General Description - RMG USM GT400 Operating Manual

4.1 General description

In this chapter, you are provided with information as to how the ultrasonic gas
meter records the data. The necessary formulas are listed for this purpose.
Figure 4.1 shows the general working principle. Transducer TD1 and TD2 are
positioned opposite to each other for the measurement and form a measurement
path with distance L. An ultrasonic pulse travels along the measuring path from
sensor TD1 to transducer TD2 more quickly than the other way around. This is
caused physically by vector addition of the flow velocity to the speed of sound, the
arrow above the ṽ shows the direction of flow.
Fig. 4.1: Two sensors form one path for the measurement
The transit time from TD1 to TD2 (:= t
re calculated according to the following formula:
Formulas
��
�� =
����12
�� + ��̅ · ��������
0
These transit times of the ultrasonic pulses are determined by the electronic
ultrasonic system. These are used to determine the average velocity ṽ along the
measuring path:
Formula, average path velocity
�� 1
��̅ = ∙ (
2 ∙ �������� ��
����12
2
�� �� − ��
����21
��̅ = ∙
2 ∙ �� �� ∙ ��
����12 ����21
4 Functional principle – Ultrasonic-flow measurement
TD12
�� =
����21
��
0
1
− )
��
����21
2
�� ����
����12
= ∙
2 ∙ �� ��
����12
) and from TD2 to TD1 (:= t
��
+ ��̅ · ��������
∙ ��
����21
Manual USM GT400 · EN10 · May 2021
33
)
TD21