This paper takes the hydraulic station system of the Jinan Iron and Steel Group's medium plate mill as an example, and introduces the successful application of a hydraulic control system for multiple distributed pump stations with different functions based on PROFIBUS-DP bus technology. Keywords: PROFIBUS-DP, PLC, hydraulic station, control system 1. Introduction The hydraulic system of the Jinan Iron and Steel Group's medium plate mill consists of several parts with different functions, such as balancing, transmission, dry oil, and thin oil. As a hydraulic system working for the same mill, it must adopt overall control to achieve reliable and simplified equipment operation and personnel operation. PROFIBUS-DP bus technology allows for the construction of single-master or multi-master systems, with up to 126 stations connected on the same bus. It uses RS-485 twisted-pair cable, two-wire cable, or optical fiber for transmission, with transmission rates from 9.6kbps to 12Mbps. Token passing is used between master stations, and master-slave transmission is used between master and slave stations. The best way to solve the hydraulic system control problem of our mill is to integrate various dispersed pump stations and operating platforms into a single S7-300 control system using SIEMENS Profibus-DP bus technology. In this control system, the various ET200 substations, S7300 master station, and PP17-II touch panel are the core components of the entire mill hydraulic system. They primarily collect and transmit field detection signals, and precisely control important parameters (such as liquid level, pressure, and temperature) of each pump station. The mill hydraulic station control system, based on Profibus-DP bus technology, allows operators to monitor the operating parameters of the pump stations in real time and perform corresponding process operations through a host computer monitoring operating system. 2. System Composition Based on the process layout of the medium plate mill hydraulic station, the entire framework of the control system is based on the Profibus-DP bus, consisting of an S7-300 PLC master control system, a WinCC monitoring station, a PP17-II operating station, and five ET200 stations, forming a master-slave hydraulic control system. (As shown in Figure 1) 2.1 PROFIBUS Fieldbus Structure PROFIBUS is a fieldbus standard based on the German national standard DIN19245 and the European standard EN50170. PROFIBUS is widely used in manufacturing, process, and building automation industries. PROFIBUS is divided into PROFIBUS-DP, PROFIBUS-FMS, and PROFIBUS-PA according to application characteristics. Their characteristics are as follows: PROFIBUS-DP (Factory Automation), quick plug-and-play; PROFIBUS-FMS (General Automation), universal, wide-ranging, multi-master communication; PROFIBUS-PA (Process Automation), application-oriented, bus-powered, intrinsically safe. PROFIBUS-DP is used for high-speed data transmission at the device level. The central controller communicates with distributed field devices through high-speed serial lines. Most data exchanges are periodic. In addition, intelligent field devices also require non-periodic communication for configuration diagnosis and alarm processing. 2.2 Master-Slave Communication Bus Structure This system adopts the PROFIBUS-DP bus structure to realize master-slave communication. The S7-315-2DP acts as the bus master, periodically scanning and reading/writing each subordinate substation (ET200M) using a polling method, and transmitting instructions to the corresponding data areas of each substation via the Profibus-DP bus. The functions of each station in the control system are as follows: 2.2.1 S7-300 PLC Master Station In the system architecture, the master station uses an S7-315-2DP (6ES7-315-2AG10-OABO) CPU, which performs periodic data communication and user program or function block calls between control systems or between human-machine interfaces (HMIs). It realizes logic control and data processing, and completes parameter control such as pressure, level, and oil temperature within the hydraulic station, as well as the gain/loss of valve group electrical actions. 2.2.2 ET200 Substation The ET200 is a high-density modular I/O station with an IP20 protection rating. It is mainly used for signal, function, and communication module expansion of the S7-300 programmable controller. The system utilizes five ET200M substations to collect and control all I/O modules, completing the acquisition of digital and analog data, control signals, and displaying the operating status of each oil pump motor and solenoid valve. Specific functions are as follows: Stations #4, #5, and #6 are the transmission station, balancing station, and lubrication station, respectively. These stations provide hydraulic power, hydraulic balancing, and lubrication for the rolling mill, enabling functions such as bed pushing, guiding, roll changing, roll system balancing, and bearing lubrication. The other three substations automatically control the oil tank level, oil pump, pressure switching protection, and oil temperature for each station. Stations #7 and #8 are the MCC and field valve group control stations, respectively. The MCC station controls the start, protection, and stop functions of each station's motors, while the field valve group controls the gain and loss of power for each field hydraulic valve. 2.2.3 PP17-II Touch Panel : The SIMATIC PP17-II is designed for more complex tasks, featuring 32 buttons, 4-color LEDs, 16 digital inputs/outputs, and one central input terminal. All operations on the rolling mill control panel are conducted via a touch panel. The programmed panel is not only flexible but also provides operators with different color indicators. 