1. Introduction Fully automated metering and batching control systems are widely used in various industries, such as metallurgy, non-ferrous metals, chemicals, cement and building materials, and food. It is the primary link in finished product production, especially in industries with continuous material supply requirements. The process control of the batching ratio directly affects the quality of the finished product and is a prerequisite for enterprises to achieve optimal economic benefits. Although the different process characteristics of each industry lead to different requirements for batching control, high reliability, advanced technology, openness, maintenance-free operation, and scalability are common goals pursued by all industries. With the widespread application of IT technology, factory automation will directly enter the e-era, and metering automation (SCADA) is also an important component. 2. System Functions Based on the above objectives, we designed and manufactured a fully automated mechatronics production line for a leading enterprise in a certain industry, encompassing multi-variety mixing and batching metering, quantity estimation, conveying, metal detection, packaging metering, and sorting metering functions. The dynamic metering scale, through a two-level fieldbus, seamlessly integrates with a PLC and HMI/IPC to form a three-in-one closed-loop dynamic batching system. The industrial control computer is connected to the factory ERP/MIS via a hub and Ethernet. The entire batching process strictly follows the selected formula ratio and flow, with multi-level alarm recording, completing the mixing, feeding, and logistics control of different raw materials, achieving integrated management and control, and optimizing the performance and efficiency of process control. It represents an advanced solution based on the FCS batching and metering monitoring system, conforming to the trend of automated metering for square roots. The system's process flow is shown in Figure 1. [align=center] Figure 1 System Process Flow[/align] 3 System Configuration The lower-level machine of this system uses a Mitsubishi Electric Melsec-A2SH series PLC as the main controller, equipped with a GOT-F940 touchscreen as the lower-level human-machine interface (HMI). Metering control consists of 12 Shanghai Yamato CFW constant feed weighers. They are networked via CC-Link fieldbus to achieve data acquisition and control, ensuring the system's reliability and real-time performance. The host computer portion uses an Advantech IPC610 industrial PC as the monitoring station, equipped with a Microsoft Windows NT 4.0 for Workstation operating system and the world-renowned monitoring software CiteCut SCADA 5.30 as the SCADA system software platform environment. The system software has rich functions such as process operation, monitoring, communication, alarm, management, trend analysis, report recording, and redundancy, and also has strong diagnostic capabilities. The system's hardware and software form the organic whole of the control system. The above configuration ensures the system's integrity, consistency, compatibility, and completeness, enabling long-term stable operation in industrial environments and providing anti-interference capabilities against electrical, magnetic, and vibrational forces, thus guaranteeing the safe operation of the entire system. The system has the following functional characteristics: • Monitoring real-time data and process flow at the production site; • Browsing various real-time/historical trend screens; • Processing and reflecting various process alarms and historical alarms; • Browsing, querying, and printing real-time/historical production reports; • Modifying and managing production process parameters and status; • Providing real-time data at the factory level for enterprise decision-makers; The structure and network configuration of this batching system are shown in Figure 2. [align=center] Figure 2. Batching System Structure and Network Configuration[/align] 3.1 Lower-level Machine Structure and Composition The 12 CFWs used in this project are mainly used to control the raw material flow. The core of the CFW is the CFC-200 instrument, which is a multi-functional metering controller that integrates regulation and calculation. The CPU is a Motorola 68K series, which integrates the outstanding instrument design technology of Daiwa Weighing Instruments. It has sufficient anti-interference performance, diversified interfaces, self-diagnostic function, self-tuning PI adjustment function and other features. It is equipped with Shanghai Daiwa C3-level resistance strain gauge load cell, Yaskawa Electric's current vector inverter 616G5 and German SEW high-performance variable frequency motor to form a complete mechatronics product, which ensures the accuracy of metering and control. Its system accuracy reaches ±0.2%. The lower-level controller uses two Mitsubishi Melsec-A PLCs in a dual-redundant structure, characterized by advanced technology, high