Research On Signal Processing Of Vortex Flowmeter Based On Stochastic Resonance

The vortex flowmeter is a flow induced vibration flowmeter and is appliedextensively to the measurement of pipe flow rate due to its many advantages.However, it is easily disturbed by the vibration from the pipeline and a variety ofequipment when it is used in industrial field. The noise signal adds to the outputsignal so that the measurement accuracy is affected especially during the low flowrate measuremt when the vortex shedding signal is too weak to submerged in noiseleading to the limitation of low flow rate measurement and application range. Thenonlinear signal processing technology based on stochastic resonance is a newlydeveloped signal processing technology. The noise energy can be transferred to thesignal energy under specific conditions, so as to improve the SNR and identify theweak vortex signal. The signal detecting technology based on stochastic resonancewas applied to the detection of vortex shedding frequency in the thesis.The mainlyworks of this thesis are listed in the following:1、The stochastic resonance characteristics of nonlinear bistable system withnoise and weak periodic signal was investigated in this thesis.The sensitivity of thesystem response to the input singal with different frequencies was given bynumerical calculation. The matching condition among the input signal, noise and thenonlinear bistable system to produce stochastic resonance was analyzed.2、According to the frequency characteristics of the nonlinear bistable systemresponse to the different periodic signal, the heterodyne stochastic resonance systemwas designed in order to adapt to the characteristics of vortex flowmeter outputsignal. By the action of the mixer, the vortex signal and the carrier signal generatethe signal with two different frequency components. The lower one is easy to getmore energy from the noise and form strong stochastic resonance in bistable system.The frequency of the vortex could be measured accurately by frequency scanning.3、 The parameters of the heterodyne stochastic resonance system wereinvestigated to know the influence on frequency measurement. In order to generateand reach the strongest stochastic resonance effect, the stochastic resonance vortex signal processing system with frequency scanning and adaptive function is developedby LabVIEW. The SNR of the system output is the criteria for parameters adjustmentto realize the vortex shedding frequency measurement.4、The experiment system of vortex flowmeter was constructed. The hardwareand software of the vortex flow detection system was designed. The vortex signalwith noise was acquired real-time. The characteristics of the heterodyne stochasticresonance system responsed to the different vortex flow rate especially to weakvortex signal in low flow rate were investigated. The frequency of the vortexshedding can be measured accurately by developed signal processing system, so doesthe flow rate. The method extends the limitation of low flow rate measurement ofvortex flowmeter effectively and provides a new signal processing method for vortexflowmeter.