Abstract: This paper introduces a wireless data acquisition and management system based on the MODBUS protocol, and applies this system to the data acquisition and management system of an oilfield joint station. It solves the problems of centralized data management for geographically distributed joint stations, the time-consuming and labor-intensive nature of manual copying, and the poor timeliness and accuracy of manual records. Keywords : MODBUS; data acquisition; radio digital transmission 1 Introduction to MODBUS Protocol MODBUS is an industrial communication and distributed control system protocol proposed by Modicon Inc., a well-known American programmable logic controller (PLC) manufacturer, and has been widely used in industrial control. MODBUS is a master-slave protocol that allows one master to communicate with multiple slaves. There are two effective data transmission methods in MODBUS: ASCII code and RTU mode. This system adopts the RTU (Real-Time Unit) method. The main advantage of this method is its high data transmission efficiency at the same baud rate. 2. Constructing a Wireless Data Acquisition System using the MODBUS Protocol Oilfield production plants typically have 5-10 joint stations, with distances between them ranging from several kilometers to over ten kilometers. Each joint station has 3-4 operating positions, with distances between positions varying from 20 to 300 meters. Each position has 10-20 production parameters, requiring real-time data acquisition. There are various methods for establishing a joint station data acquisition and management system, such as laying fiber optic cables, electrical cables, or using CDMA networks. However, examining these methods reveals that their system construction and operating costs are all very high, making it challenging to establish this system at a low cost. We used the MODBUS protocol, RS485 interface, data acquisition modules, and remote and short-range wireless data transmitters, employing a combination of wired and wireless data transmission methods. We integrated with the plant's existing local area network and used configuration software to manage the host computer. This low-cost approach enabled us to build a plant-wide joint station production data acquisition and management system with multi-terminal query and monitoring capabilities. The system structure is shown in Figure 1. Field data was acquired by multiple SSX-M03 8-channel standard signal and SSX-M04 6-channel pulse signal data acquisition modules. The SSX-M21 data acquisition and management module collected the data using wired, short-range wireless, and RS485 interface methods, following the MODBUS protocol. Because the RS485 communication interface twisted-pair cable transmission distance is less than 100kbps and can reach 1200 meters, while the short-range wireless data transmission distance is less than 500 meters, the modules could be installed in a distributed, nearby manner. The main PC collects data from each substation via RS232 and RS232-to-RS485 interfaces and the main data transmission radio uses the MODBUS protocol. The PC then performs tasks such as compiling multi-station data summaries, displaying process control flowcharts, and plotting trend curves. Simultaneously, the PC is connected to the plant's local area network (LAN), allowing terminals on the LAN to browse the entire data acquisition system and print reports in a B/S (Browser/Server) manner, completing the data acquisition and management of the plant's joint stations. [align=center] Figure 1 System Structure Diagram[/align] 3 Communication Interface Design Communication is crucial to the entire system. To ensure long-term reliable operation, the communication hardware interfaces of the SSX-M21, SSX-M03, and SSX-M04 modules are designed with full isolation to prevent line interference from damaging the acquisition modules and affecting normal system operation. The specific circuit diagram is shown in Figure 2. Data signals are received by RXD and transmitted by TXD. The transmit/receive conversion is controlled by RXD/TXD, and after isolation by a high-speed opto-isolator, the input and output are driven by the dedicated RS485 interface chip MAX487. The 9012 transistor drives the LED to observe the communication status, and the MC7805 provides power to the RS485 communication side. [align=center] Figure 2 Communication Interface Schematic[/align] 4 Communication Protocol Configuration The MODBUS communication protocol has many commands, and different command function numbers have different functions. This system mainly uses command 03 during normal operation to read one or more registers. The following describes the command to read 8 analog quantities and error status. The command is issued by SSX-M21 and responded by SSX-M03, whose address number is 11. The host calls a message requesting the reading of 8 analog quantities and error status, totaling 9 registers. Address 00001011, Function 00000011, Data Start Register Number High Byte 00000000, Data Start Register Number Low Byte 00000000, Data