Abstract: An industrial Ethernet switch for underground coal mines was designed, and the basic principles of hardware and software design were given. Broadband data communication was realized for the first time in underground coal mines.
Keywords: mine; industrial Ethernet; switch; monitoring and control
0 Introduction
Monitoring and controlling key parameters at various stages of coal mine production and safety is crucial for ensuring safe production. In my country, traditional monitoring systems include the KJ4, KJ90, and KJ95 systems, which are generally distributed systems consisting of field monitoring stations and a central control station. While these systems have played a significant role in coal mine safety monitoring, their inherent limitations—low transmission rates, lack of unified communication protocols and network structures—have become inadequate for the needs of building high-yield, high-efficiency, and modern mines due to the development of coal mine production and increasing automation. Modern coal mine production must transform traditional, single-function production and safety dispatching systems into a digital network information platform to achieve informatization and comprehensive automation of the entire mine and the entire mining area. Coal mines urgently need new technologies to drive overall automation and promote high-yield and high-efficiency production.
1. Overview of Industrial Ethernet
Compared to other control networks, including fieldbus, Ethernet boasts numerous advantages, including wide application, low cost, high communication speed, abundant hardware and software resources, and significant potential for sustainable development. It holds unparalleled advantages in many aspects, such as technology, speed, and price. With the continuous improvement of Ethernet performance and the emergence of technologies to address Ethernet real-time performance issues, applying Ethernet to industrial fields will become an inevitable choice in the industrial control sector.
Currently, Industrial Ethernet is already in practical application on the ground. At a recent seminar on the formulation of the "Safety Conditions for Coal Mine Safety Monitoring and Control Systems," relevant leaders and experts from the National Coal Mine Safety Supervision Bureau proposed that using Industrial Ethernet as the backbone transmission network underground and fieldbus as the network for connecting sensors and other field devices should be the focus of research and the direction of construction for mine transmission networks in the near future. It is foreseeable that Industrial Ethernet will also be an inevitable choice for the future construction of broadband communication networks in mines.
Mining industrial Ethernet switches are products used to build industrial Ethernet networks in coal mines. They are designed with high-performance Ethernet switch chips and network processor chips, and have industrial-grade reliability and real-time performance, meeting the needs of long-term and stable operation in harsh underground environments.
2 Hardware Design
The design of the mining industrial Ethernet switch consists of two parts: hardware design and software design. The hardware design complies with technical standards such as "General Technical Requirements for Electrical and Electronic Products for Communication, Detection and Control in Coal Mines" and "Requirements for Intrinsically Safe Circuits and Electrical Equipment for Explosion-Proof Electrical Equipment for Explosive Atmospheres". Functionally, the circuit can be divided into two parts: a switching circuit mainly based on the KS8999 chip and a control circuit mainly based on the $3C4510B chip. The system block diagram is shown in Figure 1.
Figure 1. Switch hardware system block diagramThe KS8999 chip is a high-performance Ethernet switch chip responsible for forwarding data packets between ports. The chip's backplane bandwidth is up to 2Gbps, and it includes eight 10M/100M adaptive Ethernet interfaces and one 10M/100M MII interface. In addition, there are eight sets of LED indicator interfaces, which can be used to indicate the port's connection, speed, collision and other statuses, making it easy to monitor the operation of each port of the switch.
The $3C4510B chip is a network processor chip, using an ARM7 processor core with a clock speed of 50MHz. The network processor chip also includes a MII interface, through which the switch chip and the control chip connect to facilitate data exchange between the two chips. The control chip can launch various service programs, such as serial servers and web servers, allowing users to easily manage and control the switch via network or other means. The on-chip JTAG interface is used for online monitoring of program execution during development and for writing the program to the flash memory after design completion. The core voltages of the KS8999 and $3C4510B chips are +2V and +3.3V, respectively.
Because high-speed circuit boards have high requirements for power supply ripple characteristics, the ripple at the power input terminal of the chip generally cannot exceed 5% of the power supply voltage. Therefore, the commonly used +5V power input is selected, and two reliable variable output power modules MIC29302 are used to output stable +2V and +3.3V voltages with very small ripple.
The PulseH1164 is an Ethernet physical layer isolation transformer chip, providing four Ethernet interfaces. Its main functions are filtering and isolation. The EEPROM is a 128-byte memory chip that stores various configuration information of the switch, such as VIAN, port priority, and port speed. When the switch powers on or resets, it reads the information from the EEPROM through the memory interface to complete the basic function settings of the switch. In addition, the EEPROM is also connected to the control chip $3C4510B via the IIC bus, allowing the control chip to manage and control the switch's functions by reading and writing data from the EEPROM.
The 2MB FLASH is a flash memory chip used to store software programs. Considering that the read and write speed of FLASH is relatively slow, when the switch is powered on or reset, the program in FLASH is automatically loaded into 4MB of SDRAM for execution to improve the running speed.
3 Software Design
After the hardware design and debugging are completed, software needs to be written to manage and control the switch, implementing functions such as VIAN partitioning and port priority settings. The system software is written to the FIASH chip through the JTAG interface of the network processor chip. After the switch powers on, the software program is automatically loaded into SDRAM and runs. The software mainly consists of three parts: the IIC bus control program, the web server program, and the serial port server program.
3.1 IIC Bus Control Program
The IIC bus control program is the foundation for implementing various control programs. The network processor chip $3C4510B reads and writes EEPROM through this program to perform various configurations on the switch. Both the web server and VT100 need to call the IIC bus program to write the control information filled in by the user into the EEPROM, or read the contents of the EEPROM to understand the working status of the switch.
3.2 WebServer Program
After starting the web server service, users can manage and control the switch via Internet Explorer on the server. This allows for convenient and intuitive control of various functions and monitoring of the switch's operational status. To prevent unauthorized users from arbitrarily modifying the switch, the program requires login to access the switch and modify data.
3.3 Serial Port Server Program
To facilitate basic setup of the switch before equipment installation, a serial interface circuit was designed. Users can connect the switch to an industrial control computer using a serial bus, access the switch through the switch's HyperTerminal program, and configure its IP address and other parameters.
4. Explosion-proof design
Because the underground environment is extremely harsh, in addition to considering the electrical characteristics of the circuit board during hardware design, it is also necessary to design an explosion-proof enclosure for the switch.
The design of the casing is in accordance with technical standards such as the "Coal Mine Safety Code", "Coal Mine Design Code", "Requirements for General Explosion-Proof Electrical Equipment for Explosive Atmospheres", "General Technical Requirements for Electrical and Electronic Products for Communication, Detection and Control in Coal Mines", and "Requirements for Intrinsically Safe Circuits and Electrical Equipment for Explosion-Proof Electrical Equipment for Explosive Atmospheres". The product is required to pass more than 10 safety tests, including vibration, shock, water spray, damp heat, high and low temperature operation, and voltage fluctuation, to ensure safe operation in underground environments with explosive gases.
5 Application Scheme
Using flame-retardant optical cables or flame-retardant Category 5 cables underground, mining industrial Ethernet switches can be directly connected to various devices such as substations, cameras, and centralized control systems that support the industrial Ethernet standard. Alternatively, monitoring and control systems that do not support the Ethernet standard can be connected to the switch via access gateway devices. The underground application solution is shown in Figure 2.
6 Conclusion
Mining industrial Ethernet switches are a new type of underground communication product for coal mines, supporting standard TCP/IP and IEEE 802.3u protocols.
Edited by: Chen Dong
