中文 5650 字 - 1 - 中文 5650字 附 錄 Research & Development of Virtual Oscillograph Based on LabVIEW Abstract: This paper introduces the design process of a virtual oscillograph based on LabVIEW. Mainly analyzes the amplitude value and time base adjusting methods during the real-time display. At the same time, it simply introduces the basic thought when measuring the period and frequency of the waveform gate voltage method and its application. At the end of this paper, combining the parameter measurement and waveform display of the virtual oscillograph with the modern motor close-loop lock-phase speed control, it analyzes the parameter measurements effect in PID control. Keywords: Virtual Oscillograph; Time-Base; Motion Control . INTRODUCTION In the rapidly developing industry control field, measuring technologies and apparatus become more and more important. But because of the disadvantages of the traditional instruments such as high price, single function, bad expansibility, etc., they can hardly meet the industry requirement. With the development of computer technologies and virtual instruments (VI for short), the scope designed by users becomes widely. There are many different functions with the same hardware which can make two or more machines work synchronously with the advanced bus technologies such as PXI bus technology 1.Virtual instruments become more and more popular for its upstanding characteristics like low cost, multi-function, facility and so on. All measuring instruments consist of three parts: data acquisition, data analysis and results output 2. In these three parts, data acquisition can be done by the system hardware like A/D module or digital I/O modules. Data analysis and results output can be completed by software system based on computer. So, if given some necessary data acquisition hardware, a measuring instrument based on computer can be constituted. The software technology is the essential one in the virtual instrument. 3 Visual C+, LabVIEW, LabWindows/CVI, VEE etc. are all development software environment. LabVIEW is a graphic programming language called G language, which can be used in GPIB, VXI, PXI, PCI Bus and data acquisition cards based hardware system, has powerful analyzing ability. Its graphic programming method can be used to finish the total program by dataflow clearly and simply. Using its embedded board card driver interface, we can conveniently operate a board card. 4, 5 Multi-channel digital oscillograph, which mainly used in real-time data acquisition, is one of the most widely used general measuring instruments. It also can display the changes of some electric signals and compare the differences among different signals. So the research and development of virtual oscillograph is the hotspot in the area. Making use of the Graph platte in LabVIEW, you can conveniently acquire the dynamic waveforms and make them displayed. But most virtual oscillographs based on LabVIEW use the Graph platte to operate and analyze the waveform data. Although this is very facile to use, it also has many disadvantages: (1) When the waveform changes all the time, the screen will keep refreshing and the graph platte could not properly work. (2) The operation method cant satisfy most of operators because it is different from the tradition oscillograph in operation. To solve these problems, this paper brings forward 附 錄 - 2 - some ways. In the real- time waveform display, we redevelop the waveform operation and introduce some related software arithmetic. It introduces the exploiting thinking of adjusting dynamic time base and put forward two concepts: the FIFO process and E-M process. In addition, it introduces a successful gate-voltage measure