Abstract: In power systems, accurate measurement of temperature and humidity in artificial environment chambers is required to study the external insulation characteristics of high-voltage electrical equipment. This paper applies virtual instrument technology to temperature and humidity measurement. Using LabVIEW as the software development platform and a computer as the core, along with sensors, data acquisition cards, and corresponding software, the temperature and humidity of the artificial environment chamber are measured in real time and accurately. The results are displayed in both graphical and digital formats in real time. Furthermore, the data storage function is expanded, demonstrating the flexibility and powerful functionality of virtual instrument technology in temperature and humidity measurement. Keywords: Virtual instrument; sensor; LabVIEW; temperature and humidity measurement Abstract: In the power system, to study the external insulation characteristics of high-voltage electrical equipment, it is necessary to accurately measure the temperature and humidity of the artificial environment. In this paper, virtual instrument technology is applied to measure temperature and humidity. Using LabVIEW as the software platform, a sensor, DAQ card, and corresponding software are used to accurately measure the temperature and humidity of the artificial environment on a computer basis. The results are displayed using two types of figures and data, expanding data saving functions and demonstrating the flexibility and powerful functionality of VI technology in temperature and humidity measurement. Keywords: Virtual instrument; sensor; LabVIEW; temperature and humidity measurement 0 Introduction In the power system, power equipment and transmission lines often pass through complex atmospheric environments characterized by acidic wet deposition and icing. These complex atmospheric environments bring many new technical and theoretical problems to the selection of external insulation, research on flashover prevention strategies, and ensuring safe operation of the power system. To study the characteristics of power equipment under complex atmospheric conditions, an artificial environment chamber was established to accurately measure both temperature and humidity. This allows for adjustments to temperature and humidity to meet the experimental requirements of simulating complex natural atmospheric environments. Within this artificial environment chamber, the temperature is precisely adjustable from -40 to 80°C, and the humidity from 0% to 100%RH. The artificial environment chamber is a complex system; its main parameters are temperature and humidity. These parameters need to be measured in real-time, quantitatively displayed, and stored systematically in large quantities. Previously, temperature and humidity measurements were typically performed using thermometers, hygrometers, and analog electrical measuring instruments. The temperature and humidity values ​​on these instruments were manually read and recorded. This method suffers from low accuracy, is often influenced by external and human factors, resulting in large errors, inconvenient observation, poor real-time performance, and low efficiency. Furthermore, the high voltage levels in power system measurements make direct, close-range readings difficult. To effectively solve these problems, this paper applies virtual instrument technology to temperature and humidity measurement. Using LabVIEW as the development platform, and leveraging the flexibility of communication between virtual instruments and testing hardware, as well as the convenience and simplicity of the software, a temperature and humidity measurement system is constructed, with a computer as the core, equipped with sensors, a data acquisition card, and corresponding software. 1 Hardware Composition of Virtual Measurement The temperature and humidity measurement system based on virtual instruments converts non-electrical quantities such as temperature and humidity into analog electrical quantities, then into digital quantities, which are read and processed by the computer, and finally displayed and stored on a virtual panel. It consists of two parts: hardware and software. The hardware is the foundation of this measurement system, and the software is the core. The principle block diagram of this measurement system is shown in Figure 1. [align=center] Figure 1 Principle Block Diagram of Temperature and Humidity Measurement[/align] The hardware part provides the operating platform for the virtual temperature and humidity measurement system software, completing the construction of the measurement platform and the acquisition and storage of measurement information. It consists of a sensor probe, a current transmitter, a data acquisition card, and a computer system. 1.1 Temperature and Humidity Sensor The temperature and humidity sensor in this measurement system is an integrated temperature and humidity sensor. Its temperature measurement range is -40～80℃ with an accuracy of 0.2℃, and its humidity measurement range is 0%～100%RH with an accuracy of 2%RH. It is powered by a 24V DC power supply and outputs a 4～20mA DC current. It consists of a measuring probe and a current transmitter. 