Abstract: This paper proposes a low-cost, high-reliability computer monitoring scheme based on Fieldbus networks, addressing the current situation in the gas industry. The principles, structure, and implementation methods of this scheme are discussed in detail, and its stability and wide applicability are revealed through comparative analysis with traditional schemes. Keywords: Fieldbus network; computer monitoring system; DCS system; human-machine interface; intelligent instrument 1. Introduction Due to the complex operating conditions and high ambient temperatures in the gas production industry, the previously used manual control systems are neither safe nor reliable. Therefore, computer monitoring systems are widely used in the current gas production industry to replace traditional manual monitoring. This improves measurement accuracy and increases safety and reliability. A complete computer monitoring system should include two main parts: hardware and software. The implementation of the hardware system mainly involves the system integration and architecture design of the industrial control network, while the software system mainly involves the development, debugging, and testing of the system monitoring software. In practical use, the hardware and software systems must be closely integrated and work collaboratively to achieve true computer monitoring. Fieldbus is a bidirectional, serial, multi-node digital communication system used in production sites to realize bidirectional, serial, multi-node digital communication between microcomputer-based measurement and control devices. It is also known as an open, digital, multi-point communication low-level control network. It integrates a dedicated microprocessor into traditional measurement and control instruments, giving each instrument digital computer and digital communication capabilities. Using easily connectable twisted-pair cables as a bus, it connects multiple measurement and control instruments into a network system. Following open and standardized communication protocols, it enables data transmission and information exchange between multiple microcomputer-based measurement and control devices located in the field, as well as between field instruments and remote monitoring computers, forming various automatic control systems adapted to practical needs. In the current computer monitoring systems of the gas production industry, the control system composed of Fieldbus networks and intelligent instruments has some inherent technical advantages over control systems using traditional technologies (DCS systems). First, the Fieldbus network is a fully digital field communication network that uses digital signals instead of traditional analog signals, resulting in high measurement accuracy and strong anti-interference capabilities. Second, it achieves complete decentralization of control functions, delegating control to low-level intelligent field devices, which reduces costs while increasing safety and reliability. Furthermore, bus-based intelligent field instruments can remotely set the range and zero point, and have self-diagnostic functions for instrument operation, thus enabling multi-parameter measurement and automatic compensation for environmental impact. In summary, the adoption of a Fieldbus-based computer monitoring system in the current gas production industry can achieve good measurement and control results. 2. System Monitoring Scheme: At the field monitoring layer: Intelligent instruments and I/O modules communicate with the monitoring computer in real time via the Fieldbus network. Operators can set all their parameters and collect data through the monitoring computer. Specifically, the system collects parameter information through the analog acquisition module (NIFP-AI-1000) or intelligent instruments and sends it to the bus. Then, the bus information is collected by the fieldbus interface card and sent to the field monitoring computer. The field monitoring computer then calls the SQL Server database for data storage and calls the monitoring software to display real-time data and historical curves. Simultaneously, at the production management layer, the factory management-level PC can connect to the monitoring computer via the NE2000 network card to achieve data sharing and integrated production management functions. 3. System Structure Design: In actual network design, considering the large number of existing analog instruments in the gas production industry, replacing them all with digital instruments for network integration would inevitably lead to a significant waste of existing equipment and a substantial increase in costs. Therefore, a network architecture with both types of instruments was adopted in the system structure design. For parameters that are not involved in control and have poor real-time requirements, such as flue gas temperature and gas oxygen content, the data is collected by the existing analog instruments and then converted into digital signals by the analog acquisition module (NIFP-AJ-100) before being sent to the Fieldbus network. For parameters that are involved in control and have high real-time requirements, such as gas main pressure and flue gas suction control parameters, the data is directly collected by the intelligent instrument (Sn LD302). Since the collected signals are already digital, no conversion is required, achieving the goal of rapid display and control. This monitoring system adopts a bus-based architecture, consisting of a monitoring unit (Advantech IPC610), 8-channel data acquisition/output modules (FP-AI-100, FP-AO-200), a data communication module from NI (NI FP-3000), a fiber optic transceiver (LANTECH 10M), and intelligent instruments (SmarLD302). The overall system control structure is shown in Figure 1. The management layer PC can monitor field production parameters in real time via the network. As shown in the figure, this monitoring system is a three-level network architecture composed of a field device layer network, a control layer network, and an upper management layer network. Its structure is rigorous, control is convenient, and it can effectively realize data acquisition and control. 