| Magnetic | Vortex | Turbine | Coriolis | |
|---|---|---|---|---|
| Needs conductivity | Yes (>5 µS/cm) | No | No | No |
| Works on gas / steam | No | Yes | Limited | Yes |
| Moving parts | None | None | Yes | None |
| Pressure loss | Negligible | Low | Moderate | Moderate |
| Straight run needed | 5D / 3D | 15D / 5D | 10D / 5D | Little |
| Measures mass | No | No | No | Yes |
| Typical accuracy | ±0.5% | ±1% | ±0.5% | ±0.1% |
| Relative cost | Medium | Medium | Low | Very high |
An electromagnetic meter needs a conductive liquid — above roughly 5 microsiemens per centimetre. Water, effluent, acids and slurries qualify. Oil, solvent, steam and gas do not, and no amount of specification will make a magnetic meter work on them.
A vortex meter typically needs about fifteen pipe diameters upstream and five downstream. If your line has an elbow two diameters away, the meter will read wrong and no calibration will fix it. Coriolis is the technology that cares least about this.
Almost everything measures volume. If you are billing on mass, or the density changes with temperature and you care about the actual quantity, only Coriolis measures mass directly.
A turbine meter has a spinning rotor and bearings — put slurry through it and it will not last. Magnetic meters have nothing in the bore and handle slurry well.
A meter the same size as the line often runs at the bottom of its range where accuracy is worst. Sizing one line size down and using reducers is frequently the better answer.
Liner material on a magnetic meter, sensor rating on a vortex meter and gasket selection all follow from this. Leaving it out is the most common reason a quotation has to be revised.
A local indicator on the meter, a 4-20 mA signal to a panel, a totaliser for batching, or Modbus to a SCADA — each is a different order code. Batching in particular needs a totaliser with a pulse output and often a batch controller, and adding that afterwards usually means changing the meter.
Magnetic meters must stay full of liquid, so they belong in a rising line or a low point, never at a high point where air can collect. Vortex meters need the flow fully developed. Turbine meters need a strainer upstream, or the first piece of debris ends the bearing. Getting orientation wrong wastes a good meter.
Electromagnetic meter with a hard rubber or PTFE liner, flanged, with a local indicator or 4-20 mA to the panel.
Vortex meter with integral temperature and pressure compensation, mounted with proper straight run.
Rotameter — glass tube for clean liquid, metal tube for higher pressure and temperature.
On turbine and positive displacement meters a strainer upstream is not optional — a single piece of weld slag will stop the rotor. It costs a small fraction of the meter and prevents the most common failure we are called out for.
No. It needs an electrically conductive liquid. Oil, solvents and hydrocarbons are not conductive enough.
Typically 10 to 15 diameters upstream and 3 to 5 downstream, depending on the technology and what is upstream. Coriolis needs the least.
Coriolis, at around ±0.1 per cent of reading, and it measures mass directly. It is also the most expensive by a wide margin.
A rotameter for local indication, or an orifice plate with a DP transmitter where you already have the transmitter.
If you cannot give the meter the straight run it needs, a flow conditioner shortens the requirement considerably. It is cheaper than repiping.
Either works provided the meter stays completely full of liquid. A rising vertical line is the safest choice. Avoid mounting at a high point in the pipework where air can collect against the electrodes and give an unstable reading.
Send the medium, line size, flow range and the straight run you actually have. The straight run rules out more meters than the budget does.
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