Oilfield indicator parameter monitoring system based on ZigBee technology

Oilfield indicator parameter monitoring system based on ZigBee technology

With the steady development of the global economy, the application of oil in people's production and life is more and more extensive, and the demand for oil is also increasing. People are more concerned about oil production. At present, oilfield field collection and monitoring generally use sensors to collect data, and then transmit the signal to the control center for processing through the cable. The remote and harsh environment of the oil field site, the complex terrain, the wide distribution of oil wells, the large number, the cost of laying fixed communication lines, the length of the line, the high cost of equipment, and the large investment have restricted the production monitoring of the oil field. This article proposes the application of ZigBee technology in oilfield monitoring.

1 Introduction to ZigBee Technology

In recent years, with the rapid development of micro-electromechanical systems (MEMS), system-on-chip (SOC), sensing, embedded computing, networking and communications, wireless sensor networks (WSN) have low cost, flexible networking, Being limited by the geographical environment and other advantages, it shows a broad application prospect in many fields. ZigBee technology utilizes the global common frequency 2.4 GHz, which has very significant advantages of low cost, low power consumption, many network nodes, and long transmission distance. It is currently regarded as one of the most promising technologies to replace wired monitoring networks. Compared with traditional wireless technology (see Table 1), ZigBee's characteristics mainly show the following aspects:

(1) Low power consumption. In standby mode, two AAA dry batteries can support one node to work for 0.5 ~ 1 years.

(2) Low cost. The agreement is greatly simplified, free of license bands, and free of patent fees.

(3) Low rate. 250kb / s (2.4GHz), 40kb / s (915MHz) and 20kb / s (868MHz) raw data throughput rates.

(4) Close range. The transmission range is 10 to 75m, and the RF transmission power can be increased to 1 to 3km.

(5) Large network capacity. Using St arNet, MeshNet and CluterTreeNet, it can form a large network of 65,000 nodes.

(6) Short delay. ZigBeen has a fast response time. It takes 15ms to go from sleep to working state, and 30ms to connect the node to the network.

(7) High safety performance. Provide three levels of security mode: no security settings, access control list (ACL), prevent illegal access to data and use AES-128 symmetric password.

2 Overall system plan

Acceleration sensors and load sensors regularly collect the performance parameters of each wellhead. Under the control of the ARM processor, the ZigBee wireless module is fast, and under the support of the IEEE 802.15.4 technical standard, the ZigBee network sends it to the ZigBee router and ZigBee coordinator , Send the data to the control center via satellite or GPRS network, grasp the working parameters of the oil production site in time, realize the data collection, collation and analysis, and timely issue control commands to the terminal to adjust the production.

The system is divided into four parts: data acquisition terminal, Zi gBee wireless router, ZigBee / WN coordinator and control center. The architecture of the oilfield monitoring system is shown in Figure 1. Figure 1 Oilfield monitoring system architecture

The system consists of three-level WN, with simple structure, stable performance and easy implementation. Low power consumption is the outstanding performance of this system. The ZigBee wireless network uses the 2.4 GHz frequency band. This frequency band is an ISM frequency band that needs to be applied uniformly globally. The frequency band (2.4 ~ 2.483GHz) is divided into 16 channels, the data transmission rate is 250kb / s, the symbol rate is 62.5kbaud, hexadecimal orthogonal modulation is used, and the pseudorandom with a chip length of 8 is used. The code is spread directly. GPRS transmission speed is 56 ~ 115Kb / s. Used in combination with the GPRS network, it can meet the needs of the ZigBee network to transmit data, reduce the initial investment cost of the system construction, reduce the workload of network operation and maintenance, and send the oil well indicator parameters to the monitoring center in a timely and accurate manner. The system realizes real-time monitoring through the connection of two wireless networks, ZigBee and GPRS, and discovers and handles problems in the oil field in a timely manner.

3 wireless sensor network establishment

This article fully compares the advantages and disadvantages of StarNet, MeshNet and CluterTreeNet, chooses tree-type wireless ad hoc network (Ad HocNet), uses CSMA-CA method for channel access, and each ZigBee transmission module uses multiple frequency hopping technology data transmission methods. It has better information concealment, anti-multi-frequency interference and self-healing, and increases the coverage of the network. Realize the collection, transmission and monitoring of oil well indicator parameters.

In a tree-type wireless sensor network, since the terminal device and the network coordinator are established, the terminal device is assigned a 16-bit short address, and the terminal uses this address to communicate in an unlimited number of local networks. The main coordinator first starts to establish a ZigBee personal area network, selects the ZigBee personal area network identifier, sets its short address to 0, and then sends a beacon to its neighboring devices to accept other network links to become a first-level network. All devices that have established a connection with the master coordinator are assigned a 16-bit network address. The router configures and sends its own beacon according to the information of the beacon received by the coordinator, allowing other devices to establish a connection with it, forming a secondary network of slave devices—data collection terminals. The GPRS network sends the data to the monitoring center, forming the information data link of the three-level network.


4 Hardware design

4.1 Hardware composition and function

The system hardware consists of seven modules: data acquisition sensor, controller, wireless RF transceiver, storage, power supply, GPRS receiving, and monitoring center. The sensor module is composed of a load sensor and an acceleration sensor ADX105. Its function is to collect the demonstration information of the well site. The controller module is an embedded system ARM processor. Its function is to perform data processing, power consumption management, synchronous positioning, and task management. And other operations; the wireless RF transceiver module is a CC2420RF chip developed by Phipcon. Its function is to communicate with other RF modules to transmit the demonstration parameters and control information of the oil field site; the storage module uses NAND-type FLASH memory K9F2808UOC produced by Samsung, with a capacity 8 ~ 128MB, responsible for data storage; power modules are divided into two categories: one is a high-capacity lithium battery; the other is an AC power supply after the straightening (hardware circuit shown in Figure 2). The GPRS transceiver module A-232 / 485GPRSDTU is responsible for the information transmission of the GPRS communication link and sends the demonstration parameters to the monitoring center; the monitoring center module is responsible for data collection, sorting and analysis, and feedback control commands.

