• The magnetic flow meter is one of the most flexible and universally applicable flow measurement systems available. • It provides completely obstruction-less flow metering, is nearly insensitive to fluid properties, and is capable of measuring the flow rate of corrosive fluids. • It can also involve the measurement of flow of slurries.

• This type of flow meter works on the principle of Faraday’s law of electromagnetic induction.

• The Faraday’s law of electromagnetic induction states that when conductor moves through magnetic field of given field strength, a voltage is induced in conductor which is proportional to relative velocity between the conductor and magnetic field.

• The working of magnetic flow meter is shown in the figure.

• In such type of flow meters, the electrically conductive flowing liquid works as conductor. E = CBLV Or V = E/CBL Where, E = Induced voltage in volts C = Dimensional constant B = Magnetic field in Weber/m^2 L = Length of conductor (here flowing liquid) in m. V = Velocity of conductor (here flowing liquid) in m/s.

• The magnetic flow meter consists of non-conducting pipe made up of material such as fiberglass with pair of electrodes mounted opposite to each other, as shown in the figure.

• The magnetic coils are wounded around pipe so that magnetic field generated in plane is mutually perpendicular to the axis of flow meter body.

• Electrodes installed inside the pipe calculate the flow rate and convert it to 4 – 20 mA pulse signals.

• It is one of the most accurate industrial flow meter types.

• It has no movable parts or other obstructions inside the measuring tube, and is maintenance free.

• Magnetic flow meters are therefore extensively used in industries such as chemicals, food, iron and steel, pulp and paper, and water supply.

• A magnetic or electromagnetic flow meter can be installed in a comparatively simple fashion.

• An existing pipe network can be converted into a measurement system.

•These flow meters can track both forward and reverse flow.

Advantages

• There is very small pressure loss in measurement process.

• The cost of instrument is low.

• It has a linear relationship between input and output.

• The flow rate of corrosive fluids can also be measured.

• Compensation for change in density and viscosity of flowing fluid can be done.

• The flow rate of liquids, gases and vapors can be measured.

Disadvantages

• The magnetic flow meter has to be installed in vertical position.

• The instrument becomes expensive for higher pressure not temperatures.

• It cannot be used for flow measurement of slurries.