Abstract: Based on the process characteristics of air-source heat pump water heater operation, this article introduces a computer monitoring system composed of a computer and a PLC. Using KingSCADA and a PLC, the system monitors the air-source heat pump water heater, including data acquisition and management of unit operation status, operation status display, fault alarm, and automatic switching of operating conditions. The monitoring system is simple, user-friendly, practical, and easy to operate. Keywords : KingSCADA, PLC, air-source heat pump water heater 0 Introduction Air-source heat pump water heaters are a type of high-efficiency energy-utilizing and environmentally friendly hot water system. It mainly consists of four parts: evaporator, compressor, condenser, and expansion valve. Its working process involves using a heat-absorbing medium (refrigerant) within the equipment to collect heat energy from the air or natural environment. After compression by the compressor, the temperature of the refrigerant is increased, and the refrigerant releases heat through a heat exchanger to heat the cold water, thus transferring heat from the environment to the water. The produced hot water is then delivered to users for heating or directly for hot water supply through a water circulation system. During the operation and testing of the air source heat pump water heater, real-time monitoring of the unit's operation is necessary to understand the process. Therefore, a computer monitoring system for the air source heat pump water heater based on KingSCADA and PLC was designed. 1. Design of the Air Source Heat Pump Water Heater Monitoring System The monitoring system mainly consists of a host PC system and a slave PLC control system. During operation, the slave PLC controls the operation of the water heater unit and continuously collects data from sensors at various test points, transmitting it in real-time to the host computer via an RS232 interface. The host computer then displays the water heater's operating test status in a graphical interface and saves the data transmitted by the PLC. Based on the required process, the monitoring system selected Mitsubishi's FX2N series PLC. The programmable controller primarily controls switching quantities, but this system requires the acquisition of temperature and pressure values. Therefore, an A/D conversion module is needed to convert the acquired analog temperature and pressure values ​​into digital values. This system uses the FX2N-4AD analog input module. The control block diagram of the monitoring system is shown in Figure 1. [align=center] Figure 1 Control Block Diagram of the Monitoring System[/align] 1.1 Upper Computer Monitoring Interface Design In the monitoring system, the upper computer monitoring software is written using the advanced domestic configuration software—KingView 6.5. KingSCADA 6.5 uses Windows as its operating platform and employs new technologies such as multithreading and COM components. It fully utilizes Windows' graphical editing capabilities, offering a user-friendly interface and ease of use. Each application can create an unlimited number of screens, easily forming monitoring displays. It boasts rich device drivers, flexible configuration methods, and data linking capabilities, making PC-based systems more versatile than industrial control systems developed using dedicated machines. This significantly reduces repetitive work for industrial control software developers and allows for secondary development using the abundant software resources of PCs. Using it to construct monitoring systems can greatly shorten development time and ensure system quality. When developing applications for a system using KingSCADA, three aspects must be considered: graphics, data, and connectivity. Specifically, what kind of graphical display does the user expect? How can data be used to describe the various attributes of the industrial control object? What are the connection relationships between the data and the elements in the graphical display? This system's monitoring includes two aspects: first, collecting relevant parameters of the air source heat pump water heater unit; then, analyzing the collected data to make corresponding controls to ensure the normal operation of the air source heat pump water heater unit and its compliance with process requirements. The monitoring interface designed based on the operating principle of the air source heat pump water heater is shown in Figure 2. The main control screen displays the operating status of the air source heat pump water heater in a simple and vivid way, dynamically displaying various monitoring parameters in real time, and allowing for relevant control of the air source heat pump water heater's operation. The monitoring system is designed with real-time display of fault alarm screens, query of historical alarms, and the ability to set alarm limit values. The historical curve screen can retrieve the historical records of various monitoring parameters, which are displayed in a curve form. The report screen allows for querying, editing, and printing of historical and real-time reports. [align=center] Figure 2 Monitoring Screen[/align] The screens created in the KingSCADA development system are all static, so these graphic objects must be animated to realistically describe the state changes of external objects and achieve the purpose of real-time process monitoring. The main method for implementing graphic animation design in KingSCADA is to establish a correlation connection between the graphic objects in the user window and the data objects in the real-time database, and set the corresponding animation attributes. During system operation, the appearance and state characteristics of the graphic objects are driven by the real-time acquired values ​​of the data objects, thereby realizing the animation effect of the graphics. The following is a partial design command language for the dynamic implementation of this monitoring system: if (\\this site\fan==1&&\\this site\fan movement<360) \\this site\fan movement=\\this site\fan movement+20; else \\this site\fan movement=0; if (\\this site\water valve1==1&&\\this