The Self-networking Safety Monitoring System Design in the Pit

Transcription

1 Sensors & Transducers 2014 by IFSA Publishing, S. L. The Self-networking Safety Monitoring System Design in the Pit Min LI, Yuduo WANG Being Information Science and Technology University, No. 35, Middle Road of North Fourth Ring Road, Beijing, , China Tel.: , fax: Received: 20 November 2013 /Accepted: 28 January 2014 /Published: 28 February 2014 Abstract: In most of the traditional monitoring system, wired or handled devices are used to transmit signals, which is inconvenient for power supply, signal management, transmission and maintenance. To overcome these shortcomings, it is mainly introduced how the ZigBee wireless communication protocol is used as the technical support to put forward a wireless combustible gas monitoring and networking solution in this paper. Meanwhile, the network node s hardware solution is designed on the basis of the ZigBee technology using CC2530 chip which is made by TI (Texas Instrument). Besides of networking and data collection, in order to get the real-time monitoring conveniently, the friendly human-computer interaction interface is designed carefully making use of VC as well. The study results demonstrate that the monitoring system for acquisition has a fast speed, good stability, flexible networking and high use value. Copyright 2014 IFSA Publishing, S. L. Keywords: CC2530, ZigBee, Combustible gas network, Wireless data acquisition, Monitoring. 1. Introduction Coal is one of the main energy in our country, and it plays a vital role in the industrial field. Gas, coal and gas outburst mines account for more proportion in our country. So, the coal mine gas accident is always a major hidden danger for coal mine safety production. In recent years, colliery gas explosion accidents occurred frequently. It caused a great loss to people's lives and property. It influences social stability and economic development in our country. At the same time, it also causes serious resource waste and environmental pollution when the coal methane untreated or recovery emissions into the atmosphere directly. Communication is an indispensable part of the modern society. Following the development of science and technology, the way of wireless communication advanced day by day, and the society pays more and more attention to it. In mobile devices, the location of the devices could be moved to any where according the needs and without the restriction of cable. In the meantime, it can also reduce the volume of the sensors attached on a large numbers of transmission lines. ZigBee is a new kind of short distance, low rate of wireless communication network technology, which has a good operational capacity and remote monitoring [1]. Meanwhile, it uses the 2.4 GHz frequency which is applied for free. It greatly reduces the cost of development. So that ZigBee has an increasing use in the range of low power consumption device. In order to monitor the safety status of mine much better and manner to make safety analysis timely, the terminal nodes use the gas sensor MQ-2, the temperature sensor DS18B20 and the photosensitive sensor to get mine environment information, after that the collected data is Article number P_

