Siemens SITRANS LUT400 - Universal Calculation Support

General Operation
7.11 Open Channel Monitoring (OCM)
SITRANS LUT400
Operating Instructions, 07/2019, A5E33329501-AC
147
● Sized by maximum depth of flume.
● Approach is preferably rectangular, matching width and depth for distance 3 to 5 times
the depth of the flume.
● May be installed in channels under partial submergence (ratio of downstream level to
head). Typical errors are:
– 1% @ 30% submergence
– 3% @ 50% submergence
● For rated flows under free flow conditions, the head is measured at a point downstream
from the flume entrance. Refer to the following table.
Flume Size
(Diameter in feet)
Point of Measurement
cm
inches
0.5
5
1.75
0.75
7
2.75
1.0 9 3.75
1.5
14
5.5
2.0
18
7.25
2.5
23
9
3.0
28
10.75
4.5
41
16.25
● H-flumes come with a flat or sloping floor. The same flow table can be used because
error is less than 1%.
7.11.4.7 Universal calculation support
When the primary measuring device (PMD) doesn’t fit one of the standard types, it can be
programmed using a universal characterization. When Universal is selected as the PMD type
[Primary Measuring Device (PMD) (2.15.1.) (Page 230)], then both head and flow
breakpoints(Universal Head versus Flow (2.15.5.) (Page 236)) must be entered to define the
flow.
SITRANS LUT400 supports Universal curved (cubic spline) flow calculation shown in the
following chart. (The Method of Flow Calculation (2.15.3.1.) (Page 231) for universal support
can be Ratiometric or Absolute. Refer to your PMD manufacturer’s documentation.)