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Thu 7 Oct 2021

What are the types of flow measurement?

Flow measurement is critical in any processing plant that uses a liquid or gas in a way that needs to be accurate and timely. Flow measurement enables you to work efficiently at optimum output rates whilst meeting regulatory or safety requirements. The types of flow measurement available to manufacturers used to be reasonably crude, but with the advancements in recent years of measurement technology, thanks in part to advanced electronics, wireless communications and big data, insights into real-time performance are much more widely available and affordable. We take a look at some of the types of flow measurement techniques available and their likely applications.


Differential pressure flow measurement


This type of flow measurement device works by creating a pressure differential within the flow by restricting the cross-sectional area within the pipework. The change in pressure is proportionate to a change in the velocity of the flow, and this can be measured to calculate the flow rate. Often used in oil and gas industries, refineries and chemical processing plants, they are ideal for applications where no moving parts are needed but an immediate response is critical.


Positive displacement flow measurement


These flow meters measure the volume of flow moving through a pipe and they do this using a rotating device within a housing that traps the fluid as it passes through; the flow of liquid causes the rotation and therefore allows for direct flow measurement. They can be used for viscous liquids but are often found in clean water applications where no straight pipework is available and where alternatives such as paddle wheels would create too much disturbance of the flow. Positive displacement flow meters are generally very accurate and cause minimal pressure drops, so they are a popular solution.


Velocity flow measurement


Velocity flow meters come in various forms which measure velocity rather than volume. One of the more popular options is the magnetic flow meter, which uses Faraday’s law of electromagnetic induction as the basis for flow measurement, using the fact that when a conductor (in this case, a conductive liquid such as water) moves through a magnetic field, a voltage is induced – and that voltage can be measured. Magnetic flow meters are ideal for corrosive liquids and slurries such as wastewater. 


Surface Acoustic Wave (SAW) flow measurement


Acoustic wave technology can be applied to flow measurement to measure the volumetric flow of a liquid. Similar to the technology used in seismic measurement, SAW flow meters use transducers on the outside of the pipework to act as transmitters and receivers to measure the propagation of an acoustic wave and capture data on amplitude, frequency and run times. This technology is used widely in hygienic processing such as pharmaceutical plants because not only is the data extremely accurate, but there is no interference needed with the flow at all. This means that no drop in pressure is experienced and, crucially, no contamination of the liquid or of the flow measurement device can occur. 

If you would like to understand which of the types of flow measurement device is right for your application or would like to learn more about the FLOWave flow meter, get in touch with BM Engineering and we will be happy to support you in finding the right flow measurement solution for you.

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