Abstract : To ensure a timely, accurate, and safe water supply, manual methods are labor-intensive, inefficient, and unsafe. Therefore, the water tower level control automation system was upgraded. A discrete component circuit was used to achieve automatic water tower level control, resulting in a low-cost, highly practical water tower level controller. This system includes functions such as water source detection. Independent circuits handle ultra-high and low water levels and automatically control the motor circuit. It can automatically complete the entire water supply and shutdown cycle, ensuring the water level remains within an ideal range. The upgraded water tower level control system achieves automatic water tower level control, remote monitoring, and unattended operation.
Keywords : cooling tower, automatic control, water tower level
DesignofAutomaticControlSystemforCoolingTowerWaterLevel
introduction
Water tower level control systems are widely used in residential water supply systems in my country. Traditional control methods suffer from low control accuracy and high energy consumption. Automatic control principles, however, adjust system operating parameters automatically based on changes in water consumption to maintain constant water pressure and meet water demand, thus improving the quality of the water supply system. In recent decades, automatic control technology has developed rapidly and has been widely applied in industrial and agricultural production, transportation, national defense, and aerospace industries. With the development of production and science and technology, automatic control technology has now permeated various scientific fields, becoming an important factor in promoting modern production development and scientific and technological progress. Examples include applications in daily life such as temperature and humidity control, automatic washing machines, vending machines, automatic elevators, air conditioners, refrigerators, automatic streetlights, automatic doors, and security systems. In industry, it is mainly divided into two categories: one is for industries involving gases, liquids, powders, petrochemicals, pharmaceuticals, light industry, food, and building materials, which require control of parameters such as temperature, pressure, level, flow rate, and composition. The other category involves the further processing of pre-formed materials or the assembly of multiple pre-formed materials, mainly controlling parameters such as displacement, speed, and angle. These all require the application of knowledge from the discipline of automatic control. Control theory is generally divided into two main parts: classical control theory and modern control theory.
The water industry is a leading force in promoting the industrialization of water technology. Water supply is one of the main areas of investment in urban infrastructure. Institutionally, the reform of water supply enterprise systems has become an inevitable trend in market-oriented development. Technologically, the water supply industry faces urgent requirements for the localization of key water supply equipment, the standardization of complete sets of process technologies, and the modernization of automatic control systems. High-quality water supply is a new growth point for the market-oriented development of the water industry. At the same time, it is necessary to advocate water conservation, improve water reuse rates, and gradually establish a comprehensive water industry discipline system. A comprehensive water industry discipline system is a necessary guarantee for the development of the water industry. The traditional water supply and drainage engineering discipline system can no longer fully encompass the rich connotations of the water industry and cannot adequately meet the needs of its development. The water industry discipline system is composed of water supply and drainage engineering disciplines, including: water quality and water treatment technology, water industry engineering technology, basic science of water treatment, water social science, and water industry equipment manufacturing technology. These disciplines collectively support the water industry's industrial system, with water quality and water treatment technology and water industry engineering technology being the leading disciplines within the water industry discipline system.
The emergence of modern control theory stems from the rapid advancements in science and technology, particularly the development of space technology and high-speed aircraft. This has led to increased demands for high speed and precision in controlled objects, while system structures have become more complex. Control theory is now required to address the design problems of dynamically coupled multi-input multi-output, nonlinear, and time-varying systems. Furthermore, the requirements for control performance are constantly increasing, often demanding optimal performance in certain areas and adaptability to environmental changes. These new requirements, which cannot be met by classical theory, have paved the way for the formation of modern control theory. [The last sentence appears to be an unrelated description of a specific device:] With its simple structure, long service life, high reliability, convenient operation and maintenance, and economic practicality, it is an ideal device for various high-level liquid storage applications.
1. Overview of Automatic Water Level Control System
The water tower level control system uses AC voltage to detect the water level. When the water level is below the lower limit (point B), the water pump starts pumping water. When the water level reaches the highest water level (line A), the water pump stops pumping water. When the water level drops below the lowest water level (line B), pumping resumes. This achieves automatic control.
This system employs discrete component circuits to achieve automatic control of the water tower level, resulting in a low-cost, highly practical water tower level controller. Discrete circuits handle both high and low water levels, and the motor circuit is automatically controlled. The system automatically adjusts its operating parameters based on changes in water consumption, maintaining constant water pressure to meet water demand and thus improving the quality of the water supply system.
Figure 1. Structure diagram of cooling tower water supply system
Water tower level control systems are widely used in residential communities in my country. Traditional control methods suffer from low accuracy and high energy consumption. Automatic control, however, adjusts system parameters based on water consumption changes to maintain constant water pressure and meet water requirements, thus improving the quality of the water supply system. It is also low-cost, easy to install, and has been proven through numerous experiments to have good sensitivity, making it an ideal device for water conservation and convenient water tower level control for households and businesses. The water tower level control system uses AC voltage to detect the water level. When the water level falls below the lower limit, the water pump starts pumping; when the water level reaches the upper limit, the pump stops pumping; and when the water level drops back to the lower limit, pumping resumes. This achieves automatic control.
This system employs discrete component circuitry to achieve automatic control of the water tower level, resulting in a low-cost, highly practical water tower level controller. Discrete circuitry is used to handle ultra-high and low water levels, and the motor circuit is automatically controlled.
It can automatically complete the entire working cycle of water supply and shutdown, ensuring that the liquid level is always within an ideal range. It has a simple structure, low manufacturing cost, high sensitivity, and significant energy savings, making it an ideal device for various high-rise liquid storage.
