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Articles
about Variable Area Flowmeters
All
Flowmeter Studies
About
Variable Area Flowmeters
Most
variable area (VA) flowmeters consist of a tapered tube that contains a
float. The upward force of
the fluid is counterbalanced by the force of gravity.
The point at which the float stays constant indicates the
volumetric flowrate, which can be often read on a scale on the meter tube.
VA meter tubes are made of metal, glass, and plastic.
Metal tubes are the most expensive type, while the plastic tubes
are lower in cost. Metal
tubes are used for high-pressure applications.
While
most VA meters can be read manually, some also contain transmitters that
generate an output signal that can be sent to a controller or recorder.
While VA meters should not be selected when high accuracy is a
requirement, they do very well when a visual indication of flow is
sufficient. They are very
effective at measuring low flowrates, and can also serve as flow/no-flow
indicators. VA meters do not
require electric power, and can safely be used in flammable environments.
One
important development for variable area flowmeters is the development of meters with a
transmitter output. The HART
protocol is available on some meters.
This turns the VA meter into more than a visual indicator, and
makes it possible to do control and recording.
A class of VA meters called purgemeters have been developed to
handle a variety of low flow applications.
Other areas of research include float design and materials of tube
construction, especially metal.
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