Magnetic flow meters go by many names: electromagnetic flow meters, mag meters, magnetic inductive flow meters, and magneto-inductive flow meters. They are by far one of the most popular flow measurement technologies in the world. As of 2020, one quarter of all flow meters sold are magnetic flow meters.
Magnetic flow meters have many advantages, like no moving parts to wear, which makes them very reliable. Viscous and dirty liquids can also be measured with minimal accuracy degradation. They also offer low pressure loss and can be built with a variety of different materials to handle a variety of applications.
Magnetic flow meters operate according to Faraday’s law of magnetic induction where a current is induced into a conductor as it moves through a magnetic field. The amount of current is directly proportional to the velocity of the moving conductor. In this case the media, flowing through a magnetic field generated by coils within the flow meter, acts as the conductor and is sensed by electrodes mounted within the flow meter flow body. The higher the flow rate, the more induced current.
Magnetic flow meters only measure conductive liquids and will not operate properly with media under the required minimum conductivity. Conductive liquids are characterized by the property of being able to conduct electricity. This is because there are positive and negatively charged ion particles that are free to move around. These ions enable the conductivity and the more ions there are, the higher the liquid’s conductivity will be. An increase in liquid temperature increases the activity in the ions and also increases the conductivity potential. It is typically measured in siemens per meter or centimeter.
Common examples of conductive liquids are acids, caustics, water-based slurries, salty solutions, hydrochloric acid, vinegar, lemon juice, and sodium hydroxide. Common examples of non-conductive liquids include deionized water, ultrapure water, distilled water, boiler feed water, hydrocarbons, oils, fats, and alcohols.
In comparison to other flow meter technologies, magnetic flow meters can generally deliver better accuracies. The notable exception to this would be the Coriolis flow meters. However, Coriolis meters can frequently be cost-prohibitive for most application areas in comparison to other technologies. Magnetic flow meters excel in accuracy specifically for low flow rates. Magnetic flow meters generally deliver an accuracy around 0.5%. However, some models can provide even higher accuracy, like our EPS Magnetic Flow Meter with an accuracy of 0.3%.
Depending on your application needs, the highest levels of accuracy may sound appealing or feel necessary, but ultimately it is a balance of cost and the actual need for your specific application. To learn more about accuracy in general, visit our article explaining the different aspects of the concept of accuracy.
Magnetic flow meters offer average to better than average upstream and downstream requirements. The average requirement is 5 times the pipe diameter upstream and 2 to 3 times the pipe diameter downstream. These requirements are similar to ultrasonic, thermal, vortex, turbine and paddle flow meters.
Technologies with lower requirements in general include Coriolis, variable area, and positive displacement flow meters. These flow meter technology types typically do not require any upstream or downstream requirements. Another factor to consider regarding upstream and downstream requirements is that insertion models typically will have higher upstream pipe requirements than inline models. To learn more about upstream and downstream flow meter requirements in general, visit our article on the subject.
There can always be a notable difference in turndown ratios between instruments that all fall within a specific flow meter technology type. If turndown is an important variable in your application, ensure that the exact instrument you choose meets those needs. For example, within positive displacement flow meters, turndown ratio can vary as much as from 10:1 to 100:1. However, there are some generalities that be stated about which flow meter technologies typically offer a higher turndown ratio.
Magnetic flow meters will generally deliver a turndown ratio in the realm of 40:1. This is higher than many other technologies. But it is generally true that the technology that offers the best turndown ratio is the ultrasonic technology, like our DUK Inline Ultrasonic Flow Meter, with a turndown ratio of 250:1. To learn more about what turndown is and the general turndown ratios for other flow meter technology types, visit our article.
Magnetic flow meters are used in a wide variety of applications. Some common examples include water, process water, wastewater (treated and untreated), custody transfer, chemical and corrosives, slurries, and other general industrial uses. If you aren’t sure whether a magnetic flow meter is right for your application requirements, our engineers can help you through that decision making process for free. Call us now or email us.
One of the largest determining factors in choosing between a Coriolis meter and a magnetic flow meter for your application is cost. Coriolis meters are often significantly more expensive than the average magnetic flow meter. Unless there is a determining factor within your application that a magnetic flow meter cannot accommodate, a magnetic flow meter is probably the most practical choice, especially for your budget.
One application element that would point towards the need for a Coriolis flow meter would be that the media is not conductive or not conductive enough for a magnetic flow meter. Magnetic flow meters also require a stable flow profile and this usually involved minimum straight run piping requirements upstream and downstream and consideration of any flow disruptors, such as valves, bends, and pumps. Coriolis meters do not have straight run requirements so if the installation area prohibits the piping requirements necessary for the proper functioning of a magnetic meter, then a Coriolis meter could overcome that inconvenience.
