Abstract: Based on the current situation of Baogang's integrated material yard, this paper discusses in detail the network structure and control principle of PLC control technology in process engineering. The system adopts a monitoring mode of mutual cooperation between the dispatching room and the field. When manual operation is selected, the motor operation is manually controlled on-site; when remote automatic operation is selected, the motor operation is controlled by the central dispatching room, which sends control commands to the PLC control station on-site through a fiber optic ring network. The field controllers then start and stop the equipment according to the actual control programs they have written. Practice shows that the system is reliable and highly automated. Keywords: PLC; Comprehensive materials yard; Optical fiber ring network; Control Abstract: In conjunction with the current status of Baotou Steel and Iron Group's Comprehensive Materials Yard, this article discusses the network structure and control theory of PLC technology in process control engineering in detail. This project fully utilizes the monitoring mode of the control center cooperating with the field. When the field is in manual mode, the motors are controlled manually; when a remote automatic mode is selected, they are controlled by the control commands sent by the control center, delivered to the PLC control station in the field through the fiber ring network, and the controller controls the equipment startup and shutdown according to the actual control procedures. Practice shows that the system is reliable and highly automated. Key words: PLC; Comprehensive materials yard; Optical fiber ring network; Control 1 Introduction With the introduction of computer technology into industrial control systems, PLC has become an important component of industrial automation control systems. Baotou Steel's raw material yard is a large-scale comprehensive raw material processing system, covering an area of ​​approximately 6 square kilometers. To ensure the normal operation of a large-scale modern steel enterprise, it is essential to ensure a normal, stable, and efficient supply of raw materials. Baogang's raw material yard has a complex process, many equipment, and long distance. The main production equipment in the raw material yard includes: belt conveyor, stacker, reclaimer, hopper gate machine, disc feeder, unloader, and mobile trolley. These equipment form the main systems of input, mixing, batching, and output. These transportation systems are composed of belt conveyors forming a complex transportation network with a complex process flow. In order to improve equipment efficiency and stably supply materials to the blast furnace and sintering, it is necessary to realize the automated control of raw material processing operations [1]. 2 Composition and principle of the control system The electrical control equipment is mainly composed of the GCS-1 control system of Zhejiang Zhongkong Technology Co., Ltd. and various motors and frequency converters. [align=center] Figure 1 Overall network structure topology of the system[/align] 2.1 Network structure 2.1.1 System network topology Since there are many equipment in the entire material yard, the control system is divided into 11 control stations (electromagnetic stations) according to the on-site electrical distribution principle, which respectively control the equipment of the mixing system, unloading system, ore and coke screening system, raw material input system, raw material output system, and dust removal system. Each control station employs a redundant PLC control system, communicating with the central dispatch room via a dual-layer dual-fiber ring network to monitor the equipment. The overall system architecture is shown in Figure 1. 2.1.2 Dual-Layer Fiber Ring Network Due to the large number of system substations, wide geographical area, and high reliability requirements, redundancy is used in the network structure. The dual-layer fiber ring network consists of two parallel single-layer fiber ring networks. The main network components use MOXA fiber-to-RJ45 fiber ring network switches. Besides possessing the advantages of long transmission distances and less susceptibility to interference inherent in fiber optic networks, it also retains the advantages of ring networks. Disconnection of any node or point within the ring network will not affect normal network operation; it simply transforms the original ring network into a single-bus network structure, thus improving network reliability. The dual-layer ring network structure itself provides redundancy, making the network more reliable. 2.1.3 Internal Network Structure of Control Stations Each control station is configured with redundant CPUs, providing redundancy to each station. Each station has two fiber ring network switches for connecting the two layers of fiber ring networks. Because the entire integrated material yard is a whole, with a compact process system structure and numerous interlocking signals between equipment, and our control stations are separated according to electrical stations, mainly based on the geographical location of each piece of equipment on site, the entire system is artificially divided. Therefore, data exchange between control stations will be very frequent and relatively important. Thus, we directly connect the CPU Ethernet interface to the fiber optic switch. 2.2 Control Principle The integrated material yard operation process control is a type of production process control. The raw material transportation and processing production process is an intensive operation of a group of equipment under unified control. After the raw material area renovation, there are 335 operation processes, of which 32 processes are allowed to run simultaneously; 49 groups of processes (98 processes) can switch routes during operation; 11 processes can change material types during operation; and 9 groups of processes have overlay functions. Process control requirements: 1) Processes with related equipment are called mutually "interfering" processes, and usually only one of them is allowed to run. Considering the sufficient system capacity, several processes that transport the same materials, have different starting points, and the same ending point can operate simultaneously without interfering with each other. In addition, some processes can switch between each other. 2) The integrated material yard can have up to 25 non-interfering processes without related equipment, and these processes can run simultaneously. 3) Whether it is raw material transportation or processing, the start-up, feeding, and sequential stopping of the process must fully comply with the process requirements, and all residual materials on the entire production line must be discharged before stopping. 4) The sequential start-up, sequential stopping, or equipment failure of any process will not affect other processes that are running. 