Abstract: Based on virtual instrument technology, a temperature measurement system was designed and developed using LabVIEW software. The software and hardware design methods of the system are described in detail. This system can improve working conditions, reduce costs, and increase efficiency. Keywords: Virtual Instrument; LabVIEW; temperature measurement 0 Introduction Temperature is a very important parameter in industrial production and scientific research experiments. Many physical phenomena and chemical properties of objects are related to temperature. Many production processes are carried out within a certain temperature range, and the occasions requiring temperature measurement and control are extremely wide. Current temperature measurement and control systems often use microcontroller control. This technology is widely used, but its programming is complex, control is unstable, and the system accuracy is not high. Temperature measurement systems developed and designed using virtual instrument technology employ a standard PC as the host and LabVIEW, a graphical visual testing software, as the software development platform to monitor temperature changes, collect data, and perform processing, storage, and display. The equipment is low-cost, convenient, and flexible, suitable for industrial and agricultural production and teaching. 1. Introduction to Virtual Instrument Technology and LabVIEW Virtual technology, computer communication technology, and network technology are the three core technologies of information technology, with virtual instruments being a crucial component. Virtual instruments (VI) are the latest generation of measuring instruments that break through the traditional concept of instruments. They utilize high-performance modular hardware combined with efficient and flexible software, allowing users to define and perform various tests, measurements, and control applications. Their essential characteristic is: "Software is the instrument." It is a computer-based hardware and software testing platform that can replace traditional measuring instruments such as oscilloscopes, logic analyzers, signal generators, and spectrum analyzers; it can be integrated into automatic control and industrial control systems; and it can be freely constructed into proprietary instrument systems. Virtual instrument technology possesses four major advantages: high performance, strong scalability, short development time, and excellent integration, making it a development trend in modern measurement and control technology. LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is a program development environment. It uses the graphical programming language G to create source programs in flowcharts, rather than using a text-based language to generate source code. LabVIEW also integrates all the functions required for hardware communication such as GPIB, VXI, RS-232, RS-485, and data acquisition cards. It includes built-in library functions for software standards such as TCP/IP and ActiveX. LabVIEW programs are called virtual instruments (VIs) because their appearance and operation mimic real instruments. Even users with little programming experience can use LabVIEW to develop their own applications. 2 System Design The virtual instrument temperature measurement system uses virtual instrument technology to transform traditional temperature measuring instruments, giving them more powerful functions. The system framework is shown in Figure 1. The instrument system uses the sensing element of the front-end temperature sensing device to convert the temperature of the object being measured into analog signals such as voltage or current. After power amplification and filtering by the signal conditioning circuit, it is transformed into a standard voltage signal that can be acquired by the data acquisition card. The analog signal is converted into a digital signal within the data acquisition card, and then sent to the computer bus under the data acquisition command. The acquired data is then processed using the installed virtual instrument software on the PC. [align=center] Figure 1: Block Diagram of Temperature Measurement System[/align] The temperature measurement system based on virtual instrument technology consists of two main parts: hardware and software. 2.1 Hardware System Design The hardware system consists of a front-end temperature sensing device (temperature sensor), a data acquisition card, and a PC system, mainly realizing the functions of temperature signal acquisition, conversion, and processing. [align=center] Figure 2: Hardware Circuit Diagram of Temperature Measurement System[/align] The front-end temperature sensing device of this system uses a thermistor. The thermistor RT1 and R1 are connected in series to divide the voltage, and the circuit output voltage is proportional to the temperature. Since the sensor usually outputs a relatively small signal, a suitable signal conditioning circuit (such as amplification) must be used to minimize quantization error. When the temperature increases, the resistance of the thermistor RT1 decreases, generating a linear voltage at the voltage divider point. After being held by the voltage follower, it is amplified by the LM324 in the first and second stages to output a positive linear voltage that is proportional to the magnitude of the temperature change. The analog voltage output by the measurement circuit is sent to the data acquisition card, converted into a digital signal, and then input to the PC. 2.2 Software System Design The software part mainly performs subsequent data processing, alarm, display, and other functions. Specifically, it implements functions such as data acquisition card parameter setting, data calibration, real-time display, temperature limit setting, alarm, and human-computer interaction. (1) Sensor Calibration Sensor calibration is to establish the relationship between the sensor input and output through experiments. Calibration is a verification procedure that must be performed on the instrument after the design is completed and before it is used. For the virtual temperature measurement system, calibration is to obtain the functional relationship between voltage and the temperature of the measured object so that the temperature can be calculated from the voltage. Thermistors have the advantages of high sensitivity, small size, light weight, long service life, and suitability for long-distance measurement, but their nonlinear error is large and their stability is slightly poor, so calibration is necessary. By calibrating the system using curve fitting, the temperature corresponding to any voltage within the temperature measurement range can be determined. (2) Front panel design The user interface (front panel) is an important part of the virtual instrument. The instrument parameter setting, test result display and other functions are all implemented through software. Therefore, the software interface is required to be simple, direct and easy to use. The user interface of this system is designed using LabVIEW 8.2 software as shown in Figure 3. This interface can display the changes in voltage waveforms obtained by sensor detection, data card acquisition and conversion. At the same time, the temperature values ​​obtained after calibration are displayed in three ways: waveform, pointer and numerical value, to meet the needs of different users. The over-limit alarm indication is set through Boolean switch. [align=center] Figure 3 System front panel (user interface)[/align] (3) Program block diagram design LabVIEW source code is block diagram type and provides a very rich library function, from data acquisition to instrument control, from signal generation to signal processing, from data analysis to graphic display, from file reading and writing to network communication, which greatly improves the efficiency of user programming and reduces the programming workload. The system flowchart design mainly includes modules such as device initialization, AD component initialization, analog data reading, voltage-temperature conversion, data processing and display, over-limit alarm, AD component release, and device release. Some modules directly call sub-modules (library functions) in LabVIEW, such as multiplication, subtraction, over-limit comparison, and timers; others, such as Create/Release ID and AD Int/Read/Close, are user-defined. See Figures 4 and 5 for the specific flowchart and program block diagram. [align=center] Figure 4 System Flowchart Figure 5 Temperature Measurement System Program Block Diagram[/align] 4 Conclusion A virtual temperature measurement system was implemented using LabVIEW software, improving working conditions, increasing accuracy, saving time, and reducing costs. The system has strong scalability and its functions can be further expanded, such as achieving remote temperature measurement and control. The method used to construct the measurement and control system can be extended to similar applications and has significant practical implications. The innovation of this paper lies in: using virtual instruments to construct a temperature measurement system, realizing intelligent temperature measurement with high accuracy, low cost, and strong versatility and scalability. References: [1] National Instruments LabVIEW Basic I, National Instruments, translated by Wang Minsheng et al., LabVIEW Basic Tutorial, Beijing: Electronic Industry Press, 2002. [2] Qin Shuren (ed.), Virtual Instruments, Beijing: China Metrology Press, 2004. [3] Jiang Wei, Yuan Fang, Design of Vibration Testing System Based on Virtual Instrument Technology, Microcomputer Information (Measurement and Control Automation), Vol. 22, No. 10-1, 2006, 313-314, 240. [4] Bao Xiuchao et al., Dynamic Temperature Testing System for Engine Cylinder Liner Based on LabVIEW, Small Internal Combustion Engines and Motorcycles, Vol. 35, No. 6, 2006, 43-45.