Ultrasonic flow meterFrom Wikipedia, the free encyclopedia

Schematic view of a flow sensor.

An ultrasonic flow meter is a type of flow meter that measures the velocity of a liquid or gas (fluid) by using

the principle of ultrasound. Using ultrasonictransducers, the flow meter can measure the average velocity along

the path of an emitted beam of ultrasound, by averaging the difference in measured transit time between the

pulses of ultrasound propagating into and against the direction of the flow. Ultrasonic flow meters are affected

by the temperature, density and viscosity of the flowing medium. They are inexpensive to use and maintain

because they do not use moving parts, unlike mechanical flow meters.

Contents

  [hide] 

1 Means of operation

2 Principle

o 2.1 Doppler shift flow meters

3 See also

4 References

5 External links

[edit]Means of operation

There are three different types of ultrasonic flow meters. Transmission (or contrapropagating transit-time) flow

meters can be distinguished into in-line (intrusive, wetted) and clamp-on (non-intrusive) varieties. Ultrasonic

flow meters that use the Doppler shift are called Reflection or Doppler flow meters. The third type is the Open-

Channel flow meter.

[edit]Principle

Ultrasonic flow meters measure the difference of the transit time of ultrasonic pulses propagating in and against

flow direction. This time difference is a measure for the average velocity of the fluid along the path of the

ultrasonic beam. By using the absolute transit times both the averaged fluid velocity and the speed of sound

can be calculated. Using the two transit times   and  and

the distance between receiving and transmitting transducers   and the inclination

angle   one can write the equations:

 and 

where   is the average velocity of the fluid along the sound path

and   is the speed of sound.

[edit]Doppler shift flow meters

Another method in ultrasonic flow metering is the use of the Doppler shift that results from the reflection of an

ultrasonic beam off sonically reflective materials, such as solid particles or entrained air bubbles  in a flowing

fluid, or the turbulence of the fluid itself, if the liquid is clean.

Doppler flowmeters are used for slurries, liquids with bubbles, gases with sound-reflecting particles.

This type of flow meter can also be used to measure the rate of blood flow, by passing an ultrasonic beam

through the tissues, bouncing it off a reflective plate, then reversing the direction of the beam and repeating the

measurement, the volume of blood flow can be estimated. The frequency of the transmitted beam is affected by

the movement of blood in the vessel and by comparing the frequency of the upstream beam versus

downstream the flow of blood through the vessel can be measured. The difference between the two

frequencies is a measure of true volume flow. A wide-beam sensor can also be used to measure flow

independent of the cross-sectional area of the blood vessel.

[edit]See also

Acoustic Doppler velocimetry

[edit]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

[edit]External links

Wikimedia Commons has

media related to: Ultrasonic

flow meter

[ Doppler Shift for Sound and Light] at MathPages

[ The Doppler Effect and Sonic Booms (D.A. Russell, Kettering University)]

Categories: 

Ultrasound

Flow meters

Measuring instruments

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This page was last modified on 27 February 2013 at 19:01.

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