Industrial waste gas monitoring system based on ZigBee wireless sensor network

　　Abstract: Combining ZigBee wireless short-range communication technology, a wireless sensor network system architecture for industrial waste gas monitoring is proposed. The network node hardware circuit of this scheme uses ATmega128L as the controller and CC2430 as the RF transceiver. The hardware design and software design of the nodes in the network are planned in detail, and the data security communication in the network is fully considered. The system uses the genetic clustering idea to achieve balanced energy consumption of monitoring nodes. It has the characteristics of low cost, low power consumption, easy expansion, and high security. It can monitor the waste gas content in the industrial environment air in real time and can be widely used in industrial waste gas monitoring in the field of industrial production.

　　0 Preface

　　Atmospheric pollutants can be divided into two types: natural pollutants and man-made pollutants. Man-made pollutants often cause public harm. Gaseous pollutants from fuel combustion and large-scale industrial and mining enterprises are one of the important sources of atmospheric pollution. With the continuous development of my country's industrialization and urbanization, my country's air pollution has become quite serious, and it is one of the three major acid rain areas in the world. In order to promote the formation of a sustainable low-carbon economic development model, the monitoring and governance of the atmospheric environment is an urgent task. However, the traditional wired monitoring network can only transmit data along fixed lines. The installation of the transmission medium inevitably has the disadvantages of damaging buildings, difficulty in maintenance, difficulty in expansion, and high installation and maintenance costs; at the same time, it is impossible to quickly deploy the detection system in some harsh environments (places that are not easy to wire, places that are not suitable for people to reach, temporary places, and emergency accident sites), and the monitoring method is not timely. To this end, this paper combines the development of ZigBee wireless short-range communication technology to design a wireless networking monitoring solution for industrial waste gas, which can safely, flexibly and effectively monitor industrial waste gas in real time, which is of great significance to accelerate my country's basic environmental management capabilities and improve environmental monitoring capabilities and the modernization level of environmental supervision and law enforcement.

　　1 Overall design of ZigBee wireless monitoring system

　　The industrial waste gas monitoring network based on ZigBee wireless sensor network consists of three levels: field monitoring nodes, relay stations (cluster head nodes and ZigBee coordinators) and monitoring centers. The network can cover all monitoring links of the entire factory and form a strict, all-round, three-dimensional monitoring system. In order to improve the scalability of the network and reduce the complexity of network management, this system adopts the clustering structure design idea, divides the network into several clusters, each cluster consists of a cluster head node and several ordinary nodes, and deploys ordinary monitoring nodes along each monitoring link in the factory. The cluster head node is responsible for managing and maintaining ordinary monitoring nodes within a certain range. The overall structure of the system is shown in Figure 1. Each monitoring node in the system collects various pollution parameters, and each cluster elects a cluster head node to receive data sent by all nodes in the cluster, realize data fusion function, and send it to the ZigBee coordinator. At the same time, the cluster head node can also receive the control command of the ZigBee coordinator and send it to all monitoring nodes in the cluster. Each cluster head node can send information to the monitoring center regularly through the ZigBee coordinator, and can also be set to sleep mode at ordinary times. It will start data collection after receiving the data reporting instruction from the monitoring center and send the information to the monitoring center. Each cluster head node has functions such as data collection, instruction parsing and recognition, and data sending.

　　The ZigBee coordinator is responsible for the establishment, management and maintenance of the monitoring network, such as allocating network addresses for newly added devices, the joining and leaving of nodes, etc., and uploading the collected data to the monitoring center or sending the command of the monitoring center to the cluster head node in the ZigBee network. The system monitoring center controls and directs each ZigBee coordinator. The monitoring center is both the command center of each ZigBee coordinator and the data center for the collection, processing and storage of monitoring data.

Figure 1 Industrial waste gas ZigBee wireless monitoring network structure diagram

　　2 Node Hardware Design

　　The wireless sensor terminal node consists of a data acquisition module, various signal conditioning circuits, a data processing module, a wireless communication module and a power management module.

