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Ultrasonic Flow Meters
Speed of Sound library

The non-contact ultrasonic flow meter is a non-invasive flow meter available in two types: transit time and doppler. Both technologies feature clamp on designs with transducer arrangements that can detect in-situ flowrates from outside the pipeline, without any interruption to flow or process. Transit time flow meters, or also known as 'time of flight' meters are mainly designed to the measurement of clean liquids, although many flow measurement devices have a maximum tolerance of 15% solids. The principle behind this type of non-intrusive clamp-on (strap on) flow meter is that acoustic waves with a frequency of >20kHz are emitted from one transducer to the other side of the pipe back to the opposite transducer requires less time than when traveling in the opposite direction. The differential transit time of the synchronized signals is proportional to the flow rate of the fluid. Transit time flow meter are widely accepted in all types of industries due to its accuracy, repeatability & application acceptability.


Ultrasonic flow measurement is possible with 2 methods

Doppler Type
Transit Time

Doppler type flow measurement technique is useful only for liquids containing dirt particles, air bubbles which can provide reflection hence Doppler type technique is not very accurate on clear portable liquids like pure water.

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Transit type technique is an universal technique of flow measurement and with the help of advance sensor design technology like micro structure ceramic it can handle most of the applications.

Principle of Operation : A flow meters along with pair of probes and interconnections cable is the basis hardware required for flow measurement.


Both probes A & B acts as 'Trans-Receiver'.
At first cycle, electronic unit sends a pulse to probe A and event gets memorized. The acoustic beam gets returned towards velocity, gets acknowledged by probe B generating signal called as 'ECHO'. On the reception of ECHO time gets memorized by electronic device. Electronic device calculates the time of flight TAB (Time Taken to travel from Probe A to Probe B).
At second cycle electronic unit sends pulse to Probe B and event gets memorized. Probe A acknowledges the acoustic beam that penetrates against velocity.
Electronic device calculates the time of flight TBA (Time taken to travel from Probe B to Probe A)
Electronic device calculates the flow as follows.


Q = A × V × KH

Area of Pipe
Hydraulic Coefficient
  Advantage of transit time Flow Meter  


Universality : The most important advantage of Transit Time Ultrasonic Flow meter is 'Universality'.

  a) Suitable for all types of pipe diameters : Transit Time Ultrasonic Flow meter are practically independent of pipe diameter i.e. the same flow meter can be used from 10 mm to 10000 mm pipe diameter.

b) Suitable for practically all kinds of liquids including petrochemicals, hydrocarbon, raw water, pure water, light slurries. Measurement is independent of electrical conductivity which is not possible with any type of magnetic flow meter pipe line for 5 to 6 mm.


c) Suitable for all types of pipe materials like Steel, Stainless Steel, Glass, Copper, Aluminum, PTFE, Nylon, Rubber, PVC, Polyethylene and many more.

In case of concrete pipelines, intrusive type probe assembly is used which penetrates inside the pipe line for 5 to 6 mm.


Bi-Directional Measurement : Flow measurement is possible in both directions for realistic measurement.


Easy Installation & Commissioning : Clamp-on flowmeters are very easy to install being a non-contact flow measurement. For insertion / wetted type sensors also installation is very simple and can be installed without taking shutdown (Online). This is the most important feature against other type of flowmeter like Full bore Magnetic / Vortex / Turbine / Woltman wherein you have to cut the pipe for installation which is practically impossible in many applications. In fact in existing distribution network during installation of full bore magnetic flow meter the line water wastage is more than the cost of flowmeter Hence Ultrasonic flow meters are the best choice in water industry.


Easy Maintenance : The complete Flow metering constitutes Probes, Converter and Interconnecting cables hence fault finding is very simple and hence maintenance is very easy. Secondly due to Universal Electronics, inventory cost for spares is practically zero.


Easy Shifting of flowmeter : Shifting of flow meter from one location to another is also possible without additional hardware which is not possible with other type of flowmeters.


Accuracy : The most important feature of transit time method is consistent accuracy over a period of time.
Accuracy of measurement is possible better than ± 1% of reading. Ultrasonic flowmeter does not require any flow laboratory for calibration. Since accuracy is dependent on measurement of time, which is sampled by most standard techniques, having resolutions of 40 Pico seconds.
By increasing the number of path we can achieve the accuracy up to ± 0.25%.
Accuracy can be verified at laboratories on request. It offers great benefit of compensating the effect of disturbed flow conditions by using multi path systems specially when straight runs are limited.