Keywords: Small concrete batching plant, human-machine interface - touch screen programmable controller 1. Introduction A batching plant, if not a large-scale professional commercial concrete production plant, can be defined as a small concrete batching plant. During construction, due to regional and other limitations, commercial concrete is unavailable, and construction concrete must be mixed in-house. Developing a practical and simple "Small Concrete Batching Plant Control System" is of great significance for this type of concrete production, greatly improving automation and reducing the labor intensity of workers. This control system is stable and reliable. It can automatically and continuously control the metering, feeding, mixing, and discharge of materials according to the set formula. The system can also print data. Furthermore, by using drop correction, the production accuracy of concrete is improved. 2. System Structure 2.1 Hardware Structure The hardware structure of the control system is shown in Figure 1. The system consists of two parts: a control cabinet and a power cabinet. The control cabinet consists of a human-machine interface, PLC, control panel, and intermediate relay group, installed in a convenient location in the operator's room. The intermediate relay group is powered by 220VAC. The power cabinet mainly consists of AC contactors, installed on the main mixer body, minimizing the wiring of high-power motors. The two parts are connected by a power cable and a set of control cables. This effectively reduces signal interference and improves control reliability. The PLC uses a Delta DVP-EH series controller. It is a high-speed, tightly controlled programmable controller composed of a power supply, central processing unit, and I/O components. The I/O ports are equipped with 1500V high-voltage isolation devices. The power supply is 220VAC. Communication with the human-machine interface (HMI) is achieved via an RS-485 port. Inputs include switch signals and analog signals from sensors, which are then converted and processed by an A/D converter and the CPU. Outputs drive AC contactors via intermediate relays to control the operation of field electrical appliances. The HMI uses a Delta DOP series product, powered by an AC/DC adapter (24VDC). Operators input production parameters through the HMI and touch the "Automatic Stirring" button, which automatically and continuously completes the process flow. The "Pause" button pauses or resumes the running program. A print port allows direct output of printed data. Because the system must have manual operation functionality while meeting fully automated production requirements, a control panel is added to the control cabinet. Manual operation allows each action to be performed independently. 2.2 Software Structure The HMI (Human Machine Tool) is written using Screen Editor 1.05.75 software. It includes screen options such as the main monitoring screen for the mixing plant, system settings, formula settings, drop correction, print settings, and help documentation. The PLC program is written directly using ladder diagrams. It reads/writes HMI data, collects field data, and compares and calculates based on set values. It automatically completes process control for batching, metering, feeding, mixing, and concrete discharge. 3. Operation Control System operation is divided into three steps: data processing, process control, and power output. The HMI completes data processing, the PLC performs process control, and the AC contactors provide power output to drive and control the operation of field electrical appliances. For specific operation details, please refer to the system's "Help" documentation. To ensure system stability and reliability, the following measures are taken to reduce interference and improve control accuracy: The PLC uses a separate power supply and a separate grounding wire. The grounding resistance of the entire system is required to be less than 1Ω. All AC contactors are equipped with RC snubbers. The DC cable of the intermediate relay is equipped with a diode snubber circuit. All low-voltage transmission cables are shielded, and the shielding layer is grounded at one end. 4. Conclusion The human-machine interface (HMI) is simple and intuitive, simulating the on-site process flow of the batching plant. Operators can understand the entire operating status of the batching plant on the touchscreen. Operation is extremely simple; it can be said that "operators only need to point and click on the touchscreen to complete the concrete mixing task." Authorized operators can also modify various parameters via the touchscreen. The hardware structure of the control system is shown in Figure 1.