What are the Difference between Transit Time and Doppler Flow Meters?

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Flowmeters find extensive usage in different industries. They are used to measure the flow rate of fluids which can either be in the liquid or gaseous state. One of the technologies that has found acceptance across the board is the use of the ultrasonic flowmeter. Such flowmeters give much more accurate data over the traditional flowmeters. Today with the advancement of the digital signalling has been powering these meters that allow industries to keep a tab on the exact flow of liquid or gas in a pipeline. Small and large businesses are fast adopting this as a preferred means of measuring the flow of liquid.



Doppler flowmeters and Transit Time flowmeters are two distinct types of instruments that are being used in the industry. Often we tend to confuse one for the other as both these instruments make use of the ultrasonic technology to measure the flow of liquid. There are however many difference in the way these flowmeters work and here we shall take note of the differences between Doppler flowmeters and Transit Time flowmeters. To understand the differences between the two we need it is important that we understand their working mechanism.



Doppler Flowmeters

The mechanism of this type of flowmeters is based on bouncing signals which was proposed by Christian Doppler in what is famously known as Doppler Effect. The theory is that the frequency shift is in direct proportion to the velocity of the liquid. Here the signals bounce off small particles or bubble in the moving fluid in a pipe and create what is popularly known as the 'Doppler Shift'. This is turn creates what we know as return signal frequency. Here the flowmeter measures the Doppler Shift and then it calculates resulting speed of the reflective particles. This is further multiplied by the internal diameter of the pipe through which the liquid passes to produce volumetric flow.



However this kind of flowmeters has a have disadvantage as they are don't work with liquids that don't have enough sonically reflective particles in your flow stream. While those who promote this technology criticise this argument the fact remains that if there is no reflective particle in the liquid for the signal to bounce from there is no way that it will offer you accurate results on the flow of the liquid.



Transit-Time Flowmeters

Transit-Time flowmeters also makes use of the ultrasonic technology. These work by measuring the time taken by an ultrasonic signal transmitted from one sensor, to cross a pipe where the liquid is flowing and be received by a second sensor. Here two different components namely the upstream and downstream time measurements are compared. This difference in time (Transit-Time) is calculated using a bunch of powerful algorithms to produce an accurate flow velocity. If there is no flow the transit time would be equal in both directions. When there is flow of liquid the sound travels faster in the direction of flow and slower in the direction of flow. This technology is more reliable and less expensive compared to Doppler flowmeters.



The downside of this measurement technique is the fact that the fluid should be clean and should not contain any bubble or solid particle as this will result in the higher frequency sound being attenuated and making them too weak to transverse the pipe.



You can clearly make out from the above working mechanism that both these technologies are effective in measuring the flow of liquid. However industries must make a choice based on the type of liquid that they are going to measure as both these systems have their own disadvantages.



This post is contributed by SpireMT, a leading supplier of transit‐time flow meter,Handheld Ultrasonic Flow Meter,, Transit-Time Flow Meter, Electrical Energy Meters and many more. For more information visit at http://www.spiremt.com

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