What is a Doppler flow meter? Doppler Flow Meter is a flow meter that uses the doppler effect principle to monitor the liquid flow rate.

Wall Mounted Ultrasonic Doppler Flow Meter

Doppler Flow meter use reflected ultrasonic sound to measure the fluid velocity. By measuring the Doppler frequency shift of the sound waves scattered by the moving particles in the fluid, the velocity of the fluid can be obtained. Combined with the built-in pressure water level gauge. Using the velocity area method. The flow of liquid can be measured. Suitable for flow measurement in open channels, rivers, and various full and partial open channels.

Sino-Inst offers a variety of  Ultrasonic flow meters for flow measurement. If you have any questions, please contact our sales engineers.

Features of Doppler Flow Meter

  • All functions in one design. Simultaneous measurement of average flow rate, water depth, and water temperature
  • The velocity area method is used to measure the flow, and there is no head loss. There is no need to build a standard weir.
  • The ultrasonic Doppler principle is used to measure the flow velocity. The measurement accuracy is high and the initial speed is low.
  • No mechanical rotor structure. It has no effect on the water flow state, and the measurement is more accurate.
  • Comes with a temperature sensor. It can be used to compensate for the effect of water temperature on the speed of sound.
  • It can measure instantaneous flow and cumulative flow.
  • Using frequency domain Doppler analysis algorithm. The data is stable and reliable, and the real-time performance is strong.
  • Simple installation. No need for auxiliary engineering facilities

Specifications of Doppler Flow Meter

Fluid velocity Range 20mm/s-5000mm/s
measurement accuracy ±1% of measured flow rate
Resolution 1mm/s
Liquid level Range 0-5m
measurement accuracy ±1cm
Resolution 1mm
Flow rate Range 0.001m3/s to 9999m3/s depends on the actual section
measurement accuracy ±3%
Resolution 0.0001m3/s
Other parameters Power supply range 9-24V
Collection cycle Can be set
Interface Type RS485(Modbus)
Storage temperature -20-80℃
Operating temperature 0-60℃
Protection level IP68
shell material PVC

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What is a Doppler flow meter?

Doppler flowmeter is an ultrasonic flowmeter that uses the Doppler effect of sound waves propagating in fluids. It is suitable for the flow measurement of open channels, rivers and difficult-to-build standard sections, as well as the flow measurement of various full and partial open channels.

The Doppler flowmeter uses the principle of ultrasonic Doppler to measure. By measuring the Doppler frequency shift of the sound waves scattered by the moving particles in the fluid, the velocity of the fluid can be obtained. Combined with the built-in pressure water level gauge, the velocity area method can be used to measure the flow rate of the liquid.
According to different application scenarios, it can be called river flowmeter, sewer flowmeter, channel flowmeter, farmland irrigation flowmeter, non-full pipe flowmeter, etc.

Doppler flowmeters do not need to cut off the pipeline to install pipe-segment sensors like electromagnetic flowmeters. There is no need to use a shut-off device. Do not install a fixed weir to control the flow of water from a fixed outlet.

The Doppler flowmeter can measure in both clean and muddy water, and can also measure reverse flow velocity.

Read mroe about: Irrigation Flow Meters for Agriculture Water System

Doppler flow meter working principle

For flow velocity measurement, the first thing to explain is the Doppler shift. When there is relative motion between the wave source and the observer, the frequency received by the observer is different from the true frequency of the wave source. The difference between the frequency of the received signal and the frequency of the sound source is called the Doppler shift. Its size is determined by the relative speed between the two. This physical phenomenon is called the Doppler effect.

When measuring the flow velocity, the wave emitted by the probe encounters suspended matter, solid particles, vapor bubbles, and even unstable vortices and disturbances in the medium that follow the wave. Both will produce reflected waves that deviate from the transmit frequency, resulting in Doppler frequency changes. This effect is proportional to the velocity of movement of the reflector.

The receiving probe receives the reflected wave from each point. After complex signal processing, dynamic spectrum analysis and accuracy calculation. The flow velocity of the fluid in the pipe section can be obtained.

