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The vortex flow meter is also a velocity-type flow meter that places a flow element in the flow stream that is not streamline. When the flow stream strikes the flow element, a series of vortices is produced (shedded). Hence this type of flow meter is sometimes called a vortex shedding flow meter. When a vortex is produced, it causes the fluid to create a swirling motion as it moves. A very sensitive electronic detector can detect the presence of the vortices. The number of vortices that are produced is directly proportional to the flow rate. This type of sensor is very accurate and it can also be used when the fluid has suspended solids (slurries) moving in the flow. The number of vortices that are detected can be averaged to produce a flow rate, or they can be added to produce a total flow. A frequency-to-voltage circuit and amplifier must be used to increase the small-pulse signal from the electronic detector. It’s also important to understand that the vortex-type flow meter works best in very turbulent flows. ill. 1 shows the location of the flow element in a pipe. ill. 2 and Fig.3 show several vortex flow meters.
ill. 1: A vortex flow meter. Notice the blunt object placed in the flow
stream that causes the flow to create vortices as the fluid flows around
it. Each vortex is counted with a very sensitive electronic detector.
Fig 2: Examples Vortex meters used to measure flow. These are made by
Omega Engineering. Omega’s FV-600 and FV-500 Series vortex meters operate field-proven vortex shedding principle.
The FV-600 can operate on liquids with up to 6 centistoke viscosity; however,
the minimum measurable flowrate rises to 50% of max. span. The 4 to 20
mA output is suitable for use with standard chart recorders and computer
interfaces.
ill. 3: Another vortex flow meter from Omega
Engineering. The FV101 Series, shown above, is an inline flow meter
that uses the vortex shedding measuring principle. The fluid strikes
a bluff body which imparts alternating vortices downstream of the bluff
which create a pressure on a sensor body containing a piezoelectric crystal.
The frequency of the sensor is proportional to the velocity of the fluid and is amplified and converted to a 4 to 20 mA output linear with flow.
Vortex technology means a meter with no moving parts to seize up or wear.
The meter has a 76.2 mm (0.3") high LED display of flow (units may
be displayed as liters or gallons). The vortex flow meter can be mounted
with flow in any direction and the display can be rotated 180° in the
field for viewing convenience. The FV101 Series can be used on non-viscous,
clean or dirty water-like liquids that are compatible with brass, PVDF and Viton®. Metered fluids shouldn't include long fibers or high levels
of abrasive solids. Typical applications will include: cooling loops
using water or 50% glycols, and water soluble machine coolant (up to
10%). These applications are encountered in many process industries,
including rubber, steel, fabrication, manufacturing, refining, paper,
chemical, food, petrochemical and power. Don't use this meter with flammable
liquids or gases such as air.
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