Abstract: This paper introduces a method for implementing a small-scale cement production batching control system based on fieldbus. The system employs bus technology and intelligent modules, achieving not only automatic batching control but also adding mill load and fault diagnosis functions. Practice shows that the system is low-cost, highly reliable, easy to maintain, and convenient to operate, making it a practical microcomputer-based batching system. Keywords: cement; batching; fieldbus; control system Abstract: This paper introduces the realization method of the mini-type cement material blending control system based on fieldbus. This system uses fieldbus and intelligent models to not only realize the automatic control of cement material blending, but also has the functions of milling machine load and fault diagnosis. Practice shows that this system has lower cost, higher reliability, easiest maintenance and convenient operation. It is a practical cement material blending control system. Key words: cement, material blending, fieldbus, control system 1 Introduction Currently, small and medium-sized cement plants account for an increasingly large proportion of cement production in China. To achieve the goals of energy conservation, emission reduction and quality improvement, a new type of microcomputer batching system with low cost, high reliability, easy maintenance and convenient operation is designed using fieldbus technology and intelligent modules, which meets the requirements of the numerous small and medium-sized cement enterprises in China. Therefore, we developed a small-scale cement production batching control system based on fieldbus and applied it to actual production. This system not only improves production reliability and quality, but also brings significant economic benefits to cement enterprises. 2. System Composition The entire control system consists of two main parts—a computer and a control cabinet. The computers are connected via an industrial Ethernet network, as shown in Figure 1. The batching control computer communicates with the remote data acquisition module inside the electrical control cabinet via an RS485 communication interface. RS485 is a simple industrial fieldbus standard with good anti-interference and scalability. Connecting an opto-isolated RS232/RS485 converter module to the standard RS232 serial port of the microcomputer creates the microcomputer's RS485 interface. Using this communication structure, the microcomputer and the controlled equipment have only a simple bus connection, avoiding interference caused by excessive wiring. The batching control computer can be an industrial control computer or a general-purpose microcomputer. In bus-based industrial control computers, the STD bus is less commonly used. PC bus industrial control computers are widely used due to their lower price, better software and hardware development environment, and better user interface, making the PC bus the de facto standard bus. Industrial control computers use industrial-grade power supplies, employ sealed chassis and positive pressure air supply technology, use rubber pads for shock absorption, and adopt a modular structure. They are also equipped with a real-time multi-tasking operating system that can adapt to industrial control requirements, making them highly attractive in the industrial control field. Therefore, this system uses an industrial control computer as the process control computer. [align=center]Figure 1: Composition structure of a bus-based microcomputer batching control system[/align] When selecting modules as the detection and control signal methods, the IOM4017L module is used for analog signal detection, while the electromagnetic vibrating feeder and door opening motor are controlled by the IOM4050. The IOM4017L is a portable interface unit for analog signal detection to a computer, used for analog signal detection. The IOM4050 is an interface unit for digital signal output to the computer, used for digital signal output such as motor start/stop and door opening/closing. Both have strong anti-interference capabilities, high reliability, and long transmission distances. The system features a built-in microprocessor, requiring only two wires to communicate with the control host via an RS485 network. Based on ASCII code command/low-level protocols, applications can be written in high-level languages ​​and configured into various monitoring networks using configuration software such as INTONCH and FIX. Module addresses are stored in the module's EEPROM and can be modified by the control computer. A built-in watchdog function ensures reliable operation. Multiple modules can be easily combined to form an RS485 network, with up to 255 modules connected in series in each network. The maximum transmission distance is 1200 meters. This network connects to the host computer via RS232/RS485 conversion. 3. System Functions The designed system requires low cost, high reliability, ease of use and maintenance, and easy acceptance by field operators for widespread application. Therefore, the system has the following functions: 1) Data display, editing, and statistical functions: It can display and edit station hours, proportions, adjust the system, and tare weight; automatically accumulate shift output, daily output, monthly output, and annual output. 2) Dynamic display of operating conditions: such as the vibration of the vibratory motor, the opening and closing of the motor, material discharge, and other actions are displayed realistically and vividly, with text prompts. 3) Detection and fault diagnosis functions: such as material level detection, shaft temperature detection, and mill fault diagnosis; automatic identification of material shortage and scale jamming, alarm activation, and automatic shutdown of the entire line, with the screen indicating the fault content. 4) Online expert control functions for mill load and calcium iron meter. 5) Computer-aided scale calibration function and convenient manual control function, easy, accurate, and reliable operation. 