Browse Flow Meters
Closed-pipe flow meters
Most flow measurement happens in full, closed pipes. These meters measure how fast the fluid is moving and convert that into volumetric flow. Some also calculate mass or standard volume flow.
Electromagnetic (mag) flow meters
Suitable for: Liquids (conductive only, including slurries)
Electromagnetic flow meters are among the most widely used meters for conductive liquids. They offer a wide flow range, high accuracy and little or no pressure loss, because nothing obstructs the pipe.
They work on Faraday’s law of induction. The meter creates a magnetic field across the pipe, and as the conductive liquid flows through it, a small voltage is induced that is proportional to the flow velocity. Electrodes set into a non-conductive liner pick up that voltage. With the right liner and electrode materials, mag meters suit water, wastewater, slurries and many chemicals. They can’t measure non-conductive fluids such as oils, gases or steam.
Ultrasonic flow meters
Suitable for: Liquids
Ultrasonic flow meters use sound waves to measure flow. Their transducers either clamp to the outside of the pipe or are inserted through the pipe wall.
There are two main types. Transit-time meters measure the difference in the time sound takes to travel with and against the flow, and suit relatively clean liquids. Doppler meters measure the frequency shift of sound reflected from particles or small bubbles in the fluid, so they need some solids or bubbles to work.
Clamp-on meters need no cutting of the pipe, which makes them ideal for portable use and temporary surveys. Multi-path and insertion types give highly accurate measurement over a wide flow range.
Vortex flow meters
Suitable for: Liquids (low viscosity) · Gases · Steam
Vortex flow meters have a fixed bar, called a shedder bar, across the flow tube. As fluid passes the bar, vortices form alternately on each side, like a flag flapping in the wind. The frequency of these vortices is proportional to the flow velocity, which gives very repeatable measurement with no moving parts.
Vortex meters are widely used for gases, steam and low-viscosity liquids. Multivariable versions also measure pressure and temperature, so they can calculate mass or standard volume flow internally. That makes them particularly useful for gas and steam, where process conditions can vary widely.
Mechanical flow meters
Suitable for: Liquids (clean) · Gases · Steam
Mechanical flow meters use the moving fluid to drive a turbine, paddle wheel, rotors, gears, discs or shuttles. The movement is read by a mechanical register, or detected magnetically or optically as pulses or positions.
Correctly applied, mechanical meters give a wide flow range and high accuracy. Because they have moving parts in the flow, they’re best suited to clean liquids, gases and steam.
Mass flow meters
Mass flow meters measure the mass of fluid passing through, rather than its volume. Because mass doesn’t change with pressure or temperature, they avoid the errors that density changes cause in volumetric measurement.
Coriolis mass flow meters
Suitable for: Liquids · Gases
Coriolis flow meters measure mass flow directly. Fluid passes through one or more vibrating tubes, and the Coriolis effect makes the tubes twist slightly in proportion to the mass flow rate. The meter also measures the fluid’s density from the tubes’ vibration frequency.
A single Coriolis meter gives you mass flow, density and volumetric flow, with very high accuracy and no need for separate pressure or temperature compensation.
Thermal mass flow meters
Suitable for: Liquids (some designs) · Gases
Thermal dispersion flow meters are a simple, economical way to measure gas mass flow directly. A heated sensing element sits in the flow alongside a temperature sensor. The flowing gas carries heat away from the heated element, and the rate of cooling relates to the mass flow and the gas’s thermal properties.
Because the reading depends on those thermal properties, the meter is set up for a specific gas or gas mix. The same principle is used in some liquid flow meters, where it can give a wide-range, low-maintenance measurement.
Differential pressure flow elements
Differential pressure (DP) flow measurement is one of the oldest and most versatile methods. It works for liquids, gases and steam, and suits a very wide range of pipe sizes and conditions.
How differential pressure flow measurement works
Suitable for: Liquids · Gases · Steam
A primary element, either a restriction or a probe, is placed in the pipe. Following Bernoulli’s principle, flow through a restriction creates a pressure difference between its upstream and downstream sides. That difference increases with the square of the flow rate, so the transmitter or flow computer applies square-root extraction to produce a linear flow signal.
We recommend the element based on the flow range you need and the nature of the fluid.
