Ultrasonic flow meter

Ultrasonic flow meter

A ultrasonic flow meter measures the velocity of a liquid or gas through a pipe using acoustic sensors. This has some advantages over other measurement techniques. The results are slightly affected by temperature, density or conductivity. Maintenance is inexpensive because there are no moving parts.

Ultrasonic flow meters come in three different types:
* Transmission (contrapropagating transit time) flowmeters
* Reflection (Doppler) flowmeters
* Open-channel flowmeters

Transit Time flowmeters

The most commonly used ultrasonic flowmeter is the transit time flowmeter which is used for liquids with low gas or solid content, as well as for 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.

Transit time flowmeters can be of the wetted or non-intrusive (clamp-on) type. By using at least 3 transducers, an "ultrasonic anemometer" measures wind speed and direction in open air, with no moving parts.

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)
* [http://www.cs.brown.edu/people/tld/courses/cs148/02/sonar.html Ultrasonic Acoustic Sensing] Brown University
* [http://www.electronics-manufacturers.com/info/sensors-and-detectors/ultrasonic-sensor.html Electronics-Manufacturers.com]
* [http://www.silverwinguk.com/en/technical%20pdfs/ultrasonics_vol1.htm Ultrasonic Flaw Detection for Technicians] , Chapter 2, 3rd ed., 2004 by J. C. Drury (~5 pages)

External links

* [http://http://www.em-tec.com/index.php?topic=produkte&subtopic=messverfahren Transit Time Flowmeters, Clamp-on Sensors and Vessel Transducers]
* [http://www.transonic.com/transit_time.shtml Transit Time Ultrasound]
* [http://www.theultrasonicflowmeters.com/ All About Ultrasonic Flowmeters]
* [http://www.precisionflow.co.uk Clamp on transit time and Doppler flow meters]
* Transit-Time Ultrasonic Flow Meter Resource [http://www.sierrainstruments.com/products/innosonic.html Sierra Instruments]
* [http://www.flexim.com/ultrasonicflowmeter/ultrasonicflowmeterpro_transformer.php FLEXIM] transit time clamp-on flowmeter
*RS Hydro: UK supplier of [http://www.rshydro.co.uk/ultrasonic-flowmeter.shtml Ultrasonic flow meters] .
* [http://www.flowmeterdirectory.com Flowmeter Directory] - The internets most popular source of flowmeter information.
* [http://www.eesiflo.com EESiFlo] - Concurrent Transit Time Flow Meters.
* [http://www.signal-processing.com Signal-Processing] - Ultrasonic Doppler Velocimeters for real time measurement of velocity profiles in liquids
* [http://www.met-flow.com - Met-Flow] Ultrasound Doppler Flow Meter (Competitor of Signal-Processing)
* [http://www.katronic.co.uk Katronic Technologies Ltd] - Ultrasonic flow and level measurement specialists


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