way in the measurement of the period and frequency, and based on which, the paper puts forward the application in the close-loop lock-phase System. II. RESEARCH ON THE MULTICENTER DIGITAL OSCILLOGRAPHS SOFTWARE ARITHMETIC The virtual oscillograph introduced by this paper is mainly used in laboratory for the measurement and storage of various analog signals. The main functions are: data acquisition, waveform display, parameter measurement, waveform storage and replay etc. It has 64 analog signal input channels and can take 8 signal observations at the same time with the choice of switch matrix. According to the requirement, we use the NI-6133 Daq card for the data acquisition. The block diagram of virtual oscillograph is shown in Fig. 1: 6 Now we will introduce the soft arithmetic to the basic functions of virtual oscillograph. A. Characteristics of Graph Control In LabVIEW, there are three controls for waveform displaying: Graph, Chat and x-y graph. Every control has its own advantages. This paper takes Graph control for example to discuss the soft arithmetic to the basic function of virtual oscillograph. Graph oscillograph displays all waveform data input in the screen at a time. Every time when the waveform data are input, the screen will be freshed. 7 Using its own operation tools, you can move, zoom the waveform or use the cursors to measure the parameters. But it could not work well on dynamic waveform. So its necessary to develop a more convenient operation tool to real-time display of dynamic waveform. In the virtual oscillograph introduced in this paper, there are some basic functions such as amplitude and position value adjustment, time base change, trigger mode selection etc. The oscillographs front panel is shown in fig.2. 附 錄 - 3 - B. Amplitude Value Adjustment Multi-center oscillograph can display more than one waveform at the same time, so it is very convenient to compare every signal change. Every waveform displayed should be operated separately through the selecting box on the front panel. At first, we distribute the screen into 1010 grids and set every channel a Y-axis. The value of every one of the 10 grids in the Y-axis is equal to the value of related amplitude knob control. With the property node of the waveform graph, you can set the minimum value of each Y-axis as -5 times much as the knob value whereas the maximum value set 5 times. So when you change the amplitude knob value, the minimum and the maximum value of the relevant Y-axis should be changed at the same time, the waveform display can be zoomed as required, and the zero point position is kept in the original location. Use an array to save the amplitude values every Y-axis changed. When a channel is selected, put its old amplitude value to the knob first; and after adjusting, replace the related array element with the new value. And then the amplitude value change function is finished. C. Time Base Adjustment Time base adjusting is one of the basic functions in oscillograph. The time base adjusting knobs value shows the time of every one grid of X-axis in the screen which is the nodus during the oscillograph design procedure. 