Ultrasonic flow meter: Difference between revisions

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==External links==
==External links==
{{Commons}}
{{Commons}}

* [http://www.youtube.com/watch?v=Bx2RnrfLkQg 3D animation of the Ultrasonic Flow Measuring Principle]
* [http://www.mathpages.com/rr/s2-04/2-04.htm Doppler Shift for Sound and Light] at MathPages
* [http://www.mathpages.com/rr/s2-04/2-04.htm Doppler Shift for Sound and Light] at MathPages
* [http://www.kettering.edu/~drussell/Demos/doppler/doppler.html The Doppler Effect and Sonic Booms (D.A. Russell, Kettering University)]
* [http://www.kettering.edu/~drussell/Demos/doppler/doppler.html The Doppler Effect and Sonic Booms (D.A. Russell, Kettering University)]

Revision as of 16:03, 1 July 2010

An ultrasonic flow meter measures the velocity of any liquid or gas through a pipe using ultrasonic transducers. The results get slightly affected by temperature, density or viscosity of the flowing medium. Maintenance is inexpensive because there are no moving parts. Some may be able to measure liquid level as well. With the level measurement and pipe size, flow rate and total discharge can be calculated.

Ultrasonic flow meters work with at least three different types:

  • Transmission (contrapropagating transit-time) flowmeters
  • Reflection (Doppler) flowmeters
  • Open-channel flowmeters

Transmission flowmeters can be distinguished into:

  • In-line flowmeters (intrusive, wetted)
  • Clamp-on flowmeters (non-intrusive)

Transit-Time Flowmeters (general)

The most commonly used ultrasonic flowmeter is the transit-time flowmeter which is used for liquids and gases.

Transit-time flowmeters work by measuring the time of flight difference between an ultrasonic pulse sent in the flow direction and an ultrasound pulse sent opposite the flow direction. This time difference is a measure for the average velocity of the fluid along the path of the ultrasound beam. By using the absolute transit time and the distance between the ultrasound transducers, the current speed of sound is easily found. The measuring effect can be adversely affected by many things including gas and solid content.

By using at least 3 transducers, an "ultrasonic anemometer" measures wind speed and direction in open air, with no moving parts.

Transit-Time Clamp-On Flowmeters (non-intrusive)

For clamp-on flowmetry, the ultrasonic transducers are mounted (clamped) on the outside of the pipe wall. For accurate flow computation, the transducer distance, the pipe dimensions and the pipe material has to be known. The soundspeed of the flowing medium is needed for initial transducer positioning but is updated during the flow measurement.

Doppler Flowmeters

Doppler flowmeters are used for slurries, liquids with bubbles, gases with sound reflecting particles, or single phase turbulent clean liquids.

Measurement of the doppler shift resulting in reflecting an ultrasonic beam off either small particles in the fluid, air bubbles in the fluid, or the flowing fluid's turbulence is another recent, accurate innovation made possible by electronics.

Open-channel Flowmeters

Open channel flow measurement is based on upstream levels in front of flumes or weirs although in-channel devices using cross-correlation and doppler are also used. Ultrasonic open channel flow meters are widely used to measure flows in streams, rivers and where hydraulic head is an issue. Many examples of open channel flow meter exist in the world today with varying degrees of accuracy.

References

  • Lipták, Béla G.: Process Measurement and Analysis, Volume 1. CRC Press (2003), ISBN 0-8493-1083-0 (v. 1)
  • Ultrasonic Acoustic Sensing Brown University
  • Lynnworth, L.C.: Ultrasonic Measurements for Process Control. Academic Press, Inc. San Diego. ISBN 0-12-460585-0

External links