Instructions for Use SS 20.261
Page 7
Installation with low disturbance
Local turbulences of the medium can cause distortion of measurement
results. Therefore, appropriate mounting conditions must be guaranteed
to ensure that the gas flow is supplied to the sensor in a quiet and low in
turbulence state in order to maintain the accuracy specified (see chapter
).
!
Correct measurements require quiet flow, as low-turbulence as
possible.
An undisturbed flow profile can be achieved if a sufficiently long distance
in front of (run-in distance) and behind (run-out distance) the sensor
installation site (see Figure 2) is held absolutely straight and without
disturbances (such as edges, seams, bends etc.). It is also necessary to
pay attention to the design of the run-out distance because disturbances
also generate turbulences
against
the flow direction.
L2
L
D
L1
L
= Length of entire measuring distance
L1 = Length of run-in distance
L2 = Length of run-out distance
D = Inner diameter of measuring distance
Figure 2
The following Table 1 shows the required straight conduit lengths
depending on the pipe inner diameter “D” and the different disturbance
causes.
Flow obstacle upstream of the measuring
distance
Minimum
length of L1
Minimum
length of 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 (3-dimensional change in direction)
35 x D
5 x D
Shut-off valve
45 x D
5 x D
Table 1
