Small Electromagnetic Flowmeter Applications

Electromagnetic flow meters, or magmeters as they are commonly referred to, are the natural choice for a huge range of applications where electrically conductive fluid flows are to be measured, notably potable water or waste water applications.  Their construction means that there is no obstruction projecting into the flow to sense the flow and thus no snagging risk for the inevitable build up of lime scale or even solids (in the case of the wastewater, and slurry applications).  Sizes range from 25mm (1″) diameter for food processing, brewing, bio-chemical and water applications right through to 1,800mm (72″) for large hydro-electric schemes and flood prevention schemes such as can be found in the Lousisiana levées.

For small applications of electromagnetic flowmeters, typicallybetween 25mm and 100mm (4″), the applications, are largely related to clean fluid applications that can be found in all kinds of clear fluid dosing applications in process plant and potable water purification and pipeline distribution processes.  This is the group of magmeters that tend to supplied as an integrated flow meter body pipeline insert and control transmitter to link up with the process control units using standard process control fieldbus device integration control systems such as HART, PROFIBUS DP and PROFIBUS PA.

Electromagnetic Flow meters in this range are highly accurate with accuracies of flow measurement typically ±0.5% over ranges between 0 and 600m³/hour.  Being mainly for water use, they operate between 0ºC to over 60ºC and feature a very compact and lightweight body and integrated transmitter unit that is waterproof to IP67 standard.  The meter bore is capable of being disinfected as it has a hygienic lining.

You may have wondered why the ubiquitous magmeter tends not to be made in smaller sizes than 25mm diameter bore.  This is due to the limitations of this kind of flow meter physics.  The answer is that in the magmeter, the alternating pulse of the magnetic field creates two charged ion streams in the water that in larger sizes of meter cause no modification of flow other than encourage a stable turbulent water flow which in turn discourages zero point drift.  Below 25mm, this stabilising effect is overtaken by water shear and viscosity effects and therefore, it is better to use other forms of flow measurement.



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