flowmeters were first introduced to the market in 1969.
Since that time, the number of worldwide suppliers has grown to at
least 35. Between the time
they were first introduced and today, many changes have taken place in the
vortex flowmeter market. These
include anti-vibration software and electronics, multivariable flowmeters,
reduced bore meters, plastic vortex flowmeters, and much more.
Today there is a wide diversity of choices for customers to make
when specifying or purchasing vortex flowmeters.
flowmeters operate on a principle called the von Karman effect.
This principle concerns the behavior of fluids when an obstacle is
placed in the path of flow. Under
the right conditions, the presence of the obstacle generates a series of
alternative vortices called the von Karman street.
This phenomenon occurs in liquid, gas, and steam, and has been
observed in many diverse contexts including cloud layers passing an island
and whitewater rapids.
flowmeters, the obstacle takes the form of an object with a broad, flat
front called a bluff body. The bluff body is mounted at right angles to the flowstream.
Flow velocity is proportional to the frequency of the vortices.
Flowrate is calculated by multiplying the area of the pipe times the
velocity of the flow.
order to compute the flowrate, vortex flowmeters count the number of
vortices generated by the bluff body.
They use a variety of techniques for sensing the presence of a
vortex. The majority of vortex
flowmeters use a piezoelectric sensor; however, some use a capacitive
sensor and others use an ultrasonic sensor to detect vortices.
Despite what has been slow
growth in the vortex flowmeter market, there are signs that this flowmeter
is breaking out of its slump. One
sign is the major product enhancements that have occurred in the past five
years. One perennial problem with vortex flowmeters has been susceptibility
to vibration error. Vibrations
in the line can cause a vortex flowmeter to falsely generate a vortex
signal, or to incorrectly read an existing vortex.
Suppliers have responded to issues surrounding vibration by
implementing software and electronics, including digital signal processing,
that have reduced the susceptibility of vortex meters to interference from
positive sign is the growing availability of multivariable vortex
flowmeters. Sierra Instruments
introduced the first multivariable vortex flowmeter in 1997.
This flowmeter includes an RTD temperature sensor and a pressure
transducer. By using
information from these sensors, together with detection of vortices
generated, the flowmeter can output volumetric flow, temperature, pressure,
fluid density, and mass flow. Multivariable
flowmeters measure more than one process variable, and typically use this
information to compute mass flow. This makes the flowmeter measurement more accurate in
changing temperature and pressure conditions.
the past five years, a number of new suppliers have brought out their own
multivariable vortex flowmeters. These
include ABB (Goettingen, Germany), Yokogawa (Tokyo, Japan), Krohne (Duisburg,
Germany), and Endress+Hauser (Reinach, Switzerland).
Even though multivariable flowmeters are somewhat more expensive
than their single-variable counterparts, they enable users to obtain
significantly more information about the process than single-variable
volumetric meters. This
additional information can result in increased efficiencies that more than
make up for the additional cost of the multivariable flowmeter.
further information on Vortex meters, including detailed market reports,
please see www.flowvortex.com.