Flowtime Clock: What flowtime is it?

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The World Market for Ultrasonic Flowmeters, 3rd Edition (New study, January 2008)

The World Market for Ultrasonic Flowmeters, 2nd Edition (2003) - Provides historical perspective

The World Market for Ultrasonic Flowmeters, 1st Edition (2001) - Provides historical perspective

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.

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