基于LabVIEW的虚拟双踪示波器的设计外文翻译(共22页).doc
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1、精选优质文档-倾情为你奉上外文文献A DAQ card based mixed signal virtual oscmoscopeAbstract Complex signals find many applications in SONAR, RADAR,Echo Location Systems and for studying the resonant frequencies. Digital Storage Oscilloscopcs(DSO) is used these days for acquisition and display of routine signals. This
2、 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
3、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 comple
4、x 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 LabVlEWTM based virtual instrument was designed and developed with a ca
5、pability 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 create such sol
6、utions 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, Comp
7、lex signals, JTFA1.Introduction For 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
8、 replacing the costly bench top 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 th
9、e 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 co
10、ntext 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
11、or acquisition, display an analysis. Even the conventional modern age 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 l
12、ike 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 frequ
13、encies 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 work1, a new triggering
14、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 implemented2-6. DSO uses the level trigger to display the waveform applied to it. This leads to
15、 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 successio
16、n. 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. Now for the complex signal as shown in Fig.2b, level triggering produces a trigger interval having variable number of cycles for the s
17、ame number of samples/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
18、the entire time period is displayed. To observe the shortcomings experimentally in display of complex signals on the oscilloscope Tektronix 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 var
19、ying 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 triggering Accurate triggering lies solely on correct identification of the time period of waveform under c
20、onsideration. 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 t
21、he 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
22、 of different bits are given their vectors. In WHD the different bits are given their binary weighting according to the bit position and 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 by If X and A are two binary vectors o
23、f n-bits element, then WHD for these two vectors is computed by summing up the element by element WHD and is given by For 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 b
24、e 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 bi
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