1 Introduction With the development of enterprise network integration, Internet technology and control technology are integrated, and remote control of production process technology has become an important research content of automation technology. In the field of industrial automation, control network is also developing towards the openness of system architecture, and the field of information communication is rapidly covering all levels from factory field equipment to control and management. The enterprise integrated automation solution based on Internet/Intranet has become a popular research direction [1]. Through Internet browser, relevant personnel can remotely monitor the production process, remotely debug equipment and remotely diagnose and handle equipment faults. This can not only improve the level of enterprise automation and realize unattended operation, but also lay a solid foundation for the scientific management, safe operation and effective maintenance of enterprise production operations. However, due to the existence of network delay, the network-based control system cannot be a closed-loop control. It adopts a remote supervision control scheme, while the logic control function is completed by the field equipment layer. Based on this idea, this paper proposes network control based on B/S structure and develops a real-time remote control system based on PLC and AC frequency converter. The system integrates industrial control configuration software, PLC technology, frequency conversion control technology and network communication technology. 2. Browser/server structure industrial information monitoring system Client/server technology is a widely used information processing mode[2]. Compared with the traditional centralized information processing mode, it can reduce system expenses and greatly improve the information processing performance of the microcomputer cluster connected to the network. Due to its distributed processing characteristics, it can improve the reliability of the system. In addition, due to its modular and open architecture, it is easy to connect different machines effectively, which makes it easy to expand and upgrade the system and improve the flexibility of the system. However, it also has many potential defects[3], such as difficult layout, high training costs and system maintenance costs, and the C/S structure cannot meet the cross-platform requirements of the client. Therefore, this paper uses the browser/server structure to build an industrial information monitoring system. 2.1 Characteristics of browser/server architecture With the development of Internet/Intranet technology and applications, WWW service has become a core service. Users can complete various services and application functions on the Internet through the unified interface of the browser. This computing structure, developed in the mid-1990s, based on browsers, web servers, and application servers, is called browser/service (b/s, browser/server) computing model. The b/s model inherits the network software and hardware platform and applications in the traditional c/s (client/server) model, but overcomes the above-mentioned defects of the c/s model. This new structure has the following advantages [3]: (1) The application server is easy to develop. The b/s structure is a three-layer structure that includes clients, web servers, and application servers, involving four components: browser, web server, database server, and application server. This division makes the program development simple. For example, the application server does not need to consider the communication problem with the client too much. A large amount of data transmission with the client is completed by the database server and web server, allowing developers to focus more on the improvement of functions. (2) There are many ready-made peripheral programs available. The web server and database server can use ready-made products. Only the application server needs to be developed by itself. Moreover, since the web server is responsible for a part of the communication with the database server and the client browser, the development burden of the application server is reduced. (3) The client can more easily obtain data using the B/S structure, and the most direct and significant change is reflected in the client. Unlike the traditional C/S structure, the client no longer communicates with only one application server. The client has multiple channels to obtain data. For non-real-time data, the browser can directly send a data query request to the web server, while the application server only needs to write the data into the database and does not participate in the process of the client obtaining data from the database. For real-time data, the browser communicates directly with the application server through the ActiveX control embedded in the page, while the web server and database server are unaware of this. 2.2 Industrial Information Monitoring System with Browser/Server Structure The industrial information monitoring system with the B/S structure is an extension of the C/S structure. Their network structures are basically the same, except that the functions on the server side are more distributed. The basic block diagram is shown in Figure 1. The industrial information monitoring system adopts the B/S mode, where the client directly interacts dynamically with the server through the browser, while the C/S mode adopts an event-driven approach. Each substation receives real-time information from the field control unit and writes it to the database server for storage. The web server dynamically publishes the real-time data from the database server to the internet, allowing clients to easily access this real-time information through a browser. Conversely, client control information can also be written to each substation via the web server, and then the substations write the data to the field devices, achieving remote control. In the B/S (Browser/Server) model, the browser replaces dedicated client software, allowing users to access internal enterprise data within their permissions and make decisions. Following the TCP/IP communication protocol and WWW specifications, data ports are accessed through ActiveX controls embedded in the web page, enabling remote acquisition of field data and issuing corresponding commands to control field devices based on the acquired information. Therefore, the system's openness is greatly improved, and development and maintenance are more convenient. 