Study On The Optical-Fiber Vortex-Shedding Flowmeter Based On The Optical Frequency Modulation Principle

Vortex-shedding flowmeter has become one of the most indispensable members in the kaleidoscopic family of flowmeter because of the unique measuring features. Its posterity, optical-fiber vortex-shedding flowmeter is so prospective in its application in the measurement field not only for the merits up from vortex-shedding flowmeter but also those in optical fiber sensor such as flexibility, strong endurance, anti electromagnetic interference capacity and adaptation in the flammable explosive environment.The thesis aims at the contrivance of a brand new optical-fiber vortex-shedding flowmeter, which can be applied in some formidable conditions, meantime reaches certain demand of precision. First, this thesis illuminates not only the features of the optical-fiber vortex-shedding flowmeter, but also the research status in the field both nationally and internationally. Second, it dwells upon the wave-guide discipline of the optical fiber and uses the optical-fiber as the sensor. Meanwhile the researcher carries out the research on the liquid field around a column, liquid force on the optical fiber sensor and the transmission loss along the optical fiber sensor respectively from such aspects as hydrodynamics, crystal physics and wave optics theory. Then, the author evaluates the round range of frequency to be measured and the amplitude of the AC signal which was transformed from light signal to electrical signal, analyses the security of the deformation on optical-fiber, then demonstrates the feasibility of the project, explains the discipline of frequency measurement. Moreover, the thesis illuminates much on how to use the SCM system, which can be used for frequency and volume flow measurement, the design of flowmeter's mechanical structure, the signal processing circuit and the flow accumulator. After all these efforts, the researcher designs programmed windows with VB Language to test the performance the signalprocessing circuit which includes its measurement precision and the capability of anti electromagnetic interference with the weak signal source from AFG320 and then describes the low-power consumption. In order to minimize the measurement error, the thesis puts forward some advice on improving measurement precision.Today, most of the researches on the optical-fiber vortex-shedding flowmeter are carried out on the primary stage in the lab, yet the flowmeter is foreseeable to deserve its future reputation of application because of these unique merits. Some of the efforts in the essay, such as the analysis on the transmission loss from several different angles and the application of W78E58B SCM system to frequency measurement are so creative that they will be helpful for the further research.