40
10 Applications and functions
VEGAMET 341 • 4 … 20 mA
63730-EN-210616
Note:
The number of the last switched-on relay is not saved in case of
voltage loss, this means that after the controller is switched back on
again, the relay with the shortest running time always starts first.
10.3 Flow measurement flume/weir
Waste water and rainwater are often transported to the sewage treat-
ment plant in open collection channels. The flow rate is measured at
various points in the collection channels. For flow measurement in
open waters, a constriction or a standardised channel must be used.
This constriction creates a certain backwater depending on the flow
rate. The flow rate can now be derived from the level of this backwater.
The current flow rate is shown on the display in the selected unit of
measurement (e.g. m
3
/h). In addition, the flow rate is made available
via the current output and can thus be further processed by down-
stream devices.
It is also possible to totalize the flow rate by means of a totalizer, the
result is shown on the display (e.g. in m
3
). In addition, the flow rate can
be output via a corresponding number of pulses on the relay/current
output (flow rate pulse). A sampling pulse can also be configured.
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
1.86
)
•
Venturi, trapezoidal weir, rectangular flume (Q = k x h
1.5
)
•
V-Notch, triangular overfall (Q = k x h
2.5
)
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
exp
Application
Flume
