Abstract: This paper analyzes the on-site conditions of a cigarette filter rod production line and introduces the automated and networked control process of the automatic glycerin ester conveying system for filter rod production using PLC+PC, including data acquisition and processing, detection and control of each link, and system monitoring and management. Keywords: Glycerin ester, PLC+PC, Automatic conveying control and management. Filter rod forming machines are the main equipment in cigarette filter production, and the curing agent used in their production is glycerin ester. Currently, forming machines in China only have one oil storage tank, and the glycerin ester in the tank is injected manually, averaging 2-3 times per shift. This results in high labor intensity for workers and unavoidable waste during the injection process, which is detrimental to enterprise management. Here, we introduce a PLC+PC automatic control and management system for glycerin ester. 1. On-site conditions and design concept Cigarette filter rod production lines generally consist of several to a dozen forming machines. This facilitates centralized automatic glycerin ester supply control and management. Each forming machine unit is both part of the production line and relatively independent. Therefore, the system design should include: ① The ability to detect the oil level, filling status, and start/stop status of each machine's oil tank, and to control the oil filling. The system should not be affected by the start-up, stop, or malfunction of a machine on the production line. Each machine should have a diagnostic I/O port for easy maintenance. ② The ability to control the injection and output of glycerin from the centralized oil supply tank, collecting and storing level and flow data, and displaying the data through a human-machine interface. Two pumps are used for glycerin injection into the tank, which can operate simultaneously or separately. Control can be manual or automatic. The system can accumulate and display the injected oil. Similarly, two pumps are used for grease output, operating in a one-on-one standby mode. Control can also be manual or automatic. The system can accumulate and display the total actual consumption. The oil tank filling control signal is generated by the tank level sensor, and the output signal is generated by the oil level sensor in each machine's oil tank. When there is no filling request on the production line, the output pump is in standby mode. The system has an alarm function. ③ The computer system in the workshop control room can remotely monitor and manage the entire glycerin automatic conveying system, and transmit information to the plant management control center via the network. During monitoring, the computer has a user-friendly interface with a full Chinese display. The main screen displays a 3D system status diagram, collecting, organizing, statistically analyzing, and displaying various system operating parameters, which can be retrieved and printed at any time. In case of a fault, it can automatically display the fault location, provide fault prompts, and automatically record the fault content and time. ④ The communication and control distance between the molding machine, glycerin tank, and workshop control room can reach 70m. 2. System Hardware Structure Based on the site conditions and design concept, the entire system is divided into a monitoring management layer and a field measurement and control layer, as shown in Figure 1, the system structure diagram. The monitoring management layer is handled by one PC, and the field measurement and control layer consists of a PLC master station and field machine slave stations. Each layer is connected via a PROFIBUS industrial fieldbus. Monitoring PC: An IBM PC equipped with CITECT V5 software and a CP5611 fieldbus interface card is used for monitoring. Data is acquired from the PLC and other data acquisition devices via the PROFIBUS-FMS industrial fieldbus. This connection between the industrial PC and the fieldbus forms a complete control network system capable of configuration, operation, management, storage, and printing. PLC Master Station: The PLC uses the SIMATIC S7-300 modular series, with the CPU315-2D modular medium-sized PLC as the master station. It has powerful processing capabilities and integrates a PROFIBUS-DP fieldbus interface. PLC programming and control are completed in the STES7 V5.1 programmer PG and written to the CPU315-2D. The CPU315-2D can then read the status words of all I/O modules on the bus, simultaneously controlling the injection and output of glycerin grease tank oil, acquiring and processing data on liquid level and flow rate, and controlling the ET200 slave station. For convenient field operation, the PLC is equipped with an independent OP operation panel, data processing display, and alarm functions. The main control and data acquisition input/output signals of the PLC are shown in Table 1. [align=center]Table 1 Mostly In-Out Signals[/align] Field Machine Slave Station: The slave station, centered on the ET200S remote I/O module, is used for detecting the oil level in the machine's reservoir, filling, and machine start/stop status, and for controlling the feeding. The slave station is installed inside the machine and connects to the PROFIBUS-DP fieldbus via the IM151 module. It provides output data to field devices and feeds input data to the CPU or host computer in master/slave mode. The I/O module has a programmable port for fault detection. 