Design of Multi-channel Data Analysis System Based on Virtual Instrument

Abstract: Aiming at the problems of difficult wiring and large interference when using the lead-wire test method to test the parameters of weapon systems, a storage test method based on NandFlash technology is proposed, and a multi-channel data analysis system for post-analysis and processing of data is designed and developed based on LabVIEW. The system consists of modules such as multi-channel waveform display, waveform parameter measurement, filtering processing and spectrum analysis, and waveform printing. Experimental results show that the system can complete the analysis and processing of test data efficiently and with low error, thereby realizing storage testing in harsh environments of high temperature, high impact, and high pressure.
Keywords: storage test; multi-channel; data analysis; virtual instrument

In previous test systems, the wire test method was generally used to achieve synchronous signal acquisition, display and analysis. However, in the harsh environment of high temperature, high shock and high voltage where the weapon system parameter test device works, the wire test method has complex wiring and large interference. The real-time connection between the acquisition system and the signal analysis system is extremely difficult. Moreover, during the recovery process after the test, if the system loses power unexpectedly, the test data will be lost, resulting in test failure [1]. The wire test method encountered functional bottlenecks when solving such problems. To solve such problems, the storage test method was proposed as a new test method, that is, the data acquisition and analysis system is divided into two independent subsystems. During the test, the storage test technology is used to make the sensor and the recording circuit into a whole, and directly put them into the test environment to test and store the relevant parameters. After the test, the test data is analyzed and processed by a dedicated data analysis system [2]. With the development of computer technology, the use of virtual instruments for data analysis and processing is not only efficient and accurate, but also greatly reduces the cost. Virtual instrument technology has become an important development trend of modern test technology. In this paper, a low-cost, high-precision and scalable multi-channel data analysis system based on virtual instruments is designed.
1 Overall system design scheme
The structural block diagram of the multi-channel data analysis system is shown in Figure 1.

1.1 System Hardware Structure
The hardware structure of this system is a storage test subsystem based on Nandflash technology. Nandflash is a non-volatile memory with the advantages of small size, low power consumption, and fast read and write speed. This article uses Samsung's Nandflash chip K9F4GOSUOA as the main storage device, and the control device uses ATMEL's ATmegal62 and Xi1inx's CoolRunner-II series XC2C256, combined with the timing configuration of Nandflash read, write, erase and other operations. The A/D chip uses Maxim's MAX1308. In addition, in order to realize the transmission of data from the acquisition device to the PC through the USB bus, the FT245R chip of FTDI is used as the USB2.0 interface controller.
The storage test subsystem is divided into two modules: (1) data acquisition module, which saves the collected high-speed data stream to Nandflash in real time through the control of AVR and CPLD; (2) data transmission and storage module, which controls the data saved in Nandflash through AVR, CPLD and USB dedicated chip, and transmits it to PC via USB bus for subsequent processing [3].
1.2 System software structure
LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is a graphical programming language and development environment. The software part of the system is a multi-channel data analysis subsystem developed and designed based on LabVIEW platform. Its main function is to perform post-analysis and processing on the test data stored in the storage test subsystem.
2 Software implementation of multi-channel data analysis system
The system software part is mainly used to read the stored test data file, restore the data into waveform, and perform a series of analysis and processing on the waveform. In terms of function, it consists of data fixed-point fixed-length reading, data waveform restoration and display, waveform parameter measurement, filtering processing, spectrum analysis and printing.
2.1 Design of software front panel
The front panel is a window for communication between the software and the user. Through this friendly interface, the user can control the software according to the prescribed operating procedures and obtain ideal data results. According to functional requirements, the front panel is equipped with windows or knobs such as data reading, waveform display, waveform control, filtering processing, spectrum analysis, parameter measurement, and printing.
2.2 Implementation methods of each software module
2.2.1 Fixed-point and fixed-length reading
of measurement data Fixed-point and fixed-length reading of measurement data can effectively solve the problem of excessive time consumption caused by a single reading of massive data. It can also quickly locate the area of ​​interest in the massive data and read it selectively, thereby facilitating the analysis and processing of sensitive areas in the measurement data. This module realizes fixed-point and fixed-length reading of data through the combined control operation of "starting position" and "number of reading points". Its program diagram is shown in Figure 2.

