Vega VEGAMET 841 Operating page 42

10 Applications and functions
Flume
Example rectangular
flume
42
Every flume generates a different level of backwater depending on its
type and version. The specifications of the following flumes are avail-
able in the instrument:
Predefined curves
A flow measurement with these standard curves is very easy to set
up, as no dimensional information of the flume is required.
•
Palmer-Bowlus flume (Q = k x h
•
Venturi, trapezoidal weir, rectangular flume (Q = k x h
•
V-Notch, triangular overfall (Q = k x h
Dimensions (ISO standard)
When selecting these curves, the dimensions of the flume must be
known and entered via the assistant. As a result, the accuracy of the
flow measurement is higher than with the specified curves.
•
Rectangular flume (ISO 4359)
•
Trapezoidal flume (ISO 4359)
•
U-shaped flume (ISO 4359)
•
Triangular overfall thin-walled (ISO 1438)
•
Rectangular flume thin-walled (ISO 1438)
•
Rectangular weir broad crown (ISO 3846)
Flow formula
If the flow formula of your flume is known, you should select this op-
tion, as the accuracy of the flow measurement is highest here.
•
Flow formula: Q = k x h
Manufacturer definition
If you use a Parshall flume from the manufacturer ISCO, this option
must be selected. This gives you a high accuracy of flow measure-
ment with easy configuration.
•
ISCO Parshall flume
3 ... 4 h
max
90°
2
2
Fig. 20: Flow measurement with rectangular flume: h
rectangular flume
1 Overfall orifice (side view)
2 Upstream water
3 Tailwater
4 Overfall orifice (view from tailwater)
)
1.86
)
2.5
exp
1
3
3
max.
VEGAMET 841 • 4 ... 20 mA
)
1.5
90°
4
= max. filling of the