Abstract: Due to its inherent uncertainty, Ethernet has long been difficult to apply in the field of industrial control. However, the rapid development of industrial Ethernet in recent years has made its entry into industrial control a reality. This paper introduces an example of real-time monitoring of a well network using Ethernet and performs a delay analysis on the system. Keywords: Ethernet, determinism, oil well, real-time monitoring 0 Introduction As automation systems become increasingly intelligent and flexible, the number and distribution of intelligent instruments such as sensors and controllers in these systems are constantly increasing, leading to a continuous increase in the amount of data exchange between different devices. Therefore, to ensure the real-time performance and determinism of the system, automation control networks are extremely important. When discussing control networks, fieldbus is often mentioned. While fieldbus has indeed developed rapidly in recent years, its high hardware costs and the difficulty of communication between different bus devices limit its application. Therefore, both end users and developers are seeking high-performance, low-cost solutions. With the rapid development of Ethernet, it has become a de facto industrial standard. Currently, Ethernet technology is widely used not only in office automation but also in the management networks of various enterprises. Due to its mature technology, relatively low price of connecting cables and interface equipment, and rapidly increasing bandwidth (with the emergence of gigabit and even 10-gigabit Ethernet), especially the advent of switched Ethernet technology, people are turning to Ethernet equipment to replace the relatively expensive dedicated bus equipment in control networks with cost-effective Ethernet devices. 1. Characteristics of Ethernet Ethernet is a local area network standard supported by IEEE 802.3. It was originally developed by Xerox and jointly expanded by DEC, Intel, and Xerox to become the Ethernet standard. Following the 7-layer structure of the ISO Open Systems Interconnection reference model, the Ethernet standard only defines the link layer and the physical layer. As a complete communication system, it requires the support of higher-level protocols. Ethernet's Media Access Control Protocol (CSMA/CD) has unpredictable latency. Each node in the network must compete for the right to send packets: nodes listen to the channel and can only send information when the channel is idle; if the channel is busy, they must wait. After the information begins to be sent, it is also necessary to check for collisions; if a collision occurs, the transmission must be stopped and retransmitted. Obviously, under busy channel conditions, the real-time performance of data cannot be guaranteed, which has long been a major obstacle preventing Ethernet from entering the industrial control field. However, the development of Fast Ethernet and switched Ethernet technologies has brought new opportunities to solve the non-deterministic problem of Ethernet, making this application possible. 2 Ethernet's entry into the industrial control field has become a reality In the past few years, Ethernet technology has developed rapidly. Among them, the development and application of switched Ethernet technology has greatly improved the uncertainty problem caused by the CSMA/CD media access method in Ethernet technology. Combined with Fast Ethernet and Gigabit Ethernet technologies, it has greatly improved the real-time performance and determinism of Ethernet. Compared with traditional Ethernet, switched Ethernet has made significant improvements in two aspects. First, the two are very different in their hub operation. In traditional Ethernet, the HUB sends the data received on one port to all other ports, which implements a broadcast function, meaning that only one node can send data at a time. A switch is an intelligent HUB that can identify and process the destination address of the received data and only send it to the destination port, which means that multiple nodes can send data simultaneously. Secondly, in traditional Ethernet, the connection between nodes and hubs is half-duplex, while switched Ethernet uses full-duplex, allowing nodes to send and receive data simultaneously. These two differences overcome the shortcomings of traditional Ethernet, significantly improving network performance and transforming previously "shared" bandwidth into "dedicated" bandwidth, effectively solving the bandwidth problem. In addition to these two aspects, switched Ethernet utilizes a typical switching technique: store-and-forward. Its working principle is as follows: when the switch receives a data frame from the source station, it first checks if the destination channel is idle. If idle, it sends the frame; if busy, it stores the data in a buffer until the channel becomes idle before sending it. Furthermore, if several data frames destined for the same destination are received simultaneously, the switch stores them in a buffer and then sends them sequentially. Another advantage of using switches is the segmentation of collision domains, thereby expanding the network system's coverage. Today, Ethernet has also developed technologies such as Virtual LANs (VLANs), virtual collisions, and fault-tolerant redundancy. Once Ethernet resolves the uncertainty issue, it is fully capable of entering the industrial control field and possesses advantages unmatched by fieldbuses. Currently, manufacturers are developing Ethernet products and controllers adapted to industrial environments, and many industrial Ethernet products have already entered the market, with increasingly widespread applications across various industrial sectors. 3. Application Examples With the advent of enterprise informatization, the petroleum industry is also developing towards intelligent and information-based systems. Generally, an enterprise's information system can be functionally divided into three layers: the bottom layer is the Process Control System (PCS), which performs measurement and control functions on the production site; the top layer is the Enterprise Resource Planning (ERP); and the middle layer, Manufacturing Execution System (MES), encompasses the traditionally overlapping functions of monitoring, management, and scheduling. To achieve an integrated enterprise solution and realize the integration and comprehensive application of information, information integration is required within each layer and between information sources at each layer. Compared with developed countries, my country's oil extraction technology still lags behind. Currently, over 95% of my country's oil wells are mechanically operated, and most data collection relies on manual labor. Although a MES (or MIS) management information system at the petroleum administration level has been established to some extent, seamless data transmission from the oil well site is still not possible, hindering efficient oil production