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6 Measuring point selection FLUXUS WW
UMFLUXUS_WWV1-1EN, 2018-02-28 23
6 Measuring point selection
The correct selection of the measuring point is crucial for achieving reliable measurement results and a high measurement
accuracy.
A measurement on a pipe is possible if
• the ultrasound propagates with sufficiently high amplitude (see section 6.1)
• the flow profile is fully developed (see section 6.2)
The correct selection of the measuring point and the correct transducer positioning guarantee that the sound signal will be
received under optimum conditions and evaluated correctly.
Due to the variety of applications and the different factors that influence the measurement, there is no standard solution for
the transducer positioning. The measurement is influenced by the following factors:
• diameter, material, lining, wall thickness and shape of the pipe
• fluid
• gas bubbles in the fluid
Avoid measuring points:
• in the vicinity of deformations and defects of the pipe and in the vicinity of welds
• with deposit formation in the pipe
Make sure that the pipe surface at the selected measuring point is even. The pipe may not be corrugated.
The ambient temperature at the measuring point has to be within the operating temperature range of the sensors (see
Technical specification).
Select the location of the transmitter within the cable range of the measuring point.
The ambient temperature at the measuring point has to be within the operating temperature range of the transmitter and
the sensor (see Technical specification).
If the measuring point is within an explosive atmosphere, the danger zone and gases that may be present have to be de-
termined. The transducers and the transmitter have to be appropriate for these conditions.
6.1 Acoustic penetration
The pipe has to be acoustically penetrable at the measuring point. The acoustic penetration is reached when pipe and flu-
id do not attenuate the sound signal so strongly that it is completely absorbed before reaching the second transducer.
The attenuation caused by the pipe and the fluid depends on:
• kinematic viscosity of the fluid
• proportion of gas bubbles and solids in the fluid
• deposits on the inner pipe wall
• pipe material
The following requirements have to be met at the measuring point:
• the pipe is always filled completely
• no material deposits in the pipe
• no bubbles accumulate
Attention! Observe the "Safety instructions for the use in explosive atmospheres" (see SIFLUXUS document).
Note! Even bubble-free fluids can form gas pockets when the fluid expands, e.g., before pumps and after
great cross-section extensions.