Design of vibration testing system based on Virtua

2022-07-24
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Design of vibration testing system based on Virtual Instrument Technology

vibration is the most common phenomenon in nature. Most traditional vibration testing systems use electronic measuring instruments, which are characterized by single function, special use, poor flexibility and greatly restrict the scope of vibration testing. Nowadays, there is a popular technology that introduces virtual instrument technology into the field of vibration testing. It combines computer technology and vibration testing technology to form a virtual vibration testing system. The practice shows that the virtual vibration testing instrument not only has powerful functions and diverse uses, but also has friendly user interface and simplified graphical programming method. It is widely welcomed and highly valued by the majority of users, and has become a new development direction of vibration testing

1 hardware design of virtual vibration testing system the hardware of virtual vibration testing system mainly includes acceleration sensor, force sensing rubber tensile testing machine model introducer, signal amplifier, data acquisition card and general PC

1.1 acceleration sensor

the acceleration sensor mainly tests the vibration acceleration of the vibrating body. The piezoelectric acceleration sensor commonly used in mechanical vibration measurement is a sensor based on the conversion principle of the piezoelectric effect of the charge generated on the surface of some materials after being stressed. The output charge of the piezoelectric acceleration sensor is proportional to the vibration acceleration of the object, and the charge is detected by an appropriate test system, The measurement of vibration acceleration is realized. It has the advantages of small volume, light weight, high sensitivity and wide frequency range. It is most widely used in vibration testing. The design of this system adopts a piezoelectric sensor made of parallel piezoelectric materials, which is suitable for the use of charge amplifier. The circuit feature is that the output voltage of the amplifier is only related to the charge input generated by the sensor and the feedback capacitance of the amplifier, and has nothing to do with the distributed capacitance and signal frequency formed by the cables constituting the circuit, This characteristic makes most MEG and PE manufacturers in the region of the transmission line of the charge amplifier say that the operating rate distribution capacitance of the device will be reduced, 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 collected by the data acquisition card. It is necessary to use the signal amplifier to convert the weak charge signal into a strong voltage signal that can be collected by the data acquisition card. Charge amplifier is a kind of amplifier whose output voltage is proportional to the input charge. Its core is an operational amplifier with capacitor negative feedback, input impedance and high gain. The system uses bc97 charge amplifier as an example. The charge amplifier also has a low-pass filter and an adaptive amplifier which can adjust the amplification factor according to the sensitivity of the sensor

1.3 data acquisition card

the data acquisition card used in this system is PCI-6024. It is a multi-functional interface card produced by Ni company in the United States. This card is designed based on PCI bus, with high data transmission rate and large throughput. It is the mainstream of data acquisition card design. It is a product with good cost performance. It supports DMA mode and double buffer mode, ensuring the continuous acquisition and storage of real-time signals. It supports unipolar and bipolar analog signal input, and the signal input range is -5v ~ +5v and 0 ~ 10V respectively. It provides 16 single ended/8 differential analog input channels, 2 independent d/a output channels, 24 wire TTL digital i/o, 3 16 bit timing counters and other functions. The actual measurement is that the input signal enters the data acquisition card from the input terminal through the BNC connector for data acquisition. At the same time, the communication between the system software and the data acquisition card can be completed by simply setting the measurement automation software provided by the American NI company

2 software design of the virtual vibration test system

the software design of the virtual vibration test system is to use the graphical programming language LabVIEW as the software development platform, use the modular design idea in the process of program development, and build various functional modules according to the needs of different functions. The system includes data acquisition module, data storage and reading module, data processing module and result display module, In order to integrate each module, a main interface is designed to call each module. Finally, the system is integrated and debugged

2.1 design of system main interface

in the design of system main interface, use the edit menu menu provided in LabVIEW to first take the functions to be realized as the contents of menu options so that they can be called at runtime, and then select the call of each menu in the block diagram through case cycle, so that each menu corresponds to each sub VI, and select the show front panel when called option in the execution options of VI setup in each sub VI, In this way, when an item in the menu is selected during operation, the sub VI will be selected and called

