UMG70XV3-4EN 12.01.2009 37
5 Selection of the Measuring Point
Both demands can not be observed always at the same time. In these cases, the mea-
suring point has to be selected so that the influence of noise is min. and the measuring
point is as far as possible from disturbance sources of the flow profile.
In the example, there is no measuring point area where both demands are met at the
same time. The measuring point has to be selected as far as possible from the elbow, at
a point where the influence of noise can be neglected: 3...(7.5 - 2) D on the right side of
pipe segment 1. In the example, a distance of 16 D from the elbow was selected.
example: medium: natural gas
pipe material: stainless steel
length of pipe segment 1: 20 D
length of pipe segment 2: 5 D
number of sound paths: 2
• measuring point area with developed flow profile:
disturbance source: 90° elbow
recommended measuring point area: l 20 D (complete pipe segment 2) (see Table
5.1)
• measuring point area with low influence of noise:
reflection point: flange
recommended measuring point area: l 3 D and outside of l = (7.5 ± 2) D on pipe
segment 1 (see Table 5.1)
Fig. 5.4: Measuring point area with low influence of noise and
not fully developed flow profile
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