Compound Modes; Manning Mode; Non-Surcharged Single Path Trapezoidal Integration Mode - Accusonic 8510+ series Reference Manual

3-2 Accusonic Model 8510+ Series Flowmeter
surcharged condition, certain "Pipe" mode parameters are ignored by the system, and these are indicated in
Chapter 7.

Compound Modes

The flowmeter automatically chooses one of 5 integration methods, depending on the value of the Level,
and on the status of any of the acoustic paths which are sufficiently submerged to operate, (i.e. those paths
whose elevations are defined to be less than [Level - Min. submersion]. The 5 methods are:

Zero flow if the Level (or depth of water) is below a user defined value.

Manning Equation when the depth of water is too low for acoustic paths to operate, or, within-
user defined limits, if none of the acoustic paths yields valid data.

Single Path Trapezoidal Integration when the conduit is not surcharged and only one path (or
one pair of crossed paths) is submerged, or when only one path (or one pair of crossed paths) is
able to yield valid data.

Multi-path Trapezoidal Integration when the conduit is not surcharged and at least two acoustic
paths at different elevations (any of which may be pairs of crossed paths) yield valid data.

Surcharged Integration when the pipe is surcharged. Two user-selectable methods are available:
Pipe as described for Pipe mode involving parameters of path weights and pipe area; and
Surcharged Trapezoidal where the pipe geometry and velocity integration are defined by
methods similar to those used for non-surcharged trapezoidal integration.
Note: If none of the above conditions is satisfied, the flowmeter is declared to be in a fault state. On sites
where the Manning equation is not appropriate, the facility can be inhibited by setting the parameter Manning
max lvl. to a value equal to or below the parameter Layer elevation 1.

Manning Mode

The flow is computed from the variable Level and fixed parameters of channel roughness, channel slope,
and dimensions of the conduit.
The flow = Flow scaling  Area  C  n
where:
Area = the cross-section area of fluid at the current Level, computed using layer data.
C = Manning Constant = 1.49 if English units are used, 1.00 if metric units are used.
n = the Manning coefficient of roughness.
R = Hydraulic radius, which is the Area/Wetted Perimeter.
s = Slope of the energy line. For a long pipe, the pipe slope.

Non-Surcharged Single Path Trapezoidal Integration Mode

The flow is computed from the variables Level and Water Velocity, and fixed parameters describing the
conduit.
Flow = Flow scaling  Area  Velocity  Path position coefficient.
where: Area = the cross-section area of fluid at the current Level, computed using layer data.
 R  s
-1 0.667