An electromagnetic flowmeter, also known as a magmeter, is a tool that measures the rate of flow of a liquid — or solids suspended in a liquid — through a pipe. Often, such flowmeters are used in the wastewater treatment, food processing, and medical industries. They generally rely on the conductivity of the liquid, solution, or slurry that they are measuring — as it passes through a magnetic field and generates an electric signal — which can be used to measure flow of volume.
Since a substance has to have electrical conductivity to be measured by an electromagnetic flowmeter, these tools only account for approximately 20% of all meters used. Other types include the vortex flowmeter and the ultrasonic flowmeter. An electromagnetic flowmeter, however, is often non-invasive and generally does not appreciably restrict flow in order to measure it. Also, these devices tend to be very simply designed, with almost no moving parts, so they require little maintenance and do not often have to be replaced.
In the 1830s, Michael Faraday revealed the science that would make the invention of the electromagnetic flowmeter possible. He discovered that a substance that conducts electricity and moves through a magnetic field produces an electric signal. Further developments led to the ability to interpret this signal, via various scientific calculations, to determine flow velocity.
There are a few different of configurations of electromagnetic flowmeters. They sometimes have electrodes that protrude into the pipe through which the measured substance flows. Coils on the outside of the pipe produce the magnetic field, while the electrodes pick up the electricity generated. As long as the electrodes do not build up a coating from the substance being measured, they work well.
Another kind of electromagnetic flowmeter is completely non-invasive to the pipe. In this type, the electrodes are placed just on its exterior and the coils still generate a magnetic field. One advantage of this is that the liquid that it is measuring never coats the electrodes. Also, these flowmeters can be used on closed piping systems, which are sometimes necessary to maintain purity and sanitation.
When an electromagnetic flowmeter is utilized, it must be properly grounded. Otherwise, it can pick up electrical interference, often referred to as noise, and the flow reading will not be accurate. This can be a particular problem when pipes are plastic, because they typically generate static electricity. Various grounding configurations are employed, depending on flowmeter and piping design.