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Physical and Numerical Simulation of Geotechnical Engineering 21st Issue, Dec. 2015 Research of a Mine Safety Monitoring System Based on WSN LEI Wenli 1, REN Xincheng 1, ZHANG Yang 2 1. College of Physic and Electronic Information, Yan’an University, Yan’an 716000, China 2. China Coal Research Institute, Beijing 100013, China ABSTRACT: This paper presents a mine safety monitoring system based on WSN network, which collects mine tunnel environmental parameter data through a tunnel environmental data collection node, and sending the collected environment parameter data to the ground monitoring center computer by WSN network. The monitoring center computer can view the tunnel production environmental information in real time combined with the geographic mine information, in order to ensure mine production safety and provide a reliable basis for accident recovery. Tunnel environmental data collection node is developed based on embedded system platform ARM7 which has low power consumption and high reliability. Simulated tunnel test experiments show that the system is stable, and it provides a reliable real-time early warning and rescue information for the safety of mine production. KEYWORDS: WSN, Mine safety, Monitoring, Accident rescue environments. 1 INTRODUCTION Frequent mine accidences have become the social focus. At the same time, with the rapid development of wireless communication technology and embedded technology, the application of intelligent, automated monitoring system to monitor the coal mine production environment and ensure the mine safety has become an integral part of digital mines. This paper puts forward a mine safety monitoring system based on WSN network, which collects mine tunnel environmental parameter data through a tunnel environmental data sampling node, and sends the collected environment parameter data to the ground monitoring center computer. The monitoring center computer can view the tunnel production environmental information in real time combined with the geographic mine information, which provides a reliable basis for mine production safety and accident rescue. 2 WSN NETWORK TECHNOLOGY WSN (Wireless Sensor Network) is a system formed through self-organization network connection of many microsensor nodes which have self-organizing capability. The microsensor nodes have main control chips, which can collect and process the parameter information in network coverage areas, and send out the parameter data through multi-hop. According to different sensors in WSN, WSN can measure various parameter data, including temperature, humidity, light, noise, pressure, water quality composition and gas composition, etc. WSN can be applied in different environments; the hardware and software platforms of WSN in turn are different because of different © ST. PLUM-BLOSSOM PRESS PTY LTD 3 DESIGN OF MINE SAFETY MONITORING SYSTEM Mine safety monitoring system is divided into data acquisition of tunnel environment, routing transmission and ground monitoring [4-6], as known in Figure 1. Data acquisition of tunnel environment is composed of environmental data sampling nodes with temperature, humidity and gas sensor, which is placed in the tunnel randomly or artificially. It is responsible for the underground mine tunnel environmental data collection. Routing transmission is composed of routing nodes and aggregation nodes. Routing nodes are fixed on the supports or equipment in the tunnel every 20~100 meters, according to tunnel communication environment of the production site. Its main task is conveying the tunnel environmental data collected by tunnel environmental data sampling nodes to aggregation nodes through multi-hop. Aggregation nodes are the gateway nodes between sampling nodes of tunnel environmental data and ground monitoring, which connect ground monitoring computer by wire or wireless means, and the data of routing nodes to ground monitoring center. Ground monitoring computer can view the environmental information in real time, such as temperature, humidity and gas density of mine production field, on the basis of tunnel environmental data, combined with the geographic mine information. It provides a reliable basis for mine production safety and accident rescue. The core of mine safety monitoring system is tunnel environmental data collection, which will influence the authenticity and reliability. Research of a Mine Safety Monitoring System Based on WSN DOI: 10.5503/J.PNSGE.2015.21.013 Figure 1 System composition nodes includes main control processor module, wireless transceiver module [7-8], storage unit, power supply module, clock circuit, sensor module and a control circuit, as shown in Figure 2. 