| Vortex flowmeter is designed on the basis of Karman vortex street principle. Because of excelling others in some aspects, it develops speedily from 1970's. Relevant data indicates that the proportion of the use of vortex flowmeter increases considerably in developed countries, such as Japan, European and American countries in recent years and it is widely applied to various fields.Vortex flowmeter will play a leading role in all kinds of flowmeters in the future.But existing vortex flowmeter has its own disadvantage.Its noise immunity is poor and its lower limit of measuring range is high.This thesis will research into this problem.In chapter one, the thesis expounds the recent developments in flow measuring, and describes the operational principle, advantages and disadvantages of the vortex flowmeter , and the current research on it. Technical proposal is also given in this chapter.In chapter two, describes the component of the vortex flowmeter , and determines to use triangular prism as vortex generator and piezocrystal as stress detecting sensor. A novel type of vortex sensor with suspending differential structure is brought forward . Then this thesis analyzes its operational principle . The experiment result is ideal.In chapter three, describes the limitation of the current method in vortex signal processing , determines to use spectral analysis technology for signal processing . Analyzes the characteristics of vortex signal , designs a differential charge amplifier with gain adaptive function, and analyzes its operational principle.In chapter four, selects periodogram realizes the power spectrum analysis , take advantage of Radix-4 algorithm to calculate FFT ,and describes the realization in MCU .The vortex flowmeter designed in this project has excellent noise immunity and wide measuring range ratio.In chapter five,describes the low-power realization by use of modern low-power technology.So the vortex flowmeter can be supplied by dry battery and applied in the zone where there isn't industrial electrical source .In chapter six, describes the vortex flowmeter realizes all kinds of controlling displaying and communication function. The vortex flowmeter is highlyintelligent.At last ,summarized the total thesis and introduced some theories that need more researches.The innovation in this thesis is listed below:1) Attenuate the noise from circumstance and get the differential signal with the same intensity and frequency with 180° phase difference by use of the suspending differential vortex sensor;2) Eliminate the noise with the same direction and output the signal in the full range of the A/D converter by use of the gain adaptive charge amplifier;3) Realize the power spectrum analysis for the flow signal based on a low power MCU and design a smart vortex flowmeter with low power consumption. |
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