The FPV 58 series Vortex Flowmeter is basing on kormaon's vortex street theory. When the liquid pass non-streamlined barrier, alternative vortex signal will be generated on both sides of the barrier. Piezocrystal, as the transmitter will check the signal; the analog circuit and digital circuit will convert it to current, pulse signal output in positive proportion with flow rate. The total will be clearly displayed.