Introduction Small pumping stations with a total installed capacity of less than 1000kW constitute a significant proportion of farmland irrigation and flood control pumping stations. Traditional single-unit control and centralized control methods result in high operation and management costs, especially in clustered small pumping stations with an installed capacity of less than 100kW in farmland irrigation and crop sprinkler projects. Manual operation is crucial, with labor costs accounting for a large proportion of operating costs. To reduce operating costs and improve automation of small pumping stations, a programmable logic controller (PLC) is adopted for control based on the operational characteristics of these stations. By setting operating programs, the entire pumping station can be operated and monitored, achieving semi-unmanned or unmanned operation. Networking via wireless transmission equipment enables unmanned group control of multiple pumping stations within a range of tens of kilometers, significantly reducing labor costs and allowing more limited operating funds to be used for equipment upgrades, repairs, and maintenance, thus effectively improving equipment integrity and availability. I. Automatic Data Acquisition and Detection Automatic data acquisition and detection mainly fall into two categories: analog data and digital data. The analog signal detection data mainly includes: water level, motor operating current, pump shaft temperature, motor temperature, and flow rate. The digital signal detection data mainly includes: the status of the vacuum circuit breaker in the pump high-voltage starter cabinet and the vacuum contactor in the reactor cabinet; the operating status and opening/closing position of the electric valve; the operating status of the vacuum pump; the status of the solenoid valve; the vacuum degree of the pump suction pipe; and the pump outlet pressure. Automatic data acquisition is mainly implemented by the PLC. The PLC's analog input module continuously detects the water level in the water tank through sensors, converts and processes the water level change signal, calculates the rate of rise of the water level in different segments per unit time, thereby determining the mine's water inflow and controlling the start and stop of the drainage pump. Sensors and transmitters for motor current, pump shaft temperature, motor temperature, and drainage pipe flow rate are mainly used to monitor the operating status of the pump and motor, providing over-limit alarms to prevent damage to the pump and motor. The PLC's digital input module collects various switching signals into the PLC as conditions and basis for logic processing to control the start and stop of the drainage pump. During data acquisition, the processing of analog signals involves converting analog signals into digital signals (A/D conversion), and the conversion speed is determined by the sampling law. Generally, the sampling frequency should be more than twice the highest frequency component in the analog signal, so that the accuracy of the A/D conversion can be completely restored to the original accuracy of the analog signal. The accuracy of the A/D conversion depends on the number of bits of the A/D converter. At the same time, the A/D modules used by the PLC all use integral conversion, which can average the spike noise and induced noise of the input signal, making it suitable for industrial sites with severe noise. II. System Functions and Features (1) The PLC control program adopts a modular structure, and the system can be debugged and run in segments according to the program modules. This program structure is clear, simple, easy to understand, easy to simulate and debug, and has a fast running speed. (2) The system automatically realizes the rotation of water pumps according to the water level and pressure control principle, which extends the service life of the water pumps. (3) The system can automatically select and start the nearest vacuum pump according to the location of the pump group in operation. If the vacuum degree cannot be reached within the time set by the program, the standby vacuum pump will be automatically started. (4) The system determines the start and stop times of water pumps based on the power grid load and the power supply price time periods of flat, valley and peak periods stipulated by the power supply department, in accordance with the principle of "peak avoidance and valley filling", so as to make reasonable use of power grid information and improve the power grid operation quality of the mine. (5) The PLC automatically detects the water level signal, calculates the rate of rise of water level in different water level segments per unit time, thereby judging the water inflow of the mine, automatically puts on and takes off the number of water pumps in operation, and reasonably schedules the operation of water pumps. (6) The system dynamically monitors the operation status of water pumps and their auxiliary equipment on the touch screen, displays parameters such as water level, flow rate, pressure, temperature, current and voltage in real time, alarms when exceeding limits, automatically pops up the fault screen, and automatically flashes the fault point. It has functions such as fault recording and historical data query. (7) The system has a communication interface function. The PLC can communicate with the touch screen and the ground monitoring host at the same time to transmit data, exchange information, and realize remote measurement and control functions. (8) The