USonic Flow
Measures volumetric flow by transmitting ultrasonic pulses (typically 1–5 MHz) at an angle through a pipe, alternately upstream and downstream, and computing flow velocity from the transit-time difference.
In a transit-time arrangement, transducers send sound with and against the flow. The downstream pulse arrives sooner; the instrument uses both travel times and the known acoustic-path geometry to estimate velocity. Pipe cross-section and the flow profile then relate velocity to volumetric flow. Clamp-on and inline installations have different mounting and coupling requirements.
In plain terms
Like swimmers racing downstream and upstream in a river — the time difference between their finishes reveals the river's current, regardless of how fast each swimmer is.
Why designers use it
- Measuring suitable clean liquids or gases using transit-time differences.
- Using a compatible clamp-on installation without opening the pipe.
- Measuring flow without a moving rotor in the stream.
- Supporting bidirectional measurement when specified for the exact meter.
Best for
- Natural gas
- Water utilities
- District heating
Key specifications
- Method: Transit time, Doppler and cross-correlation have different requirements
- Installation: Pipe, acoustic path, coupling and flow profile
- Process suitability: Fluid, gas/particle content, deposits and temperature
- Accuracy: Use the instrument's stated conditions
When not to use it
- When bubbles, solids or deposits attenuate the transit-time signal too strongly.
- When the pipe, fluid, coupling or flow profile is unsuitable for the chosen instrument.
- Assuming a transit-time meter has the same requirements as a Doppler meter.
Common mistakes
- Ignoring the actual pipe dimensions, acoustic coupling or required straight runs.
- Treating Doppler and transit-time methods as interchangeable.
- Assuming a generic accuracy figure applies to every fluid and installation.
Where you will find it
- A Sick FLOWSIC600 8-path ultrasonic gas meter at a Gazprom natural-gas custody-transfer station reads pipeline flow with ±0.1 % uncertainty: the multi-path geometry corrects for swirl and asymmetry that would compromise turbine-meter accuracy.
- A KROHNE OPTISONIC 6300 P clamp-on ultrasonic meter installed without shutting down a Saudi Aramco pipeline reads heavy crude flow at 12,000 BBL/h: the chip's adaptive transit-time algorithm tracks the sound speed of the crude as it changes with temperature.
- A Siemens FUS1010 IP66 ultrasonic flow meter on a Vienna district-heating loop reads 800 m³/h of 90 °C heat-distribution water: the meter's clamp-on installation kept the loop in service during commissioning, the same network that's been in heated operation since 1903.
A short history
A transit-time ultrasonic flowmeter compares the travel times of sound pulses sent with and against the flow. Moving fluid changes those times differently, and the instrument converts the difference into flow information using the measurement geometry. This method is particularly useful for suitable clean-fluid applications.
Good to know
- Doppler meters depend on suitable reflectors such as particles or bubbles; transit-time meters can be hindered by them.
- Volumetric flow also depends on pipe cross-section, not only flow velocity.