Does a Coriolis flowmeter measure volume as well?

Yes. It measures mass flow and density directly and calculates volume flow from the two. The same instrument also gives the temperature of the fluid.

Does a Coriolis flowmeter need straight pipe runs?

No. The measurement does not depend on the flow profile, so no straight run is needed before or after the meter. The OPTIMASS 5400, for example, is specified with 0 D upstream and downstream.

Can a Coriolis flowmeter measure gas?

Yes, provided it is sized for it: gas has a low density, so the pressure drop and the strength of the signal need checking. Several meters in our catalogue are rated for both liquids and gases, and the OPTIGAS 4010 is built for gas dispensers up to 350 barg.

How accurate is a Coriolis flowmeter?

For liquids, mass flow accuracy is typically around ±0.1% of the reading — the figure specified, for example, for the OPTIMASS 6400. The accuracy you actually get also depends on the installation and the process conditions; we confirm it for your application before you order.

Coriolis or electromagnetic?

An electromagnetic flowmeter measures the volume of conductive liquids, causes no pressure drop and stays affordable in large pipes — often the right answer for water. A Coriolis flowmeter measures mass, works with non-conductive liquids and with gases, and gives density as well. Where the product is invoiced or dosed by mass, Coriolis is usually the better fit.

FLOW MEASUREMENT TECHNOLOGIES

Coriolis flowmeters: measuring mass flow directly

A Coriolis flowmeter measures the mass of the fluid passing through it, not its volume, and the same instrument measures density and temperature too. That makes it the first choice for custody transfer, batching and dosing, and for liquids whose density or viscosity keeps changing.

Coriolis flowmeters in our catalogue

How a Coriolis flowmeter works

Inside the meter, the fluid passes through one or two measuring tubes. A drive coil keeps the tubes vibrating at their natural frequency, much like a tuning fork.

With no flow, both halves of the tube move in step. Once the fluid flows, the Coriolis force resists the motion: the inlet half of the tube lags, the outlet half leads, and the tube twists slightly. Two pick-off sensors, one near the inlet and one near the outlet, see the twist as a time difference between their signals. That time difference is proportional to the mass flow rate.

The same vibration gives a second measurement. The more mass the tube holds, the lower its natural frequency, so the meter works out the density of the fluid from it. A temperature sensor on the tubes corrects for the way their stiffness changes with temperature. Volume flow then follows simply: mass flow divided by density.

Because the meter weighs the flow instead of inferring it from velocity, the reading does not depend on the flow profile, and in most applications changes in pressure, temperature or viscosity need no separate compensation.

The fluid passing through the measuring tube
Drive coil: keeps the tube vibrating at its natural frequency
Inlet and outlet pick-off sensors
The twist caused by the Coriolis force when fluid flows (exaggerated)
The signals of the two sensors: the time difference Δt between them is proportional to mass flow
Temperature sensor: corrects for the change in tube stiffness

Where a Coriolis flowmeter fits — and where it does not

A strong choice for

Custody transfer and batching, where the product is invoiced or dosed in kilograms or tonnes
Liquids whose density or viscosity changes: oils, fuels, syrups, resins, chemicals
Liquids that do not conduct electricity, where an electromagnetic flowmeter cannot work
Density and concentration in the same instrument, for example the sugar content of a syrup
Small flows and precise dosing
Installations with no room for straight pipe before or after the meter

Think twice when

The line is large: size, weight and cost climb steeply with diameter. Our catalogue goes up to DN 400, but for water in large pipes an electromagnetic or ultrasonic flowmeter is usually the more economical choice
You are measuring gas at low pressure: its low density gives a weak signal and a high pressure drop through the tubes
Little pressure drop is available, especially with viscous liquids
The liquid carries a lot of entrained gas or may flash inside the meter — unless the meter is specified for it
You are measuring steam: other technologies, such as vortex, are the usual choice there

How it compares with the other technologies

Typical accuracy of each flow measurement technology, ± % of the reading, on a logarithmic scale. The further left, the more accurate. The technology of this article is highlighted.

Coriolis (the technology of this article)±0.1–0.2%
Electromagnetic±0.2–0.5%
Ultrasonic±0.5–2%
Differential pressure±0.5–2%
Variable area±1.6–4% *
Vortex±0.75–2%
Thermal mass±1–3%
Positive displacement±0.2–0.5%
Turbine±0.5–1%

Typical ranges for liquids (thermal mass: gases), ± % of the reading; for variable area, the accuracy class (*). The accuracy of a specific instrument depends on the model, the size and the installation — we confirm it for your application.

All technologies

Installing a Coriolis flowmeter

A Coriolis flowmeter needs no straight pipe before or after it: the measurement does not depend on the flow profile, so a bend or a valve right next to the flange does not affect the reading. The OPTIMASS 5400, for example, is specified with 0 D upstream and 0 D downstream.

What it does need is measuring tubes that stay full of liquid — or, in gas service, free of liquid. Orientation is chosen with that in mind:

Liquids, horizontal lineTubes facing down, so that gas bubbles rise into the pipe instead of collecting in the measuring tubes.

Gases, horizontal lineTubes facing up, so that condensate drains into the pipe instead of collecting in the measuring tubes.

Vertical lineFlow upwards. The tubes stay full while the fluid flows and drain when the line is emptied — suitable for liquids and slurries.

Avoid the highest point of the line, where gas collects, and a vertical line with downward flow, which may not stay full.
Fit control valves after the meter, so that the tubes stay under pressure and the liquid does not flash inside them.
Support the pipe on both sides of the meter; the meter should not carry the weight of the pipe or take up its thermal expansion.
Fit an isolating valve after the meter (ideally one before it as well), so that the zero point can be set with full tubes, no flow and at process conditions.