3. System Software Structure The system software mainly includes the PLC program, OP operation panel program, network configuration, and host computer monitoring software. 3.1 PLC Program The PLC program is written in the programmer PG. The SIEMENS SIMATIC S7-300's accompanying programming tool STEP7 V5.1 is used to complete hardware configuration, parameter setting, programming, testing, debugging, and documentation. A PLC program consists of organization blocks (OBs), functions (FCs), and data blocks (DBs). OBs are the interface between the system operating program and the user program, used to control program execution. The main program loops through OB1, using the CALL instruction to call the function FC program. OB1 is as follows: CALL FC1 CALL FC2 CALL FC3. FCs are user subroutines. For ease of programming and debugging, the user program adopts a modular structure, divided according to functional requirements: glycerol grease tank level and input/output flow data detection (FC1), glycerol grease input and output control (FC2), and slave station ET200 measurement and control (FC3), etc. The user program is written using a ladder logic diagram, as shown in FC3 below. DBs are user-defined storage areas for data access. In addition, the PLC program also includes auxiliary programs, such as loop interrupt OB35, time error OB80, power failure OB81, diagnostic interrupt OB82, insert/remove template interrupt OB83, CPU hardware error OB84, priority error OB85, rack failure OB86, communication error OB87, programming error OB121, access error OB122, etc. 3.2 OP Operation Panel Program: To facilitate on-site operation, an OP operation display panel is installed on the PLC master station control cabinet. It is configured using SIEMENS' SIMATIC Protool/Pro P5.0 software. Its main functions include system start/stop, automatic/manual switching, emergency stop, and display of on-site working status and data. 3.3 Network Configuration: Network configuration uses SIEMENS' SIMATIC NET, NCM S7 PROFIBUS configuration software to complete the PROFIBUS S7 communication network configuration. A CP5611 network card was installed on the upper microcomputer, and a CP342-5 communication module was installed on the PLC master station. The communication network hardware configuration between the upper microcomputer and the PLC master station was completed via a PROFIBUS S7 communication cable. 3.4 Monitoring Software Design: The monitoring computer user software was developed on the Windows 2000 platform using SIEMENS' CITECT V5 software. The monitoring computer outputs the operating status of each system device, the transient and cumulative flow of glycerin, and the glycerin tank level in the form of a 3D system status diagram. It can also operate the system by starting and stopping, selecting and controlling the output pump, and selecting and controlling the input pump. Additionally, it is equipped with STES7 V5.1, allowing for remote programming or modification of the PLC. To prevent unauthorized operation by non-professional personnel, a login window for designated personnel is provided. Since the user software runs on the Windows 2000 operating system platform, it facilitates the future establishment of a factory management network. 4. Other Considerations 4.1 Due to the harsh environment and significant interference in industrial settings, we use a 380/220V isolation transformer (with grounded inter-stage shielding) for the PLC's AC power supply, providing floating power to isolate interference introduced from the power grid. During wiring, PLC control signal lines are routed separately from AC power lines to minimize electrostatic and electromagnetic interference. This effectively isolates inputs and outputs, and high-voltage and low-voltage circuits, further reducing interference and preventing wiring errors. 4.2 Heat dissipation and dust prevention must be carefully considered in the control cabinet design. Since heat rises, heat-generating components should be placed in the upper part of the cabinet, and cooling fans should be added. The ventilation duct inlets and outlets should be dustproofed. 4.3 During on-site system commissioning, the PLC should perform counting and verification on flow meters, level gauges, glycerin tanks, etc. 4.4 If the monitoring computer, PLC, and ET200 are too far apart, a relay station should be considered. 5. Overview The automatic glycerol conveying system implemented using PLC+PC has been applied in cigarette factory production. Several years of practice have proven that the system has strong anti-interference capabilities and high control precision. It achieves full-scale, fully digital, and fully open automation and networking of the control process, including system data acquisition and processing, status detection and control of each system link, and system monitoring and management, thereby reducing production costs for enterprises. References: [1] SIEMENS, SIMATIC S7-300 Programmable Controller Hardware and Installation Manual. 2002.5 [2] SIEMENS, SIMATIC S7 V5.1 Programming Manual. 2002.5 [3] SIEMENS, SIMATIC S7-300 and S7-400 Statement List Programming. 2001.7 [4] SIEMENS, SIMATIC S7-300 and S7-400 Ladder Logic Programming. 2002.5 [5] SIEMENS, SIMATIC S7-300 and S7-400 Function Block List Programming. 2002.5 [6] Wang Yonghua et al., Modern Electrical Control and PLC Application Technology [M]. Beijing University of Aeronautics and Astronautics Press, 2003.9