Low Flow Flowmeter

The Atrato System

The Atrato system of low flow meters uses the well-proven time of flight measuring method, which is far more reliable and accurate than Doppler shift measurement, wherein, reflected signals are required from irregularities in the liquid. The strong radial ultrasonic signal sends symmetrical pulses directly into the tube; the sound travelling down the pipe can be considered as a plain wave. The signal to noise ratio is remarkable, as there is little background noise and high signal strengths. 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 flowmeter’s high-ratio between minimum and maximum flows. As the flow increases, these signals go out of phase, and this phase shift is measured to an accuracy equivalent to 250 picoseconds. 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.