2.2.2 Measurement data waveform restoration and display
This module is mainly used to restore the waveform of the measurement data and realize the control of the waveform. This part realizes five multi-channel working modes such as channel A, channel B, channel C, channel D, and full selection through a 5-frame digital CASE structure.
During the design process, the waveform display window makes the five "waveform chart" controls transparent and superimposes them with a 20×10 background grid to complete the display functions of the cursor and four-channel waveforms respectively. This design solves the problem that when multi-channel waveforms are displayed simultaneously in similar software in the past, the single-channel waveform cannot be controlled independently. Each channel is controlled by a set of "translation along the Y axis" and "base control" knobs; while the "translation along the X axis" and "time base control" of all channels are controlled by the same set of knobs [4]. Its program diagram is shown in Figures 3 and 4.

2.2.3 Waveform parameter measurement
This module is mainly used to measure the basic time domain parameters of the waveform, which is mainly divided into two parts: macro parameter measurement and cursor measurement. Macro measurement is to calculate the fixed-length data read to obtain its signal time domain parameters. Cursor measurement can be used to measure the points or areas of interest in the waveform to obtain the time domain parameters of the signal in the area[5].

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2.2.4 Filtering
Filtering is mainly used to filter the fixed-length data waveform read. This part calls the Butterworth filter, Chebshev filter, inverse Chebshev filter, elliptic filter, Bessel filter and other function units in LabVIEW to realize four filtering functions, namely low-pass filtering, high-pass filtering, band-pass filtering and band-stop filtering. The filtering purpose is achieved by setting parameters such as high cutoff frequency, low cutoff frequency, order and attenuation.
2.2.5 Spectrum analysis
According to the "Heisenberg principle", spectrum analysis of a certain sensitive area in the data can effectively solve the problem that effective information cannot be accurately obtained when performing spectrum analysis on massive data. This module mainly uses the FFT transformation in the function library to obtain the single-sided amplitude spectrum of the signal and display the result in the specified display window [6].
2.2.6 Printing
Printing is a very important data storage method. This part realizes the printing of charts, parameters and other information by calling controls such as "Add report text".
3 Operation results and analysis
After the system was built, in order to verify that the system can work normally and the performance is good or bad, an experiment was organized and a set of sine wave signal data was collected through the storage test subsystem. Its parameters are shown in Table 1.

3.1 Waveform display
After opening the program, enter the storage address of the sine wave test data file into the address bar of the four channels, and adjust each control knob to obtain the graph when each channel is displayed simultaneously (i.e. all channels are selected), as shown in Figure 5.

After comparison, it was found that the software can restore the measured data without distortion, and realize the function of simultaneous display and separate control of four-channel waveforms. Compared with previous similar software, this module can complete the waveform comparison more conveniently and intuitively.
3.2 Waveform parameter measurement
After multiple segmented reading and measurement of the data, the measurement results are compared with the parameters of the signal itself as shown in Table 2.

As can be seen from Table 2, the error of the results obtained by both cursor measurement and macro measurement is relatively small compared with the original signal parameters, and the module can correctly measure the waveform parameters.
3.3 Filtering Processing
To verify the filtering function of the system, a sawtooth wave with a frequency of 50 kHz and an amplitude of 1 V is superimposed on the sine wave signal in advance, and the mixed waveform is shown in Figure 6.

The filter parameters are set as follows: the topology is Butterworth filter, the filter type is low-pass filter, the cutoff frequency is 0.1 (normalized frequency, 20 kHz), and the order is 2. Run the filter processing function module, and the waveform after filtering is shown in Figure 7.

The sawtooth wave frequency is 50 kHz and the sine wave frequency is 10 kHz. When the filter type is low-pass and the cutoff frequency is 20 kHz, the filter successfully filters out the sawtooth wave and obtains the sine wave graph.
3.4 Spectrum Analysis
In the measurement data, 1 024 points are read from the 1 000th point for spectrum analysis, and the obtained spectrum graph is shown in Figure 8.

From the unilateral amplitude spectrum of the signal, it can be seen that most of the signal power is concentrated at the frequency point of 10 kHz, which is consistent with the facts, and there are fewer leakage and side lobes, and the signal-to-noise ratio also meets the engineering requirements.
This paper designs a multi-channel data analysis system based on virtual instruments. With the storage test technology, it can conveniently and reliably test the parameters of the weapon system, giving full play to the advantages of storage test technology that does not require leads and has strong anti-interference ability. It is an advanced means to solve parameter testing in high temperature, high impact, and high pressure environments, and has a good prospect for promotion and application.