Magnetic Flow Meter Explained | Working Principles

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⌚Timestamps:
00:00 - Intro
00:51 - What is a Magnetic Flow Sensor?
01:46 - The Magic is in the Magnet
03:09 - Faraday’s Law
05:19 - Conductive Fluids
06:41 - Other Considerations for Installation
09:12 - Summary

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Magnetic flow sensors are a very commonly used flow meter type that is useful in a wide range of applications and line sizes.

Accurate and repeatable measurement of flow is a requirement for industrial processes, including feed streams, tank recirculation loops, product transfer lines, and many others.

In this video, we will
- Introduce you to the working principles of a magnetic flow sensor,
- Describe the physical characteristics of a magnetic flow sensor that make it valuable for process control,
- Describe the ways magnetic flow sensors can be integrated into a measurement and control system.

Magnetic flow sensors convert the velocity of a flowing fluid into a measurable electrical signal that is proportional to the flow rate.

Magnetic flowmeters have no moving parts or internal flow path obstructions, so they are easy to calibrate and maintain.

Because magnetic flow meters are typically specified to be the same size as the upstream and downstream piping, there is virtually no pressure loss through the flow meter, which can be very advantageous for some flow streams, like thick slurries.

Magnetic Flow sensors are often called mag meters, and we will refer to them using this abbreviation.

Mag meters are typically full-bore sensors, meaning that the internal flow path is of the same diameter as the upstream and downstream connections.

This construction eliminates any restriction of the fluid which may alter the flow path or create a pressure drop.

Fluid passes through the mag meter in a straight line through the bore of the sensor. This regular, cylindrical geometry also allows a constant and directional magnetic field to be established across the diameter of the flow path.

The magic that creates the flow signal is based in the magnet! The mag meter is surrounded by an iron-core, permanent magnet that creates a magnetic field to be established with lines of magnetic flux which pass vertically through the entire cross-section of the pipe and the flowing fluid.

This geometry is very important. The flowing fluid will pass through these lines of magnetic flux at a 90-degree angle or perpendicular to the lines of magnetic flux.

To generate a voltage according to Faraday’s law, we must have a moving conductor.

The conductivity of liquids is measured in units of micro-Siemens-per-centimeter. Some fluids, such as seawater, have high conductivity, and seawater flow can be measured with a mag meter.

In addition to seawater, flows of wastewater, and ionic solutions such as acids can easily be measured by magnetic flowmeters.

When installing a magnetic flow meter in process piping, it is vitally important to follow the manufacturer’s recommendation for grounding.

The electrical signal produced in a mag meter is a very small DC voltage, and stray voltages along a pipe due to welding equipment or other large electrical loads in the plant.

Transmitters are always used with mag meters. They convert the small DC voltages generated by the flowing fluid into signals that can be connected to the control system.

4 to 20 milliamp, Profibus PA, Foundation Fieldbus, and IO-Link transmitter outputs are available.

When specifying magnetic flowmeters, some important aspects must be considered in addition to the conductivity of the fluid and the need for grounding rings.

If the fluid is corrosive or abrasive, a compatible liner should be specified. These liners can also be replaced if they become worn, and they do not affect measurement accuracy.

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#RealPars #sensor #flowmeter

[jeromemorgan]

That is very informative, helpful. I am a operations manager for a mechanical engineering company. I just had this mag valve assembly installed with a valuable client. Utilizing these methods of measuring is critical to any system that transfers abrasive liquid materials.

[kiranchoudhari]

I was working in cable plant. And i saw this flowmeter in petroleum Jelly pipe line. As a filling material in cable tube,

It is a big support by realpars to grow up in Automation field

[TheDrewbe]

About to install a big 12'' magnetic flow meter on a river water intake that will communicate over Ethernet/IP, this video is a good refresher on the working principles behind the meter.

[davebennett]

This is fantastic information. There are so many different flow meter technologies. It would be GREAT to see a video on the various different kinds. Especially those used for gas, since the natural gas industry is growing so fast and expanding into other areas where gas extraction is becoming economical - like landfills and manure digesters.

[riocruz]

Thank you very much for this very informative video.

[MrWaalkman]

So I was tasked to figure out why the flowmeters in the paint mix room at Spring Hill, all of the meters (47 of them!) showed "Empty Pipe?". Turns out that you need your material (in this case, paint and solvent) to be conductive. Ours wasn't.

And the previous guy had them all installed without checking conductivity, so, darn.

One of the characteristics of a Mag meter or "Wafer Mag" as they are also known, is that they don't have the same requirements as just about every other flowmeter out there in that they don't need the 10x entrance and the 5x exit of straight pipe to settle the flow down to make accurate measurements. This rule means that the pipe leading up to the meter needs to have 10 times the pipe diameter in straight pipe entering into the flowmeter, and 5 times the diameter of the flowmeter in straight pipe exiting the flowmeter. So for a 2" meter you would need 20" leading up to the flowmeter, and 10" exiting the meter (these values are considered as a bare minimum, for complex bends you will need to increase these distances).


This is all application specific stuff from here on out.

We didn't have the space, the budget, or time, for redesigning the piping so the flowmeters were pretty inaccurate. Which because of our application was just fine since we really needed to know when things were circulating. The main thing was not introducing "dirt" (or gunk) into the paint that would go on to cause problems with the robots or the product itself. The thermal meters were excellent for this since the interior of the meter is nothing more than a smooth piece of pipe. The old meters had to be hot cleaned with a caustic solution from time to time. These meters certainly did not add to the problem.


One of the other things that you want to avoid when circulating paint is to reduce the amount of "shear" which degrades the paint leading to a poor paint job. Since the meter was just another piece of pipe in the system, the new meters did not add anything to increase the amount of shear already in the system. They probably had a tiny bit better flow than the Wafer Mags, but it couldn't have been by much. But compared to almost all of the rest of the meters out there, they were vastly superior.

[syufrijal]

Amazing explanation of magnetic flow meter...very helpful

[meeder]

Magmeters usually do not use permanent magnets but rather use a coil to generate a alternating magnetic field.

[akaikangaroo]

As far as I know those flow meters actually use coils instead of permanent magnets, because coils make it possible to reverse magnetic field which helps to avoid electrolysis on the electrodes

[praveenkumarpalanivelu]

Thanks for the video, its very helpful

[paulrinehart]

I definitely like magmeters over paddle wheel sensors. I never knew that they were dependent on conductivity of the fluid, so thanks for that info.

[robertocardenosa]

Can you explain how Faraday's law can lead to that formula at 04:12? I know it as E = -dΦ/dt, and if I understood it properly, the magnetic field B = Φ/A is held constant, and hence E would be zero. What am I missing?

[maxwellmakamba]

Can i calibrate an ele tromagnetic floe meter using a prover tank

[pearlsimelane]

Hi what can cause the Totalizer to reverse?

[hermannnani]

Great video
I want to understand something about the mag meter : our mag meter is always going on and off when the fluid is passing the pipe. What can be the problem

[ajaykumarjalagam]

What is the difference between DP transmitter and flowmeter?

[cck]

Good video... Why pressure transmitters are grounded but Temperature transmitter are not grounded?
Thanks.

[idiotictom]

Can this measure water flow or does a fluid needs to be ferromagnetic?

[samuelsungstabtu]

Dont the electrodes need to be in direct contact with the flowing conductive fluid? How do you protect the electrodes from corrosion?

[Yash]

How can water be the conductor ?
We need ferromagnetic conductor