PC-04Process measurement · FT
Flowmeters for Liquids, Gases & Steam
No single flow technology suits every fluid. The measuring principle follows from the medium, its conductivity and cleanliness, the line size, and whether volume or mass is needed.
01Scope
What's included
Flowmeters for liquids, gases and steam across measuring principles.
- Electromagnetic flowmetersFull-bore meters for conductive liquids, slurries and wastewater.
- Vortex flowmetersSteam, gases and clean low-viscosity liquids, with optional temperature or pressure compensation.
- Coriolis mass flowmetersDirect mass flow and density for liquids and gases.
- Ultrasonic flowmetersInline and clamp-on transit-time meters for liquids and gases.
- DP flow and thermal massPrimary elements with DP transmitters; thermal mass meters for compressed air and gases.
- Mechanical meters and flow switchesPositive-displacement, turbine and variable-area meters; flow switches for protection.
02Compare
Measuring principles
Compare the principles against the fluid first — conductivity, phase, cleanliness and viscosity rule options in or out before accuracy is discussed.
| Principle | How it works | Suited for | Considerations |
|---|---|---|---|
| ElectromagneticMedia: Liquid | How it worksA conductive liquid moving through a magnetic field induces a voltage proportional to its velocity (Faraday's law). | Suited forWater, wastewater, slurries, acids and alkalis — no moving parts, no obstruction and negligible pressure loss. | ConsiderationsThe liquid needs a minimum conductivity (often around 5 µS/cm for standard designs), so not for gases, steam or hydrocarbons; liner and electrodes must suit the medium; the pipe must run full. |
| VortexMedia: LiquidGasSteam | How it worksA bluff body sheds vortices at a frequency proportional to the flow velocity. | Suited forSaturated and superheated steam, gases and clean low-viscosity liquids. | ConsiderationsNeeds a minimum velocity (Reynolds number), so low flows are cut off; sensitive to pipe vibration; straight-run requirements apply. |
| CoriolisMedia: LiquidGas | How it worksFlow through vibrating tubes causes a phase shift proportional to mass flow; the tubes' resonant frequency gives density. | Suited forDirect mass flow and density — dosing, batching, custody transfer, viscous and high-value products. | ConsiderationsCost and weight rise steeply with line size; pressure loss; entrained gas in liquids affects performance. |
| Ultrasonic (transit-time)Media: LiquidGas | How it worksThe difference in travel time of ultrasonic pulses sent with and against the flow gives the velocity. | Suited forClean liquids and gases; clamp-on versions install without cutting the pipe — useful for large lines, retrofits and surveys. | ConsiderationsSolids and bubbles disturb transit-time signals; clamp-on accuracy depends on pipe data and installation; straight runs apply. |
| Differential pressureMedia: LiquidGasSteam | How it worksA primary element (orifice, venturi, nozzle or averaging Pitot) creates a DP related to the square of the flow. | Suited forLiquids, gases and steam across wide ranges of line size, temperature and pressure; well standardized. | ConsiderationsPermanent pressure loss with orifices, limited turndown, and impulse lines to maintain. |
| Thermal massMedia: Gas | How it worksHeat carried away from a heated sensor by the gas stream depends on the mass flow. | Suited forGases of known, stable composition — compressed air, combustion air and fuel gas — with direct mass flow and no separate pressure or temperature compensation. | ConsiderationsCalibrated for a specific gas composition; moisture and condensate affect the reading; not for liquids. |
| Positive displacement and turbineMedia: LiquidGas | How it worksPositive-displacement meters trap and count fixed volumes; turbine meters count rotor revolutions proportional to velocity. | Suited forPositive displacement for viscous liquids such as oils and fuels; turbines for clean, low-viscosity liquids and gases — both for totalizing. | ConsiderationsMoving parts wear and need a clean, filtered fluid; turbine performance depends on viscosity. |
General engineering guidance. Limits and performance depend on the specific instrument and variant — confirm them against the manufacturer's datasheet for the selected model.
03Specify
What to specify
The parameters that decide the selection. State each with its unit; where a value is not known yet, say so — it becomes part of the engineering review.
