ABB FV4000 Operating Instruction page 19

Consequently, the vortex shedding frequency to be evaluated is dependent solely upon the flow
velocity and not at all upon media density and viscosity.
The local changes in pressure induced by vortex shedding are detected by a piezo sensor and
converted into electrical pulses corresponding to the vortex frequency.
The frequency signal from the flowmeter sensor, which is proportional to the flow, undergoes
downstream processing in the transmitter.
Fig. 7:
St = Strouhal number
L =
D184B097U02
How the Strouhal number is dependent upon the Reynolds number
Linear flow area
FV4000 / FS4000
Design and function
L
Re
G00602
Re = Reynolds number
19