How an electromagnetic flowmeter works
An electromagnetic flowmeter applies Faraday's law of induction. Coils around the measuring tube create a magnetic field across the pipe. When a conductive liquid flows through that field it induces a small voltage between two electrodes, and that voltage is proportional to the flow velocity. Because the pipe diameter is known, the transmitter converts velocity into volumetric flow.
There is nothing inside the pipe to obstruct the flow, so the meter causes practically no pressure drop and has no moving parts to wear out.
Which liquids can a mag meter measure?
The liquid must be electrically conductive. Water, effluent, slurries, pulp, acids, alkalis and most aqueous solutions are good candidates. Mag meters are not suitable for gases, steam, or non-conductive liquids such as oils, solvents and hydrocarbons — for those, Coriolis, vortex, ultrasonic or thermal mass meters are usually considered.
Selecting the right meter
| Decision | What to consider |
|---|---|
| Liner | PTFE or PFA for chemicals and higher temperatures; rubber or polyurethane for abrasive slurries and water |
| Electrodes | Stainless steel for water and general use; Alloy C, titanium, tantalum or platinum for corrosive media |
| Line size | Size for a sensible velocity range — very low velocity reduces accuracy, very high velocity increases wear with slurries |
| Process connection | Flanged, wafer, hygienic or insertion styles depending on the line and industry |
| Output | 4–20 mA with HART, pulse for totalising, or fieldbus such as PROFIBUS, Modbus or EtherNet/IP |
Installation best practice
- Keep the pipe full. Install in a rising vertical line or at a low point in horizontal pipework, never at a high point where air collects.
- Straight runs. Allow undisturbed pipe upstream and downstream of the meter as the manufacturer specifies; bends, valves and pumps upstream distort the flow profile.
- Grounding. Earth the meter and process liquid correctly — especially in plastic or lined pipes — using grounding rings or electrodes where required.
- Electrode orientation. In horizontal lines the electrode axis should be horizontal so bubbles at the top and sediment at the bottom do not cover the electrodes.
Where mag meters are used
Water and wastewater
Raw water intake, treated water distribution, effluent discharge and ETP/STP monitoring.
Power, steel and cement
Cooling water, DM water, ash slurry and process water lines.
Chemicals and pharma
Acids, caustic and dosing lines where a lined meter with the right electrodes avoids corrosion.
Verification without removal
Modern meters such as Endress+Hauser's Proline Promag range include built-in verification that checks the measuring electronics and sensor in place, which supports audit and calibration requirements without taking the meter out of the line.
Frequently asked questions
Does a mag meter need calibration?
Meters are wet-calibrated at the factory. In service, periodic verification — and, where a quality system requires it, calibration against a reference — confirms performance.
Can it measure slurry?
Yes. Choose an abrasion-resistant liner, suitable electrodes and a size that keeps velocity moderate to limit wear.
What accuracy can I expect?
Typical industrial mag meters are specified to a fraction of a percent of reading when installed correctly; check the datasheet for the exact model and range.
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