| Virtual Instrument is a great new production what is based on computer hardware andsoftware in addition bus technology inosculating with measuring and instrumentationtechnology. With the rapid development of computer science and Internet technology, the VIstandard founded on open modular criterion is becoming more and more consummate, variousadvanced instruments based on VI will emerge endlessly, and the price will be much cheaper.It is a trend that using Virtual Instrument to studying, designing and testing. After analyzing the VI's actuality, this paper researches a virtual electric parametermeasuring system applying to electrical experiment teaching: Virtual Three-phase AC ElectricParameter Measuring Device and Virtual Scope. The PC-DAQ mode is selected to constitutethe VI measuring system. And the graphical programming language LabVIEW is used assoftware development platform. A specimen of the virtual measuring system has completed. During the hardware circuit design, the signal conditioning circuit and the DAQ card isimportant to whole system's accuracy. This paper expatiates the design of signal conditioningcircuit, includes the design scheme, rationale and parameters selection. This paper also showsmatters need attention in doing printed circuit board. About the software, the idea of modularized design is emphasized in this paper. Theoptimum sampling process DMA is adopted to enhance the precision of data acquisition,many sub program module are introduced in details, they are the parameters measuring, rangeswitching & control, frequency spectrum analysis, digital filter modular and so on. Themethod how to create executable program and installation routine is also explained. The experimental results are recorded and the sampling error is also analyzed in thispaper. It can be seen that this testing system is satisfactory. At the last, this paper presents the conclusion and recommendations.
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