I. Introduction This project is a centralized control system for multiple vulcanizing tanks in the vulcanizing workshop of a synchronous belt factory in Zhejiang Province. The client required the system to both monitor the working status of all vulcanizing tanks in the monitoring room, enabling remote human-machine interaction, and to allow on-site operation and human-machine interaction at each vulcanizing tank. Due to the large number of vulcanizing tanks, the client demanded "functionality met and lowest cost" for the on-site human-machine interaction equipment. Based on this requirement, we designed a master-slave control system consisting of an industrial PC, a text-based human-machine interface, and a PLC controller. Practice has proven that this system effectively meets the client's requirements. II. Control System Design Scheme The hardware composition of the control system is shown in Figure 1. As can be seen from the figure, in this control system, the master controller is an industrial PC, and the slave controllers are a POP-HMI text-based human-machine interface + programmable logic controller (LG PLC) system. The POP-HMI text display is a low-cost HMI product selected for the on-site human-machine interaction requirements of the vulcanizing tanks. POP-HMI is a text-based human-machine interface product independently developed by Shanghai Boshen Electronics. This text display uses a monochrome (3.7") graphic dot-matrix LCD screen, providing display of Chinese characters, Western characters, numbers, and simple graphics; it uses a membrane keypad, providing functions such as number and parameter input, and custom input. It can easily connect to various manufacturers' programmable logic controllers (PLCs) and various electrical devices with serial communication capabilities, making it the best choice for low-cost field control equipment. The POP-HMI configuration development software is based on the Windows platform, with a user-friendly interface that is simple and easy to use, allowing developers to master its use in a short time. The programmable logic controller is the LG K120S series PLC, which supports both RS232 and RS485 dual serial communication, providing powerful communication capabilities. The LG PLC controlling each vulcanizing tank is remotely connected to a computer via its RS485 bus to form a centralized control system. During communication, the main control computer is the master station, and each vulcanizing tank PLC is a slave station. The communication protocol follows the MODBUS communication protocol, and the number of slave stations is currently 12. The POP-HMI text display is connected via LG... The PLC's programming port (RS232) connects to the LG PLC, using the LG PLC's proprietary communication protocol. III. Control System Function Description The main control computer in the control system is responsible for setting vulcanization process parameters, displaying operating status, recording fault alarms, and centrally managing production status for each vulcanizing tank in the entire vulcanization workshop. The POP-HMI text display is responsible for displaying the on-site operating status, setting and modifying parameters for each vulcanizing tank; the PLC controller is responsible for sequential control of the equipment, acquiring and inputting sensor signals, and communicating with the main control computer. This control system has two operating modes: manual and automatic. In manual mode, the POP-HMI text display on each vulcanizing tank's control panel is used for manual parameter setting and displaying the on-site status of each tank. In automatic mode, the vulcanization process parameters are set by the main control industrial computer; the operating status and fault alarm information of the vulcanizing tanks can be displayed simultaneously on the main control computer's monitor and the on-site POP-HMI text display LCD screen in both modes. IV. Control Software Function Description 1. Monitoring Room Industrial PC Software Functions * Setting Vulcanization Process Parameters for Multiple Tanks * Multiple vulcanizing tank operation status monitoring * Multiple vulcanizing tank fault alarm display and recording * Generation and printing of work reports 2. On-site POP-HMI text display software functions * Single vulcanizing process parameter setting * Single vulcanizing tank operation status monitoring * Single vulcanizing tank fault alarm display and recording V. Conclusion This master-slave control system has been debugged and tested. Practice has proven that the slave station of the control system, by using the low-cost, small POP-HMI human-machine interface, meets the user's requirement for "lowest cost of function implementation" for on-site human-machine interaction. Through the design and development of this control system, a typical application example of using the POP-HMI small text human-machine interface for low-cost on-site human-machine interaction in equipment is provided.