ASTM D5389-93(1997)
(Test Method)Standard Test Method for Open-Channel Flow Measurement by Acoustic Velocity Meter Systems
Standard Test Method for Open-Channel Flow Measurement by Acoustic Velocity Meter Systems
SCOPE
1.1 This test method covers the measurement of flow rate of water in open channels, streams, and closed conduits with a free water surface.
1.2 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.
1.3 The values stated in SI units are to be regarded as the standard.
1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 6.
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Standards Content (Sample)
Designation: D 5389 – 93 (Reapproved 1997)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Open-Channel Flow Measurement by Acoustic Velocity
Meter Systems
This standard is issued under the fixed designation D 5389; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.2 acoustic path length—the face-to-face distance be-
tween transducers on an acoustic path.
1.1 This test method covers the measurement of flow rate of
3.2.3 acoustic transducer—a device that is used to generate
water in open channels, streams, and closed conduits with a
acoustic signals when driven by an electric voltage, and
free water surface.
conversely, a device that is used to generate an electric voltage
1.2 The test method covers the use of acoustic transmissions
when excited by an acoustic signal.
to measure the average water velocity along a line between one
3.2.4 acoustic travel time—the time required for an acoustic
or more opposing sets of transducers—by the time difference
signal to propagate along an acoustic path, either upstream or
or frequency difference techniques.
downstream.
1.3 The values stated in SI units are to be regarded as the
3.2.5 discharge—the rate of flow expressed in units of
standard.
volume of water per unit of time. The discharge includes any
1.4 This standard does not purport to address all of the
sediment or other materials that may be dissolved or mixed
safety concerns, if any, associated with its use. It is the
with it.
responsibility of the user of this standard to establish appro-
3.2.6 line velocity—the downstream component of water
priate safety and health practices and determine the applica-
velocity averaged over an acoustic path.
bility of regulatory limitations prior to use. Specific precau-
3.2.7 measurement plane—the plane formed by two or more
tionary statements are given in Section 6.
parallel acoustic paths of different elevations.
2. Referenced Documents 3.2.8 path velocity—the water velocity averaged over the
acoustic path.
2.1 ASTM Standards:
3.2.9 stage—the height of a water surface above an estab-
D 1129 Terminology Relating to Water
lished (or arbitrary) datum plane; also gage height.
D 2777 Practice for Determination of Precision and Bias of
3.2.10 velocity sampling—means of obtaining line veloci-
Applicable Methods of Committee D-19 on Water
ties in a measurement plane that are suitable for determining
D 3858 Test Method for Open-Channel Flow Measurement
flow rate by a velocity-area integration.
of Water by Velocity-Area Method
2.2 ISO Standard:
4. Summary of Test Method
ISO 6416 Liquid Flow Measurements in Open Channels—
4.1 Acoustic velocity meter (AVM) systems, also known as
Measurement of Discharge by the Ultrasonic (Acoustic)
3 ultrasonic velocity meter (UVM) systems, operate on the
Method
principle that the point-to-point upstream traveltime of an
3. Terminology acoustic pulse is longer than the downstream traveltime and
that this difference in travel time can be accurately measured
3.1 Definitions—For definitions of terms used in this test
by electronic devices.
method, refer to Terminology D 1129.
4.2 Most commercial AVM systems that measure stream-
3.2 Definitions of Terms Specific to This Standard:
flow use the time-of-travel method to determine velocity along
3.2.1 acoustic path—the straight line between the centers of
an acoustic path set diagonal to the flow. This test method
two acoustic transducers.
describes the general formula for determining line velocity
defined as (Fig. 1 and Fig. 2):
This test method is under the jurisdiction of ASTM Committee D-19 on Water
and is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-
phology, and Open-Channel Flow.
Current edition approved April 15, 1993. Published June 1993.
Annual Book of ASTM Standards, Vol 11.01.
3 4
Available from the American National Standards Institute, 11 W. 42nd Street, Laenen, A., and Smith, W., “Acoustic Systems for the Measurement of
13th Floor, New York, NY 10036. Streamflow,” U.S. Geological Survey Water Supply Paper 2213, 1983.