Register Count High Byte 00000000, Data Register Count Low Byte 00001001, CRC Low Byte, CRC High Byte. Total 8 bytes. Slave response message (8-channel analog signal sampling value is 4095, no error): Address 00001011, Function 00000011, Data byte count 00010010. Data 1 output register high bit 00001111, data 1 output register low bit 11111111; Data 2 output register high bit 00001111, data 2 output register low bit 11111111; Data 3 output register high bit 00001111, data 3 output register low bit 11111111; Data 4 output register high bit 00001111, data 4 output register low bit 11111111; Data 5 output register high bit 00001111, data 5 output register low bit 11111111; Data 6 output register high bit 00001111, data 6 output register low bit 11111111; Data 7 output register high bit 00001111, data 7 output register low bit 11111111; Data 8 output register high byte: 00001111, Data 8 output register low byte: 11111111; Data 9 output register high byte: 00000000, Data 9 output register low byte: 00000000; CRC low byte, CRC high byte. Total 23 bytes. The SSX-M21 calls the SSX-M04 module, and the PC calls each joint station's SSX-M21, similar to the above, only the address and the amount of communication data differ. 5. Management System Interface under KINGVIEW Software After the data from each joint station enters the PC via remote wireless transmission, all data processing is performed on this PC, and the relevant screens and data are published to the local area network. Under the KINGVIEW system, the following tasks are performed: Joint station process control flowchart; Joint station oil, gas, and water data reports; Joint station crude oil water content trend curve; Joint station oil tank liquid level historical record curve; User login configuration screen, etc. Figure 3 shows the process control flowchart of one of the joint stations. [align=center]Figure 3. Flowchart of the Integrated Station's Process Automation[/align] 6. Local Area Network Browsing Interface under KINGVIEW Software KINGVIEW software itself has network functionality and can be browsed using either CS or BS methods. This system adopts the BS method, which has the advantages of ease of use and low software maintenance. Users can directly enter their local IP address in the Explorer to browse production data and print reports for the entire integrated station. 7. Network Browsing Permission Management After the plant's production status and data are published to the local area network, it is necessary to manage the personnel and departments using this resource, determining the browsing scope and permissions for different levels of personnel and departments to prevent unauthorized personnel from logging in. To achieve this, the following measures were taken in network management: Screens are grouped and published, with different levels configured for different groups of screens; Login user permissions are set in groups and levels, corresponding to the groups of screens published. This system sets three user levels, corresponding to the internal management mechanism of the oilfield: plant level, mine level, and team level. Users within the local area network log in using their pre-assigned usernames and passwords. Plant-level users can browse the production status and data of the entire plant, while team-level users can only browse the production status and data of their own team. 8. Conclusion This system adopts the widely used international standard protocol MODBUS and the RS485 communication interface. It uses a combination of wired, wireless, and local area network methods to build a joint station production data acquisition and management system. This system is low-cost, has good real-time performance, and meets the production needs of the oilfield. Because each module and each short-range data transmitter uses an RS485 interface, each module and data transmitter can be placed locally and nearby near the field data acquisition points, reducing on-site construction work and lowering system installation costs. The author's innovation lies in using the international standard communication protocol MODBUS and the standard communication interface RS485, combining wired, long-range wireless, short-range wireless, and local area network methods for data transmission, thus solving the problem of centralized management due to geographically dispersed locations and numerous data acquisition points at a low cost. Using KINGVIEW configuration software for host computer data management and interconnection with the local area network is simple, time-saving, labor-saving, and reliable. References: [1] Zhu Yi, Jiang Nianping. Application of Modbus protocol in industrial control system [J]. Microcomputer Information, 2006, (10). [2] Zhang Lei, Quan Li, Liu Qiang, Zhong Wencai. Remote data communication between DSP and PC in SRD control system [J]. Microcomputer Information, 2004, (11). [3] Zhu Hongchao, Yu Xiangjun, Lü Zhenzhong. Application of Modbus protocol in intelligent data acquisition system. 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