1) Basic Clew According to the characteristics of the Graph control, it displays all the data input at a time. So distribute the X- axis into 10 grids and make every grids time t. If the waveform could bestride the whole X-axis, the time spent to collect all the data is 10t. Suppose the boards sampling rate is f, in other word, the board collects f data every second. So the number N needed in the waveform is: N= fl0t =l0ft （ 1） Keeping the board sampling at the frequency of f, the program reads N data points from the board memory and put them to the oscillograph in every loop. Change the t value is to change the N value read from board memory every time, and thus adjust the time base in the real-time sampling. But through the experiment we can see, when the time base is too long (100ms) or too short (=v and Xi-1v, the waveform is across the gate voltage from the top down, called negative edge. At the same time, to eliminate the infection brought by interference, get ride of the positive and negative edges whose interval is less than 10 sample points. So the position of positive and negative edge is acquired. Because the sampling rate is unchangeable, so the time slot between two sampling data is fixed. Thus the signal frequency and period can be calculated. 9 Suppose the sampling rate is f0 , the period is T0, T0 = 1/ f0, sampling rates error coefficient is a. The measured signals frequency is f, period is T, T= 1/f; the frequency measured actually is fC, TC, TC= 1/fC. Suppose at every sample time the sample contains k full periods of the measured signal, and the exact time is kT . The time of the first edge cross the gate point phase is t. Because of the disperse sample, at the kth period, the time when signal passes across the gate point phase t+kT may have an error T0. Considering the sampling rate error, at the worst state, at the kth period, the time when signal passes across the gate point phase is t+kT+(kT T0 )， and the time the k signal periods pass is t+kT+(kT T0) .So there it is: Suppose the sample length is L, there is LTokT. Put it on the Eq. (2) above, there is: When a is far smaller than 1/L， increasing the L value can increase the measure precision consumedly. When a is as much as 1/L, there is no significance to increase the L value. a is fixed on systems hardware. With a, it can find the proper L value that make the sample and calculation process under the best precision. Suppose the square signal, its pulse duration is T, the one measured is TC, so there is: 附 錄 - 7 - What discussed above is the period and frequency measurement in the sampling procedure, putting forward the measurement precision theory. But to the amplitude, rise time or spectrum analyze etc. are not discussed in this paper. Using the data group collected, the user can develop other better measurements. In LabVIEW, there is plenty of measuring VIs, which can measure the parameter exactly. 10 Combining the control procedure with virtual oscillograph can achieve better effect. Next, take DC motors PWM speed control for instance, it will introduce the function that using virtual oscillograph in PID and closed loop feedback controlling. IV. APPLICATION IN MOTOR SPEED CONTROL Lock-phase technology plays an important role on motor speed control. With the technology, it can improve the precision of motor speed; and also, it does stepless speed variation control only by changing the specified frequency, that will be conveniently used on controlling more than one motor work synchronously. 11 The basic theory diagram that indicates the speed control system based on PPL closed-loop lock-phase is shown in Fig.7. Suppose the specified pulse met the motor speed is fR, the pulse from photo sensor is fF. Compare their frequency and phase in the phase comparator, and bring the signal voltage proportion to frequency and phase difference. This voltage controls the motor speed through the low-pass filter to synchronize the motor speed and the specified control signal. In case the load is fluctuating which changed the motor speed, the pulse output from photo sensor is changing at the same time. There is difference between it and the specified signal. So the output of the phase comparator through the low-pass filter and driver circuit is changing, and make the motor faster or slower until the two frequencies of feedback and specified become equal. At that time, the motor is steady again. The feedback frequency is locked to the specify frequency, so the system control precision is very high. Combining the phase comparator and computer, taking the advantage of measurement and control of virtual instruments, we can get the digital lock-phase closed loop circuit. The theory diagram is shown in Fig 8. 