|
About
Ultrasonic Flowmeters
There are
two main types of ultrasonic flowmeters: transit time and Doppler.
A transit time ultrasonic flowmeters has both a sender and a
receiver. It sends two
ultrasonic signals across a pipe at an angle: one with the flow, and one
against the flow. The meter
then measures the “transit time” of each signal.
When the ultrasonic signal travels with the flow, it travels faster
than when it travels against the flow.
The difference between the two transit times is proportional to
flowrate.
Doppler
flowmeters also send an ultrasonic signal across a pipe.
Instead of tracking the time the signal takes to cross to the other
side, a Doppler flowmeter relies on having the signal deflected by
particles in the flowstream. These
particles are traveling at the same speed as the flow. As the signal passes
through the stream, its frequency shifts in proportion to the mean velocity
of the fluid. A receiver detects the reflected signal and measures its
frequency. The meter calculates flow by comparing the generated and
detected frequencies. Doppler ultrasonic flowmeters are used with dirty
liquids or slurries. They are
not used to measure gas flow.
Ultrasonic
flowmeters were first introduced for industrial use in 1963 by Tokyo Keiki
(which later became Tokimec) in Japan.
Tokimec is located in Tokyo, Japan.
In 1972, Controlotron (Hauppauge, New York) became the first U.S.
manufacturer to market ultrasonic flowmeters in the United States.
In the late 1970s and early 1980s, both Panametrics (Waltham,
Massachusetts) and Ultraflux (Poissy Cedex, France) experimented with the
use of ultrasonic flowmeters to measure gas flow.
Initially, ultrasonic flowmeters were not well understood, and were
sometimes misapplied. Many
technological improvements have been made in the past 10 years, and the
limitations of ultrasonic meters are better understood.
Advances in transit time technology have broadened the types of
liquids that transit time flowmeters can be used on. Many transit time
meters today can handle liquids containing some impurities.
For
further information on ultrasonic flowmeters, and detailed market reports,
please see www.flowultrasonic.com.
| 
