基于LabVIEW的虚拟双踪示波器的设计

基于LabVIEW的虚拟示波器的设计毕业论文摘要虚拟仪器是现代测量技术和计算机技术相结合的产物，标志着自动测试与电子测试仪器领域技术发展的一个崭新方向．随着信息技术和计算机技术的高速发展，数字信号处理作为一门新兴的学科，其重要性日益在各个领域的应用中体现出来。

本文介绍了利用LabVIEW 图形编程语言进行虚拟仪器开发的方法，设计了一种基于PC机声卡的虚拟示波器，说明了虚拟仪器在现代测试领域中的重要地位以及其广阔的发展前景．从某种意义上说，“软件就是仪器”。

关键词LabVIEW,虚拟仪器，示波器The design of virtual wave displayer based onLabVIEWAbstractVirtual instrument is the produce that merges the computer technology and measurement technique．It stands for a brand new development directory in the field of auto-measurement and electronic measurement。

With the rapid development of information technology and the computer technology, the digital signal processing takes an emerging discipline, its importance displays day by day in each domain application. This article introduces how to develop virtual instruments using graph programming language-LabVIEW ,designs a virtual signal displayer based on PC and explains the important part and wide development prospects of virtual instrument in modern measurement technique field．In a sense, “The sof tware is an instrument”.Keywords LabVIEW, virtual instrument目录第1章绪论 (1)1.1 虚拟仪器的概述 (1)1.1.1 什么是虚拟仪器 (1)1.1.2 虚拟仪器的构成 (2)1.1.3 虚拟仪器的优点 (3)1.1.4 虚拟仪器的发展现状 (4)1.1.5 虚拟仪器的发展趋势 (4)1.2 图形化编程语言LabVIEW (4)1.2.1 什么是LabVIEW (5)1.2.2 LabVIEW的主要特点 (5)1.2.3 LabVIEW调试与运行 (6)第2章示波器的原理 (7)2.1 模拟示波器 (7)2.1.1 示波器的基本结构 (7)2.1.2 示波器的扫描原理 (8)2.2 数字示波器 (9)2.2.1 数字示波器的基本原理 (9)2.2.2 数字示波器的特点 (11)2.3 虚拟示波器 (12)第3章系统的硬件设计 (14)3.1 声卡 (14)3.1.1 声卡的工作原理 (14)3.1.2 声卡的基本结构 (14)3.2 硬件设置 (16)3.2.1 实验中声卡的参数设置 (16)3.2.2 虚拟示波器中声卡的连接方式 (16)3.3 前置运算电路 (17)第4章系统的软件设计 (18)4.1 虚拟示波器工作流程图 (18)4.2 数据采集模块 (18)4.3 频谱分析模块 (22)4.4 数据测量和显示模块 (23)第5章系统调试与程序显示 (25)5.1 虚拟示波器性能 (25)5.1.1 程序设计思路 (25)5.1.2 虚拟示波器操作界面 (25)5.1.3 虚拟示波器总程序框图 (26)5.2 虚拟示波器波形显示 (27)结论 (30)致谢 (31)参考文献 (32)附录 (34)第1章绪论1.1虚拟仪器的概述虚拟仪器是计算机技术和传统的仪器仪表技术相结合的产物,它是在以计算机为核心的硬件平台上,由用户设计和定义其功能,具有虚拟面板. 虚拟仪器技术具有高效、易用、开放、灵活、更新快、功能强大、性价比高、用户定义等诸多优点. 目前在我国应用的虚拟仪器开发平台主要有美国NI公司的LabVIEW及其相应组件和Agilent公司的HP - VEE ,其中NI的LabVIEW系列产品在我国使用比较广泛.LabVIEW是当前用于数据采集、信号处理和虚拟仪器开发的一个标准工具,而且是一个基于图形化编程语言的虚拟仪器软件开发工具,设计者可利用它方便快捷地建立自己的虚拟仪器程序而无需复杂的程序代码编写. 它适用于多种操作系统,用LabVIEW设计的虚拟仪器程序可以脱离LabVIEW开发环境,最终用户看见的是和实际的硬件仪器相似的操作面板1.1.1什么是虚拟仪器所谓虚拟仪器，就是在通用计算机为核心的硬件平台上，由用户设计定义、具有虚拟面板、测试功能由测试软件实现的一种计算机仪器系统。