4 HARDWARE DESIGN OF TUNNEL ENVIRONMENTAL DATA SAMPLING NODE Hardware of mine tunnel environmental data sample Figure 2 Hardware block diagram Main control processor module, which works under the environment of much flammable and explosive gas, such as gas in mine tunnel, can run under low power consumption; the chip should possesses ADC in order to receive analog signals collected by various sensors; it should also have strong ability of data handling capacity. After comparison of ARM, OMAP and other main processors, ARM7 S3C44B0 microsensor by Samsung Company has been chosen. ARM7 S3C44B0 microsensor, which adopts ARM7TDMI microprocessor core [9], has relatively rich peripheral interface, strong expansion capacity, and higher price performance. It is suitable to be used as a main 90 Physical and Numerical Simulation of Geotechnical Engineering 21st Issue, Dec. 2015 control processor of the mine tunnel data sampling node. Wireless receiving and dispatching module should support ZigBee to achieve low power communications and facilitate the formation of WSN network. The Nrf2401 transceiver chip is chosen, which works in ISM frequency band (2.4 ~ 2.5 GHz). The chip includes crystal oscillator, frequency synthesizer, power amplifier and modulator, which connects with ARM7 S3C44B0 main control chip through SPI bus. Its work parameter, such as output power, frequency of communications can be configured through 3-wire SPI, which has the characteristics of low power consumption, duplex communications and wide range of application. Storage unit is composed of SDRAM storage and FLASH storage. SDRAM storage is used to store operation system. FLASH storage is used to store mine tunnel environmental data. The tunnel environmental parameter sampling sensor module is composed of temperature sensor, humidity sensor and gas density sensor. The temperature sensor and humidity sensor adopt DSl8B20 chip and HIH4000 chip, whose external connection interface are simple, volume are small. It is easy to carry under the mine. Gas density sensor adopts MH-440D infrared gas sensor, which applies non-dispersive infrared (NDIR) principle to detect the existence of CH4 in the air. It has good selectivity, no oxygen dependence, stable performance and long life with a complete function of gas detection, analog voltage signal output and serial communications. Power module is composed of two 5V dry cells, AMSl117-3.3 Variable voltage chip, AMSl117-1.8 Variable voltage chip and power supply circuit. It can supply power respectively to chips on board, peripheral chips, and main control chip with voltage of 3.3 V and 1.8 V. cut-back and portability. In the process of application program development based on the uClinux operation system, almost all the Linux API function can be used, which will greatly reduce the difficulty and shorten the cycle of system development. 5.1 System Transplantation Boot loader is a small segment of boot code, which starts from initial address on hardware system before the uClinux operation system is called. It is in charge of basic hardware equipment in initialization and memory mapping, which loads the embedded uClinux operation system and file system from FLASH storage to RAM; Boot loader can online-update operation and file systems under command line. It can also wipe and modify the physical address space directly. Tunnel environmental sampling nodes adopt Blob as the boot loader, which is stable and mature. The kernel version of uClinux transplantation is Linux2.4 kernel. The porting configurations adopt graphic interface. The support of ARM7 processor in the kernel should be pointed out. The compiling of the arm-elf-gcc cross-compiler tool chain for the start of ARM platform is shown as follows. $> make menuconfig $> make dep $> make zImage The uClinux kernel image file of ELF format after compiling can be programmed to FLASH storage through serial interface or network interface. The file system of tunnel environmental data sampling nodes is romfs file system. 5.2 Application Program Development The application of tunnel environmental data sampling nodes is in charge of collection and transmission of tunnel environmental parameter data and the reception of commands from ground monitoring center computer. The application includes the tasks of temperature data collection, humidity data collection and gas density data collection. After the operation of system, hardware equipment should be initialized and operation system software should be started. When tunnel environmental data sampling nodes receive commands of data collection, tasks of environmental data collection should be started. When the tasks are finished, the data are sent to routing nodes. The routing nodes will convey the parameters of temperature, humidity and gas density collected by sampling nodes to aggregation nodes through multi-hop. Then aggregation nodes will send the data to ground monitoring center computer. When there is no command of data collection, the system will hang the collection tasks, i.e. starting the power-saving tasks and entering the power-saving mode. The process of the software is shown in Figure 3. 