JP2933016B

The present invention relates to a vortex flowmeter which is configured to calculate the flowrate of a measuring fluid flowing through a flow path using ultrasonic signals subjected to changes in the propagation time due to Karman vortices, provided with a reference signal generation means outputting a plurality of reference signals of different phases, a signal analyzing means to output an input status signal by determining the relationship between the phases of the above ultrasonic signals and each reference signal above, a plurality of the phase-detection means to output phase signals by detecting the phase differences between the above ultrasonic signals and the above reference signals, and a channel-selection means to select the above optimum phase signal using the above input status signals and to output it as the selection signal, and which computes and outputs the flowrate signals using the above selected phase signal. In such a manner, the vortices can be stably detected even if a phase change due to the vortices in vortex flowmeters is large.