Flow Measurement

What is a magnetic flow meter and how does it work

What is a magnetic flow meter and what is it used for

A magnetic flow meter is used to measure the fluid flow, magnetic or electromagnetic meters can handle slurries. These meters don’t have any moving parts and it is a volumetric flow meter. Mostly these flow meter meters electrically conductive things such as corrosive fluids. This flowmeter cannot be used with hydrocarbons or other non-aqueous solutions. The magnetic flowmeters can only be used to meter the conducting fluids such as water that has ions in it. Magnetic flow meters can measure the mass flow of a fluid and it doesn’t have any moving parts and because of this, it can handle high pressure without any leakage and also any kind of corrosive fluids.

Where should we use electromagnetic flow-meters

  • It can be used in for fluids that have a high solid percentage
  • It can be used to measure sludge, slurries, minerals, paper, sewage, and other liquids that have solid particles. Mostly normal flow meters cannot be used for these applications
  • Conductive liquids
  • It can be used with liquids that have high conductivity, which can induce a measurable voltage

How magnetic flow meters are constructed and how does it work

The important part of a magnetic flow meter is a flow tube and the flow tube is mounted directly in the pipe. There are no moving parts in this meter so that the pressure drop will be the same as in the normal pipe. Mostly the pipes are non-conductive. In the inner part of the pipe, two electrodes and an electromagnet are used. The electrodes will be in contact with the fluid and it is placed perpendicular to the direction of the fluid and the magnetic field lines. The pipe is mounted in the gap of magnet.

This flow meter is either powered by AC or DC current, and it would be applied to the magnetic coil. The liquid that flows through the pipe acts as a conductor only conductive fluids can be measured by using this meter.  This meter works according to the faraday’s law of electromagnetic induction and according to this law when a conductor moves through a magnetic field at a proper angle then the induced voltage of the conductor will be proportional to the conductor’s velocity. The pipe would be non-conductive. The distance between the electrodes is the same as the pipe diameter. So when the fluid flows through the pipe it also passes through the magnetic field that is created by the magnetic coil and because of this a voltage will be induced in the liquid and this voltage is detected by the electrodes that are placed in the pipe. The voltage induced will be proportional to the fluid flow velocity. There are no moving parts in this meter and because of this low-pressure drop so this meter can be used to check the flow rate of corrosive and dirty fluids which is not possible by using normal flow meters.

How to install a magnetic flow meter

The electrodes that are mounted in the pipe must be in electrical contact to the fluid that is measured and these electrodes must be mounted horizontally. While using this meter to measure the flow grounding must be done. In order to get proper measurements, the flow meter must be full.

What are the advantages of magnetic flow meter

  • It can handle corrosive fluids
  • It is available in large pipe sizes
  • Low-pressure drop
  • It can be used with slurries
  • Bidirectional flow measurement
  • It can be used to measure turbulent or laminar flow
  • It won’t be affected by the change in conductivity
  • Its measurement won’t be affected by temperature, pressure, viscosity, or density
  • It can handle low flows and very high volume flow rate
  • Slurries and greasy materials can be easily handled by this meter
  • Obstruction-less

What are the disadvantages of magnetic flow meter

  • Costly
  • Because of its large size, it is heavy
  • It must be full at all times
  • Inline mounting is needed
  • Measurement errors could happen because of gas bubbles

What are the applications of magnetic flow meter

  • Chemical processing
  • Food and beverage
  • Mining
  • Cosmetics


post-graduate in Electronics & communication.

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