Why Magnetic Flow Meters Provide Confidence in Measurement of Flow Rates

by | Nov 13, 2019 | Flow, Measurement Instrumentation

Trever Ball

Trever Ball

Director of Marketing for Rosemount Magnetic Flow Meters

slurry-magnetic-flow-meterMagnetic flow meters, also known as mag meters, are used in a variety of industrial processes. From oil and gas operations to dairy production and even breweries, mag meters provide essential data for fluid management. In every process, tools that provide accurate measurement are critical for driving efficiency and reliability. Faulty instruments and imprecise data lead to higher operation and maintenance costs, and lost time and materials due to confusion, misdiagnosis of issues, and outages. With the proper tools in place, you can be sure that you are making decisions based on the most accurate data available as you work to optimize your system and increase productivity.

Let’s take a look at how magnetic flow meters function and why they provide this kind of confidence in measuring volumetric flow.

What Makes Magnetic Flow Meters Different

The primary instruments in an electromagnetic flow meter are the transmitter and sensor. This type of flow meter does not require an inline turbine or piston to measure flow rates. It also does not rely on differential pressure. Instead, the sensor measures the induced voltage, which is created by the movement of conductive liquids through the pipe without any pipe obstruction. That voltage is then converted into the flow measurement by the transmitter.

Because there is no need for devices in the pipeline, this type of measurement works well with abrasive liquids, liquids at extreme temperatures, or any conditions in which a measuring device could be damaged or destroyed in the pipeline. This also means they are effective in situations with highly viscous fluids or slurries with low velocity as well as at the other end of the spectrum with high-volume process conditions.

While bidirectional flow measurement can be difficult, especially in cases where you need to vary process parameters, mag meters function without issue. They also have solid turndown ratios and can be customized to fit a diverse range of functions and conditions.

How Induced Voltage Measures Flow

A fundamental law of electromagnetism is behind the mag meter’s ability to measure fluid flow so accurately. Faraday’s Law of Electromagnetic Induction allows us to predict how a magnetic field will interact with an electric circuit. The mathematical equation stemming from Faraday’s Law is E (induced voltage) = k*B*D*V where k is a constant unique to each process flow, B is the magnetic field, D is the pipe’s diameter, and V is the velocity of the liquid.

The sensor apparatus on a magnetic flow meter contains a set of coils and two electrodes. The transmitter applies a current through the coils which generate a magnetic field inside the sensor. When the process fluid flows perpendicular through the magnetic field, negatively and positively charged particles within the fluid separate as they pass through the field. This creates the induced voltage between the electrodes. The electrode circuit carries the induced voltage to the transmitter. By knowing this induced voltage (E), constant k, the magnetic field (B), and the pipe’s diameter (D), the transmitter converts the information, using Faraday’s Law, into the quantifiable flow velocity (V).

The flow meter transmitter calculates the velocity on the spot and displays it on the local operator interface (LOI). The LOI allows users to change preferences and view these flow rates in the field.

Where Mag Meters Drive Flow Metering Process Improvements

Magnetic flow technology supports a broad range of industrial operations. Within the oil and gas sector, magnetic flow meters help optimize fracking procedures and safety. These flow metering devices ensure that an accurate total volume of fluid pumped into wells is recorded, despite measuring difficulties from particularly abrasive slurry mixtures.

Pulp and paper applications include handling pulp stock flows, confirming the correct weight paper is being made, and assessing residuals from paper processing. In food and beverage, mag meters drive optimal performance in cheese and milk flows for dairy, especially when pasteurized milk ordinance (PMO) is required. Breweries utilize the technology in taxation meters, which are used to determine the tax owed based on the amount of consumable alcohol they produce.

Wastewater service providers depend on the accuracy of magnetic flow meters in water distribution and treatment. Fortunately, this type of flow meter works well in submersed conditions. Wastewater treatment facilities, for example, have used mag meters to vastly improve their custody transfer flow measurement, resulting in more exact hauling calculations and less time lost to troubleshooting and flushing the lines to reduce build-up.

While mag meters are excellent, sturdy instruments for measuring flow rates in many circumstances, there are a few constraints. The liquids must be conductive for the magnetic field to create an induced voltage to measure. Also, the flow meter should utilize a 4-wire transmitter to ensure maximum performance, which may not work well in hazardous environments. Additionally, mag meters are unable to measure the flow rates of gases.

Wherever a process flow needs measurement, whether between two steps as a flow rate check or at the end of a process as a totalizer, magnetic flow meters can ensure your process is operating within tolerances and help provide greater insights into what is happening throughout your process. With better process insights, process optimization goes from a dream to an achievable reality.

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