Electromagnetic Flow Metering

Cutaways of electromagnetic flow meters - one
removed from service (right) and one
remanufactured (left).

Electromagnetic flow metering is widely used for conductive liquids, such as water acids and alkalis. It's also effective in many other process applications using clean, dirty, and process liquids and slurries. While electromagnetic flow metering is primarily used in full pipes, they can also be applied to partially full pipes and channels often found in effluent applications.

Electromagnetic flow metering is based on the principles of Michael Faraday's 1832 discovery. When a conductive liquid, such as water, is moved through a magnetic field a voltage is induced in the liquid at right angles to the magnetic field. The size of the voltage is directly proportional to the volume flow rate. This induced voltage is detected by sensors known as electrodes. These electrodes transfer the voltage signal to the processing electronics where it can be converted into a usable industrial standard signal.

It's important that the flow meter tube is non-magnetic, and austenitic stainless steel is the most commonly used material. It's also essential that the flow meter tube has a lining that electrically insulates it from the liquid inside, and provides a non-reactive barrier with any corrosive liquids being measured. Distinguishing between flow induced voltage changes, electrochemical noise, and plant induced noise, is a barrier to accurate electromagnetic flow metering. This can be particularly difficult in dirty and industrial applications. The choice of electromagnetic flowmeters with advanced noise suppression can mitigate unwanted noise and provide extremely high orders of accuracy as a result.

To ensure that your electromagnetic flow meters will be optimized for safety, longevity, and performance, the advice of a qualified flow instrumentation expert should be sought out. That expert will be able to help you with the best selection of the appropriate flow device for your specific application, be it electromagnetic flow meters or another flow technology.

Magnetic Flow Meters with Specialized Construction Still the Best Bet for Dredging Applications

Electromagnetic flow meters commonly measure slurry mixture flow on cutter suction dredgers and trailing suction hopper dredgers. These type of flow meters use exposed electrodes and non-conductive flow tubes. Ordinary magnetic flow meter flow tubes  are not designed to withstand the abrasive conditions prevalent in dredging. Standard magnetic flow meter electrodes  are prone to wear, breakage, and polarization requiring frequent re-adjustment. Standard electrode seals may also deteriorate and cause leaks and false readings.

As an alternative, non-invasive (non-wetted) flow meters, such as clamp-on or Doppler ultrasonic flow meters, have long been proposed because of their  ease of installation and maintenance savings. However, testing of clamp-on or Doppler ultrasonic flow meters has never panned out in dredging applications. While there has been limited success on smaller sized diameters, there are few, if any, large diameter dredging pipe application success stories.

Dredging engineers always seek the simplest and most accurate method of measuring slurry flow. Considering this, there is convincing evidence that the use of customized electromagnetic flow meters, specifically designed to stand up to the rigors of dredging, look to be the best overall option.

Dredging flow meter.
(TECO)

Dredging-specific flow meters provide wear solutions that can extend the life of equipment and keep systems at maximum operational levels. Some users report life span up to 10 years.

The dredging modifications include custom engineered ceramic brick or polyurethane liners, 3/4" stainless steel inlet and outlet protectors, independently sealed electrode wells, and field accessible Hastelloy B electrodes.

Thompson Equipment (TECO), a manufacturer of severe service magnetic flow meters located in New Orleans, will "remanufacture" any make or model of electromagnetic flow meter for dredging service. They have decades of experience servicing and remanufacturing instrumentation, and are leaders in building severe service flow meters.

Electromagnetic flow meters have always been appealing for dredging applications in terms of accuracy, resolution, and response time. Their performance problems, caused by the direct and continuous flow of abrasive slurries, are mitigated through specialized construction.  By applying electromagnetic flow meters specifically designed for the application, dredging engineers now achieve excellent reliability, long life and significant reduction in maintenance and operational costs.

Electromagnetic Flow Meters for Accurate Measurement of Flowing Conductive Fluids and Slurries

Magnetic Flow Meter
(Badger Meter)

In general, magnetic flow meters are sturdy, reliable devices able to withstand hazardous environments while returning precise measurements to operators of a wide variety of processes. The magnetic flowmeter has no moving parts. Electromagnetic meters will measure virtually any conductive fluid or slurry. This includes process water and wastewater. They provide low pressure drop, high accuracy, high turndown ratio, and excellent repeatability.  It is however, necessary to fill the entire cross section of the pipe in order to derive useful volumetric flow measurements.

Electromagnetic flow meters employ Faraday’s law of electromagnetic induction, whereby voltage is induced when a conductor moves through a magnetic field. The liquid acts as the conductor, with energized coils outside the flow tube creating the magnetic field. The produced voltage is directly proportional to the flow rate. Magnetic flow meter technology is not affected by temperature, pressure, or density of the subject fluid.

Electromagnetic flow meters tend to be heavy in larger sizes and may be prohibitively expensive for some purposes. However, irrespective of price and size, there are multiple reasons why magnetic flow meters are the instrument of choice for certain applications. They are resistant to corrosion and their ability to accurately measure dirty fluids makes them very suitable for wastewater measurement. As mentioned, there are no moving parts in a magnetic flow meter, keeping maintenance to a minimum. Power requirements are also low. Electromagnetic flow meters are available in a wide range of configurations, sizes, and construction materials to accommodate various process installation
requirements.

Severe service flow meter.
(TECO)

Severe application magnetic flow meters provide erosion and abrasion resistant designs, capable of withstanding a variety of highly erosive applications and corrosive slurries. These special-purpose  electromagnetic flow meters utilize liners made from specialty materials like magnesia stabilized zirconia ceramic or aluminum oxide ceramic, have electrodes made of exotic metals such as Hastalloy B/C, titanium, platinum, or tungsten carbide, and include specialized coatings.

Contact Thompson Equipment Company (TECO) with any magnetic flow meter requirement. Their decades of applying, repairing, re-manufacturing, and designing magnetic flow meters will assure a successful implementation.

Choosing the Right Industrial Flow Meter

Which Industrial Flow Meter to Choose?

Choosing the right flow measurement solution can have a major impact on operational and business performance. For this reason, companies anticipating a flow meter purchase should consult with a knowledgeable instrumentation supplier, such as Thompson Equipment Company (teco-inc.com), in the early stages of a project. The effort spent learning about basic flow measurement techniques, and available meter options, will ensure a successful application once the equipment is installed.

This white paper, courtesy of Badger Meter, does a great job outlining all the various types of flow meter technologies, including:

• Coriolis
• Differential Pressure
• Electromagnetic
• Positive Displacement
• Thermal Mass
• Turbine
• Impeller
• Variable Area
• Ultrasonic
• Vortex
• Oval Gear
• Nutating Disc

Download your own PDF copy of "Choosing the Right Flow Meter here, or view the embedded document below.

https://teco-inc.com
800-528-8997 for Immediate Service

Choosing the Right Industrial Flow Meter from Thompson Equipment Company