基于LabVIEW的虚拟双踪示波器的设计外文翻译外文文献A DAQ card based mixed signal virtual oscmoscopeAbstractComplex signals find many applications in SONAR, RADAR，Echo Location Systems and for studying the resonant frequencies. Digital StorageOscilloscopcs(DSO) is used these days for acquisition and display of routine signals. This instrument, found in every measurement laboratory, though potent in displaying simple periodic waveforms like sinusoids fails when frequency-varying time signals are applied, This problem surfaces because the underlying technique of oscilloscope used to trigger the waveform does not acquiesce with complex signals like chirp. Ready solution to this problem is the mixed signal oscilloscope. This is a costly solution and small laboratories cannot afford to have the costly instruments. In this paper, a cost effective DAQ card based mixed signal virtual 0scilloscope is proposed to study the complex signals. An intelligent technique, Weighted Hamming Distance (WHD) algorithm was used to accurately trigger the complex waveforms. Also for frequency domain analysis, Joint Time Frequency Analysis(JTFA) techniques were used. A LabVlEW'TM based virtual instrument was designed and developed with a capability to acquire, display and analyze the triggered signal. The integrated programming language LabVIEWTM was chosen as it offers many simple ready to use functions. In a way the proposal offers a cost effective, fast and flexible solution to treat the complex signals. The need to createsuch solutions is the consequence of costly hardware systems. The deficiency of conventional hardware. Scheme for the virtual oscilloscope for complex signals with some real time experimental results are presented in this work.Kevywords: Virtual instrumentation,Chirp signal,Data acquisition,Triggering, Complex signals, JTFA1.IntroductionFor the last two decades there has been a tremendous progress in computer technology. Measurement domain is no longer left unaffected. The way measurements are being done is totally revolutionized. Computer based measurement or say virtual instrumentation is gradually replacing the costly bench 1top instrumentation as it offers flexible,fast and cost effective solutions. Various classical instrumentation systems namely Oscilloscope, Multimeters and Spectrum analyzers ect. are almost phased out by their counter part virtual instrumentation. Our research extends the trend and demonstrates the developmen of the computer based mixed signal digital oscilloscope.Conventional signals such as the sinusoids have a constant frequency and the amplitede only varies with time throughout the signal definition. On the other hand, complex signals can be defined in this context as signals in which all the parameters vary. Fig.1 shows a typical complex signal i.e. Linear Chirp.Variation of amplitude and frequency with time can easily be understood by having a look at the signal. This requires a visually stable display of signal. The complex signal offers challenges f'or acquisition, display an analysis. Even the conventional modernage DSO is not capable of displaying and analyzing complex signals because these instruments employ simple triggering technique like level trigger. The conventional technnique of voltage trigger apparently fails when complex signals like chirp are analyzed on DSO. This is due to the very fact that these instruments consider chirp as a conventional sine wave and trigger for each cycle of the sine wave instead of triggering for the complete chirp cycle. This analysis of the chirp signal as several sine waveforms of different frequencies leads the DSO to display them as sinusoids in quick succession. As this rapid change occues at a very high rate and because of human eye not registering events occurring faster than 1/20th of a second the display appears as several overlapped sine waves. In the recent work[1], a new triggering technique was proposed for the complex signals based on WHD. Subsequent sections present the solution to the problem. For analysis of the complex signals in frequency domain JFFA technique is utilized and implemented[2-6].DSO uses the level trigger to display the waveform applied to it. This leads to trigger interval and the number of samples for this trigger interval is computed and these numbers of samples are display. The DSO considers the interval as the fundamental time period of the whole waveform and thus takes tbat much samples from its buffer and starts displaying it in quick succession. With simple waveform like a sine wave, level trigger can achieve stable display because trigger interval contains same number of cycles. This is shown in Fig. 2a.23Now for the complex signal as shown in Fig.2b, leveltriggering produces a trigger interval having variable number of cycles for the same number ofsamples/time resulting in a visually unstable display.The actual trigger interval should be one complete cycle for a chirp signal as indicated in Fig. 2c. Having done this the repeated chirp signal for this time duration will be displayed without any overlapping components as long as the entire time period is displayed.To observe the shortcomings experimentally in display of complex signals on the oscilloscope T ektronix dual channel signal generator AFG-3022 (250 MS/s, 25 MHz) was used to generate a chirp signal by choosing the sweep mode to sine waveform with its frequency varying linearly with respect to time. This signal was fed to TektronixTDS-2022 (2 GS/s, 200MHz) dual-channel DSO. The overlapping display as shown in Fig. 3 was observed.2. Intelligent method of triggeringAccurate triggering lies solely on