2 transmitted to the coordinator, the coordinator will upload the data to the PC through the USB serial port. Finally, the corresponding data is shown in the computer. 2. Analysis of ZigBee Protocol 2.1. Features of ZigBee As a wireless technical standard, ZigBee is developed by the networking, application software and security ratified by IEEE (IEEE: Institute of Electrical and Electronics Engineers) [2]. It is special for short distance communication. There are three frequency bands for this technical standard. 868 MHz frequency band is used in Europe which only has one channel. Its transfer rate is 20 Kbps. The other is 915 MHz in United States. It has 10 channels and its transfer rate is 40 kbps. The last is the 2.4 GHz frequency band which is free for. IEEE deals with the low-level media access control layer (MAC) and physical layer (PHY) protocol. ZigBee Alliance also standardizes its application layer (API) and network layer (NWK). ZigBee API framework includes application support sub-layer (APS), device objects (ZDO) and manufacturer defined application objects [3]. The features of ZigBee protocol are shown as follows: 1) Lower power consumption: ZigBee can work for up to 6 months to 2 years in energy saving mode. 2) Reliable communication: ZigBee protocol uses avoidance mechanism called CSMA-CA to avoid competition and conflict. MAC layer uses a full acknowledgment mechanism, so all the transmitted packet must wait for the acknowledgement information. 3) Low cost: The complexity of the ZigBee device is low and the working frequency is flexible and license-free at 2.4 GHz. 4) ZigBee has a strong ability of self-organization and self-healing for networking: A ZigBee network node can detect whether there is other node existing or not. At the same time, it can determine how to connect and form a networking without human intervention. So it can ensure the system to work properly Z_Stack Protocol Stack Structure ZigBee 2007/RPO protocol stack is based on Z_Stack protocol stack for free which is provided by TI company. It is a real piece of system solutions and it also ensures the ZigBee network performance. It meets the network applications to the 2.4 GHz band. It performs well in network cost and power consumption of the nodes and it satisfies the needs of commercialization. The main characteristic of Z_Stack is good compatibility, and it fully supports IEEE /ZigBee CC2530 system-on-chip solutions [3]. In addition, it also has a wealth of new features, such as wireless download, etc. The protocol stack is in the form of a half open source. Protocol stack s network layer provides full-featured API function set, and the underlying drivers can be modified according to their own needs. It is a flexible and versatile protocol stack. The design uses the protocol stack ZStack of ZigBee2007 specification. In practice the protocol stack is transplanted into CC2530 device and the application functions is modified according to the needs during the course of development to realize the visualization development of ZigBee2007/PRO [4]. The operating system of Z_Stack uses the way of polling queries. After all the devices and each layer of parts are initialization, the system will enter low power mode. Events can wake up the system and the incident can be dealt with. When the system is waken up it will enter the collection mode. It immediately goes back to the low power mode after the event processing is completed. As a result, the system will greatly reduce the power consumption. Protocol stack architecture and system operation entities are shown in Fig Function of Network Device According to the ability of communication equipment, the network equipment is divided into fully function devices (FFD) and reduced devices (RFD) in the IEEE protocol [5]. The differences between FFD and RFD are as follows. A fully function device can not only communicate with a fully function device, but also be a reduced function device. While a reduced function device can t communication a reduced function device. There are three types of logic device in the ZigBee network. They are coordinator, router and terminal node [6]. The coordinator and router belong to the full function device and the terminal node belongs to the reduced function device. A ZigBee network consists of a coordinator and many routers and end devices. The brief introduction for each of these types is shown below: 1) Coordinator: A coordinator is the first network device which is used to start the whole network. First of all, the coordinator will select a channel and a network ID (PAN ID, Personal Area Network ID) [7], then start whole network. It can also be used to help to build the network binding in application layer and security layer. The coordinator s roles mainly involve network startup and configuration. Once it completed these functions, the coordinator can be seen as a router (disappear). The whole network operation is not dependent on the presence of a coordinator because of the distribution characteristics of ZigBee. 2) Router: A router is responsible for looking for, building and repairing the network packet routing information. Then it forwards the network packet and 156

