Chapter 3 Flow Computation; Flow Computation Algorithms Overview - Accusonic 8510+ series Reference Manual

C H A P T E R 3
Flow Computation

Flow Computation Algorithms Overview

The Accusonic Model 8510+ Flowmeter may be configured with up to a maximum of ten acoustic paths
and two inputs for Level (or water depth) in one conduit or "Section." Details of the configuration are
defined by a set of parameters, the names of which appear in this document in italics.
Each path is characterized by parameters describing Length and Angle. For "Pipe" mode integration, a
Weight parameter is added: for "Compound" mode Elevation is added. Paths are numbered in order of
elevation, with the lower path numbers having lower elevations. In a Compound flowmeter, pairs of
"Crossed Paths" in a section are indicated by having the same elevation. Other Path parameters include:
Max Bad Measures, Max Velocity Change, Max Path Velocity, Signal Delay and Transducer Frequency
In Pipe mode, path transducers are energized and measurements taken for all paths which are configured.
In Compound mode, only those transducers submerged by an amount greater than the parameter Min.
submersion are energized.
If a path fails to provide a good velocity value, because the signal is not found, or the velocity appears to
exceed the Max Path Velocity parameter, then the last good velocity value is used for flow calculations
until the number of consecutive failures exceeds the parameter Max Bad Measures. If this value is
exceeded, the path is declared to have failed, and its data are then not used for flow computation, unless
and until new valid data are obtained.
If the change in velocity appears to exceed the Max Velocity Change parameter, the computed velocity is
incremented or decremented by an amount equal to the Max Velocity Change.
In Pipe mode, all Manning, Level and Layer parameters indicated by the letter "C" after their names are
ignored. The conduit geometry and velocity integration are defined in terms only of Pipe Area and Path
weights.
In Compound mode instantaneous values for velocity are averaged for paths having identical elevations,
and the averaged velocity is used as the velocity at that elevation. If one of the paths has failed for more
than the parameter Max Bad Measures, the good path will be used alone for providing the velocity at that
elevation. Paths which do not have identical elevations will be treated as separate paths in the Trapezoidal
Integration. The displayed and outputted velocities will be the individual velocities for each path. The
conduit cross-section is defined in terms of up to 8 "Layers," each layer being described by an elevation
and a width. The width of the conduit at any elevation is computed by linear interpolation between the
layer widths above and below. The elevation and width of the channel bottom are defined by Layer #1 (see
Chapter 5 for additional details). The layer elevations are independent of the path elevations. For a
rectangular or trapezoidal conduit, only two layers need be defined, the first describing the channel bottom,
and the second describing the top of the channel. For a closed conduit, the top-most layer elevation must be
equal to or greater than the elevation of the soffit or top of the conduit (or the Surcharge Level parameter).
For an open channel, the top-most layer elevation must be set above the highest possible level. The other
Section parameters required for Compound Integration are: Bottom friction, Top weight and the
Surcharged Integration method to be used (Surch Trap/Pipe). If "Trapezoidal" integration is chosen for the
3-1