Abstract: The invention encompasses a vortex flowmeter for measuring the flow rate of a fluid by detecting an alternating signal produced by Karman vortices using a sensor comprising a low pass filter for passing the frequency band of the alternating signal that is determined by the diameter and flow rate range of the vortex flowmeter; subband filters for splitting the frequency band passing through the low pass filter into a plurality of component bands; a spectrum analyzer for analyzing the plurality of component bands; and a bandpass filter for passing a frequency band to be measured according to the analysis results of the spectrum analyzer, thereby providing flow rate measurement with high precision.

Abstract: A vortex flowmeter for calculating the flow rate of a measuring fluid flowing through a flow path using ultrasonic signals subjected to changes in the propagation time due to Karman vortices, comprising a reference signal generating device for outputting a plurality of reference signals of different phases; a signal analyzing device for outputting an input status signal by determining the relationship between the phases of the ultrasonic signals and each reference signal; a plurality of phase detectors for outputting phase signals by detecting the phase difference between the ultrasonic signals and the reference signals; and a channel selector for selecting the optimum phase signal using the input status signal and for outputting the optimum phase signal as a selection signal, wherein the flow rate signals are computed and outputted using the selected phase signal. The vortices are thus stably detected even when a phase change due to the vortices in the vortex flowmeter is large.