Vortex flowmeter uses the principle of fluid oscillation to measure flow. When the fluid passes through the vortex flowmeter in the pipeline, behind the vortex generator of the triangular column, two rows of vortices proportional to the flow rate are alternately generated up and down. The frequency of vortex release is related to the average velocity of fluid flowing through the vortex generator and the characteristic width of the vortex generator, which can be expressed as follows:

f=Stv/d

Where: f is the release frequency of vortex, Hz; V is the average velocity of fluid flowing through the vortex generator, m/s; D is the characteristic width of the vortex generator, m; St is Stroh Hal number, dimensionless, and its numerical range is 0. 14-0.27. St is a function of Reynolds number, and St=f(l/Re).

When Reynolds number Re is in the range of 102~ 105, the St value is about 0.2. Therefore, in the measurement, the Reynolds number of the fluid should be within the range of 102~ 105 as far as possible, and the vortex frequency f = 0.2v/d.

Therefore, by measuring the vortex frequency, the average velocity v of the fluid flowing through the vortex generator can be calculated, and then the flow rate q can be obtained by the formula q=vA, where a is the cross-sectional area of the fluid flowing through the vortex generator.

When eddy currents are generated on both sides of the generator, the change of alternating lift perpendicular to the direction of fluid flow is measured by piezoelectric sensor, and the change of lift is converted into an electric frequency signal, which is then amplified and shaped and output to the secondary instrument for accumulation and display.