Electromagnetic flowmeters measure liquid flow through a pipe using conductivity and a magnetic field. They are non-invasive, low maintenance, and can be used in various industries. Proper grounding is necessary for accurate readings.
An electromagnetic flowmeter, also known as a magmeter, is an instrument that measures the rate of flow of a liquid – or solids suspended in a liquid – through a pipe. Often, such flowmeters are used in wastewater treatment, food processing and the medical industry. They are generally based on the conductivity of the liquid, solution or slurry they are measuring, as it passes through a magnetic field and generates an electrical signal, which can be used to measure volume flow.
Since a substance must have electrical conductivity to be measured by an electromagnetic flowmeter, these instruments account for only about 20% of all meters used. Other types include the vortex flowmeter and the ultrasonic flowmeter. An electromagnetic flow meter, however, is often non-invasive and generally does not noticeably limit flow to measure it. Also, these devices tend to be very simply designed with almost no moving parts, so they require little maintenance and don’t need to be replaced often.
In 1830, Michael Faraday revealed the science that would make possible the invention of the electromagnetic flowmeter. He discovered that a substance that conducts electricity and moves through a magnetic field produces an electrical signal. Further developments led to the ability to interpret this signal, using various scientific calculations, to determine flow velocity.
There are several configurations of electromagnetic flowmeters. Sometimes they have electrodes protruding into the tube through which the substance being measured flows. The coils on the outside of the tube produce the magnetic field, while the electrodes collect the electricity generated. As long as the electrodes don’t create a coating from the substance to be measured, they work fine.
Another type of electromagnetic flowmeter is completely non-invasive to the pipe. In this type, the electrodes are only placed on the outside and the coils still generate a magnetic field. An advantage of this is that the liquid it is measuring never coats the electrodes. Additionally, these flowmeters can be used on closed piping systems, which are sometimes required to maintain purity and sanitation.
When an electromagnetic flowmeter is used, it must be properly grounded. If not, it can detect electrical interference, often called noise, and the flow reading will not be accurate. This can be a particular problem when the pipes are made of plastic, as they typically generate static electricity. Various grounding configurations are employed, depending on the flowmeter and piping design.
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