speed, reliability, and large capacity. PLC1 is the main controller, and PLC2 is the backup redundancy. In case of failure, seamless switching between the main and backup PLCs can be implemented, and it can also be used for future project expansion. Since the 12 CFWs are distributed relatively widely, a CC-Link bus is chosen to connect them to the PLCs. The lower-level HMI is a GOT940 LCD touchscreen, ensuring that process data is accurately and promptly reflected and displayed on both the upper-level PC monitoring station and the touchscreen. Even if the upper-level controller fails or malfunctions, it will not affect the overall process control. Although the touchscreen's monitoring display is not as comprehensive as the upper-level HMI, it basically covers the entire system's monitoring and operation. 3.2 CC-Link Overview CC-Link, launched in 1996 by Mitsubishi Electric Corporation with the goals of high performance, low cost, and multi-vendor support, is a second-generation open fieldbus. It stands for Control & Communication Link. In November 2000, the CC-Link Association was established specifically to promote and develop CC-Link globally. The open fieldbus CC-Link boasts outstanding advantages such as superior performance, wide application, ease of use, and cost savings. CC-Link uses a master-slave structure with twisted-pair cable as the connection medium, supporting up to 64 slave stations. It employs broadcast polling and can achieve speeds up to 10 Mbps. A PLC or computer acting as a CC-Link master station, equipped with an AJ65SBT-RTT repeater, can achieve a maximum distance of 13.2 km. The maximum loop data capacity of the network bus is 2048 points, 512 words; the maximum instantaneous data transmission volume is 960 bytes. CC-Link features a complete set of RAS functions, including scheduled station functionality, automatic refresh, plug-and-play, master station hot standby, slave station disconnection, station online recovery, and monitoring testing. CC-Link is very convenient and simple to use, with easy hardware switch setup, wiring (3-core shielded cable), and system configuration (parameter settings are all that's needed). Currently, CC-Link supports up to 360 types of devices, such as remote I/O, sensors, weighing controllers, regulators, solenoid valves, frequency converters, touch screens, etc. It is supported by over 220 manufacturers, including Panasonic Electric Works, Yamato Weighing Instruments, Yokogawa, Siemens, Digital, NEC, etc. CC-Link is currently the only Asian product that can compete with European and American fieldbus standards. Shanghai Yamato's quantitative feeder (CFW) is connected to the CC-Link fieldbus as a remote device slave. 3.3 Configuration and Programming PLC programming uses Mitsubishi GX Developer 7.0 as the platform, employing symbolic ladder diagrams. System resources are fully considered, with extensive use of macros to reduce scan time and improve real-time control. The Melsec-A PLC is a CC-Link master, controlled by the master module A1SJ61BT11, which controls the operation and data refresh of the slave station (CFC-200 controller). During network configuration, the initialization program can be used to set network device parameters via the PLC and written into the master station's EEPROM. During program execution, data exchange between the master and slave stations is automatically linked and updated; the master CPU only needs to use FROM/TO instructions to access slave device information from the buffer memory. Communication between the upper and lower computers uses the Modbus communication protocol (RS485 mode). The network structure is master-slave, and the communication medium is twisted-pair cable. Modbus, developed by Modicon in its early days, is a classic and open serial communication protocol widely used in industrial control and is a de facto industrial network standard. It supports 21 function codes and can communicate with different products from many other manufacturers in the factory. The Modbus protocol used in this system is encapsulated in RTU (binary) format and uses CRC error checking, which can transmit information with high communication efficiency. Its derivative protocol Modbus/TCP can be applied to communication between Ethernet devices, which is in line with the current network development trend. 