VEGA VEGAMET 391 4 … 20 mA_HART - Manual (Page 47)

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8 Application examples
VEGAMET 391 • 4 … 20 mA/HART
36032-EN-130701
8.5 Flow measurement
For flow measurement in open flumes, a constriction or standardised
flume must be used. Depending on the flow volume, this constriction
generates a certain amount of backup. The flow can be determined
from the height of this backup. The flow volume is outputted by an ap-
propriate number of pulses on the relay or current output and can thus
be further processed by connected downstream instruments.
There is also the possibility to sum up the flow volume by means of a
totalizer, the result is available on the display and as PC/DCS value.
Depending on the type and version, each flume generates a different
backwater. The data of the following flumes are available in the instru-
ment:
•
Palmer-Bowlus-Flume
•
Venturi flume, trapezoidal weir, rectangular weir
•
Rectangular weir, V-Notch
Setup
The configuration of the flow measurement loop requires PACTware
with the suitable DTMs. The example refers to a flow measurement
with a radar sensor. The following setup steps must be carried out:
•
Selection of the parameter "Flow"
•
Carrying out adjustment
•
Select flume (linearization)
•
Set scaling
•
Parameter adjustment of pulse outputs
•
Parameter adjustment of the totalizer
Select in the DTM window "Parameter" the option "Flow" with the
requested unit of measurement.
Min. adjustment: Enter the suitable value for 0 %, i.e. the distance
from the sensor to the medium as long as there is no flow. These are
in the following example 1.40 m.
Max. adjustment: Enter the suitable value for 100 %, i.e. the distance
from the sensor to the medium, with the max. flow volume. This is
0.80 m in the following example.
100% 0,80m (d) = 400m 3 /h =
0% 1,40m (d) = 0m
3
/h =
Fig. 19: Adjustment of flow measurement with V-notch
Functional principle
Flume
Parameter - Flow
Adjustment