The system simulates an automatic water supply control for a water tower by using indicator lights to simulate a water pump and a toggle switch to simulate a water level monitoring signal. When the water level in the tank is below the low-level interface (S1 is ON), solenoid valve Y opens to allow water in (Y is ON), and a timer starts. After 4 seconds, if S1 is still not OFF, the indicator light for valve Y flashes, indicating that valve Y is not receiving water and has malfunctioned. When S3 is ON, valve Y closes (Y is OFF). When S1 is OFF and the water level in the tower is below the low-level water level boundary, S3 is ON, and water pump M starts pumping water. When the water level in the tower is above the high-level water level boundary, water pump M stops. Table 1-1 shows the wiring diagram for the simulated water tower water level control.
Table 1-1 Wiring List for Water Tower Level Simulation Control
2. Working principle of the PID control system for water tower level
Traditional water tower level control methods have drawbacks such as large footprint, high investment, frequent pump motor starts, high power consumption, unstable water pressure in the pipeline network, frequent pipe bursts, and serious water leakage. Not only is domestic water susceptible to secondary pollution, but the frequent pump motor starts also lead to a high equipment failure rate and difficulties in inspection and maintenance. Therefore, finding effective ways to utilize water and electricity to ensure normal water supply for various industries is now an urgent matter.
This system uses a PLC to achieve automatic control of the water tower level, designing a low-cost, highly practical water tower level controller. The system features water source detection and other functions. It employs an independent circuit for water level detection and processing, and automatically controls the motor circuit. It can automatically complete the entire working cycle of water filling and stopping, ensuring the water level remains within an ideal range. With its simple structure, low manufacturing cost, high sensitivity, and significant energy savings, it is an ideal device suitable for various applications.
To achieve precise water level control, an automatic control system must be established. Based on the inlet and outlet water levels in the water tower, the operation and shutdown of the water pumps can be automatically controlled, maintaining a dynamic equilibrium of the water level. The control system mainly consists of two parts: water level simulation detection and execution.
Based on traditional water tower and water tank supply systems, a PLC and hydraulic transmitter have been added. The PLC and configuration software are used to control the water level in the water tower, providing a practical water tower level control scheme. The system uses only proportional and integral control; the loop gain and time constant can be initially determined through engineering calculations, but further adjustments are needed to achieve optimal control performance. During system startup, the outlet is closed, and the control input controls the liquid valve to raise the water level to 75% of full capacity. Then, the outlet is opened, and simultaneously, the control input switches the liquid valve from manual to automatic mode. This switching is controlled by a single digital input.
The "Automatic Water Level Control System for Water Towers" controls a water pump in a water tower or storage tank. The tank is divided into four levels from bottom to top: B, C, D, and E. Under normal circumstances, the water level is controlled between C and D. When the water level is below point C, the water pump starts filling. When the water level is above point D, the water pump stops filling. When the water level is below point C and reaches point B, an alarm is triggered, and the water pump is manually restarted. 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 water flowing out from the overflow outlet.
① When the water level is below point B, indicator lights B, C, D, and E will all light up, and the alarm circuit will start to sound, i.e., the lower limit alarm.
②When the water level is between B and C, indicator light B goes out, while C, D, and E light up, and the water pump starts to fill with water.
③ When the water level is between C and D, indicator lights B and C will be off, while C and D will be on, maintaining the state that water is continuously flowing in.
④ When the water level is between D and E, indicator lights B, C, and D are off, and E is on, indicating a stopped state, meaning the water pump is not working.
⑤ When the water level is above point E, indicator lights B, C, D, and E all go out, the water pump stops 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 silence the alarm. The alarm confirmation light will then illuminate. After troubleshooting, the alarm confirmation light must be turned off to reset the alarm confirmation circuit and restore its fault monitoring function.
3. Water level closed-loop control system
Figure 1. Schematic diagram of water supply system control principle
M1, M2—Water pumps; Y0-Y3—Level switch; F1—Manual valve; F2—Solenoid valve
To achieve precise water level control, 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 maintain a dynamic equilibrium of the water level.
The basic principle of the water supply system is shown in Figure 3-5. The closed-loop water level regulation principle is as follows: Three hydraulic transmitters in the water tower convert the water level value into a 4-20mA current signal, which is then fed into the PLC. This signal is compared with the set value program in the PLC, and the final program is executed. The water level in the water tower is automatically controlled by switching the water pump on and off. If the PLC malfunctions, a manual control system is also available to control the water level in the water tower. The manual control uses an AC contactor.
When the water level in the upper tank is below Y3, M1 and M2 operate simultaneously, and F2 opens. When the water level rises to Y2, M2 stops, F2 closes, and M1 continues to operate. When the water level rises to Y1, M1 also stops. Opening the F1 hand valve allows water to drain from the upper tank, causing the water level to drop. When the water level falls below Y1 again, M1 starts operating. If the F1 opening is large and the outflow exceeds the inflow, causing the water level to continue dropping to Y2, M2 starts operating while F2 opens, significantly increasing the inflow and maintaining the water level. Y0 is the lower tank water shortage alarm switch. When the water level in the lower tank is below Y0, it means that the water pump inlet is short of water. At this time, the power should be automatically cut off and an alarm should sound.
4. Conclusion
This paper studies and designs a water tower level control system that uses a programmable logic controller (PLC) and a frequency converter to achieve stepless speed regulation of the water pump motor based on changes in water consumption via a pressure transmitter. This maintains a constant water pressure to meet water demand, thus achieving constant pressure water supply. This design presents a low-cost, highly practical water tower level controller. Discrete circuits are used to handle ultra-high and low water levels and automatically control the motor circuit. It can automatically complete the entire working cycle of water supply and shutdown, ensuring the liquid level remains within an ideal range. With its simple structure, low manufacturing cost, high sensitivity, and significant energy savings, it is an ideal device for various high-rise liquid storage applications.
