When looking at how ultrasonic flow measurement works, look up the Atrato. The Atrato ultrasonic flow meter uses the well proven time of flight ‘ultrasonic flow metering’ method, which is far more reliable and accurate than Doppler shift measurement where reflected signals are required from irregularities in the liquid. The Atrato crystals are plain disks with a hole in the centre forming a washer, which are excited in such a way that they oscillate radially as opposed to the normal mode of excitement which is across the thickness of the ceramic. This strong radial signal sends symmetrical pulses directly into the tube.
Because of these annular ring crystals the sound travelling down the liquid
can be considered as a plain wave. The signal to noise ratio is remarkable
as there is little background noise and high signal strengths. At times the
signal to noise ratio is as high as 3000:1. As the system is fully balanced at
zero flows the two signals are identical and cancel each other out. This gives
a very stable zero flow condition and is the basis of the Atrato’s high ratio
between minimum and maximum flows. As the flow increases these signals
go out of phase and we measure this phase shift to an accuracy equivalent to
In addition, the sound waves travelling down the tube in the Atrato operating
system are symmetrical and as a result any changes in the fluid’s velocity
profile across the pipe diameter will be averaged out by the signal as it passes
from the transmitter to the receiver. It is therefore irrelevant whether the fluid
velocity profile is fully formed with turbulent flow or completely laminar with a
classic parabolic profile. In practice this gives the Atrato an excellent immunity
to Reynolds number changes and a good high viscosity performance.