dispatcher's equipment The subsystem for local control con­ Keyboard and semigraphic colour video display tem fault finding. unit with 80 characters per line in a 48-line format. sists of a VDU with a standard keyboard and a microcomputer, CAPP, which Eight different colours are used and each charac­ The local control computer contains fa­ ter is displayed by means of an 8x6 matrix cilities for adjusting and testing the Alternative train dispatcher's equipment tor small VDU. The presentation on the display is stations Panel with lamps for indications and keys for refreshed alternately from the two data setting of train routes systems A and B. The computer con­ Computer CAPP for local control tinuously monitors receipt of status in­ Microcomputer Intel 8085 with 56 kbit memory is formation from all track devices. used for local control. The computer controls the exchange of information between the dispatcher's Subsystem for remote control equipment and the interlocking computer. It rec­ ords alarms and is also used for functional A microcomputer. FU, is used as inter­ testing of the VDU face to a remote control system. This Computer FU for remote control computer handles the exchange of in­ Microcomputer Intel 8085 is also used for remote formation between the interlocking control. This computer controls the exchange of computer and the remote control sys­ information between the interlocking computer tem. Commands are received, pro­ and the remote control system cessed and transmitted to the interlock­ Computer SID for interlocking ing computer. In the opposite direction The Ericsson computer APN 163 with micro­ processor circuits AMD 2901, 64 k word memory there is a continuous flow of indica­ and 16-bit word length is used for the interlocking tions, which are processed and stored Computer KC for concentrator function before being transmitted via the remote Microcomputer Intel 8085 with 2.25 kbit memory control system. is used for the concentrators. KC controls the exchange of information between the relay equip­ ment and the interlocking computer. A maximum Interlocking subsystem of 31 controlled devices and 28 track circuits can All information about the geographical be connected to each concentrator layout of the station is stored in the Relay sets RS interlocking computer, together with all The circuits with safety relays are mounted in possible train routes and the corre­ standard relay sets. The track circuits have free- sponding positions of all track devices. wired relays connected directly to KC The computer processes commands Track devices from the control computer such as: The track devices comprise different types of signals, points, track circuits, automatic blocks, Establish train route from signal no. level crossing plants etc. 01 to signal no. 02. 154 Communication with concentrators Communication with local and remote control interfaces Fig. 5 Program execution in an interlocking computer Information received from the devices mined by fail-safe comparison in the via the concentrators is simultaneously relay sets. processed-status information such as: Signal no. 01 shows stop. A common functional specification forms the basis of the programs, and The interlocking computer performs a the coding as well as the testing of number of tasks such as verification of these programs uses separate data sets commands, prevention of set-up of con­ (also designated A and B) in which cor­ flicting routes, setting train routes with responding data bits are mutually inver­ the associated operation of points, sig­ ted and the address bits mutually re­ nals etc. versed. Concentrator subsystem The programs contain the general inter­ Each concentrator consists of a compu­ locking rules applicable for any installa­ ter with associated relay equipment tion, whereas the data define charac­ controlling the function of the devices. teristics specific to each station. Commands from the interlocking com­ puter are stored in the concentrator Interlocking programs A and B are ex­ computer. The commands are checked ecuted sequentially once every operat­ with respect to correct concentrator ad­ ing cycle of 1 s. Based on updated infor­ dress (for example) and then fed to the mation on the actual status of track relay equipment. devices, and depending on the dis­ patcher's commands, and routes al­ The concentrator computer continu­ ready established, programs A and B ously records the status of all con­ process the respective A and B com­ nected devices during each operating mands which are then transmitted to cycle and transmits the corresponding the relay sets controlling the points and data to the interlocking computer.

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