How to Differentiate Between Doppler and Ultrasonic Flow meters

Ultrasonic fluid meters

Ultrasonic flowmeters are non-intrusive devices that use sound waves to measure liquid flow. There are two types: Doppler and Transit time. Both clamp onto the pipes outside without causing damage or interfering with flow. This prevents leakage and pressure loss, which can be common with an inline flow meter. The flow meter is also protected from liquid contact, which prevents corrosion and deterioration. Although the principle of transit time and Doppler flow meters is similar, technology can vary.

Doppler Ultrasonic flow meters

The principle of Doppler Effect is the basis for the ultrasonic flowmeter. It was first documented in Austria by Christian Johann Doppler, a mathematician and physicist. According to Doppler, the frequency of sound waves that an observer receives is dependent on the motion of the source. The Doppler ultrasonic flowmeter emits an ultrasonic beam through the pipe’s stream using a transducer. The flow meter must have solid particles or bubbles in the stream in order to reflect the ultrasonic light. A second transducer receives the signal from the beam because particles move at different frequencies.

Transit Time Ultrasonic Flow meters

Transit time ultrasonic flow meters measure time between the time and ultrasonic signal crosses a pipe and it is received by the second transmitter. Comparing upstream and downstream measurements is possible. The travel time in each direction will be equal if there is no flow. If there is flow, sound travels faster in one direction than it does against. The ultrasonic signal must travel through the pipe in order to reach the sensor. Otherwise, the high-frequency sound will not be heard and the liquid will become too weak to travel along the pipe.

Factors that Influence the Accuracy Of Ultrasonic Flow Meters

Mounting properly is crucial for accurate ultrasonic flowmeter measurements. The alignment of the transducers or the acoustic coupling may be affected by large temperature fluctuations in the pipe. All these factors should be considered during installation. All ultrasonic flow meters require full pipe to get accurate volumetric flow rates. If both transducers are below the pipe’s fluid level, a Doppler ultrasonic flowmeter will still generate flow velocity measurements. As to the question of why choose portasonic flow, click the link to find out.


Ultrasonic flow meters can be used to measure flow velocity without contact. These clamp-on devices attach to the outside of the pipe and allow measurement of corrosive fluids without causing damage to sensors. Doppler and transit times are two types of ultrasonic flowmeters that each use two different technologies. Understanding how each function allows you to choose the right flow meter. To reflect ultrasonic signals, the Doppler ultrasonic flowmeter must contain particles or bubbles. It can be used to test dirty or aerated liquids, such as wastewater or slurries. The signal from the transit time ultrasonic flowmeter will be lessened if there are large amounts of solids and bubbles in the liquid. It is best to use it with water or oil.

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