Types of flowmeters
Each measurement principle has its own strengths regarding medium, accuracy, pressure drop and maintenance. The summary below helps you quickly choose the right direction. Click through to the detailed pages per type for application examples and installation tips.
| Principle |
Media / application |
Accuracy* |
Pressure drop / moving parts |
Installation notes |
| Rotameter (float) |
Visual indication, clean liquids/gases |
Basic |
Low / Yes |
Vertical installation; plan viewing distance |
| Paddle wheel / turbine |
Clean media, water/light oil |
Medium |
Low–medium / Yes |
Straight inlet/outlet runs; sensitive to contamination |
| Oval gear (PD) |
Dosing, varying viscosity |
High |
Medium / Yes |
Calibrate on actual medium; by-pass recommended |
| Electromagnetic |
Conductive liquids (water, slurry) |
High |
Very low / No |
Full pipe; grounding; straight runs |
| Vortex |
Steam, gases, clean liquids |
Medium–high |
Medium / No |
Straight runs; sufficient Reynolds number |
| Thermal mass flow |
Compressed air and industrial gases |
Medium–high |
Very low / No |
Normalize to standard conditions (Nm³) / gas calibration factor |
| Coriolis (mass) |
Mass flow, density, custody |
Very high |
Medium / No |
Space for installation; limit vibrations |
| Ultrasonic (transit-time) |
Water (clamp-on), process, HVAC; also gas |
Medium–high |
Very low / No |
Full pipe; good acoustic coupling |
*Indicative; actual accuracy is type- and medium-specific.
Mechanical flowmeters
Electronic flowmeters
- Electromagnetic flowmeter: ideal for conductive liquids (water, slurries)
- Vortex flowmeter: reliable in steam and air applications
- Thermal flowmeter: from air to light oil
- Differential pressure flowmeter: pitot, orifice plate or venturi for high accuracy
Ultrasonic flowmeter
An ultrasonic flowmeter works with two (or more) transducers that send acoustic signals both with and against the flow direction through the medium. The difference in transit time is proportional to the average flow velocity and, combined with the pipe diameter, yields the volumetric flow rate. Clamp-on versions are mounted on the outside of the pipe, making them ideal for clean, fully filled liquids without process interruption. For gas measurement there are specialized ultrasonic meters with pressure and temperature compensation, often using multiple paths for extra accuracy. Typical applications include energy metering in HVAC, (drinking and process) water, chemical dosing, compressed-air monitoring and temporary measurements during commissioning or troubleshooting.
Coriolis flowmeter
A Coriolis flowmeter measures mass directly via vibrations in the measuring tube. Extremely accurate (up to 0.1 %) and independent of density or viscosity. Perfect for mass flow and concentration measurements.
Flowmeter for water
For water installations, the electromagnetic flowmeter is often the first choice: it has no moving parts, exhibits a very low pressure drop and remains accurate with changing viscosity and contamination. During installation, ensure a completely filled pipe, proper grounding and sufficient straight lengths upstream and downstream for a stable measurement. When mass balance, density determination or concentration is important, a Coriolis meter provides direct mass flow and extra process information. For local, quick visual checks, a rotameter remains practical and cost-effective. The final choice depends on pipe size (DN), required accuracy, medium properties and the desired output signal (e.g., 4–20 mA, pulse or digital).
Flowmeter for air
For compressed air and gases, thermal mass flowmeters provide direct mass flow and normal volumetric flow (Nm³/h), ideal for energy management and leak detection. Consider gas composition and temperature/pressure, or choose compensated models for consistent results. Vortex meters are robust for steam and dry gases and offer a wide turndown with reliable linearization, provided sufficient straight pipe is available. Ultrasonic meters are non-intrusive and suit larger diameters or retrofit; with pressure/temperature compensation they achieve high repeatability. Select the right output (4–20 mA, pulse, IO-Link/Modbus) and ensure clean, dry air to prevent sensor fouling and drift.
Flowmeter selection
Start with the medium (conductive / non-conductive, clean / with particles), the measurement objective (volume or mass) and the range/turndown. Check process conditions (pressure, temperature, viscosity, gas fraction) and installation (DN, straight runs, full pipe). Then determine the required accuracy, certifications (e.g., hygienic/ATEX) and outputs (4–20 mA, pulse, IO-Link/Modbus). Pressure sensors and pressure gauges complete your instrumentation.
Frequently asked questions about flowmeters
What does a flowmeter do?
A flowmeter continuously measures the flow velocity and the volumetric or mass flow of liquids or gases. The measurement signal (e.g., 4–20 mA, pulse or digital via Modbus/IO-Link) is read by your PLC/SCADA for control and monitoring. Many flowmeters also totalize consumption and raise alarms in case of deviations or leakage losses. Depending on medium and accuracy, you can choose magnetic-inductive, Coriolis, vortex or ultrasonic.
What is the difference between a flowmeter and a water meter?
A water meter is primarily intended for drinking-water registration and billing; it is usually mechanical (e.g., single/multi-jet or Woltman), measures only volume and shows a register (sometimes with a simple pulse output). A flowmeter is a broader instrument category for water, gases and process liquids and works with various principles (magnetic-inductive, ultrasonic, Coriolis, vortex). In addition to totalizing, a flowmeter also provides the actual flow rate and often extra process data (such as temperature/diagnostics) via 4–20 mA, pulse or digital protocols (Modbus, IO-Link). While water meters are used mainly for billing and consumption logging, you deploy flowmeters for process control, energy measurement and leak detection.
What is a flowmeter for air?
A flowmeter for air measures the flow of compressed air or gas, typically using thermal mass, vortex, or ultrasonic (transit-time) technology. Depending on the principle, it outputs volumetric flow (m³/h, Nl/min) or mass flow (kg/h) and totalizes consumption; many models correct to standard conditions (Nm³/h) for fair comparison. Typical applications include leak detection, consumption allocation per line or machine, and energy management of compressor systems. Integration with PLC/SCADA via 4–20 mA, pulse or digital protocols (e.g., IO-Link or Modbus) makes monitoring and control straightforward.
How does a flow measurement work?
A flow measurement can be based on different principles. Positive displacement meters count the volume per cycle of a chamber/rotor or piston, while vortex meters measure the frequency of vortices behind a bluff body, which is proportional to flow velocity. In electromagnetic meters, a conductive liquid flowing through a magnetic field induces a voltage (Faraday) proportional to velocity, and ultrasonic transit-time meters determine the time difference of acoustic signals with and against the flow. Coriolis meters vibrate a tube; the phase shift caused by mass flow yields direct mass flow, often with simultaneous density and temperature measurement.
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