Medium and phase
Liquid, gas, steam or slurry — the first filter on which principles are possible at all.
Flow range and unit
Minimum, normal and maximum flow in volume or mass units; the turndown needed rules out some principles.
Line size and pipe material
Sets meter size, cost and weight, and whether clamp-on or insertion designs are practical.
Fluid properties
Conductivity, viscosity, density, solids and entrained gas each favour or exclude a principle.
Process temperature and pressure
Decide pressure rating, liner and sensor materials, and — for gases and steam — the compensation needed.
Accuracy
State it as % of rate or % of full scale; custody transfer and billing have stricter requirements than control.
Allowable pressure loss
Pumping and compression energy can favour full-bore meters over restrictions.
Available straight run
Most principles need undisturbed flow profiles; short runs need flow conditioners or a different principle.
Output and communication
4–20 mA for rate, pulse for totalizing, HART or fieldbus for diagnostics and secondary variables.
Area classification and power
Hazardous-area certification, and whether the meter can be loop-powered or needs a separate supply.
04Integrate
Outputs & communication
Interfaces typically offered in this category, and what each means for the control system. Availability depends on the specific model.
- 4–20 mAAnalog
- Current loop with a live zero: 4 mA is the bottom of the range, so a broken wire (0 mA) is distinguishable from a zero reading. Two-wire (loop-powered) on most transmitters; four-wire with an active output on line-powered instruments such as analyzers — the I/O channel must match. Accepted by practically every PLC and DCS analog input.
- HARTDigital over analog
- A digital signal (Bell 202 FSK, 1200/2200 Hz) superimposed on the 4–20 mA loop — configuration, diagnostics and secondary variables over the existing two wires.
- Modbus RTUSerial
- Serial client/server (formerly master/slave) protocol, typically over RS-485: several devices share one multi-drop cable and the client polls each for its values — common on analyzers, multivariable meters and packaged equipment.
- PROFIBUS PAFieldbus
- Two-wire, bus-powered process fieldbus at 31.25 kbit/s, coupled to PROFIBUS DP — several instruments share one cable, with intrinsically safe variants for hazardous areas.
- FOUNDATION Fieldbus H1Fieldbus
- Two-wire, bus-powered digital fieldbus at 31.25 kbit/s with function blocks in the field devices — used mainly where the DCS architecture is built around it.
- Industrial EthernetNetwork
- PROFINET, EtherNet/IP or Modbus TCP — the networks that connect controllers, remote I/O, drives and HMIs, and increasingly carry device data from the field as well.
- Pulse / frequencyDiscrete
- A pulse per unit of volume or mass, or a frequency proportional to rate — used for totalizing, batching and custody-transfer counting.
- Relay / discreteDiscrete
- Switched contact or transistor output for alarms, interlocks and pump or valve control — it carries a state, not a value.
05Install
Installation practice
- Provide the upstream and downstream straight run the chosen principle requires, or fit a flow conditioner.
- Keep liquid meters full: avoid high points where gas collects — a vertical section with upward flow helps.
- Ground and bond electromagnetic meters as specified, especially in lined or plastic pipe.
- Plan isolation and bypass valves where the meter must be removed for verification while the process keeps running.
06Products
Flow products
Status · no models listed
Specific models are not listed on the site.
Our engineers can recommend instruments against your process data. The selection checklist on this page is the information that decides it — send what you have.
How a review runs
FT01Share the process data
Medium, range, conditions, connection and the system it reports to.
02Engineering review
The measuring principle and the installation are checked against the application.
03Instrument options
Suitable devices are proposed with the data needed to confirm the selection.
Next steps
Where to go next
- 01SolutionInstrumentationProcess measurement and final control elements — selected for the process conditions, installed, calibrated and loop-checked.
- 02ResourcePressure vs Differential Pressure MeasurementGauge, absolute and differential pressure — what each measures and where each is used.
- 03Related categoryDifferential PressureDP transmitters for flow, level, filter and pressure-drop measurement.
Engineering enquiry
Choosing a flow technology for your fluid?
Share the medium, the range, the process conditions and the system it has to connect to. Our engineers can help match the principle and the instrument to the application.