site\movement one<60) \\this site\movement one=\\this site\movement one+7; else \\this site\movement one=0; if (\\this site\water valve2==1&&\\this site\movement two<60) \\this site\movement two=\\this site\movement two+7; else \\this site\movement two=0; if ((\this site\water valve1==1||\this site\water valve2==1)&&\\this site\movement<90) \\this site\movement=\\this site\movement+10; else \\this site\movement=0; if (\\this site\text movement<100) \\This site\text move=\\This site\text move+10; else \\This site\text move=0; 1.2 Lower-level PLC software design In the air source heat pump water heater system, the operation of the unit is controlled by PLC. PLC is widely used in production process due to its high reliability, adaptability to industrial process site, and powerful networking function. Based on the process requirements of the air source heat pump water heater unit, specific control requirements are proposed for the air source heat pump water heater unit, mainly including start-up control, shutdown control, intelligent defrosting control, auxiliary electric heating control, automatic antifreeze control, protection control, and manual defrosting control. The PLC input/output connection is shown in Figure 3: [align=center] Figure 3 PLC Input/Output Connection Diagram[/align] The main startup program flowchart is designed as shown in Figure 4: [align=center] Figure 4 Main Start-up Program Flowchart[/align] In the air source heat pump water heater unit control system, in order to protect the normal operation of the unit, the following protection devices are designed, and their specific functions are as follows: Water Cut-off Protection Control: When the unit enters the running state, the water pump detects the water flow after starting. If a water cut-off occurs during the operation of the water pump, the protection switch will activate, the control board will output a fault alarm indicator, and the water pump and unit will stop working immediately. After the external fault is cleared, that is, when the water cut-off protection switch is closed, and the compressor has reached the start interval time, the alarm will be turned off, and the unit will start normally. High-pressure protection and over-high water temperature protection: Upon entering the operation detection state, if the pressure is too high or the water temperature is too high, the control board will output a fault alarm indication. After the external fault is cleared, the alarm will be turned off, and the unit will start normally. Low-pressure protection control: During unit operation (except during defrosting), the control system constantly monitors the status of the low-pressure switch. If the pressure is too low and an abnormality occurs, causing the switch to activate, the control board will output a fault alarm. 2. Upper and Lower Computer Communication In the process of realizing real-time monitoring of the heat pump water heater unit, the upper computer monitoring system needs to connect with the lower computer. Serial communication is the most commonly used data exchange method between KingSCADA and I/O devices. Any I/O device with a serial communication interface can use this method. The lower computer FX2N PLC basic unit module in this system provides an RS232 asynchronous serial communication port. When the control system is relatively simple and the PLC application program is successfully debugged, this communication port can be used to connect to the computer to perform read and write operations on the PLC, thereby realizing communication with the upper computer. The lower-level FX2N PLC is connected to the serial port of the computer running "KingSCADA" via an RS-232 serial communication cable. KingSCADA software embeds various PLC drivers, treating each lower-level PLC as an external device. Users only need to select the PLC type according to the device configuration wizard, and KingSCADA will automatically start the corresponding driver and establish communication with the PLC. During operation, KingSCADA software and the PLC communicate using DDE (Dynamic Data Exchange), exchanging data through the driver and the lower-level PLC, including data acquisition and data transmission commands. In this system design, communication between KingSCADA and the PLC uses the PPI communication protocol. KingSCADA communicates with the PLC through the serial port, accessing relevant PLC register addresses to obtain the status of the devices controlled by the PLC or modify the values ​​of relevant registers. The monitoring system's host computer uses the COM1 port, while the PLC uses a built-in RS-232 port. Communication is half-duplex with synchronous start and stop. Communication parameters are set to a baud rate of 9600, 7 data bits, 1 stop bit, and even parity. 3. Conclusion Air source heat pump water heaters are a new type of energy-saving product. They use ambient air as a low-grade heat source, which is inexhaustible and can replace boilers for heating and hot water supply. The innovation of this paper lies in the user-friendly and intuitive human-machine interface of the air source heat pump water heater computer monitoring system designed using KingSCADA and PLC. It also possesses a certain degree of flexibility and is easy to expand. It completely replaces the traditional control cabinet and analog screen display of the process flow, shortening the development cycle and ensuring reliable, flexible, and stable system operation. The design of this monitoring system not only improves safe production conditions but also significantly enhances the level of automation in production, providing valuable reference for the design of other monitoring systems. References: [1] Zhan Suhua, Wang Junru. Application of PLC in automatic control system of heat pump [J]. Journal of Jimei University. 2001, 6(3): 233-237 [2] Zhang Hong, Long Wei, Zhang Lijian. Control system for waste acid water treatment in steel plant based on PLC and configuration software [J]. Microcomputer Information, 2006, 11: 109-111 [3] Wang Dongtao. Design of computer monitoring system for sintering shaft furnace [J]. Computer Engineering and Design. 2006, 27(7): 1146-1148