Flow rate calculation

The ultrasonic beam emitted from the Doppler velocity sensor (transducer) encounters particles or bubbles moving in the fluid. It is reflected back and received by the Doppler flow sensor (transducer). The Doppler frequency shift of the transmitted signal and the received signal is proportional to the fluid velocity.

Doppler flow meter working principle

Among them:
u is the channel flow rate,
f1 is the working frequency of the sensor,
δfd is the Doppler frequency difference.

Flow calculation

Real-time flow velocity and water level data collected by acoustic Doppler flowmeter.
The data acquisition and processing unit receives the flow rate and water level data. Calculate the instantaneous flow rate and record it as Qs;
Then calculate the accumulated flow rate and record it as Q; its flow rate can be calculated as follows:


In the formula, A is the water area of the pipeline, and V is the average flow velocity of the section.

Q = QsT

In the formula, the instantaneous flow of Qs section, T is the accumulated time (unit h).

Read more about: Ultrasonic flow meters types & technical guide

Ultrasonic doppler flow meter advantages and disadvantages

Advantages of ultrasonic Doppler flowmeter:

  1. Contact measurement. Can accurately measure the flow rate of the fluid;
  2. Wide range of use. It can measure the flow velocity of rivers, channels, dissatisfied pipelines, and urban underground pipe network sewer scenarios;
  3. Simple installation. No baffle or weir groove is needed. The data can be measured by simply contacting the sensor directly with the fluid;
  4. Low power consumption, diversified power supply methods, 6v power supply. Optional external power supply, battery power supply, solar power supply;

Disadvantages of ultrasonic Doppler flowmeter:

  1. Cannot measure pressured pipelines, closed pipelines and high temperature environments;
  2. The water depth is less than 10cm and cannot be measured;
  3. The stable data can only be measured in a place where the water flow is stable, and there are certain requirements for the selection of the installation location;
  4. For a site with a large turbidity, it is not as good as a site with more floating objects, garbage, and bottom silt, and accurate data cannot be measured;

Ultrasonic Doppler Flow Meter Applications

Fixed Doppler ultrasonic flowmeters

Mainly used in environmental testing of urban sewage treatment plants, drainage pumping stations, and mining, oilfields, metallurgy, chemical, oil refining, paper, food and other industries.

Flow measurement of urban drainage, industrial wastewater, domestic sewage, mud, paper pulp, oil-water mixture, etc.

It is suitable for hard pipes such as steel and hard plastic pipes.

It can measure two-phase liquids containing suspended solid particles or bubbles in tubes with various tube diameters and wall thicknesses.

Doppler flow meter open channel

There are many monitoring methods for measuring the flow of water in open channels, among which the water level flow method and the velocity area method are the majority. The former uses an ultrasonic open channel flowmeter to measure, and the latter uses a Doppler flowmeter to measure in an open channel.

The methods used for different open channels are different. Here we mainly talk about what conditions the Doppler flowmeter must meet for measurement in an open channel.

The Doppler flowmeter is in full contact with the water through the flow rate sensor. The real-time flow rate is measured. Input the width, shape, and water depth of the open channel to the host. The host uses the speed area method to convert the real-time flow.

Therefore, it requires the water depth to immerse the sensor in order to obtain more accurate data.

Due to the principle of ultrasonic measurement, it is determined that the Doppler flowmeter measurement in the open channel needs to meet the following conditions:

  1. The flow rate of the water flow should be uniform, and there should be no plain flow (to ensure such measurement conditions, the site should meet the straight channel with 15 times the channel width)
  2. Water depth requirement: no sensor (Yuzheng Doppler flowmeter requires water depth ≥13cm)
  3. Width of open channel ≥50cm
  4. The water flow velocity is required to be 0.04m/s-10.00m/s. If the flow velocity is too fast, the measurement will be inaccurate
  5. There should be no rubbish and large floating objects in the open channel
  6. The water in the open channel should not be too pure, for example, pure water cannot be measured

The above six points are the conditions that need to be met simultaneously for the measurement in the open channel of the Doppler flowmeter. Of course, before the measurement, the selection of installation and the selection of the installation point are also very important.

If you still don’t understand the details, you can contact Sino-inst technical consultant to get in touch to solve your troubles in detail.

