subject: Electromagnetic Flow Meter [print this page] Modern innovations in the measurement of flow rate incorporate electronic devices that can correct for varying pressure and temperature (i.e. density) conditions, non-linearities, and for the characteristics of the fluid.
An Electromagnetic Flow Meter, 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 flow meters 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 generate an electric signal that can be used to measure flow of volume.
Since a substance has to have electrical conductivity to be measured by an electromagnetic flow meter, these tools only account for approximately 20% of all meters used. Other types include the vortex flow meter and the ultrasonic flow meter. An electromagnetic flow meter, 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.
There are a few different of configurations of electromagnetic flow meters. 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 flow meter 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 flow meters can be used on closed piping systems, which are sometimes necessary to maintain purity and sanitation.
When an electromagnetic flow meter 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 flow meter and piping design.