3. Remote Control Example Based on B/S Architecture This paper studies and develops a real-time remote control system based on a PLC and an AC frequency converter. This system integrates industrial control configuration software, PLC technology, frequency converter control technology, and network communication technology. 3.1 System Overall Structure This system is a real-time water level detection and control system for dual-tank water. It adopts a generalized hierarchical structure for monitoring systems, and the entire system is divided into three levels: field control level (PLC), upper computer monitoring level (server), and remote control level (client). The experimental platform realizes the following functions: (1) Through the programming of the lower computer (PLC), it can realize PID control and fuzzy control of water level. (2) Through the communication cable, the lower computer (PLC) and the upper computer (KingSCADA) can communicate. (3) Through the development of the upper computer industrial control software, it can collect field data and write the user information of the client to the lower computer (PLC). (4) The remote client communicates with the upper computer through the laboratory LAN, so that the remote client can browse the real-time trend chart and historical trend chart of water level, and can adjust the control parameters, select the control mode, and handle emergency accidents (start and stop the pump). The system block diagram is shown in Figure 2. 3.2 System Hardware Configuration The design of the entire water level network control system process flow is as follows: the water level is controlled by PID and fuzzy control through the PLC control program, and the calculation results are output to the frequency converter to control the start and stop and speed of the AC motor, so that the water level is stabilized at the set value. In addition, through the communication between the PLC and KingSCADA, and the communication between the remote client and the host computer, the setting of the given value, high limit, and low limit, as well as the selection of control mode and adjustment of control parameters are realized on the remote client, and the water level is monitored through alarm diagrams and trend diagrams. The specific hardware configuration of the system is shown in the attached table. 3.3 System Software Configuration Based on the above network structure, the entire system is divided into three layers, and its software design also consists of three parts: (1) Field control layer software design: the functions to be realized in this part are water level signal acquisition, PID control algorithm implementation, fuzzy control algorithm implementation, control signal output, etc. The selected controller is the Siemens S7-300 series programmable logic controller, so the matching programming software Step7 is selected, which can use ladder logic, function block diagram or statement list. The control program was developed using Step7. After successful debugging, the program was written into the PLC, so that the PLC could run offline. Through experiments, this control scheme was verified. It has high control accuracy, stable operation, and strong anti-interference ability. (2) Upper computer software design: This part mainly serves as a bridge for communication between the remote client and the lower computer (PLC). On the one hand, it is responsible for collecting PLC data and transmitting it to the remote client. On the other hand, it receives the control information from the remote client and writes it into the PLC. KingSCADA comes with the S7-300 driver, which can easily obtain PLC data. Moreover, its network function is strong and can quickly realize network communication based on TCP/IP protocol. Therefore, we use KingSCADA as the upper computer software development environment. (3) Remote client software design: This part mainly realizes the communication with the upper computer and the development of the monitoring screen. In order to facilitate the communication with the upper computer, a unified development environment - KingSCADA - is used. The entire application is distributed to multiple servers to improve the overall capacity structure of the project and improve the performance of the system. Server allocation can be based on the physical equipment structure or different functions in the project. Users can set up dedicated I/O servers, historical data servers, alarm servers, login servers, and web servers according to system needs. 3.4 Implementation and Security Management of Network Control Because KingSCADA is entirely network-based, a true client/server model, it can be installed on a network version of Windows 98/2000 or NT, and the TCP/IP protocol can be bound during network configuration to achieve remote control using its network functions. In this system, we utilize the existing LAN in the laboratory, using one computer as the server, connected to the lower-level computer (PLC) via a serial port, and setting its network identifier to "server". The remaining computers act as remote clients, with their network identifiers set to "client1", "client2", etc. All hosts run the same operating system, Windows 2000, and all have KingSCADA 6.0 installed. After completing the network connection, network parameters are set for each station, and variables for data exchange on the network, as well as the storage and referencing of alarm data and historical data, are defined. In this system, the client can not only monitor the water level control of the two tanks in real time, but also remotely modify the p, i, and d parameters using the network write-back function to improve the control effect. To ensure the safe operation of the system, each parameter has a certain modification permission, and only users with that permission can modify it, thus ensuring the security and effectiveness of network control. 4 Conclusion This paper analyzes and compares the client/server model and the browser/server model, and proposes a network architecture based on the browser/server model. Taking the laboratory dual-tank water level control system as the research object, it studies the network function of the configuration software KingSCADA in depth, and uses this configuration software to realize remote network control, thus proving the effectiveness of using the B/S model for network control.