Extended reading: Make Ultrasonic Open Channel Flow Meter Work for You

Application of Ultrasonic Doppler Flowmeter in Irrigation District

1.Check the water level and velocity curve

Portable Doppler ultrasound can be used to place it in the channel of the irrigation area. During the upstream discharge process, the water level, velocity, and flow changes are measured. The water level, velocity, and flow meter are generated.

In the later calculation, you can directly use the ultrasonic water level gauge or the radar water level gauge for online monitoring. Combine the existing water level, velocity and flow relationship to get the flow value under the current water level.

When the upstream and downstream channels of the irrigation area are changed, re-measurement is required. This method is suitable for use in irrigation areas that require cost and require mass monitoring.

2.Long-term online monitoring

Use LSX-1 Doppler ultrasonic flowmeter with telemetering terminal. Use city power or solar power system for power supply. Fix the flowmeter in the channel. The telemetry terminal periodically collects the data in the flowmeter and sends it to the server remotely via GPRS. The data can be viewed through the WEB platform.

Portable Doppler Flow Meter

Portable Doppler Flow Meter

The Portable Doppler Flow Meter uses the Doppler effect of sound waves propagating in the fluid. Hand-held design, suitable for handheld wading water flow measurement.

The Portable Doppler Flow Meter (Model: LSX-2) can obtain the velocity of the fluid by measuring the Doppler frequency shift of the sound waves scattered by the moving particles in the fluid. Combined with the built-in pressure water level gauge, the velocity area method can be used to measure the flow of the liquid. It is suitable for flow measurement of open channels, rivers, pipelines and difficult-to-build standard sections. It can work continuously for more than 12 hours on a single charge.

Transit time vs Doppler flow meter

There are two types of ultrasonic flowmeters, one is the time difference measurement method, and the other is the Doppler method. Many users often only know one of them.

Here, we make a simple comparison so that you can choose the correct model.

1.The measurement principle is different.

The main principle of the time difference method is that when the ultrasonic beam propagates in the liquid, the flow of the liquid will cause a small change in the propagation time. The change in its propagation time is proportional to the flow rate of the liquid.

At zero flow, the time required for the two sensors to transmit and receive sound waves is exactly the same. The only technology that can actually measure zero flow.

When the liquid is flowing, the transmission time of sound waves in the counter-current direction is longer than that in the downstream direction. The Doppler method uses the characteristic that the ultrasonic wave will be scattered when encountering tiny solid particles or bubbles in the propagation path.

2.The applicable medium is different.

The time difference ultrasonic flowmeter can only measure clean liquids. It will not work well when it contains more solid particles or bubbles.

The Doppler method uses the scattering characteristics of ultrasonic waves for measurement. Therefore, the Doppler method is suitable for measuring fluids containing solid particles or bubbles, but clean liquids cannot be measured.

3.The measurement accuracy is different.

The time difference method has higher measurement accuracy, and the Doppler method has lower measurement accuracy.

Since scattered particles or bubbles exist randomly, the sound transmission performance of the fluid is also different. If it is a fluid with poor sound transmission performance, the scattering is stronger in the low velocity area near the pipe wall.

However, the scattering of fluids with good sound transmission performance is dominant in the high velocity area, which makes the measurement accuracy of the Doppler method lower.

Although it adopts a structure in which the transmitting transducer and the receiving transducer are separated. In this way, only the scattering in the middle area of ​​the velocity profile can be received. However, the measurement accuracy is still lower compared with the time difference method.

4.The working conditions are different.

The time difference method is suitable for full pipe measurement.
The Doppler method is suitable for measuring the flow of full pipes, partial pipes, open channels, etc.

OMEGA Engineering has a good explanation of Doppler vs Transit Time. Let’s look together.

Video source: https://www.youtube.com/watch?v=NQWNYARWmB8

More Featured Ultrasonic Flowmeters

Sino-Inst, Manufacuturer for Ultrasonic Doppler Flow Meters. It can measure a single sound-conducting liquid medium. It can measure even liquids such as water, sea water, oil, and slurry.

Sino-Inst’s Ultrasonic Doppler Flow Meter, made in China, Having good Quality, With better price. Our flow measurement instruments are widely used in China, India, Pakistan, US, and other countries.