correct identification of the time period of waveform under consideration. For this purpose, pattern recognition scheme was implemented to identify the pattern in the signal [1] and thus obtain the time period of one complete cycle of the chirp. First, a fixed number of samples N are taken as reference pattern. Then the signal is shifted by one sample to form the test pattern. This pattern is then tested for its closeness' to the reference pattern. Closeness' can be defined as the distance by which test pattern is away from reference pattern.WHD is used as the decision function for closeness. Hamming distance is defined for two binary vectors as the number of different' bits are given their vectors. InWHD the different bits are given their binary weightingaccording to the bit position45and their weights according to the bit position and their weights are summed up. WHD of two binary n bit number x and a is given byIf X and A are two binary vectors of n-bits element, then WHD for these two vectorsis computed by summing up the element by element WHD and is given byFor a vector of dimension N, the samples are shifted N times and its closeness is computed at each shift.When these computations are done, the difference 洫in the signals is found to be minimum (ideally zero when no noise) when the cycle repeated itself. Following are the major steps involved and implemented for intelligent trigger mechanism.1. Acquiring the long enough signal using DAQ card and to convert the decimal values of samples into binary form.2.A fixed number(N) of binary samples are stored in array. The stored samples are shifted by a fixedc number of samples, n (=1,inthis case).3. The original saved samples and the shifted samples are XORed bit-by-bit.The result is then multiplied by a factor of 2, where I represent the position of bit.4.The summation of all the resulting values gives the WHD for nth shifts.65.A plot of WHD vs. n is made and the minimum is calculated by peak detection method. The difference between two successive minima is the trigger interval in number of samples.6. The number of samples multiplied by the sampling rate results in trigger interval (in seconds).As a test case WHD algorithm is implemented for the following triangular waveforrn in Fig.4.The waveform is sampled at 8 points per eycle. Each sampled value is 3 bit length.The step by step implementation is given below.WHD waveforrn is plotted using WHD(1), WHD(2), …, WHD(8), and the location of the minima gives the triggering interval. Fig.5 shows the WHD waveform also clearly indicating the trigger interval at 8th sample.The WHD VI(Fig.6) was developed for this task. It takes the waveform, whose triggering interval is to be found, and the no of samples, on which computation is to be done, as input and outputs the sample at which minima occurs along with the value of minima and the WHD waveform. For typical chirp signal WHD waveformis obtained as shown in Fig.7. The number of samples between two consecutive minima is equal to the number of samples in one cycle of the waveform. The product of the number of samples with the sampling interval is the triggering interval of the input signal. Thus, the virtual instrument could also display complex waveformswith considerable aese. Fig.7 shows triggering interval of 5 cycles.3. Frequency domain analysisFor simple signals the frequency analysis is performed by traditional tools like FFT. For such signals the Fourier Transform works well as their frequency components remain constant throughout the signal existence and hence there is no need forthe time-frequency relationship. In case of complex signals the frequency varies with time. FFT fails to analyze these signals as it gives information about thefrequency and its amplitude. Time information is lost.78In order to overcome this difficulty, there are JTFA tools iike Short TimeFourier Transform(STFT) and Wavelet Transform. These are implemented for the signals under consideration.The STFT is a modified form of Fourier Transform. In this technique the signal is rnultiplied with a window function and their product's Fourier Transform (2).The main principle behind this technique is that the window function(w) breaks down the signal into segments of small finite durtion. The frequency component of the signal during this segment is assumed to be constant. By computing the Fourier Transform for this segment the frequency vs. amplitude information is obtained. Then the window is moved to another segment by a step having the same duration as the previous one giving the frequency component for that segment. Thus the frequency for different time intervals gives time-frequency relationship.However, there is a disadvantage with this tecnique. The size of the window function used is fixed, thus STFT will have same resolution for low and high frequencies. Resolution is the certainty by which one can determine time or9frequency information. It is generally seen that a larger window leads to better frequency resolution and a small windowleads to better time resolution. Thus, it depends upon the user whether he wants frequency or time resolution. Even if there is a need for change of resolution, the user has to do the same manually.To overcome the resolution problern, a more advanced technique called Wavelet Transform is used these days. In this the window size can be altered, using a scalingparameter a. The equation for Wavelet Transform is given as wherea is the scaling parameter,b is the translation parameter,x(t) is the signal to beanalyzed andis the wavelet functionThe wavelet function <(t) is known as the mother wavelet ．