Abstract: This paper introduces virtual instruments and LabVIEW, and proposes a general design scheme for a virtual signal oscilloscope analyzer. Based on this, the software design of each part of the instrument is described in detail. After testing and practical application, the instrument functions normally, operates reliably, and can meet the needs of university laboratories and scientific research, thus achieving the design requirements. Keywords: LabVIEW, virtual instrument, virtual oscilloscope, virtual analyzer Abstract: Based on the introduction of virtual instrument and LabVIEW, this paper presents the overall design of a virtual signal oscilloscope analyzer, and details the software design of different parts of the analyzer. After testing and practical application, the analyzer functions normally and reliably, meeting the requirements of laboratories and scientific research in higher education institutions, thus achieving the design goals. Keywords: LabVIEW; virtual instrument; virtual oscilloscopes; visual signal analyzer 0 Introduction Oscilloscopes not only provide a visual representation of electrical signals over time, but also allow direct observation of basic parameters such as amplitude, frequency, and period of measured signals. Signal analyzers can perform time-domain and frequency-domain analysis of signals and are widely used in medicine, biology, mechanical engineering, geology, and university laboratories. Oscilloscopes have become the most typical instruments for time domain analysis, and are also the most common, most numerous, and most frequently used instruments in the current measurement field. However, oscilloscopes and analyzers are expensive, and their functions are fixed and cannot be changed according to needs. With the development of virtual instrument technology, people have proposed to use virtual instrument software to develop virtual instruments based on general hardware and computer technology for laboratory and engineering practice [1][2][3]. In order to make full use of the characteristics of virtual instruments and the functions of computer software, we designed and developed a virtual signal oscilloscope analyzer. This instrument not only has the basic functions of a general digital oscilloscope, but also realizes some functions of a signal analyzer to meet the experimental and scientific research requirements of general colleges and universities. 1 Virtual Instruments and LabVIEW 1.1 Features of LabVIEW LabVIEW is a general graphical software development environment launched by NI (National Instruments) in the United States. It uses graphical programming instead of text programming used by general high-level languages ​​to create applications. It is a general programming language based on data flow control, suitable for any programming task, and has an extended database [4]. LabVIEW is an open environment with simple connection to measurement hardware, which can quickly complete data acquisition and can be easily connected to various instruments; it has more than 600 built-in analysis functions, which can easily extract useful information, perform measurement data analysis and signal processing; it also has strong data display, interface design and data management functions. It greatly facilitates research work in testing and measurement, fault diagnosis, process control and industrial automation, and has therefore been widely used in many fields around the world such as aerospace, communications, automobiles, machinery, semiconductors and biomedicine. 1.1 Introduction to Virtual Instruments Virtual instruments are computer-based instruments, which are test platforms composed of existing computers, general hardware and special software. The biggest feature of virtual instruments is that they give full play to the capabilities of computers, have strong data processing capabilities, and users can define and manufacture various instruments according to their own needs. The difference between various instruments is mainly in the software [5]. Virtual instruments are an important development direction in the current measurement and control field, and LabVIEW is considered to be the standard data acquisition and instrument control software. The program written in LabVIEW is called Virtual Instruments (VI). Its program panel is programmed in a graphical block diagram form, which is simple and fast; its front panel is an interactive user interface, which is equivalent to the instrument panel of a real physical test instrument, making it convenient for users to operate. At present, LabVIEW has become one of the main software for developing virtual instruments. In this development, we chose LabVIEW 8.0 as the development platform for the signal oscilloscope analyzer. 2 Overall Design [align=center] Figure 1 Block diagram of the virtual signal oscilloscope analyzer[/align] The virtual signal oscilloscope analyzer we developed is mainly used for data acquisition, display, waveform storage and playback, time domain and frequency domain analysis of electrical signals. It not only has the functions of a general digital oscilloscope, but also the basic functions of a signal analyzer, so as to be applied in laboratory teaching and scientific research. The instrument is mainly composed of the following functional modules (Figure 1): (1) Data acquisition module. On the front panel of data acquisition, the channels, sampling rate, number of sampling points, maximum/minimum voltage values ​​and signal connection methods are set. Data acquisition is completed in the control panel using the functions of DAQmx related functions. (2) Signal display and triggering module. This module mainly controls the display ratio of the signal by adjusting the time base and the Y coordinate values ​​of the two channels respectively to complete the time domain display of the signal, and provides trigger control so that the time domain display has the function of trigger display. (3) Basic parameter measurement module of the signal. It mainly calculates some basic statistical quantities of the two channel signals: amplitude, peak-to-peak value, effective value and frequency, etc. (4) Signal storage and playback. It mainly completes the storage of the acquired signal and recalls the previously stored acquisition results for time domain display and time domain frequency domain analysis. (5) Signal analysis module. It sets the filtering and windowing selection of each channel signal, completes the autocorrelation, autopower spectrum, amplitude frequency and harmonic analysis, and cross-correlation and cross-power spectrum analysis between the two channel signals. 