Abstract: This paper describes the application of automated devices in a water tower water level control system. By analyzing the shortcomings of several automatic water tower water level control systems, an improved design idea is proposed. After hardware design and debugging, the design of a water tower water level controller is completed. Keywords: Automatic control system, water tower, water level In today 's society, automated devices are ubiquitous. Driven by the demand for control technology, control theory itself has also made significant progress. The monitoring and control of water tower water levels no longer require manual operation. Practice has proven that automated operation has irreplaceable application value. The automatic water level controller for water towers has the function of detecting and controlling various liquid levels. The design analyzed its advantages and disadvantages, considered the resistance of various liquids, and is a product that can be put into actual production. 1. Design Analysis: The controlled object of the "automatic water level control system for water towers" is a water pump, and the container is a water tower or storage tank. Under normal circumstances, the water level is controlled between points C and D, as shown in Figure 1(a). When the water level is below point C, the water pump starts to fill water, as shown in Figure 1(b). When the water level is above point D, the water pump stops filling water, as shown in Figure 1(c). When the water level is below point C and reaches point B, an alarm is triggered, and the water pump is manually started, as shown in Figure 1(d). When the water level exceeds point D and reaches point E, an upper limit alarm is triggered, and the water pump is forcibly stopped, with the water flowing out from the overflow port, as shown in Figure 1(e). [align=center] Figure 1 Design Analysis Schematic Diagram[/align] To accurately control the water level, a closed-loop control system must be established. Based on the inlet and outlet water levels in the water tower, the water pump can be automatically controlled to keep the water level in a dynamic equilibrium state. 2 Analysis of existing design schemes: (1) Automatic water level controller composed of 555 timer. As can be seen from Figure 2, the circuit design is too simple and does not consider the troubleshooting method for abnormal situations. For example, if the probe fails, the system cannot detect it, resulting in abnormal operation of the water level controller; no alarm circuit is designed, and it is not convenient to read the actual water level value. [align=center] Figure 2 Automatic water level control system[/align] (2) Automatic water level control system designed with 51 microcontroller. The 51 microcontroller is actually a small microcomputer. In addition to the hardware circuit connection, software development and application are also required. This will make the design very complicated. At the same time, from the perspective of electromagnetic compatibility, the software design has system instability. In practical applications, in order to meet the actual conditions of the factory, most automated control devices adopt pure hardware circuit design. In addition, the circuit cannot detect the conductivity of the liquid and is not suitable for the situation where the liquid properties in the water tower change. [align=center] Figure 3 Water tower water level control circuit[/align] 3 Optimal scheme: 3.1 System block diagram The control system is mainly divided into two parts: analog detection and logical judgment. As shown in Figure 4, the simulated detection actually measures the potential difference between four probes (B, C, D, and E) and point A (i.e., ground). In the water tower, the four probes (B, C, D, and E) in the clear water are essentially connected to probe A via a variable resistor. When the resistance changes, the potential values ​​at each point differ. Through logical judgment, different outputs are obtained, i.e., different actions are controlled. [align=center] Figure 4 System Block Diagram[/align] 3.2 Schematic Diagram Figure 5 shows the schematic diagram of the optimal solution. As shown in the figure: Under normal circumstances, the water level should be between C and D. At this time, the logic level of the four probes B, C, D, and E is 0011, i.e., in a hold state. When the water level is below point C and between B and C, the logic level of the four probes B, C, D, and E is 0111, i.e., in a water intake state. When the water level is above point D and between D and E, the logic level of the four probes B, C, D, and E is 0001, i.e., in a stop state. When the water level is below point B or above point E, the logic level of the four probes B, C, D, and E is 1111 or 0000, and the water tower's alarm circuit starts working, generating a lower limit alarm or an upper limit alarm, i.e., low alarm and high alarm. At this time, the alarm equipment needs to be manually turned off by the staff to clear the alarm. [align=center] Figure 5 Final wiring diagram of the water tower water supply system[/align] 3.3 System Optimization As can be seen from Figure 5, each of the four probes B, C, D, and E is connected to an operational amplifier. In actual operation, when a probe malfunctions, the system can detect it in time and will not cause false alarms. Meanwhile, an alarm confirmation circuit was added. This way, the alarm device will be activated when a malfunction occurs or the water level in the water tower is too low or too high. Once an alarm is triggered, the problem can be addressed promptly. After the problem is resolved, staff can manually deactivate the alarm device. Therefore, the optimized solution enhances the system's reliability, stability, and practicality. 4 Feasibility Test of Water Tower Level Controller 4.1 Feasibility Test Figure 6 shows the front view of the water tower level controller, which consists of a power indicator light, an alarm confirmation light, a water level indicator light, and an alarm confirmation switch. When the power is on, the power indicator light is on. When the water depth in the water tower is at different positions, the water level indicator lights B, C, D, and E show different conditions. [align=center] Figure 6 Appearance of Water Tower Level Controller[/align] ① When the water level is below point B, indicator lights B, C, D, and E are all on, and the alarm circuit starts to alarm, i.e., a lower limit alarm. ② When the water level is between B and C, indicator light B is off, and C, D, and E are on, and the water pump starts to fill the tank. ③ When the water level is between C and D, indicator lights B and C are off, while C and D are on, maintaining the inlet water flow. ④ When the water level is between D and E, indicator lights B, C, and D are off, while E is on, indicating a stopped water flow, meaning the water pump is not working. ⑤ When the water level is above point E, indicator lights B, C, D, and E are all off, the water pump is not working, and the alarm circuit starts to trigger an overflow alarm, i.e., an upper limit alarm. ⑥ The alarm circuit can be manually shut off. Simply press the alarm confirmation switch to deactivate the alarm. At this time, the alarm confirmation light will illuminate. After troubleshooting, the alarm confirmation light must be turned off, the alarm confirmation circuit will reset, and its fault monitoring function will be restored. 4.2 Feasibility Analysis This scheme adopts a pure hardware circuit design, avoiding the instability factors in software program design and improving reliability in practical applications. Furthermore, this system has good compatibility with different types of liquids. When the liquid in the water tower changes, simply adjusting the resistance value in the potentiometer to the same order of magnitude as the resistance value of the liquid will easily achieve the water level control operation for that liquid. The test proved that this water tower level controller not only achieves precise control of the water tower level, but also has practicality for industrial production. 5 Conclusion This article introduces the self-designed water tower level controller and systematically elaborates on the design scheme and finished product test. The test proved that the system has high stability during operation and fully meets the pre-specified standards. It is a water tower level controller that can be put into production. References: (1) Hu Shousong, ed. Automatic Control Principles. Fourth Edition. Beijing: Science Press, 2001 (2) Liu Bao, ed. Modern Control Theory. Second Edition. Beijing: Machinery Industry Press, 2004 (3) Gene F. Franklin, J. David Powell, Abbas. Emami-Naeini, Feedback Control of Dynamic Systems, Publishing House of Electronics Industry (4) Zhu Xiaoqing, ed. Process Detection and Control Technology and Application. Beijing: Metallurgical Industry Press, 2002. (5) Yao Bowei and Sun Rui, eds. Fundamentals of Control Engineering. Beijing: National Defense Industry Press, 2002. (6) Li Chaoqing, ed. Microcontroller Principles and Interface Technology. Concise Revised Edition. Beijing: Beijing University of Aeronautics and Astronautics Press, 1998. (7) Dai Wenjin and Zhang Weiguo, eds. Automation Professional English. Wuhan: Wuhan University of Technology Press, 2001. (8) Tan Zhenfan, ed. Automatic Control Professional English. Harbin: Harbin Engineering University Press, 1999.