Coriolis meters also offer a true mass measurement, while magnetic flow meters provide a volumetric flow measurement. This also means that a Coriolis meter can provide density measurement where a magnetic flow meter cannot. Your application may be affected by certain parameters that would be better served by a mass flow measurement. Coriolis meters also generally offer a higher turndown ratio than magnetic flow meters for applications where the flow is not as uniform in velocity.
To clarify, all the different flow meter technologies measure by mass or by volume. Mass flow meters generally refer to thermal mass flow meters or Coriolis mass flow meters. Most other flow meter technologies like magnetic, ultrasonic, variable area, and others all measure volume. So the term “mass flow meter” references two very different technologies. To see the difference between Coriolis meters and magnetic flow meters, please see the preceding paragraph for an in-depth comparison.
Thermal mass flow meters, also known as calorimetric or thermal dispersion meters, operate based on temperature as the name implies. To learn more about thermal flow meters, visit our thermal mass flow meter technology page. Thermal mass is generally for gas applications and mag meters are generally for liquid applications. Also, mag meters are for volumetric high liquid flows, thermal are generally for lower flows.
There is one major factor that would consistently recommend an ultrasonic flow meter over a magnetic flow meter. This would be the size of the pipe where the flow meter needs to be installed. Ultrasonic flow meters come in typical inline models where they are installed into the piping system, and they also come in clamp-on models. Ultrasonic clamp-on flow meters, also known as strap-on or portable flow meters, utilize two transducers affixed either more permanently or temporarily on the outside of the pipe and an evaluating electronic. The size of the pipe is accommodated for by the manner in which the transducers are attached to the pipe.
That means that it is much less costly to pay for a strap of some sort to go around a large pipe diameter than it is to pay for the materials to make a large flow body for an inline meter. For large pipe diameters, clamp-on ultrasonic flow meters will usually be the best solution from a cost effectiveness standpoint. Not only do they require much less material to manufacture, which brings lower costs, but the shipping costs are also significantly less for clamp-on models as they can be sent in small boxes, whereas large bore flow meters may require special shipping arrangements due to their size.
Installation for clamp-on ultrasonic flow meters can also offer savings because it does not require system downtime or significant installation fees. They are simply affixed to the outside and do not require pipe alterations. Clamp-on models are also not subject to any pressure changes or pressure drops. To view an example of a clamp-on ultrasonic flow meter, visit our DUC product page.
For inline flow meters in smaller to average pipe diameters, comparing magnetic technology with ultrasonic technology becomes a little less straightforward. Both offer technology that does not require any mechanical elements or moving parts. This generally translates into less maintenance and longer service life as there is nothing significant that experiences wear over time and use. Neither technology has parts that impede into the flow stream. Both can deliver good accuracy, although magnetic flow meters are generally known to deliver slightly better accuracies on average, especially for lower flow velocities. Both can also offer good turndown ratios and the costs are generally not vastly different.
The highest differentiating factor between inline magnetic flow meters and ultrasonic flow meters for the majority of applications is going to come down to the type of media to be measured. Magnetic flow meters require the media to have a minimum conductivity. There are many liquids that do not meet these requirements and would not be suitable for a magnetic flow meter. In these instances, an inline ultrasonic flow meter may be a great option, especially if similar levels of accuracy, turndown, and lack of mechanical elements are desired. For a great magmeter alternative for non-conductive media, take a look at our inline DUK Ultrasonic Flow Meter that offers a turndown ratio of 250:1.
Magnetic flow meters generally come in either inline models, where they are installed directly into the piping system via connections to the piping system, or insertions models where the measuring probe is installed via a hole in the piping. Magnetic flow meters are not available in clamp-on models. Some insertions meters come with special capabilities that allow them to be removed while the system is continuing. These extraction devices offer a wide variety of advantages, chief among which is that there is no required downtime for any meter maintenance.
While it may seem like the obvious and easiest approach is to size the meter from the application’s pipe size, that is not the way to go if you want your meter to function correctly. Magnetic flow meters require a stable flow profile. One element of that is ensuring that there is always full pipe moving at a velocity necessary for the meter to function correctly.
The best approach is to understand the maximum and minimum flow ranges that will pass through the meter. Choose a meter that can adequately accommodate and read the flow for both the peak and the bottom end flow. Also ensure that within those ranges, the flow is kept to an acceptable velocity as well. If you would like help determining the right size magnetic flow meter for your application, we would be happy to do the work for you. Please call us or email us and we would be happy to assist you.
Your Meter’s Manual: Always consult your flow meter's user manual for exact installation details and direction. Below are installation recommendations based on one of our flow meters.
Bypass Pipe Option: For easy dismounting to clean or empty the sensor, a bypass pipe may be installed. This installment option is recommended for highly contaminated media.