3.4 Detailed description of the monitoring system The monitoring system is developed and run on the Citect SCADA 5.30 32-bit industrial control software. Citect is a world-leading SCADA product. It is a SCADA software based on the Windows NT platform for distributed control systems. It has a unique "scalable structure". It provides users with great application flexibility and system openness. It has a wide range of applications in the field of industrial automation and is one of the best automation software today. (1) Citect SCADA Citect SCADA has a built-in real-time multi-tasking programming language with a Cicode script. With the rich function library it provides, complex applications can be developed flexibly. This is one of its advantages over other SCADA software. The monitoring system adopts a tree structure and has a variety of screen calling methods to facilitate operation and use. The system screen is divided into menu home page, batching overview monitoring, equipment monitoring, formula management, trend group record, alarm group record, report, operation log, debugging and maintenance, help and other screens. In order to ensure the safe and reliable operation of the system, the monitoring system provides multi-level user management functions, divided into three types of permissions: operator, administrator and engineer, to ensure the system's security mechanism. In the development of this batching monitoring system, the actual process conditions were combined and the strengths of CiteCrustAda were fully utilized. The main functions completed include formula setting, process selection and switching, process interlocking, process start, sequential stop, fault stop, process alarm, quantitative control of total amount, batching flow adjustment and production statistics calculation. (2) System interface The interface diagrams of the system are shown in Figures 3, 4 and 5. [align=center]Figure 3 Ingredient System Interface[/align] [align=center]Figure 4 Overall Ingredient Interface[/align] [align=center]Figure 5 Recipe Management Interface[/align] CiteCruise adopts a client/server architecture, connecting to the factory ERP/MIS via an Ethernet link (TCP/IP protocol) as an I/O server. CiteCruise provides common methods such as DDE/NetDDE, OPC, ODBC/SQL, COM/DCOM, and CTAPI to achieve data exchange between Windows applications and I/O. Historical data in this batching system accesses the database server Microsoft SQL Server 7.0 via ODBC/SQL. For real-time data exchange, the CTAPI interface provided by CiteCruise is used. It is suitable for various data exchange methods, is more flexible, avoids code redundancy in various applications, improves memory utilization, and provides external application (VB, VC++, etc.) interfaces through DLL functions, allowing user applications to directly manipulate CiteCruise's tag variables and supporting remote OLE API functions via TCP/IP. (3) The steps for VB to call DLL functions, following the principle of declaration before calling: • public declare function ctopen lib"ctapi.dll" (byval scomputer as string, byval suser as string, byval spassword as string, byval nmode as long) as long. • public declare function cttagwrite lib"ctapi.dll" (byval hctapi as long, byval stag as string, byval svalue as string) as long. • public declare function cttagread lib"ctapi.dll" (byval hctapi as long, byval stag as string, byval svalue as string, byval dwlength as long) as long. ctopen(): Connects to the CiteCut API. cttagread(): Reads CiteCut I/O variables. cttagwrite(): Writes to CiteCut I/O variables. As can be seen from the above, using DLL functions is similar to using VB's own functions, which is very simple. Users can monitor real-time data and query historical data through any workstation on the internal enterprise network. 4 Implementation Summary This batching system has been in operation for more than three years. The system is very stable and reliable, and easy to operate and maintain. The experience gained during the implementation of the project is as follows: (1) As a second-generation open fieldbus, CC-Link was successfully activated in one go in the harsh field environment using domestically produced shielded communication cables, with a communication speed of 10 Mbps. (2) The recipe function of CiteCada 5.30 is expanded by the scripting language CiCode. The latest version of CiteCada has integrated Cirecipe into the standard configuration as an ActiveX control, which greatly improves the configuration efficiency. (3) It is designed for future expansion of system functions. 5 Conclusion In summary, the SCADA system architecture based on open fieldbus products, combined with PLC/PC and industrial control software, has the characteristics of flexibility, diversity, advanced technology, openness, short implementation cycle, and low cost (including operation, maintenance, and upgrade costs). It can seamlessly and freely combine different types of products from different companies into one, and based on integrated network platform technology, it realizes the needs of safety, transparency, and economy. Among them, the solution of combining fieldbus with Ethernet is the mainstream and hot spot of future automation development, and it is believed that its use in various industries will increase. References [1] Yang Xianhui. Fieldbus Technology and Its Application [M]. Beijing: Tsinghua University Press, 1999. [2] Qin Qiang. Open Fieldbus Originating in Asia and Facing the World [J]. Domestic and Foreign Mechatronics Technology, 2001, (5). About the Author Zhong Hua (1964-) Male Electrical engineer of Shanghai Dahe Weighing Instrument Co., Ltd., mainly engaged in the design, research and application of weighing and automation.