Nivus NivuFlow 650, Инструкция по эксплуатации, Страница: 30 / 173

Instruction Manual
NivuFlow 650
page 30 NF 650 - rev. 01 / 29.06.2020
The more paths are used in the asymmetrical or disturbed profile and distributed in the flow
cross-section, the more accurately the flow can be determined.
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. 19-2 Two-path transit time measurement principle
If the sensors are installed in an angle of 45°, the distance between sensors 1 and 2 or sen-
sors 3 and 4 is equal to the inside pipe diameter.
19.2 Flow Calculation
In the case of using single-path or multi-path installations in one level under the condition
Q = v
average
· A
and given
• v
average
= average flow velocity and
• A = cross-sectional flow area,
a velocity coefficient “k” is introduced to compensate for the difference between the measured
velocity v
g
and the average velocity v
average
within the cross-sectional area.
The velocity coefficient “k” depends on the Reynolds number and is therefore not a constant.
Reynolds number and velocity coefficient are not visible or changeable, they are integrated in
the software and are included in the background calculations.
The flow rate can then be calculated by using the signal transit time as follows:
Q = k · A · v
g
= k · A ·
L
·
1
-
1
2 · cos
a
t
2
t
1