1.1.1 Sensor Probe The temperature section of the sensor probe uses a PT1000 thin-film platinum resistance thermometer as the temperature sensing element, while the humidity section uses a capacitive humidity sensor with polyimide as the humidity sensing medium. The sensor converts temperature changes into resistance changes and humidity changes into capacitance changes, ultimately converting them into current changes, but the current values ​​are very small. In high-voltage experiments in the laboratory, the surrounding electromagnetic pollution is severe, and the small current obtained by the probe is easily distorted by contamination. Therefore, an analog-to-digital converter is added to the probe to directly convert the obtained small current into a digital signal. This digital signal is then transmitted to the current transmitter for processing using a high-temperature wire with a PTFE sheath. This significantly improves the signal's anti-interference and long-distance transmission capabilities, while the long-distance transmission of the measurement signal allows measurement personnel to operate away from high-voltage measurement areas. 1.1.2 Current Transmitter The current transmitter conditions the signal through its circuit board, primarily to ensure the transmitter's output signal is compatible with the data acquisition card. The data acquisition card's input level is 0–5V, while the sensor probe's output signal is typically very small. Therefore, amplification measures must be taken to reduce quantization errors, while filtering out spurious components mixed into the signal, and processing such as bandwidth compression, impedance transformation, shielding grounding, and signal linearization is performed. The digital signal measured by the probe is transmitted to the current transmitter, where it is converted into a weak electrical signal by the digital-to-analog converter. This weak electrical signal is then amplified, filtered, compensated, and linearized by the transmitter's signal conditioning circuit, outputting a 4–20mA current signal. This current output makes it a current-type sensor, equivalent to a constant current source, thus less susceptible to interference from contact resistance, lead resistance, and noise, improving the signal's long-distance transmission capability and anti-interference ability during transmission. The current output signal is then transmitted to the data acquisition card via a shielded cable. A 250-ohm non-inductive precision resistor is connected in series at the end of the shielded cable as a sampling resistor, converting the output signal into a 1-5V voltage standard signal, which is then sent to the data acquisition card for digital processing. A schematic diagram of the sensor connection to the measurement circuit is shown below: [align=center] Figure 2 Schematic diagram of sensor connection to the measurement circuit[/align] 1.2 Data Acquisition Card The data acquisition card is the entry point for the virtual instrument. It acquires the conditioned signal at a certain frequency and stores it on the data acquisition card. Data is then sent to the computer memory for processing via a bus using polling, interrupt, or DMA methods. The data acquisition card is an essential piece of hardware for testing virtual instruments. The 1-5V voltage signal output from the current transmitter is acquired by the card, then converted into a digital signal that the computer can receive by the built-in analog-to-digital converter. Finally, it is controlled and processed by the written LabVIEW program and displayed on the front panel. The data acquisition card used in this measurement system is the RBH8301 domestic general-purpose data acquisition card. This card has high-performance data acquisition capabilities, employs a high-precision, high-density FPGA logic chip, and a USB 2.0 bus interface. It connects directly to the computer's USB interface via the USB bus, requiring no external power supply and powered directly by the USB bus. 2. Software Design and Program Implementation of Virtual Measurement This measurement system uses LabVIEW as the control software. LabVIEW, also known as a virtual instrument program, is a development environment based on the graphical programming language G, serving as a programming platform for instrument control and data acquisition. The LabVIEW program controls the data acquisition card to acquire data. After the voltage analog signal is acquired by the data acquisition card, it is input into the computer. The LabVIEW program analyzes and processes the acquired data, restoring the signal to the corresponding temperature and humidity digital signals, which are then displayed on the front panel in various ways or saved as data files. 