Magnetic Flow Meter

Overview

A magnetic flow meter (magmeter) measures volumetric flow by applying Faraday's law of electromagnetic induction. As conductive fluid passes through a perpendicular magnetic field, ions in the liquid move with the flow and experience a Lorentz force, creating a voltage proportional to flow velocity. Two electrodes in the tube sense this voltage; electronics amplify it and output flow. Magnetic meters have no moving parts, handle slurries and abrasive liquids, and produce no head loss, making them standard in water treatment, mining slurry, and food processing.

The meter comprises a Field Coil System generating the perpendicular magnetic field, a Flow Tube Assembly lined with insulating material, and a Electrode Assembly detecting the induced voltage. The Converter Electronics amplifies the millivolt signal and calculates flow rate using the known tube diameter. The Enclosure and Housing houses the electronics, while Process Flange Connection couples the meter into the pipeline.

How it works

The field coil system energizes at AC or DC, establishing a uniform magnetic field perpendicular to the flow direction. When conductive fluid (liquid with ions, slurry, or conductive water) flows through this field, positive and negative charge carriers experience opposite Lorentz forces, pushing them toward opposite tube walls. This charge separation builds a potential difference across the tube diameter, typically 1–100 millivolts depending on flow velocity.

The Electrode pair mounted diametrically opposite the field direction sense this voltage directly. The Signal Conditioner filters noise and the Microcontroller calculates volumetric flow using the proportionality V = k × B × D × v, where B is magnetic field strength, D is tube diameter, and v is flow velocity. Because measurement depends only on field and diameter, not on fluid density, viscosity, or particle size, magnetic meters are immune to changes in liquid properties that plague orifice or turbine meters.

Non-conductive fluids (oils, gases without ionization) cannot be measured because no charge carriers exist to produce the Lorentz voltage. The insulating Tube Lining prevents electrode shorting and protects the tube from corrosion while allowing fluid contact with the electrodes. Installation is flexible: the meter works equally in any orientation, and provides zero flow indication if the liquid stops, unlike positive-displacement meters that continue spinning.