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4 Functional principle – Ultrasonic-flow measurement
Legend
36
Typical values at very good flow conditions for middle paths are at 2-3%, for the
outer paths, the turbulence increases to 4%. If these values are above 10%, then
disturbed conditions can be assumed affecting the measurement accuracy. At
lowest velocities the turbulence calculation is switched off.
Profile and symmetry factor
For a fully developed flow the middle path (3 + 4) have the highest velocity, the
two outer paths (1 + 2; 5 + 6) are more or less equal. The profile factor ( PF ) is
typically between 1.05 to 1.20; at values below 1.00 or above 1.50, the flow condi-
tions should be checked.
2 ( ��̅
���� =
( ��
+ ��̅
1
Profile factor
The symmetry factor ( SY ) usually is between 0.9-1.10; at values below 0.75 or
above 1.25 the flow conditions should be checked.
( ��̅
+ ��̅
5
���� =
( ��
+ ��̅
1
Symmetry factor
Meter performance
This value ( MP ) indicates whether the velocity of all ultrasonic paths could be
measured and involved in the flow calculation. It is calculated on base of the last
20 measurements (same as turbulence).
∑
1..100
���� =
Manual USM GT400 · EN10 · May 2021
v ̅
=
Time averaged flow velocity along the ultrasonic path
i
v ̅
=
Flow velocity along the ultrasonic path
j,i
=
N = number of measured values according to parameter
N
E-9 "moving average cnt". For a significant determination
of turbulence, the number should be at least 10.
+ ��̅
)
3
4
) + ( ��̅
)
+ ��̅
2
5
6
)
6
)
2
∑
1(˄��
= ����)˅0(˄��
��=1..6
��,��
600
≠ ����)
��,��
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