We can use electromagnetic flow meters in tons of products in all kinds of segments. What we need are a minimum conductivity and volumetric flow. The article explains the installation, application, advantages, and disadvantages of this kind of flow meter. It also talks about the electromagnetic flow meter applications and which products fit them.
How does an electromagnetic flow meter work?
An electromagnetic flow meter, also known as magmeter, uses Faraday’s law, also known as the law of electromagnetism. Imagine we have a magnetic field and we want to see how it interacts with an electric circuit. In this interaction, we can create an electromotive force (EMF), also known as electromagnetic induction.
Faraday also discovered the concept that electric voltage is directly proportional to the velocity of the movement and strength of the magnetic field. Now, the electromagnetic flow meter borrows this law to measure volumetric flow, which means we can only use it in conductive fluids. It has two field coils, installed on opposite sides of the meter, and two electrodes, one on each wall, to measure voltage.
The coils create a magnetic field in the measuring tube. When the fluid passes through the field, it creates a voltage, measured using the electrodes on each wall. This voltage is directly proportional to flow velocity.
To know ultrasonic flow meters, you can read the Visaya Article on Ultrasonic flow meter
Electromagnetic flow meter applications
We can use electromagnetic flow meters in tons of products in all kinds of segments. We just need a minimum conductivity and a need to know the volumetric flow.
As for price, electromagnetic flow meters give some of the best bang for your buck if you can fit one in the process. Vortex flow meters come second, and maybe between them, we can find ultrasonics and so on. Of course, some company portfolios may have devices which defy my statements, so a research here is important.
One point about electromagnetic flow meters: the liner that insulates the measuring tube. All electromagnetic flow meters have them. So with a product in contact all the time with that liner, we will need a material that will withstand your product.
If we use the wrong material, we can run into corrosion and abrasion, shortening the life of the measuring tube. Also, the process temperature is important here.
The electrodes have similar needs, as they too remain in constant contact with the fluid. Usually, we have two electrodes to measure the voltage, but we can have a ground electrode on the bottom of the measuring tube and empty pipe detection on the opposite side. These facts can eliminate electromagnetic flow meters as an option for your process, so during the sizing process, we need to check them out.
Volume or mass flow?
Even though electromagnetic flow meters start out as volumetric flow devices, they can measure mass flow, too. But how? The answer is simpler than we can imagine – just plug in the density of the product, and the electromagnetic flow meter will calculate the mass flow.
The electromagnetic flow meters can do it themselves, but usually, as a high-end feature, we may need a density meter for an assist. Second off, when we set the density value, we need to make sure this value remains stable, or the accuracy will suck. So, one should read the density from a density meter and calculate the mass flow based on the right information.
Mining companies often use an electromagnetic flow meter to measure slurry flow, with certain liners to reduce abrasion and a densimeter to send data for the electromagnetic flow meter to translate into an online mass flow measurement.
Electromagnetic flow meter installation
Meeting some installation requirements to keep good accuracy throughout the device’s life is important. Unlike Coriolis flow meters, we have a bunch of stuff to deal with for an electromagnetic flow meter.
To know more about the working principle of Coriolis flow meter, you can read the Visaya Article on Coriolis flow meters
The best way to install it is vertical, with the product going up, we have a filled or empty pipe. Half-filled pipes can cause measuring problems for the electromagnetic flow meter. Of course, we can install it horizontally, as long as you avoid half-filled pipes.
We might also need to modify the pipe. Some vendors claim that their meters will work on half-filled, so if we foresee that as an issue, then one must look into those claims.
Moreover, high temps in your process mean that we should install the device upside down. Again, some devices claim that they can skip this bit, but typically you need at least five times the meter size before the meter and two times after. This point can vary, so follow the recommendations in the manual from the vendor.
And finally, some applications need ground rings, but for others, the ground electrode will suffice. You definitely need good grounding, but we need to cover this topic carefully, so let’s save it for another article.
When to use an electromagnetic flow meter?
All measurement principles have their strengths and weaknesses, which determine when they are the best option.
- Working principle independent of temperature, pressure, and viscosity
- Measures from water to slurry
- No pressure loss
- No moving parts
- Good size range
- Minimum conductivity required
- Incrustation can cause errors
- Low conductivity has low accuracy
To know about the types of flow meters in the industry, you can read the Visaya Article on flow meters
If you want to know more about electromagnetic flow meters or other products, you can get in touch with our engineers!