system protection functions include the following. Over-temperature protection: When the bearing temperature or stator temperature exceeds the allowable value during long-term operation of the water pump, an over-limit alarm is triggered by the temperature protection device and PLC. Flow protection: When the water pump is started or running normally, if the flow rate does not reach the normal value, the flow protection device stops the water pump and automatically switches to starting another water pump. Motor failure: The PLC and touch screen monitor electrical faults such as overcurrent, leakage, and low voltage of the water pump motor and participate in the control of electric gate valve failure: The motor protection system monitors the gate valve motor for overload, short circuit, leakage, phase loss, and other faults and participates in the interlocking control of the water pump. (9) The system control has three working modes: automatic, semi-automatic, and manual. III. System Scheme 1. Production process analysis Taking a small drainage pumping station with an installed capacity of 6 units of 37kW as an example, its operation process is shown in Figure 1. This type of pumping station mainly operates by rotating and circulating water pumps. The number of pumps in operation is automatically adjusted according to the inflow and water level of the inlet pool to maintain the water level of the inlet pool at a relatively stable predetermined point. 2. Requirements of the process flow for the system (1) Number of pumps started and running time: The number of pumps started and the running time are determined according to the inflow and water level of the inlet pool. (2) Start-up and circulation of pumps: The system is required to achieve the same start-up and shutdown time for each unit in a cycle when it is not necessary to start 6 pumps at the same time. This is done by adding or removing 1 pump in each time period, so as to avoid some units working continuously for too long and some units running for too short time, and effectively avoid some units being worn out and some units being shut down for a long time. (3) Electrical control: The pumps are required not to start and stop frequently in a short period of time, which would affect the stability of the power distribution system. The pump has reliable and reasonable overload and overcurrent protection during startup and operation, and has low water level protection, high water level alarm, large inflow warning and continuous water level measurement functions. 3. System Structure The system mainly consists of: PLC main control module, power supply module, touch screen, digital and analog input and output modules, field instruments and other auxiliary equipment. The structure is shown in Figure 2. (1) PLC main control module: responsible for issuing and receiving various operating program instructions, is the central part of the entire control system, and requires high reliability and stability. (2) Power supply module: a stable and reliable power supply is an important condition for the safe and reliable operation of the entire system. The power supply module is required to be stable and reliable, and have a certain power margin. 2.3.3 Touch screen: the touch screen is the human-machine interface device in the entire system. It is required to be durable and beautiful, and can clearly display various operating and setting information. 2.3.4 Digital and analog input and output modules: this part is the key equipment for the PLC device to correctly receive information and issue instructions. It is required to have high reliability and stability, and can realize certain electrical and magnetic isolation functions. 2.3.5 Field Instruments: The PLC system determines the operating status of the controlled equipment and whether it is suitable for the operating environment by receiving signals from field instruments. Therefore, field instruments are required to have high reliability, stability, and accuracy. 2.3.6 Other Auxiliary Equipment: Auxiliary equipment such as cooling fans and UPS uninterruptible power supplies are essential for the entire system and greatly contribute to improving system reliability and lifespan. 2.4 System Selection Example: Taking a flood control and drainage pumping station already in operation as an example, the main control module is a Mitsubishi FX2N-48MR PLC module; the digital input expansion module and analog input expansion module are Mitsubishi FX2N-16EX and FX2N-4AD models respectively; and a 10-inch 16-color touchscreen is used. The wiring principle is shown in Figure 3. 4 Conclusion: Programmable Logic Controllers (PLCs) small-scale automatic control systems have advantages such as low cost, high reliability, low energy consumption, and suitability for operation under various environmental conditions. Furthermore, by changing the software settings without altering the system hardware composition, they can adapt to the needs of various process operation modes, making them an ideal replacement for traditional relay control. Especially in small pumping stations of farmland water conservancy systems, the realization of unmanned or semi-unmanned operation has broad application prospects and value. [b]References:[/b] ［1］Xu Xiaosong, Qian Cunyuan, Xie Weida. Soft stop control of asynchronous motor pump control soft starter[J]. Power Electronics Technology, 2001, 35 (3) ［2］Xue Junyi, Yao Yannan. Microcomputer Control System and Its Application[M]. Xi'an: Xi'an Jiaotong University Press, 1993 Editor: He Shiping