Magnetic Flow Meter Explained | Working Principles
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- Опубликовано: 29 июн 2024
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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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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.
Thanks fo ryour support, Jerome! We are happy to hear that.
definitely very important theoretical insight
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
Amazing explanation of magnetic flow meter...very helpful
Thank you so much, we're happy to hear that!
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.
Glad to hear that!
Thanks for the video, its very helpful
Glad to hear that! You're very welcome
I enjoyed this video, so helpful
Glad it was helpful!
Thank you sir. Great video.
Glad it was helpful!
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.
Thanks for your support, Dave! I will happily forward your suggestion to our course developers.
Thanks again for sharing and happy learning!
@@realpars Need to design Electro magnetic flow I need some support
Can I calibrate using a prover tank
Love you guys and I love magnets
Nice job. well done.
Thank you very much, Mahdi!
Great Graphics for the video
Glad you like them!
Excellent 💯💯💯 realpars
Thank you, Kiran!
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
👏👏👍from Kazakhstan
I very like this video my friend
Thank you very much!
Good 👍
Thank you!
Superb
Thank you very much!
Best video
Thank you!
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
You can try testing the sensors by manual sensor test just to make sure the sensors are working properly.
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.
GOOD
Magmeters usually do not use permanent magnets but rather use a coil to generate a alternating magnetic field.
Being involved with mags for over 40 years I've never seen one with permanent magnets
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Good
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.
If the conductivity is to low you can't measure anything with it. The modern magmeters can achieve measurements in liquids as low as 1 to 5 uS/cm with certain limitations.
If it is really low and you need high accuracy than your best option is coriolis mass flow. Otherwise you can also use vortex or ultrasonic flowmeters in liquids with low conductivity.
Can i calibrate an ele tromagnetic floe meter using a prover tank
👍great~~
Thank you!
Good video... Why pressure transmitters are grounded but Temperature transmitter are not grounded?
Thanks.
The accepted wiring method for all transmitter types is to use a shielded twisted pair cable, with the shield grounded only at one end, usually at the PLC or DCS I/O cabinet.
@@realpars Thanks for your kind clarification.... Keep it up...
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?
Nevermind. I managed to see the light. Hehehe
Glad to hear that, Roberto! Happy learning
Can this measure water flow or does a fluid needs to be ferromagnetic?
The fluid needs to have a conductivity of greater than 10 us/cm. Distilled or purified water have conductivities less than 10 us/cm. Therefore, a magnetic flow meter is not suitable for these fluids. Tap water typically has greater than 10 us/cm conductivity and can be measured by a magnetic flow meter. Wehn in doubt, look up the conductivity of your liquid stream using an internet search or ask your magnetic flow meter vendor for the data.
Excellent video.... What type of flowmeter to be used for DM water or fluids with less than 10 us/cm conductivity?
Thanks.
Just about any of the rest. De-Mineralized water shouldn't present any problems with the material that the flowmeter is made of (unlike DI water). Without knowing your application, I can say that ultrasonic is not a good choice, too finicky in my opinion.
And some that should be okay - depending:
Thermal meters also present no obstructions, so it makes a good choice for media such as paints that tend to "gunk up" inside the pipe.
Coriolis is great, but expensive.
Positive displacement is an option, but will wear over time, making them eventually inaccurate.
Differential Pressure is the "normal" choice, and would probably work fine for you.
Vortex should be fine.
There are other options out there, this is just off of the top of my head.
The bottom line is that without knowing your application (so what's your Reynolds number anyway?), it is impossible to give you a definitive answer. So contact a flowmeter specialist and have them take a look at your application.
Mr Waalkman gave a good response to this question. I find that vortex flow meters give a good balance of performance, ease of installation, almost zero maintenance, and applicable over a broad range of Reynolds numbers.
@@MrWaalkman Thanks for your such a detailed response.... Appreciate!
@@cck0728 You're welcome. :)
Hi what can cause the Totalizer to reverse?
Thank you for reaching out with your question. The resolution might vary based on the installation method and setup. I recommend reviewing the installation manual and engineering design specifications for guidance. Alternatively, reaching out to your vendor can provide specific insights into potential issues. Wishing you successful troubleshooting and learning from RealPars!
Can I calibrate these using a prover tank if so please tell me how
Is this suitable for metal pipe?
Yes, metal pipe is preferred for the installation of magnetic flowmeters.
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How can water be the conductor ?
We need ferromagnetic conductor
Tap water or process water contains minerals and other dissolved solids that are conductive. We just need a fluid with a minimum conductivity in order to use a magnetic flow meter effectively.
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🙏🌹🌹🌹
Could that be also a solution for Ex-Areas?
sure . there are magmeters also for EX areas
When selecting a flow meter for installation in a hazardous area, you need to ensure that the meter is approved for operation in the specific classification of installation. This may affect which manufacturer/model number you use and the method of installation, including wiring. And yes, there are magnetic flowmeters which are rated for installation in electrically classified areas.
What is the difference between DP transmitter and flowmeter?
Thanks for your comment, and topic suggestion! I will go ahead and forward this to our course developers, hopefully we can create a course lesson answering that.