How does an electromagnetic flowmeter(EMF) work? How to choose the lining and electrode of electromagnetic flowmeter? What are the advantages of electromagnetic flowmeters in applications?

 

An electromagnetic flowmeter works by measuring the flow rate of a conductive liquid in a pipe using Faraday's law of  electromagnetic induction. The flow meter consists of a pipe through which the liquid flows, and electrodes that apply  a magnetic field to the liquid. When the liquid flows through the magnetic field, a voltage is induced in the liquid,  which is proportional to the flow rate.

When choosing the lining and electrode of an electromagnetic flowmeter, it is important to consider the compatibility  with the liquid being measured. The lining material should be chemically resistant to the liquid to prevent corrosion  and ensure accurate measurements. The electrode material should also be compatible with the liquid to maintain  conductivity and prevent fouling. 

Flow tubes, Liners, and Probes

The dimensions of short form magmeters usually meet these guidelines as well. Magnetic flow tubes and liners are available in many materials and are widely used in all the process industries, including food, pharmaceutical, mining, and metals.

Some liner materials (particularly PFA) can be damaged when pry bars are used while installing it or removing it from process piping. They can also be damaged by over-torquing the flange bolts. Liner protectors are available to help prevent such damage.

Any flow tube can generally be used with any transmitter offered by the same manufacturer. Depending on its construction and features.

Magnetic flowmeters also can be packaged as probes and inserted into process pipes through taps. These probes contain both the electrodes and magnetic coils. The flowing process fluid induces a voltage at the electrodes, which reflects the velocity at the probe tip and not the average fluid velocity across the pipe. These magmeters are inexpensive and retractable. Therefore, the process does not have to be shut down to install or remove them. Metering accuracy is highly dependent on the relationship between the measured velocity and the average velocity in the pipe.

Electrodes

In conventional flow tubes, the electrodes are in contact with the process fluid. They can be removable or permanent if produced by a droplet of liquid platinum as it sinters through a ceramic liner and fuses with the aluminium oxide to form a perfect seal. This design is preferred due to its low cost, its resistance to abrasion and wear, its insensitivity to nuclear radiation, and its suitability for sanitary applications because there are no cavities in which bacteria can grow. On the other hand, the ceramic tube cannot tolerate bending, tension, or sudden cooling and cannot handle oxidising acids or hot and concentrated caustic.

In a more recent capacitively- coupled design, non-contacting electrodes are used. These designs use areas of metal sandwiched between layers of liner material. They are available in sizes under eight inches in diameter and with ceramic liners. Magmeters using these non-contacting electrodes can "read" fluids having 100 times less conductivity than required to actuate conventional flow tubes. Because the electrode is behind the liner, these designs are also better suited for severe coating applications.

The advantages of electromagnetic flowmeters(Magmeters) in applications include their high accuracy, reliability, and ability to  measure a wide range of flow rates. They are also unaffected by changes in temperature, pressure, or viscosity of the  liquid being measured, making them suitable for various industrial applications such as water treatment, chemical  processing, and food and beverage production.