Abstract This paper addresses the problems of high water consumption and low level of automation in the irrigation system of a garden nursery. A programmable logic controller (PLC) is applied to achieve automatic monitoring of the irrigation system; frequency conversion technology is used to automatically adjust the pump speed based on water pressure, thus saving water and electricity. This achieves the goals of automatic monitoring and water and electricity conservation in the irrigation system, while also saving manpower, improving irrigation quality, and generating good economic benefits. Keywords : Programmable controller, frequency converter, automatic monitoring, water- saving irrigation in the nursery Plants, this article sets forth the following Points: applying the PLC carries out the automatic supervisory control to the irigation system; applying the frequency converter technique and utilizing the hydraulic Pressure regulates the rotate speed of the water pump automatically. benefits. Keywords： PLC efrquency conveertr automatic supervisory Controlling Water Saving Irrigation 1 Introduction Landscape flower and tree nurseries generally have three planting areas: outdoor sand bed nursery area, potted flower area, and greenhouse flower area. Traditionally, they mainly rely on outdated methods such as water pipe irrigation, water pipe spraying, and manual spraying for watering. This involves a large amount of manpower and wastes a lot of water resources; if a complete set of automatic irrigation monitoring systems is introduced, the price is high. To address the above problems, programmable logic controllers (PLCs) and frequency converters are applied to the irrigation water supply control system. This not only enables automatic monitoring of the irrigation water supply system of the flower and tree nursery, but also allows for flexible control of water application time according to actual needs, achieving the goals of saving water and electricity, reducing irrigation costs, and improving irrigation quality. 2 System Technical Requirements 2.1 Water Application Requirements The site mainly adopts three irrigation methods: outdoor sand bed nursery area spraying, potted flower area sprinkler irrigation, and greenhouse flower area drip irrigation. The three irrigation methods and irrigation time can be flexibly set according to actual needs. The irrigation system requires automatic control, opening and closing the water supply solenoid valves of each area as needed. The pressure is controlled within the range of 0.3-0.6MPa by using a towerless water supply device. This achieves the goal of saving manpower, water and electricity, and ensuring accurate control of irrigation time and improving irrigation quality. 2.2 Control Requirements (1) Manual and automatic control functions. Considering the reliability, flexibility and economy of the system, the system is required to have both manual and automatic control functions. (2) Other requirements. In case of rainy days, the automatic monitoring system is required to automatically stop the spraying of the outdoor sand bed nursery area and the sprinkler irrigation of the potted flower area according to the amount of rainfall, while the drip irrigation of the greenhouse flower area is not controlled by the amount of rainfall. 3 System Design Scheme 3.1 System Hardware Connection Diagram [align=center] Figure 1 System Hardware Connection Diagram [/align] As shown in Figure 1, the system hardware connection diagram shows that the system mainly consists of a time controller, a programmable controller, a frequency converter, a pressure sensor, a solenoid valve, a water pump, etc. 3.2 System Control Program Flowchart [align=center] Figure 2 System Control Program Flowchart[/align] 4 System Control Process 1. Selection of Programmable Controller: This system is an application system for switch quantity control. Based on the number and type of I/O points, the core component selected is the FXZN-32MR programmable controller from the FX2N series of Mitsubishi Corporation, Japan. Its input and output port allocation is shown in Table 1. [align=center]Table 1 Input and Output Port Allocation[/align] 2. Implementing Automatic Control Functions of Irrigation Water Supply System Using Programmable Controller Technology. The system uses a timer controller to time the opening and closing of the power supply and the time of each group of spraying, sprinkler irrigation, and drip irrigation. The switching signal 1 output by the timer controller is used to control the opening and closing of the power supply through contactor KM. The switching signals 2-7 output by the timer controller are used as the input control signals (XZ-X7) of the programmable controller. Based on the input signals, the outputs of the programmable controller (Y1-Y6) control the start and stop of each group of spraying, sprinkler irrigation, and drip irrigation via solenoid valves (YVI-Yv6). The working status of each group of solenoid valves is displayed by indicator lights (HL3-HLg), realizing the light alarm function of the solenoid valve control circuit on/off. The rainfall sensing mechanism signal (x10) automatically stops the outdoor sand bed nursery spraying and potted flower area sprinkler irrigation via the programmable controller, while the greenhouse flower drip irrigation is not affected by the amount of rainfall, achieving the purpose of automatic irrigation control. 3. Switches (XO, X)I are the stop and start control signals for the automatic operation of the programmable controller. During automatic operation, pressing the stop automatic operation signal SB7 (XO) and the start automatic operation signal SBS (XI) can realize the stop and start of the automatic operation process. 4. The output terminal (Y)0 controls the start and stop of the frequency converter via the intermediate relay, and then the frequency converter controls the start, stop, and operation of the water pump. 5. Utilizing the built-in IPD adjustment function of the frequency converter, the output frequency of the frequency converter is controlled by the analog output signal of the water pressure sensor (terminals 4 and 5 of the frequency converter); the output frequency of the frequency converter then controls the speed of the water pump, thereby achieving the purpose of automatically controlling the water pressure of the pipeline network and saving energy. The irrigation water supply network is monitored by the water pressure sensor. When the solenoid valve fails to operate, causing water supply blockage, the water pressure sensor sends a switch signal (xll), which is confirmed after a 3-minute delay; the programmable controller immediately stops the frequency converter, thus stopping the water pump. The normally open contact of the solenoid valve is used to realize the light alarm function for the on/off of the solenoid valve control circuit. The 24V DC power supply for the water pressure sensor is supplied by the programmable controller. 6. In case of a fault, the abnormal on/off signal (X12) is output at terminals A and C. The programmable controller immediately stops the frequency converter and stops all solenoid valves. At the same time, an alarm bell is output (Y7), which can be extinguished by button SBg (X13). Because there is only one motor, the overload protection function of the motor is achieved by utilizing the built-in electronic overcurrent protection of the frequency converter. 7. Frequency Converter Selection: The rated power of the water pump in the water supply system is 7.5kW, the rated voltage is 380V, and the rated frequency is 50Hz. A Mitsubishi FR-E540-7.skw frequency converter from Japan is selected based on the motor's power. 8. The automatic and manual control modes are switched using the changeover switch SA, indicated by indicator lights (HL1-HL2). In manual control, the operation of the water pump and the switching of each solenoid valve are manually controlled via buttons SBO-SB6, also indicated by lights (HL3-HLg). 9. The switching signal 1 output by the timer controller controls the opening and closing of the power supply via contactor KM. During non-system operating hours, the timer controller automatically disconnects the power supply to the programmable controller and the frequency converter. This reduces power consumption and extends the equipment's lifespan. The timer controller continues timing even during power outages, ensuring accurate control of irrigation time. Operators can control the start and stop of the entire system by operating the timer controller. 5 Conclusion After a year of operation, compared with the same period, the monthly water and electricity savings are more than 30%, and the number of workers has also decreased, resulting in significant economic benefits. References [1] Zhong Zhaoxin, Fan Jiandong. Programmable Controller Principles and Applications, South China University of Technology Press [2] Variable Frequency Technology, China Labor and Social Security Press [3] Mitsubishi Variable Frequency Speed ​​Controller User Manual About the Author Bi Guanghui, male, graduated from Southwest Jiaotong University in 1992 with a bachelor's degree in Electrical Engineering and Electrification. I have been engaged in teaching electrical automation and electrical skills training and guidance for many years as an electrical lecturer and maintenance electrician technician. I am currently mainly engaged in teaching and research on programmable controllers and frequency converters, as well as system design and installation guidance.