Instruction manual
NivuFlow Mobile 600
page 26
rev. 00 / 04.09.2017
The transit time difference can be approximated if:
• the main flow direction is known and
•
C >> ʋ
1-2
is assumed
Here the formula below is used:
2
2
1
2
1
2
c
L
t
−
−
⋅
=
∆
υ
assumed:
• L
1-2
= length of acoustic measurement path between sensors 1 and 2
• C = speed of sound within water
•
ʋ
1-2
= average flow velocity between sensors 1 and 2 along the measurement path
The more paths are used for transit time measurement and the more paths are used to cover
the wetted cross section, the higher the accuracy of the flow measurement.
1
Sensor 1, path 1
2
Sensor 2, path 1
3
Sensor 1, path 2
4
Sensor 2, path 2
D Pipe diameter (at sensor installation in an angle of 45°)
Fig. 13-2
Two-path transit time measurement principle
If the sensors are installed in an angle of 45° the distance between sensors 1 and 3 or sensors
2 and 4 is equal to the inside pipe diameter.
If used in multi-path set-ups the angle of deviation “α” of the flow direction can be determined
additionally by assuming identical flow velocities.
This angle can be calculated by comparing the measurement results from the individual paths.