Magnetic flow meter.

A pipe section labeled MAG with a pair of inline electromagnetic coils. Magmeters work on conductive fluids and produce a clean linear signal without moving parts.

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How it's drawn.

ISA 5.1 magnetic flow meter symbol. Pipe section labeled MAG with electrode coil pair

An inline pipe section marked as a magnetic meter, working on conductive fluids without moving parts. It produces a flow signal directly, so unlike a plate or venturi it does not need a separate differential-pressure element. Mounting is wafer between flanges on smaller lines or flanged on larger ones.

Variants.

Wafer mounting. Clamped between flanges on lines from 1 inch up to about 4 inch.
Flanged body. Standard line connection above 4 inch, lined and unlined options.
Insertion, probe-style. Single-point measurement in large pipes where a full-bore meter is impractical.
Sanitary, hygienic. Tri-clamp ends and FDA-compliant liners for food, beverage, and pharma service.
Pulsed DC excitation. Current standard, low zero drift, immune to most process noise.
AC excitation. Older technology, simpler signal conditioning, susceptible to slurry noise.
Liner options. PTFE, PFA, hard rubber, polyurethane, ceramic. Chosen for chemical and abrasion resistance.
Electrode materials. 316 stainless, Hastelloy C, tantalum, platinum-iridium for aggressive service.

Typical usage.

Water, slurry, conductive chemical service. Won't work on hydrocarbons, non-conductive. Maintenance-free in clean service. In slurry service the electrodes need periodic inspection.

Telling it apart.

A magnetic meter works only on conductive fluids. It does not read non-conductive hydrocarbons.
It outputs flow directly, so it does not need the differential-pressure transmitter that an orifice or venturi requires.
Wafer and flanged versions differ in how the body mounts, usually carried as a note rather than a different symbol.

Common questions

What conductivity does a magmeter need to work.

The standard minimum is 5 microsiemens per cm, which covers any aqueous solution including tap water, slurries, and most chemicals. Low-conductivity magmeters reach down to about 0.05 microsiemens per cm for demineralized water and dilute acid service.

Why will a magmeter not measure hydrocarbons.

Hydrocarbons are non-conductive. They do not induce a voltage across the electrodes when the fluid moves through the magnetic field. Crude oil, refined products, LNG, and natural gas all need a different primary element such as Coriolis, vortex, ultrasonic, or differential pressure.

Magmeter vs Coriolis. When to choose which.

Magmeters measure volumetric flow on conductive fluids, are line-size-friendly up to 100 inch, and tolerate dirty or slurry service. Coriolis measures mass flow directly on any fluid including hydrocarbons, but is expensive above 6 inch and sensitive to entrained gas. For water, slurry, and aqueous chemicals choose a magmeter. For hydrocarbons or custody transfer choose Coriolis.

What ISA 5.1 tag identifier does a magnetic flow meter use.

The functional tag is FT, flow transmitter or FIT, flow indicating transmitter followed by the loop number. The instrument type field on the I/O list typically reads magnetic flow meter or simply magmeter. The signal class is AI, analog input, 4-20 mA or HART for the transmitter output.

How much straight pipe does a magmeter need upstream and downstream.

Typical installation requires 5 pipe diameters upstream and 3 diameters downstream of any disturbance, elbow, valve, reducer. This is less restrictive than an orifice plate, 10 to 20 diameters and comparable to a Coriolis or vortex meter. Manufacturers publish exact numbers per model in the IOM.

Related.

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One page of flow-element geometry, including the magnetic meter and the elements it is drawn next to.

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How it's drawn.

Variants.

Wafer mounting. Clamped between flanges on lines from 1 inch up to about 4 inch.

Flanged body. Standard line connection above 4 inch, lined and unlined options.

Insertion, probe-style. Single-point measurement in large pipes where a full-bore meter is impractical.

Sanitary, hygienic. Tri-clamp ends and FDA-compliant liners for food, beverage, and pharma service.

Pulsed DC excitation. Current standard, low zero drift, immune to most process noise.

AC excitation. Older technology, simpler signal conditioning, susceptible to slurry noise.

Liner options. PTFE, PFA, hard rubber, polyurethane, ceramic. Chosen for chemical and abrasion resistance.

Electrode materials. 316 stainless, Hastelloy C, tantalum, platinum-iridium for aggressive service.