3 allows other devices to join the network. In fact, it serves as a transit. When it is far from the coordinator, the end device can not communicate with the coordinator directly, it will realize the multiple hops by a router. In the often case, the router should have been active all the time, so it must use the main power supply. But when using a tree network topology, it allows the router be carried out in accordance with the certain interval period, which the batteries can be used to power. 3. Hardware Design of the System 3.1. System Requirements Analysis 1) Monitored environmental parameters. There are two main environment parameters: gas concentration and temperature. High temperature can cause the coal spontaneous combustion and the harm of poisonous gas and dust will increase. Otherwise, high gas concentration can cause the gas explosion. Therefore it is necessary to monitor the parameters real-time. 2) The ZigBee wireless module underground can adapt to the environment. It can especially work for a long time. In addition, they should be no direction bind area and not bound by direction, and can identify the existence of multiple devices. 3) The system should have the stable and reliable communication function and can be extended. Once some devices failures are found, other devices can find the right communication ways and can t affect the operation of the whole system. 4) The system should have automatic alarm function. When the gas concentration or temperature overrun, system need to be able to send out alarm information in time, so that worker underground can respond quickly and reduce the loss of life. 5) The collected data should be sent to the monitor center as quickly as possible, and analysized and processed. At the same time, workers can take corresponding measures according to the cases Overall Design of Monitoring System Fig. 1. Protocol stack architecture and system operation entities. 3) Terminal node: A terminal node has the function of joining and exiting the network. It can also accept and send a network message. But it can t forward routing message. The terminal node does not have the specific responsibilities to maintain the network, so it can maintain sleep or in wake state and it can be a battery-powered device. In general, the requirements of terminal node for storage space are relatively small (Especially the needs of the RAM). ZigBee support three types of network topologies: the star network, tree network and the mesh network [6]. The advantages and disadvantages of the three networks are introduced as followed respectively: 1) In the star network topology structure, the communication is between terminal device and the coordinator (called PAN). All star networks and other star network are running independently. And they don t interference each other. It identifies its uniqueness by choosing a PAN. The advantage of the star network is that the structure is simple. But the disadvantage is that its communication distance is short and can be only used on a small scale. It is not suitable for wide applications. In addition, the star network s communication is not reliable. 2) Mesh network is a multi-hop system, in which any two devices can communication with each other (except two terminal devices). When some devices can t work in the mesh network, other nodes can choose other path to communicate with the network. In this way, the reliability of communication is increased. The structure of the network has a father transmission distance than star network, but the disadvantage is that the power consumption is higher than that of start network, because the router nodes 157

4 must listen to the information and changes on a path all the time. 3) In a tree network, the terminal node is usually used to send the data to its parent node. Then its parent node is used to complete the data forwarding. In this way the scope of the communication can expanded and the reliability of communication network can be improved. Here adopts the tree network topology monitoring and network. Compared with the mesh network, this type of network topology can reduce the redundancy and the total power consumption. Although this type of network s reliability is poorer than mesh network, but its power consumption is lower. From the comprehensive consideration, the system chooses the tree network. System structure diagram is as shown in the Fig. 2 below: SOC network (WSN) to be chosen. This network is mainly used in the filed of internet of things, automatic control and monitoring system, etc. The application of the ZigBee SOC solutions represented by CC2530 has been set off the upsurge in the part of colleges and some companies [8]. CC2530 chip supports IEEE standard, ZigBee, ZigBee RF4CE and energy application. It can improve the performance and meets the 2.4 GHz ISM frequency band application requirements for low consumption and low cost based on ZigBee. Fig. 3. The schematic diagram of the system. Fig. 2. Network topology of the System The Core Hardware Circuit Design This system is mainly composed of two parts: the underground part (terminal node and router node) and the monitoring center up ground (a terminal node and the PC). The terminal node and the router node underground is mainly composed of CC2530 microcontrol chip, antenna module, sensor unit, power module, and peripheral circuit. The sensor module includes: gas concentration sensor, temperature sensor, light intensity sensor. The monitoring center is the center of the data acquisition of the ZigBee, including the coordinator node, USB serial communication unit and PC monitoring part. The network topology of the system is as shown in Fig. 3 below: 3.4. Overall Design of Monitoring System Because of the characteristics of ZigBee, it is determined that it will be the best for the ZigBee Meanwhile, CC2530 supports the wireless communication of the general low power device. It is also equipped with a standard or proprietary network protocol stack (Z-Stack, RemoTI, SimpliciTI) to simplify the development. Thus it greatly shortens the development cycle. It has built-in kernel 8051 single-chip microcomputer and there is no need to buy master control chip. The chip can simplify the hardware of the system and has more advantages than others. Therefore it is widely used in the field of automatic control and monitoring, etc. Core hardware circuit design [9] is shown in Fig Design of Software System This system s software uses the IAR EW (Embedded Workbench) for 8051 integrated development environment. And it uses TI company launched open source C streamline protocol stack to complete programming. It has the advantage of good portability and readability. Users need only to modify the code of application layer. The code of the ADC collection is written by the system and the terminal node s information is received by coordinator. In this solution the design of low-power mode is made full use of, and the event polling mechanism is used. 158

