Abstract: This paper introduces the design scheme of a virtual vibration testing system. The system uses an accelerometer, charge amplifier, data acquisition card, and PC as the hardware development platform, and LabVIEW graphical programming language as the software development platform. It applies virtual instrument technology to vibration testing, making the system's testing functions more powerful and the testing process more convenient, representing the future direction of vibration testing. Keywords: Virtual instruments; LabVIEW; Vibration testing Abstract: This article introduces the design proposal of a virtual vibration measurement system. The system uses acceleration sensors, an electric charge amplifier, a data acquisition card, and a PC as its hardware development platform, and the graphical programming language LabVIEW as its software development platform. The system utilizes virtual instrument technology for vibration measurement. In this way, the measurement function is more convenient, and the measurement process is more efficient. It represents the future development direction of vibration measurement. Keywords: Virtual instruments; LabVIEW; Vibration measurement; 0 Introduction Vibration is the most common phenomenon in nature. Traditional vibration testing systems mostly use electronic measuring instruments, which are characterized by limited functionality, specialized nature, poor flexibility, and significantly restrict the scope of vibration testing. Currently, a technology that introduces virtual instrument technology into the field of vibration testing is gaining popularity. This technology combines computer technology and vibration testing technology to build virtual vibration testing systems. Practice shows that virtual vibration testing instruments are not only powerful and versatile, but also have a user-friendly interface and simplified graphical programming methods, making them widely welcomed and highly valued by users, and becoming a new development direction for vibration testing. 1. Hardware Design of the Virtual Vibration Testing System The hardware of the virtual vibration testing system mainly includes an accelerometer, a force sensor, a signal amplifier, a data acquisition card, and a general-purpose PC. 1.1 Accelerometer The accelerometer primarily measures the vibration acceleration of a vibrating body. Piezoelectric accelerometers are commonly used in mechanical vibration measurement. They are sensors that utilize the piezoelectric effect, where a charge is generated on the surface of a material under stress. The amount of charge output by the piezoelectric accelerometer is proportional to the vibration acceleration of the object. By detecting the amount of charge using an appropriate testing system, the vibration acceleration can be measured. It has advantages such as small size, light weight, high sensitivity, and wide frequency range, making it the most widely used in vibration testing. This system design uses a piezoelectric sensor made of parallel piezoelectric material. A charge amplifier is suitable because its circuit characteristic is that the amplifier's output voltage is only related to the amount of charge input generated by the sensor and the amplifier's feedback capacitance, and is independent of the distributed capacitance formed by the cables constituting the circuit and the signal frequency. This characteristic makes the distributed capacitance of the charge amplifier's transmission line insensitive, and the transmission distance can reach hundreds of meters. 1.2 Charge Amplifier The charge signal output by the piezoelectric sensor is relatively weak and cannot be directly acquired by the data acquisition card. A signal amplifier is needed to convert the weak charge signal into a stronger voltage signal that can be acquired by the data acquisition card. A charge amplifier is an amplifier whose output voltage is proportional to the input charge. Its core is an operational amplifier with capacitive negative feedback, high input impedance, and high gain. This system uses the BC97 charge amplifier as an example. The charge amplifier also includes a low-pass filter and an adaptive amplifier that can adjust the amplification factor according to the sensor sensitivity. 1.3 Data Acquisition Card The data acquisition card used in this system is the PCI-6024, a multi-function interface card manufactured by National Instruments (NI). This card is designed based on the PCI bus, offering high data transfer rates and throughput. It is a mainstream data acquisition card design and offers good cost-performance. It supports DMA mode and double buffering mode, ensuring uninterrupted real-time signal acquisition and storage. It supports unipolar and bipolar analog signal inputs with input ranges of -5V to +5V and 0 to 10V, respectively. It provides 16 single-ended/8 differential analog input channels, 2 independent D/A output channels, 24-line TTL digital I/O, and 3 16-bit timer/counters, among other functions. In actual measurement, the input signal enters the data acquisition card through a BNC connector. Communication between the system software and the data acquisition card is easily accomplished using Measurement Automation software provided by National Instruments (NI). 2. Software Design of the Virtual Vibration Testing System The software design of the virtual vibration testing system utilizes the LabVIEW graphical programming language as the software development platform. A modular design approach is employed during program development, with various functional modules built according to different needs. This system includes a data acquisition module, a data storage and retrieval module, a data processing module, and a result display module. A main interface is designed to integrate these modules and facilitate their use. Finally, the system is integrated and debugged. 2.1 System Main Interface Design In the design of the system's main interface, the Edit Menu provided by LabVIEW is used. The functions to be implemented are first listed as menu options for runtime invocation. Then, the menu items are selected via a Case loop in the block diagram, making each menu item correspond to a sub-VI. In the VI Setup's Eexecution Options of each sub-VI, the "Show Front Panel When Called" option is selected. Thus, during runtime, when a menu item is selected, that sub-VI is selected and invoked. 