2.2 data acquisition module

the data acquisition module uses the AI waveform scan module in the analog iuput function block in LabVIEW for acquisition control. According to different needs, continuous signal acquisition or single signal acquisition can be selected, and the acquisition channel, sampling rate, sampling points, windowing method, average times and display spectrum type can be controlled. The time domain value and frequency domain value of the signal can also be observed by moving the cursor, In terms of trigger mode, you can also select signal trigger or free acquisition. When the signal is triggered, you can select trigger level, trigger edge, pre reserved points before triggering and other parameters

2.3 data storage and reading module

the main function of the data storage module is to store the time domain data corresponding to the image displayed on the display in the binary file; The parameters related to the collected data, such as average times, data length, analysis bandwidth, trigger point sampling point, collection time, etc., are stored in a text file with the same name as the data file, which is convenient for the data reading module and users

the data reading module can easily read and write files. The process of reading and writing files in LabVIEW is as follows: open a file to read and write contents in a certain format, and finally close the file. The main functions used in the data reading module are: open file function, read file function and close file function

2.4 data processing module

the program design of data processing module is the 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, cepstrum analysis and so on. Time domain analysis includes autocorrelation and cross-correlation analysis. Amplitude range analysis can be used for statistics of mean, variance, probability density and probability distribution. Data preprocessing can be used for input of calibration coefficients of each channel and filtering with digital filters. Low pass, high pass, band-pass and band stop filtering can be used. FFT based frequency analysis includes auto power spectrum, cross power spectrum, amplitude Cepstrum and frequency response function, The frequency response function can be excluded according to the need. Different estimation formulas are used for adjusting the screws connected between the oil pump and the motor. The real part and imaginary part, amplitude frequency, phase frequency and coherence function can be displayed. In addition, in frequency domain analysis, each signal can be windowed to reduce leakage, mainly including rectangular window, Hanning window, Hamming window, index window, etc. by making full use of computer resources, the number of FFT points can be calculated from 512 points to 16384 points, and multiple averages can be carried out to reduce errors. Two channels can be arbitrarily selected to calculate frequency response function and cross power spectrum. In signal analysis, sub VI modules such as auto power spectrum, spectrum unit conversion and power frequency estimate are called

2.5 data display module

the data display module displays the collected data and analyzed data on the display. At the same time, it also contains many auxiliary display items, including coordinate unit display, maximum value and its corresponding position display, time limit display, data collection file index display, for users to observe the system test results

3 actual test of virtual vibration test system

this paper introduces the whole development process of the virtual vibration test system. In order to verify the correctness of the whole system program, the hammer method is used to test the specimen, the hammer equipped with a powerful sensor is used to hammer the test structure, the acceleration sensor is used to pick up vibration, and the two signals are amplified by the charge amplifier and sent to the data acquisition card, The acquisition conditions are set by software to control the acquisition, and the collected data are stored and analyzed. During acquisition, set 2 sampling channels, the sampling frequency is 1000Hz, the average number of times is 5, the number of acquisition points each time is set to 1024, the trigger channel is 0 channel, the trigger level is 100mV, the trigger edge is the default rising edge, and the number of pre reserved points is 20. From the test results, the excitation signal and response signal reflect the typical shape of the excitation and response signal when the hammer method is used. It can be seen that the system program runs well and the system reliability is high

This paper introduces the design of virtual vibration testing system. Practice has proved that it is feasible to use LabVIEW and PC based data acquisition card to construct a virtual vibration test system. The test system has powerful functions, and its modular programming makes program expansion very convenient. It can be predicted that virtual instrument technology will have a broader application space in the whole testing field

5 the author's innovation

the design of vibration test system adopts advanced virtual instrument technology, which improves the test accuracy of the system, saves development time and reduces development cost

reference

[1] Lei Zhenshan, LabVIEW 7 Express practical technology course, China Railway Publishing House, 2004

[2] liujunhua, virtual instrument graphical programming language LabVIEW course, Xi'an University of Electronic Science and Technology Press, 2001

[3] Wang Zong, microcomputer information for the design of the vibration performance test system of the seeker locator based on Virtual Instrument Technology, 2005.5

[4] Zhang GengXian, high-end quality 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

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