Flow Body Lining: If the flow body is lined with PTFE, the flow meter must be installed with extra care. The tube lining is bordered at the flanges (seal). This must not be damaged or removed as it prevents the fluid from penetrating between the flange and flow body, damaging the electrode insulation.
Flow Meter Connections: The sensor is installed between the pipes using proper screws, bolts, nuts, and seals. When installing, do not exceed any torque recommendations. Make sure grounding rings are also installed. Any mounted gaskets must not impede into the pipe cross-section. Do not use conductive sealing compounds such as graphite. This could result in a conductive layer, building up on the inside of the flow tube, which will short-circuiting the measuring signal.
Installing in a Pipeline with a Larger Diameter: The flow meter can be installed in pipes with larger nominal sizes by using pipe tapers, but the resulting pressure loss must be taken into consideration. To avoid flow interruptions in the flow tube, a reducing angle of 8° for the tapers should not be exceeded.
Vibrations: To eliminate the effects of vibrations and prevent premature damage to the transmitter, the sensor must be supported near the flanges for flange flow meters.
Horizontal Pipeline Routing: The preferable installation point is in slightly ascending piping.
Open Inlet or Outlet: Where possible, the device should be installed in a syphon. The empty pipe detection circuit of the transmitter is an additional safety feature for recognizing empty or partially filled pipes. Solids may accumulate in the syphon so installing a cleaning aperture in the pipe is recommended.
Downward Pipes: Where there are downward pipes, a syphon or a ventilation valve should be placed after the sensor. This avoids negative pressure in the pipeline which may damage the sensor lining. This also prevents a breakdown of the flow, reducing the risk of air inclusions in the media.
Long Pipelines: In long pipelines there is always a danger of pressure surges so regulation and shut-off devices should be placed behind the sensor. However, when installed in vertical piping, especially when using sensors with PTFE-lining and high operating temperatures, the regulation and shut-off devices should be placed in front of the sensor due to the danger of vacuum.
Pump Installation: To avoid negative pressure and damage to the tube lining, never install flow meters on the suction side of pumps. If necessary, arrange for pulsation dampeners when using piston, diaphragm, or hose pumps. Consider the space requirements beforehand with respect to a potential removal of the device in the future.
Magnetic Flow Meter Grounding: Grounding is a necessity for safety and operation. The grounding connections must be at protective conductor potential and this potential must be identical to the potential of the media. The grounding cable should not transmit any interference voltage.
Do not simultaneously ground other electrical devices with this cable. The measuring signal tapped at the electrodes amounts to only a few millivolts. Correct grounding is an important prerequisite for accurate measurement.
The transmitter requires a reference potential to evaluate the measured voltage on the electrodes. In the simplest case, the non-insulated metal pipe and/or the connecting flange may be used as a reference potential. When pipes are lined with electrically insulating materials or pipes are made of plastic, the reference potential can be obtained from a grounding ring or grounding electrode.
These establish the necessary conductive connection to the media and are made of a chemical-resistant material. The material used should be identical to the measuring electrodes. The outside diameter of the grounding ring should be at least equal to the diameter of the flange or be dimensioned in such a way that the grounding ring is positioned inside the flange bolts and is centered by these. The terminal lugs routed to the outside must be connected to the FE terminal in the junction box of the sensor. During installation ensure that the inner diameter of the seals do not protrude over the grounding disk.
While there are many options in the field of magnetic flow meter instrumentation, there are few who manufacture, sell, and actively support their products. KOBOLD offers a unique experience in that we provide all three services. We are proud of our products, and we know them inside and out and are here to share both our products and our expertise with you regarding magnetic flow meter solutions. Call us or email us today if there is anything we can help you with regarding magnetic flow meters.
Many of our magnetic flow meters are made in the USA, here in our Pittsburgh headquarters and manufacturing facility. We take great pride in providing American made solutions. We offer a comprehensive line of magnetic flow meters including those for chemicals, insertion installations, and large diameter piping. To learn more about our magnetic flow meter line, visit our magnetic flow meter product page.
Learn more about why you should partner with KOBOLD for your application.
Liquids, Pastes, Slurries | No Pressure Drop | Unaffected by Temp, Pressure, Density, & Viscosity | UP to 580 PSI | HART Communication
Made in the USA | Top Seller | Plastic - Wide Variety of Material Combinations | Chemicals, Acids, Caustics | Switch, Batch, Totalize | 0.18...180 GPM
Cost Effective for Large Lines | Low Installation Cost | Minimal Maintenance | SS, PTFE, or PFA Coated | High Accuracy | HART Communication
KOBOLD USA is a subsidiary of KOBOLD Messring GmbH, a world-leading instrumentation engineering business founded in Germany in 1980 by Klaus J. Kobold. With patented technology and superior service, the company quickly established itself as one of the global leaders in sensor and control systems with high quality products. The KOBOLD brand name became synonymous with superior quality and technological advancement in instrumentation engineering.