Abstract: This paper introduces an automatic control system for multiple siphon centrifuges based on a programmable controller. It focuses on the composition of the system, the functions of each part, and the control process. With the development of programmable controller functional modules, its application in industrial production process automation has been expanded. Keywords: Siphon centrifuge, programmable controller, communication 1 Introduction Siphon centrifuge is a centrifuge with a special structure. It adds a rotating siphon device to the drum of a scraper centrifuge, thus having advantages that ordinary scraper centrifuges do not have, namely, improving the filtration driving force and filtration efficiency, increasing production capacity, and extending the effective cycle [1]. However, the normal performance of the advantages of siphon centrifuge is based on the premise of accurate operation and control of the centrifuge. Siphon centrifuges are continuously operated and cyclical. The control between each process is strictly based on time or conditions. The opening and closing control of each valve and the coordinated work of the siphon tube cannot meet the requirements under general manual operation conditions. Programmable controller (PLC) is a computer control equipment commonly used in industrial sites [2]. With the enhancement of its extended functions and communication capabilities, it is increasingly used in complex distributed computer control systems. This paper utilizes the communication function of a programmable logic controller (PLC) to control the operation of multiple siphon centrifuges. This not only allows for accurate and decentralized control of each centrifuge to ensure normal and efficient operation, but also enables centralized acquisition, display, and modification of each centrifuge's operating parameters via a host computer, achieving the goals of control and risk dispersion, and centralized display and operation. 2 System Composition The system composition is shown in Figure (1). [align=center] Figure (1) Block diagram of the multi-centrifuge control system[/align] (I) PLC Functional Modules The PLC serves as the basic controller of the control system. The PLC collects signals downwards and controls the centrifuges in the industrial field. One PLC controls one siphon centrifuge. This includes controlling the start and stop of the centrifuge's main motor, the action of each solenoid valve, the advance and retreat of the siphon tube, and the control of display and alarms. The PLC collects analog signals in each sampling cycle, including the main motor's current signal, the temperature of the front and rear bearings of the main unit, and vibration signals. The PLC transmits field signals upwards through the data channel and receives signals from the host computer. As the main body of the entire control system, the performance and reliability of the PLC play a crucial role. We selected the S-series programmable logic controller from Guangyang Electronics Co., Ltd. Its module composition is shown in Table (1). Table (1) Composition of Programmable Controller Module The CPU is SZ-4, which can install 128 input/output points. The average processing speed of the instruction is 1-2.5µs, and there are 2 general communication ports. Z-4AD2 is a 4-channel voltage-type analog input module with DC0-5V input and 12-bit resolution. It mainly collects four analog signals: current, temperature and vibration. Z-16ND2 is a 16-point DC24V input module, which inputs the switching signals of start/stop buttons and limit switches. The two output modules are Z-16TD2, which are 16-point open collector outputs. They output the switch signals of contactors that control the start/stop of motors, various solenoid valves required for centrifuge operation, indicator lights and alarms. Z-01DM is a communication module, which facilitates signal transmission with the host computer. Z-05B is a power supply frame that can install 5 input/output modules. The rated power supply is AC100-200V 50/60HZ, and the output current is 2.6A. By calculating the total power consumption of all modules on the frame, it does not exceed the power supply capacity provided by the power supply frame, and it can be used safely [3]. (II) Process flow of centrifuge The centrifuge is mainly composed of spiral assembly, door cover assembly, drum assembly, base housing assembly, siphon assembly, transmission device, hydraulic system and electrical control system. The process flow diagram of centrifuge is shown in Figure (2). [align=center] Figure (2) Process flow diagram of centrifuge[/align] Each operation of each cycle of centrifuge is automatically completed under the control of the electro-hydraulic system. Manual operation can be used during the debugging stage of the machine. (III) Communication system Upper-level communication is carried out on the CCM network through the data communication module Z-01DM. The CCM protocol enables the communication host to maintain the initiative of communication, and the slave can only respond to its call. The communication station number, transmission mode and parity check mode are set by the system parameters. When connecting, the converter D-01CV is used to convert the RS-232C cable connecting the upper computer and the RS-422 cable connecting the PLC communication module. (iv) The host computer transmits or collects centrifuge operation information to the basic controller PLC and maintains and manages the PLC. The host computer is implemented using an industrial control computer and uses configuration software to implement graphical monitoring and human-machine interface. 3 Control Flowchart The control flow diagram of the PLC is shown in Figure (3). After the PLC is powered on, it first performs a system self-test, including checking the CPU module, the operating status, the battery system, the I/O module, and the communication function. The system normally performs periodic sampling of analog signals, and outputs an alarm when the upper limit value is exceeded. The system can be operated manually or automatically. Automatic operation follows the centrifuge process flow and is executed in the order of the process, with time or conditions as the start or end of each process. [align=center] Figure (3) System Control Flowchart[/align] 4 Conclusion Due to the development of programmable controllers in analog signal processing, operation instructions, control laws, and communication functions, its application field in industrial power field control has been broadened. As a separation device with a unique structure, the siphon centrifuge is very suitable as a control device for its process characteristics and operation control requirements, so as to give full play to the high efficiency advantage of the siphon centrifuge. References [1] Huang Jiaming Rotary Siphon Centrifuge [J] Chemical Machinery 1981 (6): 14-19 [2] Pi Zhuangxing et al. System Design and Application Examples of Programmable Controllers [M] Machinery Industry Press 2000 [3] S Series Programmable Controller SZ-3/4 User Manual [Z] Huaguang Electronics Industry Co., Ltd. 1997