3 Design of signal oscilloscope analyzer 3.1 Design of front panel The front panel of the VI program is an interactive user interface, which is equivalent to the instrument panel of a real physical test instrument. When designing, we should fully consider the requirements of human-centered design, consistency, relevance, feedback and simplicity, based on the relevant theories of ergonomics, so that the front panel is easy to operate and comfortable, and will not cause fatigue even after long-term use. When designing the front panel of this analyzer (Figure 2), we mainly considered the following aspects: (1) The color of the entire panel and buttons is mainly dark gray, simply divided by some thin blue frames, so as to make the interface clear and concise, which meets the requirements of information display interface comfort in ergonomics; (2) The signal display uses the Graph control, and the display area should be as large as possible so that the signal situation can be clearly observed. The cursor function of Cursor Legend is used to enable the instrument to read data points; (3) Since there is a lot of content on the front panel, the items are grouped according to categories, and the categories are grouped together with thin blue frames, so that the entire panel is not cluttered and clear at a glance, which meets the "functional zoning" principle of display in ergonomics; (4) When designing the front panel, we should refer to the existing oscilloscope panel form as much as possible to make the user operation simple and convenient. [align=center] Figure 2 Instrument Data Acquisition and Display Front Panel (Running)[/align] 3.2 Data Acquisition [align=center] Figure 3 Signal Oscilloscope Analyzer Main Block Diagram Program[/align] In LabVIEW, data acquisition tasks can be set using the MAX interface, or tasks and channels can be set using the data acquisition assistant provided by DAQmx, thereby generating program code. In this design, since the goal is to develop a general-purpose platform based on NI's data acquisition card, we used the Task, Channel, and Timing functions in DAQmx to complete the settings for tasks, channels, and clocks, and compiled a data acquisition setting sub-VI. In the main program, a loop is used to read data, and data acquisition and analysis processing can also be completed. The specific program can be seen in the main block diagram program in Figure 3. 3.2 Signal Display and Trigger In terms of signal time domain display, three aspects need to be controlled: one is the time base (scan rate), i.e., the change of the X-axis coordinate of the Graph control; another is the amplitude (range), i.e., the change of the Y-axis coordinate of the Graph control; and the third is the trigger display control. By using the property node of the Graph control, the change of the time base signal is adjusted by changing the value of the Graph's XScale.Range property. For a single-channel virtual signal oscilloscope analyzer, the amplitude change can be controlled using the same method as the time base signal. However, since we have multiple channels input separately, we need to independently control the signal coordinate change in the Y-axis direction according to the specific situation of each channel signal. Therefore, we extracted the y-component of the signal separately and created a sub-VI to control the Y-coordinate change to achieve independent control of the amplitude change. Based on the SCOPE.VI sub-VI provided by LabVIEW, a Trigger sub-VI was created, which together with the Y-coordinate change sub-VI constitutes the Y display trigger sub-VI. 3.3 Signal Storage and Playback LabVIEW data storage generally uses four file formats: text files, binary files, data log files, and waveform files. Text files are a universal format, while data log files and waveform files are file formats that only LabVIEW can read. Data log files and waveform files are relatively simple to operate and can be used in this design. Since we mainly process waveform data, we chose waveform files as the file format for storage and playback. 3.4 Basic Signal Parameter Measurement and Analysis [align=center] Figure 4 Signal Analysis Block Diagram Program[/align] To clearly see some basic information of the signal during data acquisition, a basic quantity measurement module was developed, mainly measuring the frequency, amplitude, peak-to-peak value, and RMS value of the signal, and displaying the above parameters of the two channels respectively. Switching the front panel from data acquisition to the time-domain and frequency-domain analysis panel can display the analysis results of the measured signal. Here, we developed a signal analysis sub-VI (Figure 4) and a cross-correlation analysis sub-VI. The amplitude-frequency diagram, autocorrelation, and self-power analysis results are shown in Figure 5. [align=center] Figure 5 Amplitude-frequency diagram, autocorrelation, and self-power analysis of channel A signal[/align] 4 Conclusion During the debugging process of the program, we tested it using a virtual card and NI's PCI 6221 and USB 6008 cards respectively. The running results were stable and the functions were normal, meeting the design requirements of data acquisition, display, waveform storage and playback, time-domain and frequency-domain analysis, etc. It has been applied to laboratory scientific research and teaching, and has achieved good results. The author's innovations include: proposing the development of a virtual oscilloscope analyzer, which combines the functions of an oscilloscope and a signal analyzer, realizing the basic functions of both instruments; and using programming rather than changing control properties to achieve independent display and control of the amplitude of the two channels, laying the foundation for the development of multi-channel instruments. References [1] Ai Yanting, Huang Fuxing, et al. Software design of virtual signal analyzer based on LabVIEW [J]. Microcomputer Information. 2005, 5:171-172. [2] Guo Yingfu, Luo Xiaoli, et al. Design of virtual dynamic analyzer based on LabVIEW [J]. Mining Machinery. 2006, 4:125-126. [3] Zhou Weilin, Yang Huayong, Li Qingfeng. Design of digital filter based on LabVIEW [J]. Microcomputer Information. 2006, 5-1:163-164. [4] Hou Guoping, Wang, Ye Qixin. LabVIEW 7.1 programming and virtual instrument design. Beijing: Tsinghua University Press, 2005. [5] Yang Leping, Li Haitao, et al. LabVIEW programming and application (2nd edition). Beijing: Electronic Industry Press, 2005.