2.1 Scale Transformation The data acquisition card does not acquire direct readings of the temperature and humidity values ​​at the measurement point, but only voltage analog electrical signals representing those values. In practical applications, after the measured analog signal is detected and converted into a digital quantity, it only corresponds to the magnitude of the parameter. It often needs to be converted into a dimensional engineering quantity familiar to the operator and easy for people to observe before it can be calculated and displayed meaningfully. This is called engineering quantity transformation or scaling transformation. To derive the temperature and humidity values ​​of each measuring point from the acquired analog voltage signal, a scaling transformation is required. This transformation is implemented by a LabVIEW program. The scaling transformation formula is as follows: 2.2 Block Diagram Program LabVIEW programs are programmed using block diagrams, which are graphical source code representations of the program. Block diagram programming specifies the input and output of signal data to manipulate and control the input and output functions defined on the front panel, completing the control of signal acquisition and analysis processing functions. The program adopts a modular approach, dividing the entire program into a data acquisition module, a data conversion and processing module, a temperature and humidity display module, a data storage module, and a data playback and recall module. Each module is written as a sub-VI, each module completes its defined task, and the main program calls each sub-VI. (1) The data acquisition module sub-VI controls the data acquisition card to collect data. This mainly includes: initializing the data acquisition card, starting data acquisition, reading the acquisition results, and stopping data acquisition. Initializing the data acquisition card completes the parameter settings for the data acquisition card. (2) The data conversion and processing module sub-VI performs scaling transformation and data conversion on the acquired results. It restores the voltage data signal to the corresponding temperature and humidity digital signal and converts the acquired array data into string format for easy saving. (3) The temperature and humidity display module sub-VI provides a real-time display mode to display the processed data in real time. The display modes include direct numerical display and graphical display. (4) The data storage module sub-VI mainly saves the processed data for browsing historical data. Since the real-time display and processing are quite fast, when the user needs to perform detailed analysis of the data, they can select the save data button to save the acquired data in string format and generate an electronic spreadsheet file with the time as the file name for future data analysis and process description. (5) The data playback recall module sub-VI is used to play back the stored data. When the user needs to analyze and process the collected data, the data can be recalled for analysis in offline state. [align=center] Figure 3 Flowchart of calling the data acquisition module sub-VI[/align] 2.3 Front panel The front panel consists of controls, indicators and decoration. LabVIEW provides rich graphical controls for the front panel to simulate the working mode of traditional instruments. The required controls and indicators are placed on the front panel to realize instrument control, data input and result display. When the program is running, only the front panel appears on the computer screen, serving as the interface between virtual measurement and the user. As long as the corresponding control parameters are written on the front panel as required and the sampling channel is set, temperature and humidity measurement can be performed. The front panel of the temperature and humidity measurement of a certain day using this measurement system is shown in the figure below: [align=center] Figure 4 Front panel of virtual instrument temperature and humidity measurement[/align] 3 Conclusion The emergence of virtual instrument technology has opened up a new way for the development of testing systems. This paper designs a virtual instrument-based artificial environment chamber for temperature and humidity measurement, which is an application of virtual instruments in testing and measurement. It fully utilizes computer hardware and software resources, employing sensors, data acquisition cards, and LabVIEW language to achieve digital temperature and humidity measurement. It features short development time, a user-friendly interface, convenient operation, and intuitive result display. This not only facilitates measurement control and observation but, more importantly, improves the accuracy and real-time performance of data acquisition and readings, thereby increasing the accuracy of high-voltage experiments. The innovation of this paper lies in applying virtual instrument technology to the digital measurement of temperature and humidity in an artificial environment chamber within a high-voltage laboratory. To transmit measurement results to areas far from the high-voltage experimental zone and to achieve good electromagnetic interference resistance, the sensors employ digital signal transmission and current output. The LabVIEW program uses sub-VIs for easy calling and program portability. The measurement results are output graphically and numerically, and the storage function of the measurement results is expanded to meet the needs of future high-voltage experimental analysis and the retrieval of temperature and humidity parameter values. References: [1] Yang Leping, Li Haitao, Yang Lei. LabVIEW Programming and Application [M]. Beijing: Electronic Industry Press. 2005. [2] Wu Guangjie, Wang Haibao. Multi-channel virtual temperature monitor during injection process [J]. Automation Instrumentation, 2004, 2: 30-32. [3] Wang Yanfang, Feng Jun, He Haihong et al. Design of constant temperature section measurement system based on VI [J]. Microcomputer Information, 2006, (22) 5: 170-171.