What are Magnetic Flow Meters?

A volumetric flow meter with no portable components is called a magnetic flow meter. It is ideal for usage in wastewater treatment. It is generally used for liquids that are conductive or dirty.

As mentioned, magnetic flow meters work best with dirty liquids. That is why these are not ideal to use with hydrocarbons or distilled water. These are extensively used in industry because they are easy to use. These are efficient and inexpensive to use for contaminated agricultural residues. These also produce very accurate results.

Magnetic flow meters are alternatively known as mag meters too.

How Magnetic Flow Meters Work

Magnetic flow meters calculate the velocity of the flowing liquid in a pipe using Faraday’s Law of Electromagnetic Induction. According to Faraday’s Law wires travel in a magnetic field to generate charge. Similarly in magnetic flow meters liquid flows through a magnetic field generated by the meter. Since this liquid is conductive it will generate a voltage signal while passing through that magnetic field. This process is shown in Figure 1.

The electrodes detect the voltage signal. The intensity and amount of voltage signal produced are directly proportional to the fluid velocity flowing through the pipe as specified by Faraday’s Law. Liquid flow is then calculated by processing the detected voltage signal. This is done by a transmitter as shown in figure 2.

Types of Magnetic Flow Meters

There are three main types of magnetic flow meters. Each of those is briefly introduced below:

• Insertion Magnetic Flow Meter

  Magnetic flow meters of this type can be used in a wide range of pipe sizes. These meters usually work best when installed upstream of the pipeline. It can handle a wide range of corrosive liquids.

  

• In-Line Magnetic Flow Meter

  These flow meters produce the best results when higher flow rates must be accurately measured. There is very little to no margin for mistakes like in water treatment or food/pulp processing.

  

• Low-Flow Magnetic Meters

  It is best suited for applications requiring a low flow of liquid. It requires almost no maintenance compared to other magnetic flow meters because it is less affected by mechanical debris.

  

Usage of Magnetic Flow Meters

Among all the flow meters on the market, 24% alone are magnetic flow meters. This shows its high utility and application across multiple industries. Application of magnetic flow meters can be found in

• Water/Wastewater industry- both treated and untreated water like in figure 3
• Mining and Mineral processing- water/slurry produced during the process and media flows
• Power Sector
• Pulp and paper industries
• Chemical industries- corrosive and abrasive chemical solutions
• Construction Industry- highly corrosive sludge like acid and caustic soda

Merits of Magnetic Flow Meters

The merits of Magnetic flow meters top any other flow meters. It is generally very easy to use and cost effective and can handle extremely abrasive liquids.

• It uses very little power to operate. Some mag meters can operate on power as low as 15 watts.
• Their erosion resistance can be enhanced as per requirement by using simple abrasion resistant liners.
• Smaller electrodes do the job; hence, fewer electrode metals are generally required.
• These can measure liquid flow rates ranging from 0.125” to even 10’ cubic.
• Magnetic flow meters are very efficient because they can measure multidirectional flow.
• Since these have no moving parts, the risk of damage and frequent repairs is minimized.

Precautions for Magnetic Flow Meters

Magnetic flow meters are usually simple and safe to use. But here are some of the precautions one must keep in mind while using these to bring accurate results:

• Ensure that the liquid/ sludge used is conductive. Otherwise, it won’t generate a voltage signal.
• Magnetic flow meter should be installed in a manner that it is always filled with liquid, or else it will affect the flow measurements.
• High temperatures even for a shorter period can render a magnetic flow meter flawed.
• While using mag meters in a vacuum, make sure the liner doesn’t collapse.
• Using an electromagnetic flow meter near its conductivity limit can cause the flow meter to collapse and stop functioning.