Xylem Flow Converter 713 - Manual (Page 3)

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Flow converter 713
Thank you for choosing Flow converter 713. Flow con-
verter 713 is a modern construction, in which the relation
between functions, and "userfriendliness“ and precision
is optimum. In order to gain full use from the equipment,
we recommend that you read the instructions very thor-
oughly. Should any problems occur during installation or
operation, our technicians will be at your disposal.
Flow converter 713 is for the measurement of flow in
open flumes and weirs. The method of measurement
and linearization complies with the norm ISO 1438. This
norm indicates how the head over the weir and flumes
are constructed, and how the calculations for lineariza-
tion are to be arrived at. The flowrate is generaly speek-
ing determined by using the following mathematical
function:
Flow Q = f(level x · constant)
where the exponent x and the constant depends on the
weir or the flume.
Technical section with the principles of measuring
The flow converter has 3 different linearization systems
depending on how the volume of water is measured.
• One choose between a number of predefined flumes and
weirs, e.g. Parshall flumes and V-notch weirs.
• If the flume or weir differ from the normal types of flumes
and weirs, the formula Q(h)=k x h n can be applied, where
k and n are keyed in directly.
• Some times it can be desirable to linearizate a levelsignal
which does not follow a mathematical expression. As an
example a flow can be measured in a partly filled pipe,
where the menu point-linearization can be applied.
Flowconverter 713 converts the level to flow from these
examples. Some of the examples are simplified. The ISO
1438 norm indicates a number af calculation methods
for flumes and weirs. The Flowconverter 713 uses these
methods where it is possible.
Rectangular sharp edged weir
according to ISO 1438
Rectangular sharp edged weir is supplied in two types:
- with side contraction
where the opening has a smaller width than the feeder
and
- without side contraction
where the width of the opening corresponds to the width
of the channel (B = b).
Rectangular sharp edged weir
with side contraction:
ß = minimum 45°
d ~ 1- mm
Universal formula: (Kindsvater/Carter)
Q = 3600 × Ce Ч 2/3 Ч 2g × b
e
× h
e
1,5
where: Q = flow in m
3
/h
b = width of weir in [m]
b
e
= effective width of weir in [m]
b
e
= b + k
b
h
a
= height in [m]
h
e
= effective height in [m]
h
e
= h
a
+k
h
, k
h
= 0,001
h
b
= depth below edge in [m]
B = flume width in [m]
L = distance to sensor,
4 - 5 × h
a max.
g = acc. due to gravity = 9,81 m/s
k
b
is a correction factor in meter.
For determination of k
b
b/B = 0 k
b
= 0,0024 m
b/B = 0,2 k
b
= 0,0024 m
b/B = 0,4 k
b
= 0,0027 m
b/B = 0,6 k
b
= 0,0036 m
b/B = 0,8 k
b
= 0,0042 m
b/B = 1,0 k
b
= -0,0090 m
Ce is a contraction coefficient (no unit) depending on the
ratio of b/B and h
a
/h
b.
For determination of Ce
b/B = 1,0 Ce = 0,602+0,075 h
a
/h
b
b/B = 0,9 Ce = 0,598+0,064 h
a
/h
b
b/B = 0,8 Ce = 0,596+0,045 h
a
/h
b
b/B = 0,7 Ce = 0,594+0,030 h
a
/h
b
b/B = 0,6 Ce = 0,593+0,018 h
a
/h
b
b/B = 0,4 Ce = 0,591+0,0058 h
a
/h
b
b/B = 0,2 Ce = 0,588-0,0018 h
a
/h
b
b/B = 0 Ce = 0,587-0,0023 h
a
/h
b
β
Edge
d