4 System Software Design The microcomputer batching system is widely used in the batching of raw and clinker in cement plants. The early batching system used the DOS operating system and was developed in C language. With the widespread use of the Windows operating system, we redesigned the original system using Visual C++. The microcomputer batching system adopts a single document interface and uses static link libraries to form an executable file. The "real-time" monitoring requirement is achieved by a timer method with a timing interval of 0.5 seconds. Each cycle completes data communication, input/output detection, control algorithm, output refresh, alarm output, and screen display operations. Data communication is implemented using multithreading. Command and data input is achieved using the command and data input methods provided by the Windows operating system. Menu functions are used for command input, such as run, pause, and print, while dialog boxes are used for data input. Bitmaps are used to display the operating condition diagram, and animation effects are generated by periodically calling different screens. Figure 2 shows the animation effect of the operating condition diagram. The mill load control adopts a control method combining fuzzy logic and expert systems. The expert system determines the fuzzy parameters, and the fuzzy algorithm determines the feed rate. The main fuzzy control functions used include: fuzzification (void fuzzylize()); fuzzy rule inference (void fuzzyRule()); defuzzification (void refuzzylize()); and fuzzification correction (void modifyFuzzy()). The main expert control functions used are: inference function `int what(struct TREE *root, char *relate, char *name1, char *name2)`; rule matching `int matchRule(struct TREE *root, char *relate, char *name1, char *name2)`; fact lookup `struct FACT *factFind(char *relate, char *name1, char *name2)`; [align=center] Figure 2 Animation of the working condition diagram[/align] 5 Implementing network data exchange using the OPC interface OPC (OLE for Process Control) is an industry standard that adopts a Client/Server model. The development of OPC software includes the development of OPC Server software and OPC Client software. The OPC automation interface in VB provides a convenient and quick programming method for the development of OPC Client software. The intelligent control VB software of this system is written according to the Client model to develop the OPC interface software. The OPC Client software must be able to connect and disconnect from the OPC Server and must understand the interrelationships between the various objects on the OPC Server. OPC servers consist of three types of objects: Server, Group, and Item. [align=center] Figure 3: Flowchart of OPC Server Development Kit Usage[/align] 5.1 Communication Mechanism between OPC Server and OPC Client OPC clients need to connect to the OPC server and establish OPC groups and OPC data items. To access process data, OPC clients need to specify the computer name, OPC data access server name, and the definition of OPC items provided by that server beforehand. Clients access process data by accessing the OPC groups and OPC items they have established. Clients select the device as their data source. Client process data access includes reading and writing process data; process data reading/writing uses synchronous read/write. 5.2 Development of OPC Server Applications The server program needs to call the toolkit interface, and its flowchart is shown in Figure 3. 5.3 Development of OPC Client Applications The interaction between the client and server mainly includes: creating and connecting to the server object; adding groups and items; and performing data read and write operations. The client OPC interface and control program flowchart are shown in Figure 4. [align=center]Figure 4 Client Program Flowchart[/align] 6 Fault Diagnosis Rules To promptly identify problems in production, this system has added a fault diagnosis function based on production experience. The main principles are as follows: Electric Vibratory Feeder Overflow: When the computer-controlled electromagnetic vibratory feeder signal is 0 (stopping the electric vibratory feeder), the electric vibratory feeder continues to feed material, which is called electric vibratory feeder overflow. The main manifestations are a control signal of 0 and a continuously increasing pressure detection signal. Causes: ① Thyristor breakdown ② Electric vibratory feeder malfunction ③ Output board malfunction. Electric Vibratory Feeder Jam: When the computer-controlled electromagnetic vibratory feeder signal has an output (not 0), the electromagnetic vibratory feeder does not vibrate. The main manifestation is: when the electric vibratory feeder control has a signal, the weight detection remains unchanged. Causes: ① Thyristor failure; ② Electric vibratory feeder malfunction; ③ Output board malfunction; ④ Weight detection circuit malfunction. Hopper Overflow: The electric hopper door fails to close. The main manifestation is that the weight is only the tare weight. Causes: ① Electric hopper door closing device malfunction; ② Relay malfunction; ③ Detection board malfunction. Hopper jamming: The motor cannot open the door. The main symptom is that the weight cannot be reduced. Causes: ① Faulty motor door opening device; ② Faulty relay; ③ Faulty detection board. Timeout: This refers to the inability to complete the entire batching process within the specified time period, causing the cycle to lengthen. Cause: The vibratory motor amplitude is too small, and the time is too large, resulting in excessively long feeding time. Fault stop: ① The measuring range reaches full scale. For example, if the A/D input is 0-5V, when the input is greater than or equal to 5V, the A/D conversion value cannot reflect the actual weight. ② The measuring range exceeds a certain limit. For example, if the small hopper can only weigh up to 100 kg, when this value is reached, ③ the cycle cannot be completed for a long time. If each cycle is 20 seconds, and it is not completed within 60 seconds, then the machine will stop. 7 Conclusion This control system has been applied in several small cement plants. Practice has shown that the system meets the control function requirements, has good stability, reliable control, flexible and convenient monitoring and operation, and complete functions. Furthermore, the addition of numerous functions to the system, such as displaying historical data, fault alarms, and printing, enables operators to quickly identify faults occurring in production, shortening troubleshooting time, improving process management, and significantly reducing labor intensity, thus bringing substantial benefits to the enterprise. The author's innovation lies in proposing a low-cost, bus-based cement microcomputer batching system. This system is simple in structure, highly practical, and also possesses fault diagnosis capabilities. References: [1] Huang Jinfeng, Li Zhanxian. Microcomputer batching system based on fieldbus [J]. Automation Technology and Application. 2002, 21(3), 35-36 [2] Wang Jianmin, Sun Tieqiang. VC language development of industrial control software and design of microcomputer batching software [J]. Journal of Hebei Polytechnic University, 2002. S1, 25-27 [3] Huang Cailun, Peng Xianwu. Microcomputer batching system for cement raw materials [J]. Microcomputer Information, 1998, 6: 23-25 ​​[4] Shi Linsuo, Wang Tao, Liu Shunbo. Implementation of client application based on OPC specification [J]. Microcomputer Information. 2003, 5, 69-69. E-mail: [email protected]