D 5389
t
AC 5 traveltime from A to C (upstream),
t
CA 5 traveltime from C to A (downstream), and
B 5 length of the acoustic path from A to C.
4.3 The discharge measurement or volume flow rate deter-
mination made with an AVM relies on a calibrated or theoreti-
cal 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 accu-
racy. 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 (see
Fig. 3).
FIG. 1 Velocity Component Used in Developing Travel-Time
Equations
5. Significance and Use
5.1 This test method is used where high accuracy of velocity
or continuous discharge measurement over a long period of
time is required and other test methods of measurement are not
feasible due to low velocities in the channel, variable stage-
discharge relations, complex stage-discharge relations, or the
FIG. 2 Voltage Representation of Transmit and Receive Pulses at
Upstream and Downstream Transducers
1 1
B
t t
F G
V 5 CA2 AC (1)
L
2 cos u
where:
V 5 line velocity, or the average water velocity at the
L
depth of the acoustic path,
u5 angle of departure between streamflow and the
acoustic path,
FIG. 3 Example of Acoustic Velocity/Flow Measuring System
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presence of marine traffic. It has the additional advantages of 6.3 Attenuation—Acoustic signals are attenuated by absorp-
requiring no moving parts, introducing no head loss, and tion, spreading, or scattering. Absorption involves the conver-
providing virtually instantaneous readings (1 to 100 readings sion of acoustic energy into heat. Spreading loss is signal
per second). weakening as it spreads outward geometrically from its source.
5.2 The test method may require a relatively large amount Scattering losses are the dominant attenuation factors in
of site work and survey effort and is therefore most suitable for streamflow applications. These losses are caused by air
permanent or semi-permanent installations. bubbles, sediment, or other particle or aquatic materials present
in the water column. Table 1 presents tolerable sediment
6. Interferences
concentrations.
6.1 Refraction—The path taken by an acoustic signal will 6.4 Mechanical Obstructions—Marine growth or water-
be bent if the medium through which it is propagating varies borne debris may build up on transducers or weed growth,
significantly in temperature or density. This condition, known boats, or other channel obstructions may degrade propagation
as ray bending, is most severe in slow moving streams with and timing of acoustic signals.
poor vertical mixing or tidal (estuaries) with variable salinity. 6.5 Electrical Obstructions—Nearby radio transmitters,
In extreme conditions the signal may be lost. Examples of ray electrical machinery, faulty electrical insulators, or other
bending are shown in Fig. 4. Beam deflection for various sources of electromagnetic interference (EMI) can cause fail-
temperatures and specific conductivities are shown in Fig. 5 ure or sporadic operation of AVMs.
and Fig. 6.
7. Apparatus
6.2 Reflection—Acoustic signals may be reflected by the
water surface or streambed. Reflected signals can interfere 7.1 The instrumentation used to measure open-channel flow
with, or cancel, signals propagated along the measurement by acoustic means consists of a complex and integrated
plane. When thermal or density gradients are present, the electronic system known as an acoustic velocity meter (AVM).
placement of transducers with respect to boundaries is most Three or four companies presently market AVM systems
critical. This condition is most critical in shallow streams. A suitable for measurement of open-channel flow. System con-
general rule of thumb to prevent reflection interference is to figurations range from simple single-path to complex-multi-
maintain a minimum stream depth to path length ratio of 1 to path systems. Internal computation, transmission, and record-
100 for path lengths greater than 50 m. ing systems vary depending on local requirements. Most AVM
FIG. 4 Signal Bending Caused by Different Density Gradients
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NOTE 1—Transducer directivity or beam width determined at the 30-dB level of the transmitted signal pattern. The signal is propagated beyond the
beam width but at a weak level. In the shaded area the detection is so great that signals cannot be received directly for any transducer beam width.
FIG. 5 Beam Deflection From Linear Temperature Gradients for Different Path Lengths
NOTE 1—Transducer directivity or beam width determined at the 30-dB level of the transmitted signal pattern. The signal is propagated beyond the
beam width but at a weak level. In the shaded area the deflection is so great that signals cannot be received directly for any transducer beam width.
