Pipe Mode - Accusonic 8510+ series Reference Manual

Surcharged Trapezoidal Integration
The flow is computed from the path velocities and the cross-section area (which is computed from the
layer parameters and the Surcharge Level parameter).
When paths at more than one elevation are good, the Flow is computed in the same manner as for non-
surcharged trapezoidal integration, except that the flow in the panel between the uppermost good path (or
pair of crossed paths) and the top of the conduit or soffit is set to:
= Area between uppermost good path and soffit  Vel
Q
Top
When only one path (or pair of crossed paths) is good, the total section Flow calculation simplifies to:
The Flow = Flow scaling  Area  Vel
where: Area
For multi-path installations, the value of Bottom Friction is usually set between 0.5 and 0.8. The lower
value is used when the lowest path is very close to the bottom of the channel.
For single path installations with the path located near to the bed, the value for Bottom Friction should be
set according to:
Channel shape
Rectangular
Rectangular
Round
Round

Pipe Mode

In Pipe mode, the conduit is surcharged, and flow is computed by the product of average water velocity and
the conduit cross-section area. The average water velocity is obtained from the sum of the path velocities,
each weighted according to its position in the conduit.
The cross-section area is a fixed value defined by a single user-defined parameter, Pipe area.
The other user-defined parameters are: Flow scaling and Weight for each path W
to 10)
Flow
where
Details of the method, including path configurations and weights to be used in special formulae for
different pipe shapes, are described in the ASME PTC 18 or IEC Pub 41 codes for hydraulic turbine
efficiency testing. The formulae and the weighting factors used in the codes differ from the more general
formula used in the flowmeter. Examples of weights to be inserted in the flowmeter are given in Chapter 7,
under Path Parameters.
In the event of one or more paths failing, the flowmeter is capable of calculating Flow by invoking a "Path
substitution" routine. The Flow continues to be computed from those paths which remain good, however
the uncertainty increases with the number of paths failed. For this routine to operate, the following two
conditions must be met:

The number of good paths must be equal to or greater than the Section parameter Min good Paths.

The flowmeter must have completed the Learn routine.
During the Learn routine, which must be implemented at the pipe's normal flow (non-zero!), a table of
time-averaged historic flow components (V
= the surcharged cross section area of conduit computed from the
Layer data and the Surcharge Level parameter.
Path elevation / Surcharge Level
= Flow scaling  Pipe area 
V = velocity for path n.
n
 (1 + Bottom Friction)/2
A
10%
20%
10%
20%

 V
W
n n
 W
) is recorded and stored in the flowmeter's protected
n n
Flow Computation
 (1 + Bottom Friction)/2
N
Bottom Friction.
1.6
1.4
1.3
1.1
( n is the path number 1
n
3-5