Flowmeters are not always installed in locations where there is a stable
and undisturbed flow. In fact, accessing such ideal measurement conditions is
often difficult, or impossible.
Disturbances in the flow profile could be caused by numerous factors but
generally happen due to any 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 the 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. 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.
It’s important, therefore, to identify when disturbances to the flow
might be happening, and then, offer an appropriate solution.
However, 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 are,
therefore, 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 when looking at potential locations for meter
Katronic has published a document
on their website highlighting how dual-path ultrasonic flowmeters can be used
to improve measurement results under non-ideal installation conditions.