FIG. 6 Beam Deflection From Linear Conductivity Gradients for Different Path Lengths
systems must include the capability to compute an acoustic line erroneous readings during acoustic interruptions caused by
velocity from one or more path velocities together with stage river traffic, aquatic life, or gradual degradation of components.
(water level) and other information related to channel geometry 7.1.2 Flow Readout Equipment—This equipment is func-
necessary to calculate a flow rate per unit of time, usually cubic tionally separated into three subsystems. These subsystems
3 3
millimetres per second (m /s) or cubic feet per second (ft /s). may or may not be physically separable but are discussed
7.1.1 Electronics Equipment—There are several methods separately for clarity.
that are currently being used to implement the electro-acoustic 7.1.3 Acoustic Tranceiver—This system generates, re-
functions and mathematical manipulations required to obtain a ceives, and measures the traveltimes of acoustic signals. The
line-velocity measurement. Whatever method is used must acoustic signals travel between the various pairs of acoustic
include internal automatic means for continuously checking the transducers and form the acoustic paths from which line
accuracy. In addition, provision must be included to prevent velocities are determined.
D 5389
TABLE 1 Estimates of Tolerable Sediment Concentrations for
AVM System Operation Based on Attenuation From Spherical
Spreading and From Scattering From the Most Critical Particle
Size
NOTE 1—Sediment concentrations in milligrams per litre.
Selected Path distance (m)
Transducer
Frequency
5 20 50 100 200 300 500 1000
(kHz)
1000 6300 1200 400 — — — — —
500 — 3500 1200 530 230 — — —
300 — 7900 2800 1300 560 350 — —
200 — 11 000 4000 1800 830 520 280 —
100 — — 10 000 4600 2200 1400 770 350
30 — — — — 8800 5700 3200 1500
7.1.4 Processor—The processor performs the mathematical
operations required to calculate acoustic line velocities, makes
decisions about which acoustic paths should be used on the
basis of stage, performs error checking, calculates total volume
flow rate, and totalizes volume flow.
7.1.5 Display/Recorder—Generally, the output of the sys-
tem is a display or a recorder, or both. The recorder normally
includes calendar data, time, flow rate, stage, and any other
information deemed desirable, such as error messages. Equip-
ment of this type is often connected to other output devices,
such as telemetry equipment.
7.2 Acoustic Transducers—Transducers may be active (con-
taining Transmitter and first stage of amplification) or passive
(no amplification) depending on path length and presence of
FIG. 7 Responder System
electromagnetic interference EMI. Acoustic transducers must
be rigidly mounted in the channel wall or bottom. Means must
8. Sampling
be provided for precise determination of acoustic path eleva-
8.1 Sampling, as defined in Terminology D 1129, is not
tion, length, and angle to flow. The transducers and cabling
applicable to this test method.
must be sufficiently rugged to withstand the handling and
9. Preparation of Apparatus
operational environment into which they will be placed.
Additionally, provision shall be made for simple replacement 9.1 Site Selections:
of transducer or cable, or both, in the event of failure or 9.1.1 Channel Geometry—The gaged site should be in a
damage. section of channel that is straight for three to ten channel
7.3 Stage Measuring Device—There are several methods widths upstream and one to two channel widths downstream.
for measuring stage and inputting this information to the The banks should be parallel and not subject to overflow. There
system. The actual method used depends on the particular should be minimal change in cross-section area between the
installation requirements. Some examples include visual upstream and downstream transducer locations. Calibrating
measurement/manual keyboard entry, float/counterweight or discharge measurements must be made along the acoustic path
bubbler systems with servo manometers connected to analog where large differences exist in cross-sectional area between
conversion equipment or digital encoders, upward looking the upstream and downstream transducers. AVMs are not
acoustic transducers, or other electronic pressure sensors. usually suitable for wide shallow channels, except by using
7.4 Power Supply—Several venders currently offer battery- multiple horizontal paths.
powdered AVMs as well as systems operating on 110 V ac 9.1.2 Channel Stability—The cross sections should not be
standard commercial electric power. Availability of electricity
subject to frequent shifting and the relationship between stage
should be considered during site evaluation prior to equipment and cross-section area must be stable or frequently measured.
selection.
Sites with unstable vertical velocity profiles should be avoided,
7.5 Cabling—All interconnected ca
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