A Doppler flow meter is a type of ultrasonic flow meter. These devices use a scientific principle called the Doppler Effect to measure the flow through a pipe. This works in such a way that the Doppler flow meter is clamped onto the outside of the pipe, so that it does not disrupt flow, as is required for other types of flow meter.
Ultrasonic Doppler flow meters transmit an acoustic signal into the flow stream at a specific frequency. This signal reflects off particulate, either solids or gas bubbles.
The reflected signal is detected by the receive transducer. The flow meter compares the transmit time & receive frequencies & computes the frequency shift. This frequency shift is proportional to the liquid’s flow velocity is known as the Doppler Effect.
Doppler Flow Meters are only used for liquids containing gas bubbles or particulates. Some of the applications where Doppler has advantage over Transmit time are Treated Waste Water, Raw Water, Slurry, Sewage, Viscous Liquids, Acid, Pulp Stock, Food Products, Aerated Water, Cooling Water etc.
But the liquid stream must have particulates, bubbles, or other types of solids in order to reflect the ultrasonic signal. This means that the Doppler flow meter is not a good choice for the water and very clean fluids.