Highest measurement accuracy despite difficult measurement conditions

When installing a flow meter, it is generally assumed that the meter will be mounted at a measurement point with stable and undisturbed flow. In reality, however, it is often difficult or even impossible to achieve such ideal measurement conditions. Disturbances in the flow profile can be caused by numerous factors, but are usually a result of changes in the pipe through which the fluid flows. This can be caused by a different slope or angle of the piping due to pipe bends, by a change in diameter due to a reducer or diffuser, or by installed valves and pumps. These changes in flow conditions result in a shift in the flow profile, such that the point of maximum flow velocity is no longer located in the center of the pipe.

Local changes in the flow profile resulting from these pipe modifications pose a problem for most flow meters installed in this area. The reason is that, regardless of the measurement technology used, it is assumed that the observed flow condition occurs at the point of fastest flow and that no other external influences are at play. This raises the question of how to recognize when flow profile disturbances occur and, secondly, how best to deal with them.

It should also be noted here that certain measurement techniques are less susceptible to this effect than others. Coriolis flow meters, for example, calculate flow rate and density based on vibrations inside the pipe within the measuring element and, as such, are not affected by flow profile disturbances in the same way. Users of clamp-on flow meters—as with many other measuring devices—must, above all, take flow conditions into account by ensuring that the meter is installed in a suitable location.

To achieve reliable measurement results even under difficult flow conditions, dual-channel flow meters are used. In addition, care must be taken to ensure the ultrasonic sensors are properly positioned on the pipe. Guidance on two-channel flow calculations can be found on the right as well as in the download section of the website. All newly published user manuals are also available for download there. The chapters “Installation of Ultrasonic Sensors” and “Installation Locations” describe in detail what to consider when selecting the pipe section for mounting the sensors—both in general and, in particular, near sources of interference.