Flexim FLUXUS G704 - Page 35

UMG70XV3-4EN 12.01.2009 35
5 Selection of the Measuring Point
in the distance of l
S
± 2 D from the reflection point
Pipe wall signal and measuring signal reach the transducer simultaneously.
l
S
- distance to reflection point
D - outer pipe diameter
c
F
- sound velocity in the medium
c
P
- sound velocity in the pipe
n - number of sound paths
example:
medium: natural gas
pipe material: stainless steel
c
P
: 3000 m/s
c
F
: 400 m/s
number of soundpaths: 2
l
S
= 7.5 D
The range (7.5 ± 2) D is disadvantageous for the transducer installation.
Table 5.2: Measuring points to be avoided
disadvantageous
l
s
l
s
n
2
---
c
P
c
F
------
D=