Base Line Correction Via Polynomial - RMG USM GT400 Operating Manual

4 Functional principle – Ultrasonic-flow measurement
Legend
38
th
A 4 degree polynomial permits the so-called basic correction of the device:
4.2.1

Base line correction via polynomial

Formula - Basic correction of the device
���������� − ��
�� =
1
2
��
��
Legend
The constants const-Gx (x = m2, m1, 0, 1, 2) are calculated from the measured
value pairs of the deviation with the respective flow velocity. The calculated correc-
tion F1 is used for the corrected average flow velocity for F in the formula above.
Formula, corrected meter factor
�� = �� ∙ ��
���� ��
The process volume flow and the corrected process volume flow result, as listed
above, from the multiplication of the corresponding velocities with the pipe cross-
section. The correction formulas above are therefore accordingly easy to transfer
to the volume flows.
Polynomial
The characteristic curve correction is also carried out via a 4
that represents the error curve of the device.
Manual USM GT400 · EN10 · May 2021
= Corrected process volume flow
Q
mk
= Corrected weighted flow velocity
v
wk
= Inside pipe diameter
D
i
= Characteristic curve correction
K
k
���������� − ��
��2 ��1
+ + ���������� − ��
2
��
��
= Deviation of the error curve
F
1
= Average flow velocity
v
w
= Constants of the basic correction
const-G
x
(x=m2, m1, 0, 1, 2)
��
∙ (1 + ) → ��
�� ��
100
+ ( ���������� − �� ) ∙ ��
0 1
��
1
= �� ∙ �� ∙ (1 +
�� ��
100
2
+ ( ���������� − �� ) ∙ ��
�� 2 ��
(%)
(m/s)
)
th
degree polynomial