Its scaled and time shifted versions are known as the daughter wavelets. These daughter wavelets having varying size offer different frequency and time resolutions at different frequencies. The scale parameter a represents the freequency component in an inverse relation. Thus the valuc of scale is inversely proportional to frequency component.Initially the wavelet function has scale a=1 and is placed at the starting of the signal. The wavelet transform and thus the frequency component of that segment. Then the wavelet function is moved by b steps and the wavelet transform is computed for that segment. This procecdure is continued till the end of the signal. Thus Wavelet transform for a=1 and all the time steps till the end of signal getscomputed. Similarly the wavelet function is again placed at the start of the signal but with changed value of scale a. Theprocedure is continued till the Wavelet transform for each scale and time step combination has been computed.It can be observed that the computation of Wavelet Transform leads to a lot of redundancy.To reduce the redundancy, the scale values and the time steps can be linked using dyadic sampling. a= 2" and b=k 2' where n and k are integers. This leads to reduction in redundancy. This is called Discrete Wavelet Transform(DWT).4. ImplementationA DAQ card based virtual instrument was designed and developed inLabVIEW TM programming environment. This virtual instrument has the capability to generate intelligent software trigger as described above for complex waveforms like chirp. The main decisionns during design of the virtual instrument are: choosing the data acquisition card and, what is equally important, choosing the set of features the instrument should offer. The choice of the data acquistion card has a great influence on the efficiency of the whole instrument[7，8].Particular DAQ cards are differentiated by price and, the specification it offers.A low cost NIPCI-6035E, 16bit, 200KS/s card was chosen. The hardware was programmed at maximum sampling rate. A separate problem is designing software, which, in that case, is the main part of instrument design phase. The major features of the developed virtual instrument are:The capability to acquire and process simple and complex waveforms.Dual channel mode: The instrument is capable of displaying two inputs simultaneously and can perform simple mathoperations between the two.Auto set: Runs the WHD code to re-compute the trigger interval for the new signal and thus achieve a stable display. In case, the two inputs do not have the same frequency, the LCM of the trigger intervals of A and B is found to so that integral number of cycles of both the channels can be shown simultaneously.Time domain measurements: The signal being displayed in time domain are measured on various parameters-Amplitude-Peak to peak-Mean(DC)-RMS101112Fig. 9. The results of wavelet transrorm implemented in the virtual instrument. (Channel A analyzing sine signal and Channel B analyzing a chirp signal). Frequency Domain Aalysis: The plot of Magnitude vs. frequency, Phase vs. frequency and the facility to choose the windowing function.STFT based Joint Time Frequency Analysis (JTFA): The spectrogram with the additional choices of the plotting the graph with scale in decibels, windowing functions and the window length for STFT analysis.Wavelet based Joint Time Frequency Analysis(JTFA)：The scalogram which plots scales vs. time steps, choice of time-frequency sampling parameters like time steps and scales and the choice of wavelet functions.For the frequency domain analysis, DSP toolkit available withLabVIEW softwarewas utilized. Standard functions are available in the toolkit. The virtual instrument thus developed is intelligent as it takes different actions with different signals contrary to a digital storage oscilloscope. Trigger implemented enables us to obtian the correct value of the time period and a stable display. Analysis of complex signals can also be performed using this instrument. Fig.8 shows the front Panel of the virtual instrument showing Time-domain measurements. Fig.9 shows the time frequency relationship on both the channel B analyses the chirp signal. As seen clearly the chirp signal shows the varying frequency with time.5. Limitations of developed virtual instrumentSamples for few cycles are required to determin the triggering interval. One need to optimize tbe appropriate sampling rate and the number of samples to be processed. The processing time taken by the WHD technique is directly proportional to the number of samples and hence to the sampling rate as the higher sampling rate leadsto the more number of samples per cycle. The time required to compute trigger also depends upon the speed of the computing system. For large amount of data (if high sampling rates us fixed), computationally heavy WHD algorithm and other features for more analysis, the butter might overflow leading to loss of data. Every time the input waveform is changed user has to do retriggering.6. Conclusion and discussionSuccessful development of the virtual instrument with the capability of acquiring, displaying and analyzing complex signals is done. The instrument over comes the shortcomings of theDSOs, found commonly in laboratories, in achieving stable display for complex signals. The developd instrument is cost effective and flexible in nature and had the large number of features to choose from. The computer towards the measurement systems. The VI developed is expected to go a long way in the instrumentation area.1314 基于混合信号的数据采集卡的虚拟示波器摘要：复杂的信号在声纳、雷达、回声定位系统和谐振频率的研究中有多种应用。