2.2 Data Acquisition Module The data acquisition module uses the AI ​​Waveform Scan module in the Analog Input function block of LabVIEW for acquisition control. Depending on different needs, continuous signal acquisition or single signal acquisition can be selected. The acquisition channel, sampling rate, number of sampling points, windowing method, averaging times, and spectrum display type can be controlled. The time and frequency domain values ​​of the signal can be observed by moving the cursor. For triggering, signal triggering or free acquisition can be selected. When signal triggering, parameters such as trigger level, trigger edge, and number of points to reserve before triggering can be selected. 2.3 Data Storage and Retrieval Module The main function of the data storage module is to store the time-domain data corresponding to the image displayed on the monitor into a binary file; and to store parameters related to the acquired data, such as the average number of times, data length, analysis bandwidth, trigger point sampling point, and acquisition time, into a text file with the same name as the data file, for easy use by the data retrieval module and the user. The data retrieval module can easily perform file read and write operations. The LabVIEW file read and write process is: open a file – read and write content according to a certain format – finally close the file. The main functions used in the data retrieval module are: open file function, read file function, and close file function. 2.4 Data Processing Module The design of the data processing module program is a key part of the system software design. It needs to complete many functions such as digital filtering, windowing processing, spectrum analysis, power spectrum analysis, correlation analysis, and cepstral analysis. Time-domain analysis includes autocorrelation and cross-correlation analysis. Amplitude-domain analysis can perform mean, variance, probability density, and probability distribution statistics. Data preprocessing allows for inputting calibration coefficients for each channel and filtering with digital filters, including low-pass, high-pass, band-pass, and band-stop filtering. FFT-based frequency analysis includes autopower spectrum, cross-power spectrum, amplitude cepstrum, and frequency response function. The frequency response function can be estimated using different formulas as needed, and the display of real and imaginary parts, amplitude and phase frequencies, and coherence functions is selectable. Furthermore, during frequency-domain analysis, windows can be applied to each signal to reduce leakage, including rectangular windows, Hanning windows, Hamming windows, and exponential windows. This fully utilizes computer resources; the number of points for FFT calculation can range from 512 to 16384 points, and multiple averaging can be performed to reduce errors. Any two channels can be selected to calculate the frequency response function and cross-power spectrum. The signal analysis utilizes sub-VI modules such as auto power spectrum, spectrum unit conversion, and power frequency estimate. 2.5 Data Display Module The data display module displays the collected and analyzed data on the monitor. It also includes many auxiliary display items, such as coordinate unit display, maximum value and corresponding position display, time limit display, and data acquisition file index display, allowing users to observe the system test results. 3 Actual Testing of the Virtual Vibration Testing System This paper introduces the entire development process of the virtual vibration testing system. To verify the correctness of the entire system program, a hammer impact test was conducted on the specimen. A force hammer equipped with a force sensor was used to impact the test structure, and an accelerometer was used to pick up the vibration. The two signals were amplified by a charge amplifier and sent to the data acquisition card. The acquisition conditions were set by the software to control the acquisition, and the acquired data was stored and analyzed. During acquisition, two sampling channels were set, the sampling frequency was 1000Hz, the average number of times was 5, the number of acquisition points per time was set to 1024, the trigger channel was channel 0, the trigger level was 100mV, the trigger edge was the default rising edge, and 20 points were reserved. The test results show that the excitation and response signals accurately reflect the typical shapes expected during hammer-impact excitation, indicating that the system program runs well and the system has high reliability. 4. Conclusion This paper introduces the design of a virtual vibration testing system. Practice has proven that constructing a virtual vibration testing system using LabVIEW and a PC-based data acquisition card is feasible. The testing system is powerful, and its modular programming makes program expansion very convenient. It is foreseeable that virtual instrument technology will have a wider application space in the entire testing field. 5. Author's Innovation The design of the vibration testing system adopts advanced virtual instrument technology, which improves the system's testing accuracy, saves development time, and reduces development costs. References [1] Lei Zhenshan, LabVIEW 7 Express Practical Technology Tutorial, China Railway Publishing House, 2004 [2] Liu Junhua, LabVIEW Tutorial, Graphical Programming Language for Virtual Instruments, Xi'an University of Electronic Science and Technology Press, 2001 [3] Wang Zong, Design of Vibration Performance Testing System for Guide Head Position Target Based on Virtual Instrument Technology, Microcomputer Information, 2005.5 [4] Zhang En, Vibration Testing and Analysis Technology, Tsinghua University Press, 2000 [5] National Instruments Corporation, LabVIEW Use Manuals, July 2002 [6] National Instruments Corporation, DAQ PCI-6024 User Manual, July 1998