Having worked in the subway for many years, do you know how subway shield doors ensure stable communication?

Summary: As the preferred mode of transportation for people, subway is particularly important for safety and reliability. In a complex subway control system, how to ensure the stability of communication? This article will discuss the communication protection solution from the simple topology of the communication unit in the subway system.

With the rapid development of my country's economy, the construction of subway projects is also in the process of rapid development and continuous improvement. As people's preferred mode of transportation, the comfort and convenience of subways are increasingly concerned, and safe and reliable operation is particularly important.

Figure 1 Beijing's complex subway lines

Do you know what the integrated subway monitoring system includes?

Fire alarm system (FAS);

Environmental and equipment monitoring system (BAS);

Power monitoring system (SCADA);

Screen door/security door system (PSD).

At the same time, the ISCS system is interconnected with the following systems:

Public address system (PA);

Closed-circuit television surveillance system (CCTV);

Automatic Fare Collection (AFC);

Access Control System (ACS);

Signaling System (SIG);

Clock system (CLK);

Passenger Information System (PIS);

Communication centralized alarm system.

Thanks to the complete operation control network, the subway has become safer and more comfortable, and each system is in an orderly manner to protect the safety of the subway. Today, let's take a look at how the subway screen door system (PSD) is established and works.

The platform screen door for urban rail transit is a high-tech product that integrates disciplines such as architecture, machinery, materials, electronics and information. It isolates the track from the platform waiting area and is equipped with sliding doors corresponding to the train doors, which can be opened and closed with multi-level control.

The subway shield door system based on CAN bus means that the PSD (central interface disk), PSA (remote alarm disk) and each DCU (door control unit) in the system are all network nodes mounted on the CAN bus. The CAN bus distribution structure can ensure that the failure of one node in the network will not affect the normal operation of other nodes in the network. The shield door can be fully controlled and the operating parameters can be modified through the network.

Figure 2: The composition framework of the subway platform screen door system

PSC: Central interface panel, PSC is the core of the platform screen door/safety door control system. Each platform screen door/safety door equipment is equipped with a set of PSC;

PSD: Subway screen doors can be divided into three parts: sliding doors, fixed doors, and emergency doors;

PSA: Remote alarm panel, used to monitor the status of the shielding door, diagnose shielding door faults, operating status, etc.;

PSL: Local control panel, an electrical switch combination on the platform side that controls the operation of the platform screen door on that side, allowing station staff and train drivers to operate the platform screen door when the train system control fails;

DCU: The door control unit is the control device of the sliding door motor. Each sliding door unit of the shielding door is equipped with a door control unit and installed in the top box.

Figure 3: Division of subway platform screen door system

The shield door control system still uses hard-wire transmission for some important nodes and commands, such as between PSC and signal system, PSB and PSL (local control panel), and the sending and feedback of shield door opening and closing commands. In addition to the DCU connection via CAN bus, PSC communicates with LESS (local environment monitoring system) via RS-485, communicates with PTE via RS232, and communicates with the display via Ethernet. The subway shield door system is shown in the figure below.

In view of the particularity of the subway operation site, it is necessary to protect the external and internal signals, isolate the interference from the bus data communication, and ensure safety and reliability. At present, the authoritative standard for subway platform screen doors is "CJ/T 236-2006 Urban Rail Transit Platform Screen Doors" issued by the Ministry of Construction of the People's Republic of China.

This standard specifies the technical requirements, testing and packaging, transportation and storage of platform screen doors for urban rail transit. The standard clearly requires that the platform screen doors must pass GB/T 17626~GB/T 17626.6, GB/T 17626.8, and GB/T 17626.11 in the electromagnetic compatibility test section 6.1.2.5.

Figure 4 CJ/T 236-2006 electromagnetic compatibility requirements for shielding door systems

In order to meet the shield door standards proposed by the Ministry of Construction, the field data bus interfaces of each DCU, namely the CAN-bus interface, RS-485 interface, RS-232 interface, etc., need to be isolated for power supply and communication to completely cut off the ground loop interference between modules. Of course, the power supply part also needs to be isolated.

ZLG Zhiyuan Electronics has been focusing on signal isolation and transmission conditioning for 20 years, providing reliable and leading signal isolation and acquisition template-level solutions for the industrial field.

ZLG Zhiyuan Electronics combines years of technology accumulation and customer development trends to cater to market demand and technological innovation, and has launched a surface-mount isolation module. Compared with traditional designs, surface-mount products not only have higher integration and reliability, but also support all commonly used patch packages in the industry. They are suitable for occasions that require high-stability CAN bus communication, can maximize the user's production efficiency, and help users improve the bus communication protection level.

Currently, we have launched isolated CAN transceivers, isolated RS-485 transceivers, etc., with isolation voltage up to 3500V and ultra-wide temperature adaptability range, which can conquer complex and harsh industrial sites.