Instrumentation · 8 min read · Updated June 2026
Flow Meter Selection: Matching Technology to the Fluid
Magnetic, Coriolis, vortex, ultrasonic or differential pressure — each wins somewhere. A decision guide by fluid type, accuracy need and installation reality, with the questions that decide it in five minutes.
No flow technology wins everywhere. The fluid decides first — then accuracy, pressure drop, straight-pipe availability and budget negotiate the rest. Here is the decision as we walk through it with customers.
Electromagnetic (magmeter)
The default for conductive liquids: raw and drinking water, wastewater, slurries, chemicals, food products. No moving parts, no pressure drop, excellent turndown and bidirectional measurement. Hard limits: the fluid must conduct (above about 5 µS/cm) — so no hydrocarbons, no gases, no steam, no demineralized water. The Promag W 400 is the water-industry standard with drinking-water approvals and custody-transfer options.
Coriolis
Direct mass flow plus density and temperature from one meter, with accuracy to 0.1 %. The choice for custody transfer of liquids, batching by mass, and fluids whose density varies with composition or temperature — fuels, LPG, syrups, solvents. It costs the most and large line sizes get heavy, but it eliminates the density-compensation problem entirely and needs no straight pipe.
Vortex
The steam workhorse. A vortex meter handles saturated and superheated steam, gases and clean liquids with a rugged sensor and no moving parts; with integrated temperature measurement it computes saturated-steam mass flow directly, which is why the Prowirl F 200 is the standard instrument in boiler houses and energy monitoring. It needs a minimum velocity to shed vortices — poor at very low flow — and demands straight run upstream.
Ultrasonic
Clamp-on versions measure through the pipe wall: zero intrusion, retrofittable without cutting pipe, ideal for large lines and temporary verification. Inline transit-time versions reach custody-transfer class for water and hydrocarbons. Aerated or dirty fluids degrade transit-time measurement — Doppler variants tolerate them at lower accuracy.
Differential pressure (orifice, venturi, cone)
Still everywhere and still fine for many duties: mature, any pipe size, any fluid with known properties, and the transmitter can be replaced without touching the primary element. The costs are permanent pressure loss, limited turndown (square-root relationship), and impulse-line maintenance. A high-static DP transmitter such as the ABB 266HSH is the usual pairing for steam and feedwater.
Five questions that decide it
- Is the fluid conductive? → magmeter first.
- Is it steam? → vortex (or DP for very large lines).
- Do you need mass or density? → Coriolis.
- Retrofit without cutting pipe? → clamp-on ultrasonic.
- Custody transfer? → Coriolis or calibrated inline ultrasonic/magmeter, with certificates.
Comparison at a glance
| Technology | Fluids | Typical accuracy | Pressure loss | Straight pipe |
|---|---|---|---|---|
| Electromagnetic | Conductive liquids | 0.2–0.5 % o.r. | None | 5 × DN |
| Coriolis | Any liquid, dense gas | 0.1–0.2 % o.r. | Moderate | None |
| Vortex | Steam, gas, clean liquid | 0.75–1 % o.r. | Low | 15–20 × DN |
| Ultrasonic clamp-on | Clean liquids | 1–2 % o.r. | None | 10 × DN |
| DP (orifice) | Any, known properties | 1–2 % of span | High | 10–30 × DN |
Send us the fluid, line size, flow range, temperature and accuracy target — we return a comparison across at least two technologies on lifetime cost, not just purchase price. Request a quote.
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Quick answers
Can a magnetic flow meter measure oil or steam?
No. Electromagnetic meters need a conductive liquid (above about 5 µS/cm). Hydrocarbons, gases and steam need vortex, Coriolis, ultrasonic or DP meters.
How much straight pipe does a flow meter need?
Typical inlet requirements: magmeter 5 × DN, vortex 15–20 × DN (more after reducers and valves), Coriolis essentially none, clamp-on ultrasonic 10 × DN or more. Always check the manufacturer's installation drawing.