Railway System

In the traditional dual Fieldbus solution, the redundant PLCs at each station is responsible for the BAS system equipment at one end. Some equipment needs to be operated in linkage, such as the link of fans and dampers distributed at different station ends in normal mode. The redundant PLCs at each end of the station are responsible for the BAS system equipment, such as the linkage of fans and dampers at different station ends in normal mode and the link of air conditioning systems at both ends in fire mode. In the conventional metro design, the redundant PLC at both ends of the station adopts the hot standby mode, configured with two backplanes, two CPUs, two power supplies, etc. But all modules are placed in the same room or even in the same control cabinet; when a fire or power failure occurs in the room, it is easy to cause the overall loss of the redundant PLC. And once the redundant PLC at one end is out of service, the redundant PLC at the other end may lead to the overall system failure due to interlocking action failure. Parallel wiring is used between PLC and R I/O, and the two buses are distributed close to each other in the local control box. In case of fire or other particular circumstances, it is effortless to cause the two buses to be interrupted simultaneously, resulting in the loss of contact between the system and R I/O.

HoweVis Technology proposes deploying dual redundant Layer 2 industrial Ethernet switches to form a gigabit fiber self-healing ring network to connect the redundant PLCs at the two ends of the station hall. The ITU-G.8032 ring network protocol is enabled, and the self-healing time reaches milliseconds (less than 20ms). If one end of the redundant PLC has an overall failure and withdraws from service, the system will immediately switch to the other end of the set of redundant PLC to continue working. It ensures that the system can operate normally under terrible conditions and that the commands issued by the central station can transmit to the field equipment.

The fiber optic ring network based on industrial Ethernet adopts distributed wiring (with breakpoint protection function), and the fiber optic is spread into a ring in the station. In case of fire or other special conditions, the bus will immediately switch the transmission path, which will not cause an interruption of communication between PLC and R I/O. The primary transmission medium in the traditional dual Fieldbus solution is the communication cable. In the complex environment, the communication cable is easily disturbed by various electromagnetic interference sources in the metro. Using a fiber-optic medium can avoid the influence of electromagnetic interference on the system from the root. The electromagnetic compatibility of HoweVision Technology equipment itself reaches industrial level 4, which greatly ensures the stability and reliability of transmission in a complex environment.