scheduling and management. This example introduces the use of an Ethernet control network to monitor oil wells, extending the oilfield information network to the wellhead, achieving real-time transmission of oil well data and seamless information network connectivity, forming an integrated information network for oilfield production management and monitoring. [align=center] Figure 1 System Block Diagram[/align] As is well known, oil well management is a crucial aspect of oilfield production management, characterized by remote locations, heavy workloads, and high technical difficulty. This system fully considers the geographical characteristics of the oilfield. The central control room is located at the transfer station. Oil wells far from the central control room utilize wireless communication, while wells closer to the transfer station use wired connections. The system block diagram is shown in Figure 1. The system uses OptiLogic Ethernet RTUs (10Mbps) from Optimation (USA) as intelligent terminal devices for data acquisition and operation control at oil wells and metering stations. Each RTU can transmit data from up to three oil wells (current, voltage, oil temperature, oil pressure, load, coded signals, etc.). The RTUs within the station are mainly used to collect data on liquid level, temperature, pressure, and flow rate from storage tanks, water injection terminals, and automatic metering terminals. The system uses wireless Ethernet routers (MAP811) and wireless Ethernet bridges (MAP811E) from Macromate (Taiwan) as wireless communication equipment between the production team and the oil wells. It adopts direct-sequence spread spectrum (DSSS) transmission, achieving a speed of up to 11Mbps and supporting the TCP/IP protocol standard. The operating frequency band is the 2.4GHz ISM free band, a channel not restricted by the Radio Management Committee. This frequency band is also less susceptible to interference. Communication between the wellhead and the monitoring workstation is achieved through directional antennas at the wellhead and omnidirectional antennas installed by the production team. The central control room switch connects the monitoring workstations and various devices. Through the switch's VLAN (Virtual Local Area Network) function, separate VLANs are set up between the monitoring workstations and other ports, reducing unnecessary broadcast traffic and data conflicts. The system uses Think&Do control software from Entivity Corporation (USA) as the monitoring configuration software for the monitoring workstations in the central control room of the oil production team. This system refreshes all I/O data at a scan rate of 50ms using the Think&Do application software running on the monitoring workstations and saves all data in categorized text files (.TXT). Raw data from the monitoring workstations is transmitted to the data server in a timely manner via 100M Ethernet for querying by higher-level systems. Real-time data communication between them can be achieved through the DCOM standard interface or Think&Do's TnDNTag control. The data server and the oil production plant and management bureau can query field data through a remote login program. The above example describes a demonstration project in an oil production plant of Changqing Oilfield. This system uses 5 RTUs to monitor 10 wells. Typically, when the number of RTUs in the collision domain is less than 5, almost no conflicts occur. Therefore, as long as the number of RTUs connected to each MAP811 does not exceed 5, for larger systems, different collision domains can be divided using switches (as shown in Figure 2). Utilizing the store-and-forward function of the switches, the determinism of the system can be fully guaranteed. [align=center] Figure 2 System Expansion Diagram[/align] 4 Network Latency Analysis To gain a clearer understanding of the real-time performance of the system shown in Figure 1, we can analyze the maximum latency of the system. The system will experience maximum latency in the following situations: (1) the RTU response time is the longest; (2) there is the maximum number of collisions when passing through MAP811; (3) the switch experiences the maximum queuing latency. According to data provided by Optilogic, the response times of its Ethernet RTUs are shown in Table 1. The maximum response time of the RTU at the wellhead in this system is the response time generated by the RTU that collects data from 3 oil wells, including 3 digital modules and 3 analog modules. Its response time is: Tres = Tbas + 3×Tmd + 3×Tma= 1.6+0.3+3×0.2+3×0.73= 4.69ms (1) Where Tres is the total response time of the RTU, and Tbas, Tmd, and Tma are the response times of the RTU rack, digital modules, and analog modules, respectively. The Think&Do response time limitation function requires that the RTU response information be received within a set time. If the corresponding information is not received within the set time, the connection with the RTU is disconnected. The response time of a system consisting of 5 RTUs connected to MAP811 was tested using this function. The results are shown in Table 2. As can be seen from Table 2, when the set value is above 15ms, no RTU is disconnected for a long time. Therefore, the maximum delay generated by MAP811 can be considered as: Tmap = 15-Tres = 15 - 4.69 = 10.31ms (2) It is worth mentioning that if the RTU is directly connected to the switch using a network cable, the delay of the entire system will be reduced by the delay generated by MAP811, which will greatly enhance the real-time performance of the system. The maximum delay of the switch store-and-forward occurs when 4 frames arrive at the same time (Figure 1), and the delay generated at this time will be less than 1ms[1]. In this way, the maximum delay of the entire system will not exceed 16ms, which can fully meet the real-time requirements of a general system. In practice, we set the response time limit to 20ms, which can ensure that no RTU is disconnected for a long time. Even if an RTU is occasionally disconnected, it can be reconnected through Think&Do's Rescan function. Table 1. Ethernet RTU Response Time Table 2. RTU Response Time After MAP811 5. Conclusion The well network real-time monitoring system described in the above example is now operational. Compared to previous methods (such as data transmission radios), the system's real-time performance has been significantly improved. The successful operation of this system also proves that Ethernet can fully meet the real-time requirements of industrial control. Simultaneously, Ethernet can directly and seamlessly connect with the plant information management system without any dedicated equipment. This realizes the extension of the oilfield information network to the wellhead, the real-time transmission of oil well data, and the seamless linking of information networks, forming an integrated information network for oilfield production management and monitoring. 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