An electromagnetic flowmeter, or simply a magnetic flow meter or mag meter, is a type of volumetric flow meter. As the third most common type of flowmeter, electromagnetic flowmeters fall behind differential pressure and positive displacement flow meters, but are still highly important for many industrial applications.
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Electromagnetic flowmeters function based on Faraday's law of electromagnetic induction, which is why they are also known as induction flow meters. Faraday's law of electromagnetic induction states that the induced electromotive force or EMF in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit. Using this law, electromagnetic flowmeters measure the change in induced voltage of the conductive fluid flowing across a controlled magnetic field. Typical conductive materials include strong acid, salt, strong alkali, high viscosity fluid and liquid-solid mixed fluid. While many industries utilize electromagnetic flowmeters, the most common of which include food and beverage, wastewater, HVAC, chemical processing, industrial and pharmaceutical. Electromagnetic flowmeters best serve applications that require low pressure drops and low maintenance such as water conditioning, chemical batching and process control.
In the construction of an electromagnetic flowmeter, a magnetic field is created within a metering tube through energized coils. As a result of the magnetic field, a potential difference that is proportional to the flow velocity perpendicular to the flux lines becomes both evident and measurable. In order to mitigate difficulties that arise while trying to measure this potential difference, the magnetic field is constantly reverse, which cancels out the static potential difference. However, this constant reversing causes permanent magnets to be unsuitable for use in electromagnetic flow meters. There are two main types of electromagnetic flowmeters, in line and insertion, neither of which having any moving parts. In line electromagnetic flowmeters consist of a conducting liquid within a straight run of regular to small-sized pipe that is attached directly to the process line. Electric coils are place around the pipe in order to create the magnetic field, with a pair of electrodes set up across the wall of the pipe. This type of flow meter has a very high accuracy rate and can be as accurate as .5% of the flow rate. Insertion electromagnetic flowmeters consist of a conducting liquid within a large straight pipe that is inserted perpendicular to the flow path, requiring a threaded hole within the processing pipe. Electric coils are placed near the processing pipe, with a pair of electrodes placed at the tip of the flow meter. This type of flow meter is very sensitive to electrical noise.
