A magnetic flow meter, or mag meter, is a volumetric flow meter with no moving parts and no obstruction in the pipe - ideal for dirty, corrosive, or slurry-laden conductive liquids like produced water. This guide explains how a mag meter works using Faraday's law of induction, its key limitation, and where it fits in oil and gas water handling.
Magnetic Flow Meter in one line: A magnetic flow meter measures the volumetric flow of an electrically conductive liquid by applying Faraday's law: the liquid moving through a magnetic field induces a voltage proportional to its velocity, which the meter converts to flow rate. It has no moving parts and no restriction, so it works well on dirty or corrosive water.
A mag meter uses Faraday's law of electromagnetic induction: a conductor moving through a magnetic field generates a voltage. Field coils on the meter body create a magnetic field across the pipe, and the conductive process liquid is the moving conductor. As the liquid flows, it induces a small voltage across a pair of electrodes mounted flush in the pipe wall, at right angles to both the field and the flow. That voltage is directly proportional to the average flow velocity, so the transmitter multiplies it by the pipe's cross-sectional area to get volumetric flow rate.
Because the measurement depends only on velocity and the fixed pipe area, a mag meter reads true volumetric flow regardless of the liquid's density, viscosity, temperature, or pressure. The bore is a full open pipe lined with a non-conductive material such as PTFE or hard rubber, so there is no obstruction, negligible pressure drop, and nothing to wear out or clog.
The critical limitation is that the liquid must be electrically conductive - typically above roughly 5 microsiemens per centimeter. That rules out hydrocarbons, refined products, and most gases, which are non-conductive. It makes the mag meter a poor fit for crude or gas measurement but an excellent fit for water. In oil and gas that means produced water, disposal and injection water at saltwater disposal wells, and utility or fire water lines.
Its obstructionless, no-moving-parts design is a major advantage on abrasive, scaling, or solids-laden water that would erode a turbine rotor or plug an orifice. The transmitter outputs rate and total as 4-20 mA, pulse, or a digital protocol into a PLC, RTU, or flow computer. Merobix, as a cloud SCADA, reads those digitized flow tags from that controller over Modbus, DNP3, or OPC UA to trend water volumes and alarm on abnormal disposal or injection rates.
No. A mag meter requires an electrically conductive liquid, and hydrocarbons and gases are essentially non-conductive. It is used almost exclusively for water in oil and gas - produced water, injection and disposal water, and utility water. For crude or gas, operators use Coriolis, turbine, ultrasonic, or orifice meters instead.
Almost none. The meter is a full-bore open pipe with an inert liner and no protruding parts, so it presents essentially the same restriction as the surrounding pipe. This obstructionless design also means nothing to clog on slurries and no moving parts to wear, which is why mag meters last well on dirty produced water.
Typical mag meters achieve accuracy in the range of about 0.2 to 0.5 percent of reading over a wide turndown, provided the pipe stays full and the electrodes remain clean and unfouled. Accuracy degrades if the pipe runs partially full, if a coating insulates the electrodes, or if the liquid drops below the minimum conductivity.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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