5 Each layer will enter the low power mode after initialized. Once the event occurs, the terminal node is waked up and begins to enter the interrupt event handling events. Consequently, the system will enter low-power mode after the end of the interruption. This software architecture can significantly reduce power consumption. Fig. 4. The solution of core hardware circuit design Design of the Coordinator The coordinator is initiator of the coal mine gas monitoring networks. It is a central part of the whole network. After powered on, a network is firstly initialized and established by the coordinator. And then the coordinator listens whether a node exists. If node application request is found, the coordinator will assign network address to the node. It will send the data via USB serial to PC when receives data from other nodes. The program flow diagram is shown in the Fig. 5. The source code of coordinator sending data to PC is as follows: void HalSendFrame(uint8 cmd,uint8 id,uint8 datal, uint8 datah) { uint8 Ackbuf[7]; Ackbuf[0] = 0xef; Ackbuf[1] = cmd; Ackbuf[2] = id; Ackbuf[3] = datal; Ackbuf[4] = datah; Ackbuf[5]=Ackbuf[1]+Ackbuf[2]+Ackbuf[3]+ Ackbuf[4]; Ackbuf[6] = 0xfe; HalUARTWrite ( SERIAL_APP_PORT, Ackbuf, 7); } Fig. 5. Program flow chart of coordinator Design of the Terminal Node The terminal node is used to collect data through gas sensor, temperature sensor and complete simple data processing. Then it will send the data to the 159

6 coordinator by wireless module. Its working process is shown in Fig. 6, below: Start Initialize Software and hardware Apply for the network N Join successfully? Y Collect data Send data N Send successfully? Y Set sleep mode Wake up node if time interrupt Fig. 6. Program flow chart of terminal node. The following is the main source code of the data content of the terminal node: void LightCtl_SendTheMessage( void ) { UINT8 themessagedata[7]; themessagedata[0] = 0x82; //CMD themessagedata[1] = SensorID; // ID read_data(&themessagedata[2]); //Temperature themessagedata[4] = myapp_readgas(); //Gas concentration themessagedata[5] = myapp_readlightonoff(); //light intensity themessagedata[6] = myapp_readalarm(); //alarm infromation DataChange(&theMessageData[2],ch); //data process HalLcdWriteString("temp is:", HAL_LCD_LINE_1 ); HalLcdWriteString( (char *)ch, HAL_LCD_LINE_2 ); LightCtl_DstAddr.addrMode = (afaddrmode_t)addr16bit; LightCtl_DstAddr.endPoint = LightCtl_ENDPOINT; LightCtl_DstAddr.addr.shortAddr = 0x00; if ( AF_DataRequest( &LightCtl_DstAddr, &LightCtl_epDesc, LightCtl_CLUSTERID, (byte)osal_strlen( themessagedata ) + 1, 8, (byte *)&themessagedata, &LightCtl_TransID, AF_DISCV_ROUTE, AF_DEFAULT_RADIUS) == afstatus_success ) { // Successfully requested to be sent. } else { // Error occurred in request to send. } } 5. Experimental Results 5.1. PC Communication Protocol In protocol, the universal asynchronous receiving and transmitting serial communication mode is adopted, and the baud rate is set up to bps. There are 8 data bits and 1 stop bit. The checksum is the sum of the command code and data area. The command format is in Table 1. Table 1. Program flow chart of terminal node. Frame header Command High Low Checksum Frame tail 0xEF CMD DataH DataL Sum 0xFE The detailed commands and data format (PC) is as follows: 1) Shake hands command (0xC0): a handshake command is sent to the coordinator by PC when it is running. If the coordinator receives correctly, handshake is echoed successfully, otherwise returns error information. Then the PC determines the state of coordinator according to this information. For example, EF C C0 FE. 2) Uploaded the temperature command (0xC1): this command is sent by PC to inform the node to send the temperature information. 3) Uploaded the gas concentration command (0xC2): this command is sent by PC to inform the node to send the data of gas concentration. 4) Uploaded the light intensity command (0XC3): this command is sent by PC to inform the node to send the data of light intensity Results of the Monitoring System The solution of the combustible gas monitoring system in coal mine is simulated in the paper. First of all, the interaction display in PC is designed with the VC++6.0 software, including the design of serial communication and monitored data display interface. In this way, such parameters as the combustible gas concentration, environment temperature and light intensity underground can be seen clearly in the 160