附 錄 - 8 - In the diagram, motor speed is converted into square signal in proportion it refers to through the photo-sensor. If the speed value measured by virtual oscillograph is lower than the necessary one, the output frequency should be increased; oppositely, the output frequency should be decreased. In the actual controlling, the anticipant speed can be achieved quickly by comparing the frequency measured and specified, adjusting through PID. Following the PID theory, putting the secular equation and Jury criterion together, there are: Therefore, to keep the system working steadily, we should set KP = 1, KI = 1/2 It is quickly to adjust the output frequency to the anticipated one by PID revision. We can get the proper square signal through the wave form generator with the specific frequency, and the low-pass filter can convert it into relevant control voltage. The whole procedure is quick and steady. Using the measure function of virtual oscillograph can complete the same work as lock phase speed control system. Its advantage to traditional lock- phase speed control system is that it can use the control theory in the procedure, optimizing the control method. At the same time, the whole changing signal curve can be seen in the virtual oscillograph, the operator can clearly see the control and feedback state so as to solve the problems met with better methods. Using the multicenter and bus technology, it can control more than one motor at the same time, make them work synchronously, that is propitious to product line management and remote control. V. CONCLUSION The virtual oscillograph in this paper not only has the functions that common oscillographs have such as data acquire and display, parameter measurement, but also can be used in industry control, as an important part in motor speed control system. In the actual application, its flexibility is popular with more and more people. With different hardware, more complex and agile measuring system will be produced. With the development of computer and measurement technology, virtual instrument technology will play a more important role in many fields. VI. ACKNOWLEDGMENT This work is supported by natural science foundation of China under the research project 50375008 and 60575052. VII. REFERENCES 1 W.Jang, and F.Yuan,Design, of multicenter virtua oscillograph, China measurement technology, Vol.30 No.4, July, 2004. 2 F. M. Li, B. L. Ren, and W. W. Liu, the means of designing virtual instrument applications in LabVIEW environment, Journal of Shenyang University, Vol. 16, No.2, Apr.2004, China 3 J. C. Dong, Design of virtual oscilloscope based on LabVIEW, Journal of Qingdao University, Vol 17, No.3, Sept. 2002 附 錄 - 9 - 4 Getting started with LabVIEW, National Instruments Corporation, USA, 2003 5 J. H. Liu, Graphic language LabVIEW on virtual instruments tutorial, XiDian University Press, Xian China, 2001 6 M.Li, and Z.M.Wang, Design and implementation of virtual instrument based on LabVIEW 7i, Instrumentation Analysis Monitoring, No.4, 2004, China 7 LabVIEW user manual, National Instruments Coorperation, USA, 2003 8 B. Du, Measuring frequency and pulse-width in virtual- scope, Measurement & Control Technology, Vol 20, No.1, 2001, China 9 Data