「基于LABVIEW的虚拟示波器设计—虚拟示波器」虚拟示波器是一种通过计算机软件来模拟传统示波器的工作原理和功能的设备。

它可以用于信号的检测和分析，具有方便、灵活、实时性强等优点。

本文将介绍基于LABVIEW的虚拟示波器设计。

LABVIEW是由美国国家仪器公司（National Instruments）开发的一种基于图形化编程的开发环境。

它可以实现快速的数据采集和处理，适用于各种工程应用。

借助LABVIEW的强大功能，我们可以设计出一个功能完善的虚拟示波器。

首先，我们需要从外部设备中获取信号。

LABVIEW支持多种类型的数据采集设备，如数据采集卡、传感器等。

我们可以通过连接这些设备，将信号输入到LABVIEW中。

LABVIEW提供了丰富的数据采集和处理函数，能够方便地获取并处理输入信号。

接着，我们需要设计一个用户界面，用于显示信号和调节示波器的各个参数。

LABVIEW中提供了多种界面控件，如图表、调节器等。

我们可以根据需要，在用户界面中添加这些控件，并设置相应的属性。

通过LABVIEW的可视化编程方式，我们可以直观地完成用户界面的设计。

在信号显示方面，虚拟示波器需要能够实时地显示输入信号的波形。

LABVIEW提供了图表控件，可以用于显示波形图。

我们可以将获取到的信号数据传递给图表控件，然后设置相应的显示参数，如坐标轴范围、背景颜色等。

这样，用户就能够清晰地看到输入信号的变化。

除了实时显示信号波形外，虚拟示波器还应具备其他功能，如调节触发电平、选择触发方式等。

LABVIEW中提供了丰富的函数库，可以方便地实现这些功能。

我们可以通过在用户界面中添加调节器、开关等控件，并将其与相应的函数进行关联，从而实现示波器的各个参数的调节。

总之，基于LABVIEW的虚拟示波器设计具有很大的灵活性和可扩展性。

我们可以根据需求进行定制，实现更多功能，如频谱分析、数据存储等。

同时，LABVIEW提供了强大的数据处理和可视化功能，能够让我们更加方便地进行数据分析和结果展示。

双踪信号发生器
设计思路：
信号发生器是一种能提供各种频率、波形和输出电平电信号的设备。

在测量各种电信系统或电信设备的振幅特性、频率特性、传输特性及其它电参数时，以及测量元器件的特性与参数时，用作测试的信号源或激励源。

1)总体设计思路
在波形的选择上，使用条件结构，枚举选择对应的波形。

生成的波形可加入均匀的白噪声，通过前面板的开关可以选择是否加入噪声，通过开关的布尔量可以将暂停波形页面。

上图为使用条件结构，枚举选择对应的波形
上图为整体结构的框图
2) 前面板的设计
前面板实现输入波形、频率、幅值、相位、占空比的设置，还有通道及是否加入白噪声的选择。

上图为双踪信号源前面板整体图形
3) 程序框图
对于不同的波形选择，这里采用枚举选择的方式,通道一波形及参数设置如下图所示：
对于通道一、通道二、通道一与二同时显示波形图也是枚举类型的采用条件结构。

程序框图如下：
对于是否加入均匀白噪声的程序框图如下：
软件功能：
1) 单一通道波形显示：
当运行LabView时首先按下运行按钮，运行指示灯亮。

选择通道、波形及输入参数得到通道一显示波形如下图所示：
2) 双通道波形显示
在通道选择处选择“通道1与通道2”，设置好波形及输入参数得到通道一显示波形如下图所示：
3) 添加均匀的白噪声
在添加噪声处选择是否加入噪声，并设置好波形及输入参数。

因噪声不稳定所以加入噪声后可以点击运行按钮，运行指示灯灭，此时图像暂停。

如下图所示：
4) 退出
当完成所需信号的发生时，点击“关闭”按钮即可退出该虚拟仪器的使用。