ASTM: D5389: Flow Measurments by Acoustic Velocity Meter (AVM)
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Official Method Name
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Standard Test Method for Open-Channel Flow Measurement by Acoustic Velocity Meter Systems |
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Current Revision
| Reapproved 1997. Current edition approved April 15, 1993. |
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Media
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WATER |
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Instrumentation
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Acoustic Velocity Meter |
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Method Subcategory
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Physical |
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Method Source
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Citation
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Brief Method Summary
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Acoustic velocity meter (AVM) systems, also known as ultrasonic velocity meter (UVM) systems, operate on the principle that the point-to-point upstream traveltime of an acoustic pulse is longer than the downstream traveltime and that this difference in travel time can be accurately measured by electronic devices. The discharge measurement or volume flow rate determination made with an AVM relies on a calibrated or theoretical relation between the line velocity as measured by the AVM and mean velocity in the flow segment being measured. Taking more line velocity measurements across the channel at different elevations in the acoustic plane and performing a numerical integration or weighted summation of the measured velocities and areas of flow can be used to better define the volume flow rate. The spacing between acoustic paths, the spacing between the top path and the liquid surface, and the spacing between the lowest path and the bottom are determined on the basis of stream cross-section geometry or estimates of the vertical-velocity distribution and by the required measurement accuracy. In addition to several line velocity measurements, it is necessary to provide water level (stage) and cross-sectional area information for calculation of the volume flow rate |
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Scope and Application
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This test method covers the measurement of flow rate of water in open channels, streams, and closed conduits with a free water surface. The test method covers the use of acoustic transmissions to measure the average water velocity along a line between one or more opposing sets of transducers - by the time difference or frequency difference techniques. |
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Applicable Concentration Range
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None. |
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Interferences
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Refraction - The path taken by an acoustic signal will be bent if the medium through which it is propagating varies significantly in temperature or density. This condition, known as ray bending, is most severe in slow moving streams with poor vertical mixing or tidal (estuaries) with variable salinity. In extreme conditions the signal may be lost. Reflection - Acoustic signals may be reflected by the water surface or streambed. Reflected signals can interfere with, or cancel, signals propagated along the measurement plane. When thermal or density gradients are present, the placement of transducers with respect to boundaries is most critical. This condition is most critical in shallow streams. Attenuation - Acoustic signals are attenuated by absorption, spreading, or scattering. Absorption involves the conversion of acoustic energy into heat. Spreading loss is signal weakening as it spreads outward geometrically from its source. Scattering losses are the dominant attenuation factors in streamflow applications. These losses are caused by air bubbles, sediment, or other particle or aquatic materials present in the water column. Mechanical Obstructions - Marine growth or waterborne debris may build up on transducers or weed growth, boats, or other channel obstructions may degrade propagation and timing of acoustic signals. Electrical Obstructions - Nearby radio transmitters, electrical machinery, faulty electrical insulators, or other sources of electromagnetic interference (EMI) can cause failure or sporadic operation of AVMs. |
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Quality Control Requirements
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Sample Handling
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Maximum Holding Time
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Relative Cost
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Greater than $400 |
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Sample Preparation Methods
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