3 General principles
FLUXUS G809
3.6 Selection of the measuring point taking into account the flow profile and the influence of noise
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UMFLUXUS_G809V2-2EN, 2020-06-25
3.6
Selection of the measuring point taking into account the flow profile and the
influence of noise
• Select an area on the pipe where the flow profile is fully developed.
• Select the measuring point within this area so that the influence of noise can be neglected.
Sometimes, both demands cannot be reconciled at the same time. In these cases, the measuring point has to be selected
in such way that the influence of noise is min. and the measuring point is as far from the disturbances of the flow profile as
possible.
Example
fluid: natural gas,
c
γ
= 400 m/s
pipe material: stainless steel,
c
β
= 3000 m/s
length of pipe segment 1: 20 D
length of pipe segment 2: 20 D
number of sound paths: 2
l
s
= 7.5 D
• area with developed flow profile:
disturbance source: 90° elbow
recommended area for the measuring point: l ≥ 10 D (complete pipe segment 2)
• area with low influence of noise:
reflection point: flange
recommended area for the measuring point: l ≥ 3 D and outside of l
S
= (7.5 ± 2) D on pipe segment 2
Fig. 3.12: Area for the measuring point with a favorable flow profile and low influence of noise
Considering flow profile and influence of noise, the measuring point can be selected in the area 3...(7.5 - 2) D on the
right side of pipe segment 2 (with max. distance from the elbow).
In the example, a distance of 36 D from the elbow was selected.
20 D
20 D
36 D
(7.5 - 2) D
3 D
disadvantageous measuring range
10 D