5 SOFTWARE DESIGN The software of tunnel environmental data sampling nodes runs on hardware platform, with the function of tunnel environmental data collection. It is composed of the underlying operating system and tunnel environmental data collection application program. The operating system consists of hardware drivers which supplies interface function for writing of environmental data collection programs. The operation system of tunnel environmental data sampling nodes adopts embedded uClinux system. The system consists of boot loader, uCLinux kernel image file and file system [10]. The uClinux is a lightweight embedded Linux version, which is specifically aimed at the CPU without MMU (memory management unit). It follows the GNU License, which has good network performance, complete file support system, high reliability, and the property of 91 Research of a Mine Safety Monitoring System Based on WSN DOI: 10.5503/J.PNSGE.2015.21.013 Figure 3 The software flow chart of the mine tunnel environmental data collection node temperature and humidity parameter data are actually measured in four periods under simulated tunnel environment. The test data are compared with the actual data. The test data under simulated tunnel environment are listed as follows in Table 1. 6 TEST RESULTS The tunnel environmental data sampling nodes operate stably after module test and integration test. The tunnel Table 1 Tunnel temperature and humidity environment parameter data Humidity Test Values (RH%) Humidity Actual Values (RH%) Error Values (%) Temperature Test Values (℃) Temperature Actual Values (℃) Error Values (℃) 1 48.3% 50.1% -1.8 15.0 14.8 0.2 2 49.5% 50.2% -0.7 18.5 18.9 -0.4 3 46.1% 48.1% -2.0 21.0 21.0 0 4 47.0% 49.1% -2.1 17.1 17.4 -0.3 92 Physical and Numerical Simulation of Geotechnical Engineering 21st Issue, Dec. 2015 The test result shows that the statistical errors of the temperature and humidity parameter data collected by tunnel environmental data sampling nodes are small. The ground monitoring center computer can view the tunnel production environmental information in real time through WSN network. The collection, transmission and reception of the system data are stable, which provides a reliable real-time early warning and rescue information for the safety of mine production. 2. REN Xincheng (19667- ), male, professor, main research: electronic information technology, communication system design. Physics and Electronic Information College of Yan’an University, 716000. 3. ZHANG Yang (1984- ), male, master, main research: coal mine safety. 7 CONCLUSION [1]. BIBLIOGRAPHY YUAN Shenfang, QI Lei, TONG Yao, ZHANG Bingliang, GAO Shang. FPAA Based Self-repairing Wireless Sensor Network Node [J]. Chinese Journal of Scientific Instrument. 2012, 33 (7): 1588-1593 [2]. LI Weibin. Research of Mine Environment and Personnel Monitoring System Based on Wireless Sensor Networks [D]. Xi'an: Chang'an University. 2009: 5-11 [3]. WANG Ji, XU Guobao, SHEN Yuli. Sea Water Heavy Metal Monitor System Based on Wireless Sensor Network [J]. Computer Measurement & Control. 2009. 04: 643-645 [4]. PENG Yu, WANG Dan. A Review: Wireless Sensor Networks Localization [J]. Journal of Electronic Measurement and Instrument. 2011, 25 (5): 389-399 [5]. ZHANG Qianqian, ZHANG Yikui, PAN Yong. Kind of Fusion Protocol Node Design Based on Internet of Things [J]. Electronic Measurement Technology. 2011, 34 (8): 85-87 [6]. MU Naigang. Introduction of ZigBee Technology [J]. Telecommunications Technology. 2006. 3: 84-86 [7]. NIU Haijun, FAN Yubo, YANG Songyan, LI Lifeng, LI Deyu. Design of An Ultrasound Bladder Volume Measurement and Alarm System Based on ARM and DSP [J]. Chinese Journal of Scientific Instrument. 2011, 32 (8): 1858-1863 [8]. SUN Yi. ARM-Linux Embedded System Development Foundation [M]. Xi'an: Xidian University Press. 2008.08 [9]. ZHANG Ru, SUN Songlin, YU Xiaogang. Embedded Systems Technical Foundation [M]. Beijing: Beijing Posts and Telecommunications University Press. 2006. 01 [10]. LIU Miao. Design of Embedded System Interface and Linux Driver Development [M]. Beijing: Beijing Aerospace University Press. 2006. 5 (1) A tunnel safety monitoring system is developed, which is based on the WSN network. It describes in detail the hardware architecture of tunnel environmental data sampling nodes, the select of hardware chip, and the ways of connection. It also explains the implementation processes of the software platform and application program. (2) The low power consumption of main control chip ARM7 processor is suitable to run under the underground environment. Test results show that through WSN network, mine safety monitoring system can view the tunnel production environment data in real time. The collection, transmission and reception of the system data are stable, which provides a reliable real-time early warning and rescue information for the safety of mine production. Later paper aims at collecting the data of methane concentrations under tunnel environment and further verifying the performance of the system. FUND PROGRAM Natural Science Foundation of Shannxi Province (2012JK0439), Science and Technology Projects of Yan’an (2011kg-22), Natural Science Foundation of Yan’an University (YD2012-04), High-level university construction Special Foundation of Shannxi Province (Physics- 2012SXTS05). AUTHORS 1. LEI Wenli (1982- ), male, lecturer, main research: embedded system. Physics and Electronic Information College of Yan’an University, 716000. Email: [email protected] 93