The Doppler Effect Ultrasonic Flow meter use reflected ultrasonic sound to measure the fluid velocity. By measuring the frequency shift between the ultrasonic frequency source, the receiver, and the fluid carrier, the relative motions are measured.
The resulting frequency shift is named the Doppler Effect.
This method requires that there is some reflecting particles in the fluid, but it is not suitable for clear liquids.
Doppler meters may be used where other meters don't work. This might be liquid slurries, aerated liquids or liquids with some small or large amount on suspended solids.
Ultrasonic flow meters installed on the outside of the pipes will not have any influence on pressure loss in the pipe. Ultrasonic meters installed in the flow - like individual meters or similar - may influence on pressure loss like valves or similar.
The Doppler flow meters performance is highly dependent on physical properties of the fluid, such as the sonic conductivity, particle density, and flow profile.
So non uniformity of particle distribution in the pipe cross section may result in a incorrectly computed mean velocity. The flowmeter accuracy is sensitive to velocity profile variations and to the distribution of acoustic reflectors in the measurement section.
Unlike other acoustic flow meters, Doppler meters are affected by changes in the liquid's sonic velocity. As a result, the meter is also sensitive to changes in density and temperature. These problems make Doppler flowmeters unsuitable for highly accurate measurement applications.