Rockwell Automation 1734sc-IE4CH E+H Instruments via HART to PlantPAx User Manual - Manual (Page 98)

98 Rockwell Automation Publication PROCES-UM002A-EN-P - July 2014
Appendix D Prowirl 73 Flowmeter
Vortex meters work on the principle of the Karman vortex street. When fluid
flows past a bluff body, vortices are alternately formed on both sides with
opposite directions of rotation. These vortices each generate a local low pressure.
The pressure fluctuations are recorded by the sensor and converted to electrical
pulses. The vortices develop very regularly within the permitted application
limits of the device. Therefore, the frequency of vortex shedding is proportional
to the volume flow.
The K-factor is used as the proportional constant:
Measured Variables
• Volumetric flow (volume flow) is proportional to the frequency of vortex
shedding after the bluff body.
• The temperature can be output directly and is used to calculate the mass
flow for example.
• The measured process variables volume flow, temperature or the calculated
process variables mass flow, heat flow or corrected volume flow can be
output as the output variables.
v
K-Factor =
Pulses
Unit Volume [dm 3 ]