2.4 WinCC Operation Monitoring Host Computer WinCC is an integrated human-machine interface and monitoring management system. Through its graphical designer, alarm logger, marker logger, report designer, global scripting, control center, and user management functions, it integrates information and operations for the entire hydraulic system. The rolling mill hydraulic station operation monitoring system is used to monitor the hydraulic station system's operation in real time, displaying various key operating parameters and providing comprehensive system alarm and fault displays. 2.5 Detection System and Actuators The detection system of the hydraulic control system includes displacement sensors, pressure sensors, temperature sensors, level sensors, and control limit switches. The actuators of the hydraulic control system mainly consist of motors and various solenoid valves distributed on-site. By controlling the energization and de-energization of each solenoid valve, the rolling mill's central shaft connection, the balance of the work roll support roll, and the pusher and roll changing systems are controlled. The main actuators are solenoid valves. According to the rolling mill production process requirements, we divide the rolling mill hydraulic valve group into four valve groups: balancing, transmission, pusher, and shaft connection control. Each valve group is divided into pulse-type solenoid valves and general solenoid valves according to the control function requirements. 3. System Software Application 3.1 System Hardware Configuration The hydraulic control system uses SIEMENS STEP7 programming software for system hardware configuration and program development. The hardware master station is a CPU315-2DP, and the hydraulic station control system hardware configuration is shown in Figure 2. 3.2 System Software 3.2.1 PROFIBUS Property Settings PROFIBUS property settings include Transmission rate and Profile. (See Figure 3) 3.2.2 Program Function Blocks: The PLC and ET200 station are the main components of the system. Five substations are installed, primarily at the control sites of various pump stations, pump station duty rooms, and the operation sites and consoles of the rolling mill, which are relatively far from the central control room but have concentrated control points. Each ET200 is responsible for collecting and transmitting all I/O signals of its station and completing all pump station control, realizing remote communication of the rolling mill hydraulic control system and achieving the goal of unified control of various functional pump stations within the rolling mill hydraulic system. According to the system process requirements, the program is divided into 6 functional blocks. Data from the PLC master station and 5 ET200 substation modules are uniformly applied within the 6 FC functional blocks, controlling the functions of each substation and achieving overall system integration of the hydraulic station. FC1 is the control function block for the balancing station subsystem, FC2 for the transmission station subsystem, FC3 for the control cabinet within the MCC control cabinet, FC4 for the hydraulic pipeline valve group subsystem, FC5 for the dry and thin oil lubrication subsystem, and FC6 for other auxiliary facility subsystems. Each OB organization block performs its corresponding function in the software. (See Figure 4) 3.2.2 PP17-II Operation Panel Software Settings The 32 buttons provided by the PP17-II operation panel are configured and defined according to the process operation requirements. Specific operations include work roller and upper support balancing, east and west hanging cylinder raising and lowering, upper and lower handrail balancing, east and west frame roller entry and exit, axial clamping, roller changing entry and exit, and working condition selection. The color definitions of the 32 LED status indicators on the panel are shown in Figure 5. 3.2.3 WinCC System Monitoring The WinCC monitoring station in the system displays graphics, data, and soft switches for operator control. The equipment is organized into multiple screens according to the functional steps of the processing technology, including system overview, balance system, transmission system, dry/light oil system, lubrication system, valve group system, pressure regulation settings, and system operating mode interfaces. The WinCC monitoring station receives real-time data from the PLC and displays corresponding process data and operating status for operator monitoring. The operating status of each pump station motor, the oil supply system's level, pressure, temperature, solenoid valve working status, and limit status are transmitted to the host computer via the DP network and displayed on the monitoring screen. In particular, alarm and trip values ​​are set for the interlocks of each system. Various operation, alarm, and trip information are displayed in the WinCC system's alarm log. When an alarm occurs, the alarm record is displayed in the alarm column, and the screen flashes a color to alert the operator of the malfunction. Various data are processed to generate various reports and historical data is stored. Especially noteworthy are the pre-alarm values ​​set for various data related to the stable operation of the rolling mill, allowing operators to adjust the system pressure and other parameters according to actual conditions to ensure stable and efficient production, thus ensuring the stable operation of the entire hydraulic system and preventing various accidents. (See Figure 6.) 4. Conclusion Since its commissioning, the hydraulic control system of the four-roll mill at Jinan Iron and Steel's medium plate plant has achieved reliable operation of the entire hydraulic station system, fully meeting the rolling mill's process requirements. The rolling mill hydraulic station control system based on the Profibus-DP bus is flexible in operation, simple in maintenance, easy to expand, and stable in operation. Author Introduction: Duan Wenyu (1981-), male, from Duchang, Jiangxi Province, graduated from Jiangxi University of Science and Technology in 2004 with a major in Electrical Automation. He is currently an assistant engineer at Jinan Iron and Steel Group's Medium Plate Plant, engaged in electrical automation work. Office phone: 0531-88866237