Electromagnetic Flow Meter

Electromagnetic flow meters induce a voltage in a conductive liquid moving through a magnetic field. Full bore, no obstruction, no moving parts, and the most accurate technology for water and slurry duties at this price point.

The one hard limit

Conductivity. Below roughly 5 microsiemens per centimetre there is no usable signal. Mains water, wastewater, slurries, acids and alkalis are all fine. Deionised water, oils, solvents and most hydrocarbons are not, and no amount of installation care will fix that.

Liner and electrode decide the service life

The pipe body is the cheap part. What fails is the liner and the electrodes.

• PTFE for aggressive chemicals and high temperature, up to about 180 degrees Celsius.
• Hard rubber for water and slurries with abrasive solids. Cheapest and toughest for that duty.
• PFA where you need PTFE performance with better resistance to abrasion and thermal cycling.
• Electrodes in 316L for general water, Hastelloy for chlorides, titanium for oxidising media, tantalum for the really aggressive acids.

Installation points that get missed

Grounding. On a lined or plastic pipe you need earthing rings, and they are almost never shown on the P&ID. A floating earth turns the meter into an antenna and you get noise instead of flow.

The pipe has to run full, and the meter needs about 5D upstream and 3D downstream. That is far more tolerant than a vortex meter, which is why magnetic meters are often the practical answer on a cramped skid.

Where they are the wrong answer

Non-conductive fluids, gas, steam, and very small lines where DN15 is already the floor. For those, look at ultrasonic or vortex.