Instructions for Use
– SCHMIDT
®
Flow Sensor SS 23.400 ATEX 3
Page 9
L = Length of entire measuring section
L1 = Length of run-in distance
L2 = Length of run-out distance
D = Diameter of measuring section
Figure 3-2
The following Table 2 specifies the required straight lengths of the pipe
sections depending on pipe diameter in case of different disturbances.
Flow obstacle upstream of measuring distance
Minimum length of distance
run-in L1
run-out L2
Light bend (< 90°)
10 x D
5 x D
Reduction,
expansion,
90° bend or
T-junction
15 x D
5 x D
Two 90° bends in
one plane
(2-dimensional)
20 x D
5 x D
Two 90° bends
with 3-dimensional
change in direction
35 x D
5 x D
Shut-off valve
45 x D
5 x D
Table 2
This table lists the
minimum values
required in each case. If the listed
straight conduit lengths cannot be achieved, measurement accuracy may
be impaired or additional actions are required like the use of flow rectifiers
7
.
Under laminar conditions a quasi-parabolic speed profile emerges over
the pipe cross-section, whereas the flow velocity at the pipe walls remains
7
E.g. honeycombs made of plastics or ceramics; profile factor may change there-fore.