5) It has a complete display and alarm function for the process status evolution process, which can ensure safe operation and flexible and convenient operation [2]. 2.2.1 Belt control program Belt control includes: ordinary belt control and forward and reverse belt control. The principle is similar. The following is a brief explanation of ordinary belt control as an example. When the automatic start conditions of the equipment are met, press the start button in the automatic state (or when the sequential start conditions are met). First, the electric bell signal is output to issue a start alarm. At the same time, the timer starts. After 3 seconds, the belt start command is output to the field contactor to make it act, start the motor, and at the same time return the equipment running signal. Together with the start output command, it will be used to maintain the DO output. When the stop button is pressed, the automatic start circuit is disconnected, there is no DO output, the contactor disconnects, and the equipment stops. When the conditions for manual start are met, pressing the manual start buckle in manual mode connects the manual start circuit, sending a belt start output command to the field contactor. The contactor actuates, starting the motor and simultaneously returning a running signal, which, along with the start output command, self-holds the DO output. When the manual stop button is pressed, the manual start circuit is disconnected, there is no DO output, the contactor disconnects, and the equipment stops. 2.2.2 Equipment Interlock Stop When the selected material line equipment is running normally, if one piece of equipment in the line stops (due to a fault or non-fault shutdown), the upstream equipment of that piece of equipment in the selected material line will be interlocked to stop, while the downstream equipment will continue to run. For example, if the selected material line A1→A2→A3→A4→A5→A6 are all running, when A5 fails and stops, its upstream equipment A1→A2→A3→A4 will all stop, while the downstream equipment A6 will remain running. Since the material yard control is a sequential control process, this can avoid material accumulation due to intermediate equipment failures, effectively reducing economic losses. 2.2.3 Equipment Start-up Before starting the equipment in sequence, ensure that each piece of equipment in the selected material line is ready for automatic start. Select the appropriate material line, press the start-up button, and the equipment will start sequentially from the bottom up along the selected material line. Start-up will continue until all selected material lines have started or 100 seconds after the start-up command is issued, at which point the start-up will reset. If start-up fails or for other reasons requires stopping the equipment, press the start-up reset button to manually reset it. 2.2.4 System Reversal When the selected material line equipment is running normally, if a small-scale change to the material line is needed instead of stopping the entire system, the "System Reversal" operation can be performed. System reversal will not stop the entire system, but after reversal, the "System Reversal" button should be clicked promptly to end the operation. 2.2.5 Emergency System Stop Unpredictable situations often occur on-site. If each piece of equipment requires manual stopping by on-site operators, the speed may be insufficient, making it difficult to achieve immediate shutdown of the entire line in case of an emergency. Setting an "emergency stop" in the software ensures a rapid response to on-site accidents, minimizing operator injuries and economic losses. When the "emergency stop" button is pressed on the monitoring screen, all equipment in the entire material yard system will stop unconditionally. 3 System functions (1) Select different processes such as feeding, stacking, picking, and emergency picking according to production needs, and control the sequential start, simultaneous start, sequential stop, simultaneous stop, emergency stop, and fault stop of the equipment in the process. (2) Select different iron-containing raw materials according to production needs, change or set the proportion of various iron-containing raw materials, and realize the feeding of selected raw materials according to the proportion through the automatic batching control system. (3) Report printing function. The original proportion and the new proportion can be printed out after each change of proportion; the total amount of batching and the consumption of various raw materials in each shift can be counted and printed out at the end of the shift; the total amount of batching and the monthly consumption of various raw materials can be counted and printed out in the form of a report at the end of each month. (4) Alarm function. This control system can monitor the operating status of various key equipment in real time during the production process. If the operating parameters of the equipment exceed the preset upper and lower limits, an alarm message will be issued on the host computer in the main control room to remind the operator to take corresponding measures. (5) Fault recording function. This system can record the equipment that malfunctions during operation, the time of the malfunction, and simple information about the malfunction, which is convenient for maintenance personnel to maintain the system equipment [3]. 4 Conclusion Since the system was debugged and put into operation, it has been running well. Practice has proved that the network structure of the GCS-1 control system and the fiber optic ring network is well adapted to occasions with many control devices, many data acquisition substations, wide geographical distribution, high real-time requirements, and high system reliability requirements. It solves the problem of data exchange between the control stations of the integrated material yard and the central control station, and enables the field equipment to be centrally controlled in the central dispatch room, saving a lot of operators and project investment. In the whole system, the combined use of PLC, frequency converter and network reduces the laying of field cables, improves the reliable operation and automation of equipment, reduces the amount of equipment maintenance, and saves manpower and reduces intermediate links in the production process, effectively improving production efficiency. References [1] Wang Chonglun. Application of PLC in the automated control system of Maanshan Iron and Steel raw material yard [J]. Electrical Application, 2005, 24(1): 110-112 [2] Fu Yinghong, Li Xiaofan, Xiang Jinjie. Discussion on soft PLC technology, products and control schemes [J]. Microcomputer Information, 2000, 16(5): 27-29 [3] Zheng Chen, Gong Jianping. Principles and Applications of Modern Programmable Controllers [M]. (Third Edition). Beijing: Science Press, 1997