26 UMFLUXUS_G6V4-2EN, 2011-03-29
FLUXUS G60x 5 Selection of the Measuring Point
5.3 Influence of Noise
The ultrasonic waves do not only propagate in the medium but also in the pipe wall (see
Fig. 5.1). They are reflected at flanges.
Fig. 5.1: Propagation of ultrasonic waves
The reflected pipe wall signals can disturb the measurement, especially if:
• the measuring point is close to the reflection point
• the pipe wall signals and measuring signals are received by the transducer at the same
time
Tab. 5.3: Measuring points to be avoided
measuring point directly at the reflection point (l
S
< 3 D):
ultrasonic waves in the pipe wall (pipe wall signal)
ultrasonic waves in the medium (measuring signal)