System Introduction

Metro, as one of the primary choices of transportation, is composed of different subsystems, for example, Electrical and Mechanical Control System (EMCS), Fire Alarm System (FAS), Fire Extinguishing System (FES), Supervisor Control and Data Acquisition System (SCADA), Automatic Fare Collection System (AFC), Dispatch Supervision System (DSS) and so on. DSS is the most important subsystem and is a distributed system including dispatching central subsystem, telecommunication maintenance subsystem, communication network subsystem and station subsystem. The core of DSS is railway signal interlocking system, whose reliability, safety, stability and real-time decide the safety of metro operation.

A lot of metro tracks are laid at the station and connected by switches. The track that train runs at the station is called route, which is decided by the place of switch and it needs to be protected by signal machine. If the switch is not in the right position or there is a train running on route, the signal machine which is used to protect this route will not release signal to guarantee the safety of train operation. The relation of switch, route and signal which depend on each other and restrain each other is called interlocking. These equipments to implement interlocking are called interlocking equipment. The diagram of interlocking equipment is shown as follows.

The self-protection and electrical integrated interlocking system of train are important operation equipments which prevent the impact and derailment of train and guarantee safe operating.
The main function of system includes:
1)To control the route setting and interlocking of train; to detect the train´s section occupancy; to realize interval control of train according with the controlling principle of occlusion moto avoid tremendous accidents such as rear-end collision, head-on collision and side collision.
2)To send away train order to implement overspeed protection.

Grade of Microcomputer Interlocking

Control and surveillance grade is the first grade of system. It is called man-machine conversation grade (watch keeper room) and it realizes the function of information display of system control process and input of system control order. The second grade is interlocking logic process grade that realizes relational calculation of signal interlocking. The third grade is execution indication grade that implements the function of operating status collection and real-time control. The console that watch-keeper operates is used to implement the function of voice reminder and alarm through the collection of button signals. The computer adopts serial data communication connection,and cooperative control ,realizing the real-time control of station signal, switches and routes in the fourth grade. Each computer works independently when the system is running. If any malfunction occurs, the computer will quit from the system automatically or carry out maintenance operation online immediately to ensure the system running properly.
1) Man-machine Conversation Layer
The Data that is inputted with keyboard and mouse will be transmitted to interlocking computer and the information of station will be shown on the graphic monitor. If the scale of station is too big, it will cause the problems that the burden of interlocking computer is overload and multiple terminal operation will be required. Operation order collecting machine is set to judge the validity of input order, convert it into a fixed format and transmit to interlocking computer.
2) Interlocking Calculation Layer
Interlocking microcomputer is the core of system and it is responsible for judgment of operation input, adjustment of interlocking signal, calculation of analysis and logic, generation of control order, fault diagnosis and so on. For the reason that its reliability and security influence the overall faultsecurity of system, two interlocking microcomputer are prepared and one of them is for cold backup, which can be switched by hand.
3) Hybrid Driver Layer
Hybrid driver layer is responsible for collecting the information which needs to be displayed, converting operational order instruction from interlocking microcomputer into fault-security control signal. It mainly features double checking the operational instruction from microcomputer.
4) Combined Circuit Layer
Combined circuit layer is responsible for implement the conversion of safety logic between the display information of local surveillance equipment and the output driver signal of PLC, and makes the input and output information of PLC with the fault-security capability. On the other hand, the process of measurement and control of surveillance equipment including information collecting mechanism and the flow of equipment driver is standardized by special circuit.
5) Surveillance Object Layer

Choice for Interlocking Host

Interlocking host is the most important equipment to ensure safety, high efficiency and reliability of operations management, which adopts the pattern of redundant double backup, RS-485 communication method and fault-security design. EVOC rugged computer is a good choice to meet the requirements of the whole design: FSC-1623CVDNA fanless motherboard with onboard low voltage CPU or VME-1641CVD2NA motherboard for ODM, signal acquisition card PCL-733 (32-channel isolated digital input) and control simulation output card PCL-726 for detecting switch position, switch voltage, track voltage and current, metro position and so on.
Hardware Configuration of Interlocking Host (Backup Machine):

System Evaluation

Microcomputer interlocking system replaces the out-of-date relay electric centralized interlocking system to ensure the reliability, security and efficiency of operation of station. EVOC is in the leading position of Chinese domestic industrial automation and embedded intelligent platform industry, and the reliability, availability and serviceability of our products satisfy all the requirements of interlocking.