7 monitoring room, the upper limit of each node data can also be set in the monitoring room easily. Once the data received is more than the setting threshold value, the buzzer will alarm. So it is convenient for the underground personnel to make corresponding measures to reduce the occurrence of danger. The system uses three acquisition nodes and a coordinator. First, the coordinator is powered on, the configuration of hardware and software is initialized. And then the sensor devices are joined to the network and the binging is exceeded after the network is stable. Once the coordinator connects with the sensor devices successfully, it will come into the process of data collection. The data acquisition is made every second. The serial port device number is set to COM1 port and baud rate is set to bit/s. Click the open button to open the serial. If the coordinator is connected to the computer, the status light will be on. At this point, the collection data under the coal mine can be observed. Data acquisition results are shown in Fig. 7. Fig. 8. System monitoring results. 6. Conclusions With the use of ZigBee wireless communication protocol as the technical support, the coal mine combustible gas monitoring and network is designed and stimulated combining the inconvenience of the traditional coal mine safety monitoring, and the friendly interaction display is designed with VC++6.0 simultaneously. The construction of the data frame of acquisition device is made of 6 bytes and the maximum transmission rate is up to 250 kb/s. The transmission baud is set to 38.4 kb/s between the coordinator and PC. Thus 150 node s data can be received and seen every second probably. The experimental results show that: the system has a good real-time performance, flexible network and quick acquisition speed. It solves the problem of wiring difficult for the monitoring field and has a high use-value. References [1]. Wangjing Cai, Huibing Qin, Design of a wireless data acquisition system based on the simplify ZigBee protocol stack, Journal of Mechanical & Engineering, Vol. 28, Issue 2, 2011, pp [2]. Weicong Zhang, Xinwu Yu, Zhongcheng Li, Wireless network sensor node design based on CC2530 and ZigBee protocol stack, Application of Computer System, Vol. 20, Issue 7, 2011, pp [3]. Hongmin Yin, The design of mine safety monitoring system based on ZigBee, Master thesis, North University of China, May [4]. Cunfeng Hou, Jufang Xie, Dong Hu, A ZigBee technology based on CO2 monitoring node design and implementation, Agricultural Science & Technology and Equipment, Issue 3, March 2012, pp [5]. De Liu, ZigBee Net working technology based on CC2530, Programmable Controller & Factory Automation, Issue 6, 2012, pp

8 [6]. Yinhui Huang, Xin Li, Yueying Wang, Design of mine monitoring system based on ZigBee wireless network technology, Automation & Instrumentation, Issue 7, 2010, pp [7]. Wenzhong Li, Chaoyu Duan, Introduction and actual combat of ZigBee wireless network technology, Beijing Aeronautics and Astronautics Press, [8]. Jinglan Weng, Study on data acquisition system based on ZigBee technology, Master thesis, Jiangsu University of China, June [9]. Zhiqiang He, Design and research of wireless gas detection system based on ZigBee technology, Master thesis, North University of China, May [10]. Yan He, Design of temperature data acquisition system based on ZigBee technology, Computer and Modernization, Issue 8, 2012, pp Copyright, International Frequency Sensor Association (IFSA) Publishing, S. L. All rights reserved. ( 162