The “Karman” vortex meter principle is clearly illustrated by a flag waving in the wind. As the air passes across the flag pole, vortices peel off and the flag is shaped by these pressure area’s. You will notice that, at low wind velocity, the flag will move slowly from side to side. As the wind increases, the flag will start to flutter and ripple, representing the increased frequency and intensity of these flag pole generated vortices as they pass. Wind velocity can thus be determined by measuring the frequency of that flutter.

The small vortex strut of the Cadillac Vortex Meter sheds the vortices, which then pass through an ultrasonic beam, generated by flush mounted transducers (see illustration), where they are detected and counted. The frequency of these vortices is directly proportional to the fluid velocity and exact volumetric flow rate is computed knowing the internal cross sectional area. Each vortex meter is tested to determine the relationship between velocity/flow rate and vortex frequency, which results in a meter K-factor expressed in “Pulses/Gallon”. This volumetric relationship is then converted to relative engineering units, which the flow meter converter can then retransmit via a 4-20 mADC current signal or conditioned pulse.

An optional LCD Indicator/Totalizer can display and totalize in engineering units of the users choice. For compressible mediums, such as gases and steam, the meter amplifier can correct for temperature and pressure with the MASS option, which includes a temperature element in shedder bar and look up tables for ideal gases and steam. For mediums other than saturated steam an external pressure source must be provided as shown in the drawing below. Outputs from the meter with the MASS option are compensated and linear for the compressible medium being measured.