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How Does a Magnetic Flow Meter Work?

Apr. 14, 2021

The electromagnetic flowmeter is a volumetric flowmeter without any moving parts. It is ideal for waste water applications or any conductive or water based dirty liquids. The electromagnetic flowmeter is also ideal for applications requiring low pressure drop and low maintenance costs.

Electromagnetic flow meters are not normally suitable for hydrocarbons, distilled water and many non-aqueous solutions. The flow instrument manufacturer will next explain the following issues:

How does an electromagnetic flowmeter work?

How to use an electromagnetic flow meter Magnetic Flow Meter

Industries that use electromagnetic flowmeters.

How does an electromagnetic flowmeter work?

Electromagnetic flow meters use a magnetic field to generate and direct the flow of liquid through the pipe. When a conductive fluid flows through the magnetic field of the flowmeter a voltage signal is generated. The faster the fluid flows, the greater the voltage signal generated. An electrode sensor located on the wall of the flow pipe receives the voltage signal and sends it to an electronic transmitter, which processes the signal to determine the flow rate of the fluid.

How to use an electromagnetic flowmeter

Electromagnetic flow meters measure the velocity of electrically conductive liquids (e.g. water, acids, caustics and slurries) in pipes. The electromagnetic flowmeter measures correctly when the conductivity of the fluid is greater than approx. 5 μS/ cm. Using an electromagnetic flowmeter on fluids with low conductivity (e.g. deionised water, boiler feed water or hydrocarbons) causes the flowmeter to shut down and measure zero flow.

Electromagnetic Flowmeter

These flow meters do not block the flow and can therefore be used for clean, hygienic, dirty, corrosive and abrasive fluids. Electromagnetic flowmeters can be applied to electrically conductive liquids and therefore hydrocarbons and gases cannot be measured using this technology due to their non-conductive nature and gaseous state respectively.

Electromagnetic flow meters do not require much upstream and downstream straight pipe and can therefore be installed in relatively short flow meters. Electromagnetic flowmeters typically require 5-10 diameter upstream straight pipes and 5-2 diameter downstream straight pipes measured from the plane of the electromagnetic flowmeter electrodes.

Industries that use electromagnetic flowmeters

Electromagnetic flowmeters account for approximately 24% of all flowmeters sold today. Applications in the water, wastewater, mining, mineral processing, power, pulp and paper and chemical industries where dirty liquids are found. Water and wastewater applications include the custody transfer of liquids in the mains between water/wastewater areas. Electromagnetic flow meters are used in water treatment plants to measure treated and untreated sewage, process water, water and chemicals. Applications in the mining and mineral processing industry include process water and process slurry flows as well as heavy media flows.

With due attention to materials of construction, it is possible to measure the flow of highly corrosive liquids (e.g. acids and caustics) and abrasive slurries. Applications for corrosive liquids are typically found in chemical industrial processes and in chemical feed systems used in most industries. Slurry applications can often be found in the mining, mineral processing, pulp and paper and wastewater treatment industries.

Electromagnetic flow meters are commonly used where liquids are transported by gravity. Ensure that the flowmeter is oriented so that the flowmeter is completely filled with liquid. Failure to ensure that the flow meter is completely filled with liquid can seriously affect the flow measurement.

Take care when operating the electromagnetic flowmeter under vacuum conditions as some electromagnetic flowmeter bushings can collapse and be drawn into the pipe under vacuum conditions, causing catastrophic damage to the flowmeter. Note that vacuum conditions may occur in pipelines that do not appear to receive vacuum service (e.g. where gases may condense (usually under abnormal conditions)). Similarly, excessive temperatures in an electromagnetic flowmeter (which can occur briefly even under abnormal conditions) can cause permanent damage to the flowmeter.

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