4 System Software Design: The configuration software for FP-3000, FP-AI-100, and FP-AO-200 is NI Configrator software from NI. The system monitoring program is developed using Visual Basic 6.0, providing users with a user-friendly interface for monitoring and setting information about field equipment. It offers various real-time and historical curve displays, enabling management of field equipment and displaying real-time parameter lists and printing reports. 4.1 Software Functional Block Structure Diagram: The specific tasks of each functional block are as follows: 1. Process Flow Display: Displays the main production process and related parameters. 2. Trend Recording: Displays field data trends in curve form, allowing viewing of historical records within six days. 3. Parameter List: Displays all parameters in tabular form, including parameter name, parameter type, and related ranges, and can print reports according to specified times. 4. Control System: Sets corresponding PID control parameters graphically. This mainly involves proportional band, integral time, derivative time, and other related parameters. 5. Alarm Module: Displays alarm information for relevant parameters. This mainly involves alarm time, alarm type, fault source, and other parameters. During implementation, the main interface centrally schedules each functional module to complete the corresponding display and operation. 4.2 Main Issues Encountered During Development: 1. The communication mechanism between the monitoring program and data I/O: Industrial field data is mostly real-time and dynamic. Therefore, if the monitoring system wants to achieve dynamic data acquisition and processing, the traditional single-threaded programming approach often cannot effectively coordinate the communication between the data acquisition and data processing modules. Windows is a multi-tasking operating system, and a Windows application (process) can run multiple tasks (i.e., threads) concurrently. In our monitoring system design, we fully utilize the multi-threading technology of the Windows system, setting up dedicated threads for data acquisition and data processing. We handle the communication between the data acquisition and data processing threads through a combination of asynchronous I/O and event-driven I/O. The different functions of the two threads are as follows: ① Control thread (main thread): Used to calculate, store, and display the data received from the communication thread. It can also set the control parameters of the field device network layer, send commands to it, and change its corresponding operating status through user interaction. ② Communication thread (auxiliary thread): Responsible for listening to the serial port status, handling the communication of data and instructions between the monitoring system and the underlying network; storing the uploaded data in the specified data buffer and sending messages to the control thread to notify that the acquired data has arrived; and detecting communication timeouts. In summary, by using multithreading technology, the serial port is monitored in an auxiliary thread. When data arrives, it is read and reported to the main thread based on event-driven mechanisms. Control commands are sent from the main thread, and asynchronous I/O technology, relying on overlapped operations, allows serial port read/write operations to run in the background. Through I/O event-driven mechanisms and rapid switching between threads, the monitoring system can achieve near real-time performance in practical applications. 2. Selection of Real-Time Database Engine The specific implementation of the monitoring system adopts a high-efficiency, multi-tasking OPC internal real-time database engine. The OPC interface is a unified specification. It is a software interface based on OLE, developed by independent vendors. With the support of Microsoft, this interface has been developed into an industry standard by major companies in the automation field. An OPC server is a program that provides a standard OPC interface for applications from various manufacturers. Regardless of the communication network and protocol used, accessing process data through the OPC interface is always consistent. An OPC server constitutes an intermediate layer. This layer lies between the application that allows access to the processed process data and the various network protocols and interfaces that allow access to that data. This ensures rapid real-time data acquisition while enabling open support for heterogeneous systems. 4. Conclusion: The application solution presented in this paper has broad applicability and can be applied to many areas of the gas industry. For example, it can be used in tank station management, coking gasification monitoring, and external network monitoring management. This solution can improve safety and reliability while achieving ideal monitoring results. Please click to download the original document: Application of Computer Monitoring System Based on Fieldbus Network in the Gas Industry.pdf