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Ultrasonic Flow Meters , Level Sensors , Water Quality Monitoring
RS Hydro > Flow Meters > Doppler

Doppler Flow Meter

Doppler Flow MeterPortable Doppler flowmeters work in a similar way to transit time meters and open channel doppler flow meters in that they emit ultrasonic signals into the flow path. Permanent and portable doppler flowmeters are generally used where no other flowmeter can be used - primarily in the process and wastewater industries. Although fixed and portable doppler flowmeters do not share the same accuracies as transit time meters, they are reknowned for establishing flowrates in very difficult measurement conditions. However, it is recommended that where conditions allow, alternative technologies should be used.

Some of the pipe doppler flowmeters available from RS Hydro:

Polysonics Hydra SX30
The Hydra SX30 is designed for the measurement of fluids which contain particulate.
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The Doppler effect, named after Austrian physicist J. C. Doppler who first described it for sound in 1842, states that waves emitted from a source moving toward an observer are squeezed; i.e. the wave's wavelength is decreased and frequency is increased, as shown in the schematic below. Conversely, waves emitted from a source moving away from an observer are stretched; i.e. the wave's wavelength is increased and frequency is decreased. To use the Doppler effect to measure flow in a pipe, one transducer transmits an ultrasonic beam of c.0.5 MHz into the flow path. Liquid flowing through the pipe must contain sonically reflective materials such as solid particles or entrained air bubbles. The movement of these materials alters the frequency of the beam reflected onto a second, receiving transducer. The frequency shift is linearly proportional to the rate of flow of materials in the pipe and therefore can be used to develop an analog or digital signal proportional to flow rate.

Advantages of Doppler Flowmeters

Drawbacks and Limitations of the Doppler Flowmeter

Which Portable Doppler Flowmeter ?

You can obtain a quotation for the following doppler flowmeters using our online instrumentation store.

Manufacturer Model Verdict
Greyline PDFM-IV 70%
EESIFLO EASZ-10P 50%
Polysonics SX30/40/50 80%

The above verdicts are based RS Hydro's own experience and that of its customers.

Applications

Doppler flow meters can measure almost all fluids containing significant entrained deposits or air bubbles. The basic requirement is that the fluid can conduct ultrasound and have an acceptable axis-symmetrical flow.

This is a test

Typical applications include:

Specifications

Although specifications are different between the various manufacturers, the following is intended as a guideline to their performance and specification.

Flow Range 0.06-10m/sec (Bi-Directional)
Accuracy ±1-5% of reading
Repeatability Typically ±0.5%
Pipe Size 12.7-5000mm

Operating Temperature

Transducers -40°C to +120°C
Transmitter -20°C to 60°C
Datalogging Typically>100,000 data points, time stamped
Output 4-20mA, RS232
Power Built-in battery with external 12v input, 8-24 hours operation
Dimensions Typically 325 x 275 x 150mm
Weight (Control Unit) Typically 3-7kg

Technical Notes

In order to obtain the optimum accuracy from a doppler sensor, the following conditions must apply:

Requirement
Location At least 10 diameters of straight-length pipework must exist upstream of the measurement point, and 5D downstream. Ideally these distances should be as large as possible.
Liquid Medium It is essential that the type of fluid is known. Also that there are no air bubbles and that the solid content does not exceed 5%.

Pipe Condition

The pipe wall exterior should be free from dirt, paint or corrosion. For optimum accuracy the interior wall should also be free from deposits or corrosion.
Solid Content Solid Content ideally should be >5% or contain air bubbles.