acquisition fundamental , National Instruments Corporation, USA, 2003 10 Beyon and J. Y., Hands-on exercise manual for LabVIEW programming, data acquisition and analysis, Upper Saddle River, N. J. Prentice Hall PTR, 2001 11 W. P. Huang, A single-chip microcomputer-based DC motors speed regulating system with all-digital and PLL control, Coal miner automation, No.3, 1997 附 錄 - 10 - 基于 LabVIEW 的虛擬示波器研究和開發(fā) 摘要 ：介紹了一種基于 LabVIEW 環(huán)境下開發(fā)的虛擬示波器的軟件設(shè)計過程；重點介紹了示波器實時顯示過程中的幅值和時基調(diào)整的方法，在保證實時性的前提下，對于 長短 時基顯示分別提出了各自的處理算法；同時，簡要介紹了波形的時頻測量的基本思想：門檻電壓法及其應(yīng)用；并在此基礎(chǔ)上，將其應(yīng)用于現(xiàn)代電機(jī)閉環(huán)鎖相調(diào)速系統(tǒng)，分析了參數(shù)測量在 PID 控制中的作用；實驗結(jié)果表明，該虛擬示波器實時性能良好，對系統(tǒng)的閉環(huán)控制起到了很好的作用。 關(guān)鍵詞： 虛擬示波器；時基；運動控制 . 引文 在高速發(fā)展的工業(yè)控制領(lǐng)域，測量技術(shù)和儀器變得越來越重要。但由于傳統(tǒng)手段的弊端，如價格 昂貴、功能單一、可擴(kuò)展性不好等，很難滿足業(yè)界的要求。隨著計算機(jī)技術(shù)和虛擬儀器的發(fā)展，用戶的設(shè)計范圍變得比較廣泛。用先進(jìn)的總線技術(shù)，同樣的硬件可以使兩個或者兩個以上的機(jī)器同步工作，實現(xiàn)很多不同的功能，如 PXI 總線技術(shù) 1。這些突出的特點，例如成本低、多功能等使得虛擬儀器的使用越來越廣泛。 所有的測量儀器都包括三個部分：數(shù)據(jù)采集部分，數(shù)據(jù)分析部分和結(jié)果輸出部分 2。在這三個部分中，數(shù)據(jù)采集部分可以由硬件系統(tǒng)的 A/D 模塊或數(shù)字 I/O 模塊來完成。而數(shù)據(jù)分析和結(jié)果輸出部分可由計算機(jī)基礎(chǔ)上的軟件系統(tǒng)來完成。因此，如 果給予一些必要的數(shù)據(jù)采集硬件，基于計算機(jī)便可構(gòu)成測量儀器硬件。同時，在虛擬儀器中，軟件技術(shù)也是必不可少的 3。 Visual C+， LabVIEW，LabWindows/CVI， VEE 等都是開發(fā)的軟件環(huán)境。 LabVIEW 是一個叫做 G 語言的圖形化編程語言。它可用在以 GPIB、 VXI 總線、 PXI 總線、 PCI 總線和數(shù)據(jù)采集卡等為基礎(chǔ)的硬件系統(tǒng)，具有強(qiáng)大的分析能力。它的圖形化編程方法可以用簡單 清晰 的數(shù)據(jù)流來完成總程序。 利用其嵌入式板卡驅(qū)動程序界面，我們可以很方便地操作一個板卡 4,5。 多通道數(shù)字示波器主要用 于實時數(shù)據(jù)采集，是一個最廣泛使用的通用測量儀器。它還能夠顯示出一些電信號的變化并比較彼此之間的差異。因此，研究和開發(fā)虛擬示波器是一個熱點領(lǐng)域。在LabVIEW 中利用 Graph platte，你可以很方便 地 獲取動態(tài)波形，并 把 它們顯示出來。大多數(shù)基于LabVIEW 的虛擬示波器都使用 Graph platte 來操作和分析波形數(shù)據(jù)。雖然 它 很容易使用，但也存在不少缺點：（ 1）當(dāng)波形一直變化時，屏幕就會一直刷新， Graph platte 就不能正常工作；（ 2）它的操作方法并不能滿足大多數(shù)的使用者，因為它在操作時不同于傳統(tǒng)的示波器。本文提出了一些辦法來解決這些問題。在實時顯示波形時，我們重建了波形操作并 介紹 了一些相關(guān)的軟件算法。在介紹中利用了時基上的動態(tài)調(diào)整并提出兩個概念： FIFO 進(jìn)程和 E-M 進(jìn)程。此外，還介紹了一個在測量時間和頻率中成功測量門檻電壓的途徑，并在此基礎(chǔ)上提出了在鎖相環(huán)系統(tǒng)中的應(yīng)用。 II. 多通道數(shù)字示波器軟件算法的研究 本文介紹的虛擬示波器主要用于實驗室中各種模擬信號的測量與存儲。其主要功能有：信號采集、波形顯示、參數(shù)測量、波形存儲與回放等。具 有 64 路模擬信號輸入通道，通過開關(guān)矩陣的選擇，可同時進(jìn)行 8 路信號的觀測。根據(jù)要求，硬件上選用 NI - 6133 同步采集卡作為信號采集模塊。該虛擬示波器的主要實現(xiàn)框圖如圖 1 所示 6。 附 錄 - 11 - 下面將介紹虛擬示波器基本功能的軟件算法實現(xiàn)。 A： Graph控件的特點 LabVIEW 提供了 3 種波形顯示方式 ： Graph， Chat， X-Y Graph。每種示波器各自具有不同的特點。本文以 Graph 為例，介紹虛擬示波器基本功能的程序?qū)崿F(xiàn)。 Graph 示波器是將一次輸入示波器的波形數(shù)據(jù)全部顯示出來，每進(jìn)行一次數(shù)據(jù)輸入操作， 便會刷新屏幕一次 7。利用自帶的操作工具，你可以移動、縮放波形或使用光標(biāo)來測量參數(shù)。但是它不能用于動態(tài)波形。因此，我們有必要開發(fā)一個更為方便的波形操作工具以實現(xiàn)動態(tài)波形的實時顯示。 在本文中介紹的虛擬示波器，有一些基本的功能，如有幅值位置及時基調(diào)整、觸發(fā)方式選擇等。圖 2 顯示了該示波器的前面板。 B：幅值調(diào)整 示波器具有多通道同時顯示的功能，便于各個信號之間的比較。對于每一條顯示的波形，應(yīng)該能夠分別對其進(jìn)行操作。通過面板上的通道選擇框，選定某一條波形后，可以單獨對該波形進(jìn)行操作。將示波器屏幕分成 1010 個網(wǎng)格。對于幅值調(diào)整按鈕，其上 的 數(shù)值對應(yīng)示波器縱軸方向每一小格所代表的信號幅度。因此，可以為每條波形設(shè)置一個 Y 坐標(biāo)軸，利用波形圖的屬性 節(jié) 點，將每個坐標(biāo)軸的最小值 設(shè)置 為幅值調(diào)節(jié)旋鈕所對應(yīng)數(shù)值的 -5 倍，最大值為其對應(yīng)數(shù)值的 5 倍。這樣，在改變幅值大小的同時改變波形所對應(yīng) Y 軸的最大最小值，將顯示的波形按照要求放大或縮小，同時保持波形 的 零點位置不變。 設(shè) 置 一個幅值數(shù)組，用于存儲每次調(diào)整后的波形幅值大小。這樣，每當(dāng)選擇某一條波形時，先將其上一次調(diào)整的幅值數(shù)據(jù)賦給幅值調(diào)整按鈕，在調(diào)整完畢后， 用 新調(diào)整的值覆蓋相應(yīng)的數(shù)組元 素。這樣，即完成了波形幅值調(diào)整的功能。 C：時基調(diào)整 時基調(diào)整是示波器中最基本的功能之一。時基調(diào)整按鈕的數(shù)值表示屏幕網(wǎng)格每一小格所代表的時間。這是示波器設(shè)計過程的難點。 附 錄 - 12 - 1） 基本思路 根據(jù) Graph 示波器的特點， 要 將一次輸入的所有波形數(shù)據(jù)點全部顯示出來。故將屏幕 X 軸分成10 格，設(shè)每格所表示的時間為 t，如果波形能夠橫跨整個 X 軸，則采集該段波形所需的時間為 10t。再設(shè)板卡采樣頻率為 f，即 1s 內(nèi)采 f 個數(shù)據(jù)點。因此，所需要波形數(shù)據(jù)點個數(shù) N 應(yīng)為： N= fl0t =l0ft （ 1） 保持 數(shù)據(jù)采集板卡以頻率 f 采集，程序在每一次循環(huán)內(nèi)讀取板卡內(nèi)存的 N 個數(shù)據(jù)并放入示波器中顯示。改變 t 的值即改變每次讀取的 N