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AS 2360.8.1-2007 pdf free download
AS 2360.8.1-2007 pdf free download.Hydrometry-Measurement of free surface flow in closed conduits Part 8.1 : Methods.
For single-path systems, the estimated velocity is used directly to derive the mean velocity in the measuring section. In multi-path systems, the cross section is normally divided into a number of horizontal segments or slices defined by the positions of each pair of transducers in the vertical. The velocities derived for different paths are then used to derive the flow in their assigned segments by multiplying the mean velocity in the segment by the area of the segment. The flows in each segment are then summed together to provide an estimate of the total flow in the entire cross section. If there is an error of greater than a few degrees in the determination of the angle between the direction of flow and the flight path ((n, large errors can occur in the determination of the velocity. Such errors can occur when skew flow occurs, In order to minimize this type of error, cross-path systems are installed. Cross-path systems are where a second line of transducers is installed diametrically opposite the first. Discharges are usually computed separately for each line of transducers and averaged to compensate for skew flow.
Depth measurements are also required In order to determine the area of flow for the estimation of discharge.
‘Transit time’ ultrasonic open channel flow gauges have been used successfully on small artificial channels 0,5 m wide to larger rivers with widths up to at least 500 m.
The technology is also used for pipe flow measurement. For pipe flow measurement, it is possible to obtain clamp-on units whereby the transducers can be clamped onto the outside of the pipe. As these units require the pipe to be running full, they are not suitable for measuring flows in closed conduits with a free water surface.
The technique is described in detail in ISO 6416.
6.5.2 Attributes and limitations
‘Transit time’ ultrasonic systems are usually relatively easy to install, are non-obtrusive, can be highly accurate (see 6.5.4) and can often be more cost-effective than other feasible alternatives. ‘Transit time’ ultrasonic flow gauges are bi-directional enabling the measurement of reverse flows.
Excessive attenuation of the acoustic signal can occur due to high levels of suspended solids, entrained gases and temperature gradients. Nevertheless, the technology is now used for measuring raw effluent at the inlets to waste water treatment works where the ultrasonic path lengths are short and the attenuation can be tolerated. However, sensor fouling can be a problem when measuring raw sewage, and, at least requires regular maintenance. There is also a minimum depth requirement that is a function of the frequency of the transducers and the length of the flight path. A limitation of the technique when using systems with only one path or a limited number of paths, is the fact that as the water level changes, the system will be sampling a different part of the velocity distribution. In such cases, it is necessary to determine a relationship between measured velocity and the mean cross-sectional velocity. This is described in ISO 6416.AS 2360.8.1-2007 pdf free download.
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