ONICON F-2600 - Manual (Page 13)

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F-2600 & F-2700 Vortex Flow Meter Manual 02/15 - 0808-7 / 19204 Page 13
1.2 HOW THE ONICON VORTEX MASS FLOW METER OPERATES
Figure 1. In-Line Multi-Parameter Vortex Mass Flow Meter
ONICON F-2600 Series & F-2700 Series Vortex Mass Flow Meters use a unique sensor
head to monitor mass flow rate by directly measuring three variables. fluid velocity,
temperature and pressure. The built-in flow computer calculates the mass flow rate
and volumetric flow rate based on these three direct measurements. The sensing head
is built into the vortex meter’s flow body. To measure fluid velocity, the flow meter
incorporates a bluff body (shedder bar) in the flow stream and measures the frequency of
vortices created by the shedder bar. Temperature is measured using a platinum resistance
temperature detector (PRTD). Pressure measurement is achieved using a solid-state
pressure transducer. All three elements are combined into an integrated sensor head
assembly located downstream of the shedder bar within the flow body.
1.2.1 Velocity Measurement
ONICON’s vortex velocity sensor is a patented mechanical design that minimizes the
effects of pipeline vibration and pump noise, both of which are common error sources
in flow measurement with vortex flow meters. The velocity measurement is based on the
well-known Von Karman vortex shedding phenomenon. Vortices are shed from a shedder
bar, and the vortex velocity sensor located downstream of the shedder bar senses the
passage of these vortices. This method of velocity measurement has many advantages
including inherent linearity, high turndown, reliability and simplicity.