How to measure in case of a disturbed flow?

Dual-channel flowmeters: for the best results under the worst of flow conditions.

One of the assumptions made when installing a flowmeter is that the instrument in a location where there is a stable and undisturbed flow. The reality is though that accessing such ideal measurement conditions is often difficult, or impossible. Disturbances in the flow profile could be caused by numerous things but generally are a result in a change to the pipe through which the liquid is flowing. This could be a change of angle or plane through bends, a change of diameter through a reducer or diffuser or some other process equipment such as a valve or pump. These changes in fluid condition cause the flow profile to shift with the point of maximum fluid velocity no longer being located in the centre of the pipe.

Localised flow profile changes resulting from these pipe modifications will cause problems for most flowmeters installed in the same area. The cause is that regardless of the measurement technique used, there is an assumption that the observed flow condition is happening at the point of fastest flow and that no other outside influences are in play. The initial question is therefore what can be done to identify when disturbances to the flow might be happening, and then secondly to offer an appropriate solution.

It should me mentioned at this point that certain measurement technologies are more immune to this effect than others. Coriolis flowmeters for example calculate flow and density based on the vibrations of the internal tubing within the meter body and as such are not constrained in the same way as other instruments. Users of clamp-on flowmeters, along with many other devices, need to take the flow condition into account looking at potential locations for meter installation.

In order to provide guidance in how best to do this, we recommand to download the document highlighting how dual-path ultrasonic flowmeters can be used to improve measurement results under non-ideal installation conditions.

Download the technical information sheet ‘Dual Path Measurement‘.