　　The block diagram of the node hardware structure is shown in Figure 2. The data acquisition module is mainly composed of various gas sensors, humidity sensors and temperature sensors. Each sensor unit collects the concentration of various organic and inorganic waste gases in the factory monitoring environment, and then converts the physical quantity of the gas concentration into a corresponding electrical signal according to the exhaust volume, temperature, concentration and chemical and physical properties of the gas. The signal conditioning unit circuit conditions the collected signal and sends it to the data processing module.

　　The microprocessor of the data processing module adopts ATmel's ATmega128L microcontroller, which is a low-power, highly integrated microprocessor chip with 128 kB of program memory (Flash), 4 kB of data memory (SRAM) and 4 kB of EEPROM, 8 10-bit ADC channels, 2 8-bit and 2 16-bit hardware timers/counters, 8 PWM channels, programmable watchdog timer and on-chip oscillator, on-chip analog comparator, JTAG, UART, SPI, I2C bus and other interfaces. ATmega128L can work in normal operation mode and 6 different levels of low-energy operation mode, suitable for low-energy application occasions. In the design of this monitoring system, ATmega128L uses 7. 3728MH z crystal oscillator as the working clock of ATmega128L, and 32.768 kHz crystal oscillator as the real-time clock source.

Figure 2 Wireless monitoring node structure diagram

　　The wireless communication module completes the interaction with the coordinator node and is responsible for monitoring data transmission and reception and exchanging control messages. The wireless sensor terminal node is based on the Texas Instruments CC2430 wireless module, which is a ZigBee system-on-chip CMOS solution that complies with the IEEE802.15.4 standard. It has a 2.4GHz RF radio transceiver, memory and microcontroller inside. It uses a high-performance and low-power 8-bit MCU (8051) with 128 kB of programmable flash memory and 8 kB of RAM, and also includes ADC, timer, AES-128 coprocessor, watchdog timer, power-off detection circuit, etc.

　　When the microprocessor is working at full speed (32MHz), in the receiving and transmitting modes, the current consumption is about 27mA. In the sleep mode, CC2430 consumes only 0.5uA of current, and an external interrupt or RTC can wake up the system; in the standby mode, the current consumption is less than 0.3uA, and an external interrupt can wake up the system. In addition, since CC2430 has a FLASH storage module and has a certain data storage capacity, it can reduce the number of RF operations and thus reduce power consumption.

　　Industrial waste gas monitoring applications often need to be carried out for a long time, which requires the sensor nodes to have sufficient energy. For this reason, low-power, low-voltage chips are used when selecting node chips. The system uses ordinary batteries or rechargeable lithium-ion batteries, and the power management chip uses AD's ADP3338-3.3, SOT-223 package. Since the coordinator is always in the receiving and sending state, it is powered by an external power supply.

　　To save energy, the terminal monitoring node is in sleep state most of the time, and the power consumption is less than 1 ??A. When the monitoring node has no sensing task and does not need to send data, the node communication module and data acquisition module are turned off to save energy.

　　After receiving the data packet, the coordinator will return to the original route to send confirmation information to the terminal monitoring node and realize handshake communication with the monitoring node. If the monitoring node does not receive the confirmation message, it will continue to send data until it receives the confirmation message. In addition, considering that in the same sensor network, different nodes have different energy requirements and consumption, which makes some nodes consume energy faster and become the energy bottleneck of the entire network. In order to balance the energy consumption of each node, this system uses a clustered network for data collection and transmission. First, the optimal number of clusters is determined according to the distribution density of sensor network nodes, and the sensor network is clustered by K-means; then, combined with the residual energy of the nodes, the global optimization ability of the genetic algorithm is used to select a suitable cluster head node for each cluster. Then, each monitoring node in the cluster sends the collected data to its corresponding cluster head node. The cluster head transmits the received data to the ZigBee coordinator through a single-hop route after fusion processing to complete the data transmission.