4. 2 hardware modules and functions

ZigBee technology supports two types of physical devices: full-function devices (FFD) and reduced-function devices (RFD). The oil well field parameter collection terminal is the part with the lowest communication requirements in the network. The structure and function are simple. It is powered by batteries. Most of them are in sleep state to save energy to the greatest extent. The communication module of the data collection terminal adopts RFD; ZigBee router has data storage And the receiving and sending capabilities, route discovery capabilities, from device connection, routing table maintenance, data forwarding, to maintaining network links and other functions, use FFD; ZigBee coordinator is always in working condition, is the core of the network, except for the completion of the router In addition to its functions, it also has the functions of formulating network rules, selecting appropriate channels, establishing networks and delivering addresses, using FFD.

Acquisition terminal (circuit block diagram shown in Figure 3), CC2420 is connected to the P1. 0 ~ P1. 7 interface of the ARM chip through the SPI bus. The high-capacity battery serves as the power supply for the terminal module, and provides a voltage of about 3.3V for the sensor module, RF module, and MCU / ARM7 through the LD0 low-dropout linear regulator AM11 17-3.3. ARM chip needs 3.0 ~ 3.6V (3.3V ± 10%), CC2420 needs 2.0 ~ 3.6V. The power indicator shows the power supply voltage. The sound and light alarm unit alarms abnormal conditions. The crystal oscillator circuit enables ARM7 to communicate synchronously with the RF module. The block diagram of the ZigBee router module is shown in Figure 4.

The hardware circuit of the ZigBee coordinator is connected to the A-232 / 485GPRS / DTU at the right end of the MCU, and the power supply requires 4.5 to 35V. The power supply is powered by a power cord (220V AC is converted to 5V DC through rectification, voltage stabilization, and filter circuits. The block diagram of the ZigBee coordinator module is shown in Figure 5.

The collection terminal, router and coordinator all have FLASH memory, and the system can store the collected data in a large amount in case of unexpected situations to prevent data loss. The terminal and router are powered by lithium batteries, and the coordinator is powered by a power cord, which enhances the stability of the power module.

5 Software design

The software part consists of program modules such as monitoring center, ZigBee coordinator communication, ZigBee routing communication, transceiver module communication in the ZigBeeRF module of the data collection terminal, system initialization program (as shown in Figure 6), and information collection terminal.

The monitoring center program is responsible for the management and control of the entire network, including the MCU of the wireless sensor node, RF transceiver, data collection, status detection, data processing, and control of the equipment connected to the node (the main program is shown in Figure 7); The ZigBee wireless communication module program is responsible for wireless data transmission and reception, including RF and baseband. The former provides the air interface for data communication, and the latter provides the physical channel and data grouping of the link; the ZigBee router and coordinator communication program is responsible for link management and control , Perform baseband communication protocols and related processing procedures, including link establishment, frequency selection, link type support, media access control, power mode, and security algorithms. The collection terminal program and the coordinator program are shown in Figures 8 and 9, respectively.

The software design is divided into three levels: data collection, data information transmission and monitoring center. The program running between data collection and information transmission is written in C ++ Builder6.0 or assembly language to achieve the control program language, which is generated and executed by the ARM compilation system. program. The monitoring center software is developed by Vi BasicBar 6.0, and the data is stored in SQL Server database. IEEE802.15. 4 / ZigBee development system adopts wireless valley C51RF-3-ZMD2. The software adopts structured design, which is convenient for improvement and maintenance, meanwhile, it has a beautiful interface and easy operation.

6 System low power design

In the ZigBee network node, only considering the power consumption of the MCU can energy saving be achieved, and ZigBee's low power consumption characteristics can be highlighted. The CC2420 is in sleep mode with a transmit power of only 10mW. The current consumption is 17 mA in transmit mode, 15 mA in receive mode, and 0.7 μA in sleep mode. The device can sleep most of the time and wake up periodically. In sleep mode, the transceiver circuit is turned off, which greatly reduces power consumption. When waking up, it checks the channel and synchronizes with the coordinator to send or receive data. The ARM chip supports two power-saving modes: idle mode and power-down mode. In power-down mode, the oscillator is turned off and the processor status and registers, peripheral memory, and internal SRAM values ​​are maintained. A reset or a specific interrupt that can still work without a clock can terminate the power-down mode and restore the chip to normal operation.

This article is controlled by software, the ARM chip and CC2420 work intermittently in the receiving state. When not receiving data, the chip CC2420 is in sleep mode, and the ARM chip is in power-down mode (power consumption is almost zero), which can greatly reduce the power consumption of the system. The MCU exits the power-down mode through an external interrupt (external interrupt EINT3 generated by the sleep mode timer of the 32kHz crystal oscillator of CC2420, pin 15) and continues to work. So as to extend battery life and achieve energy-saving purposes.

7 Conclusion

ZigBee technology is a two-way micro-power format wireless access technology with simple structure, low power consumption, low data rate, low cost and high reliability. It integrates computer technology, sensor technology, wireless broadband communication technology, digital control technology and many other disciplines. The combination of ZigBee technology and ARM technology realizes the wireless transmission of oilfield signals, the efficient use of spectrum, and the production of information. With the increasing frequency of spectrum resources and the high cost of networking, the in-depth study of ZigBee WSN has far-reaching significance.


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