Types of differential pressure flow element
• Orifice plates: a simple, low-cost plate with a precisely sized hole
• Pitot tubes: measure the difference between the impact and static pressure at a point in the flow
• Averaging pitot tubes (such as Annubar): sample pressure across the pipe for a more representative reading
• Cone meters (such as V-Cone): a cone-shaped restriction that conditions the flow, needing less straight pipe
• Venturi tubes: a smooth taper with low permanent pressure loss
• Laminar flow elements: produce a differential pressure that is close to linear with flow, giving wide rangeability
Open channel flow measurement
Open channel flow meters measure flow where the liquid has a free surface: streams, waterways, irrigation channels, open sewers and partially filled pipes, where conventional pipe meters can’t be used.
Weirs and flumes
Suitable for: Liquids
The traditional method places a weir or flume of known shape in the channel. A level instrument measures the depth of liquid upstream, and the known relationship between depth and flow for that structure gives the flow rate.
Area-velocity and non-contact flow meters
Suitable for: Liquids
Newer open channel meters measure both the surface velocity and the liquid level, and calculate flow from the velocity and the wetted area of the channel. They use microwave (radar) Doppler, laser or ultrasonic methods.
These meters can be a cost-effective alternative to weirs and flumes, because they install in most channels and streams without modifying the channel itself. Non-contact types mount above the water, away from debris and fouling.
Choosing the right flow meter
There are many ways to measure flow, so we start with the data you need and how you want it presented, then work through the details of your process.
Volumetric, standard or mass flow?
The first question is what you need to measure. For liquids under stable conditions, a volumetric flow meter is often enough, and mass flow can be inferred with only a small error from density changes. Where true mass flow or density matters, a Coriolis meter measures it directly.
Gases and steam are compressible, so volume alone can be misleading when pressure and temperature change. For these fluids, measure pressure and temperature as well and apply known formulae to calculate mass flow or standard (normal) volume flow. A multivariable vortex meter or a Coriolis meter can do this in one instrument.
What we consider
• the fluid’s properties, the flow range and the accuracy you need
• the process connection and pipe details
• the pressure and temperature of the fluid and its surroundings
• your preferred units and outputs: volume or mass, rate or total, pulse, analogue or digital output, and local display
• power, installation and maintenance requirements
• hazardous area, compliance and certification requirements.
Which technology suits your fluid?
| Technology | Liquids | Gases | Steam |
|---|---|---|---|
| Electromagnetic | ✓ (conductive only) | – | – |
| Ultrasonic | ✓ | – | – |
| Vortex | ✓ (low viscosity) | ✓ | ✓ |
| Mechanical | ✓ (clean) | ✓ | ✓ |
| Coriolis | ✓ | ✓ | – |
| Thermal mass | Some designs | ✓ | – |
| Differential pressure | ✓ | ✓ | ✓ |
| Open channel | ✓ (open channels and part-full pipes) | – | – |
As well as supplying the right meter, we can service and repair many types of instruments to keep your measurement running. We also offer flow meter verification, a check of your meter’s performance against a reference. Flow verification is not part of our IANZ-accredited calibration services. See our Calibration & Service page for more.
Frequently asked questions (optional)
What’s the difference between volumetric, standard and mass flow?
Volumetric flow is the volume passing per unit of time at actual conditions. Standard (or normal) volume flow corrects a gas volume to reference pressure and temperature, so readings can be compared. Mass flow is the mass passing per unit of time, which doesn’t change with pressure or temperature.
Which flow meter is best for slurries?
Electromagnetic flow meters are the usual choice for conductive slurries, because nothing obstructs the pipe and suitable liners resist abrasion. Doppler ultrasonic meters are another option, as they rely on particles in the fluid.
Can I measure flow without cutting into the pipe?
Yes. Clamp-on ultrasonic flow meters mount on the outside of the pipe, which makes them well suited to temporary surveys, portable checks and pipes that can’t be shut down.
How do I measure flow in a partially filled pipe?
Use an open channel flow meter. Area-velocity meters measure both the liquid level and its velocity, and calculate flow even when the pipe isn’t running full.
Can you check my flow meter is still reading correctly?
Yes. We offer flow meter verification, which checks your meter’s performance against a reference. It is a verification, not an IANZ-accredited calibration; our accredited calibration covers pressure, temperature, humidity, infrared and gas detection instruments.
Why do gas and steam flow readings need compensation?
Gases and steam change density with pressure and temperature, so the same volume can hold different amounts of fluid. Measuring pressure and temperature, or using a meter that does so internally, corrects the reading to mass or standard volume flow.