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8
TECHNICAL DATA
96
SITRANS FX330
www.siemens.com/flow
05/2016 - A5E36751269-AA
8.1 Functional principle
Vortex flowmeters are used to measure the flow of gases, vapours and liquids at completely
filled pipes.
The measuring principle is based on the Karman vortex street. The measuring tube contains a
bluff body at which vortex shedding occurs and which is detected by a sensor unit located behind.
The frequency ffff of the vortex shedding is proportional to the flow velocity vvvv. The non-dimensional
Stouhal number S
S
S
S describes the relationship between vortex frequency ffff, width b
bb
b of the bluff
body and the average flow velocity vvvv:
The vortex frequency is recorded at the flow sensor and evaluated at the signal converter.
Figure 8-1: Functional principle
=
f
S . v
b