Flowmeters 101

flowmeter principle

Magnetic Flowmeters – How they work

Flowmeters play a vital role in sanitary processing.  They are used to measure incoming raw materials, incoming water supply, CIP solutions, ingredients in your formulation, final product production and even waste water leaving the plant.  Considering their use in critical applications, ensuring that you are using the right type of meter with the correct level of accuracy for your application can be the difference in the quality of your product and save you thousands of dollars in lost revenue or profit.

flowmeter principle

Magnetic Flowmeters

Magnetic flowmeters (or mag meters) use Faraday’s Law of Electromagnetic Induction to determine the flow of liquid through a pipe.  This type of flowmeter works by generating a magnetic field and channeling that through the liquid in the pipe.  Faraday’s Law states that flow of a conductive liquid through the magnetic field will cause a voltage signal that can be sensed by electrodes on the tube walls.   When the fluid moves faster, more voltage is generated.  The voltage generated is proportional to the movement of the liquid.  Transmitters process the voltage signal to determine liquid flow.

The signals produced by the voltage are linear with the flow.  With this, the turndown ratio is very good without sacrificing accuracy.

Pros and Cons

IZMAG flow sensor

Since these flowmeters measure conductivity, obviously the fluids measured need to be conductive – water, acids and bases.   Low conductive liquids, such as deionized water or gases, can cause the flowmeter to turn off and/or measure zero flow.  There is no obstruction in the path of the liquid, therefore no induced pressure drop across the meter.  One other benefit of mag meters is that they can be used on gravity-fed liquids.  With gravity-fed liquids, the flowmeter orientation should be vertical so that the flowmeter is completely filled with liquid.  These flow meters are sensitive to air bubbles because the meter cannot distinguish entrapped air from the liquid.  Air bubbles will cause the meter to read high.

Mag meters are typically chosen because they have no obstructions, are cost-effective and provide highly accurate volumetric flow.  Additionally, they can handle flow in either direction and are effective at low and high volume rates.