Ultrasonic flow meters come in two fundamentally different configurations: clamp-on (transducers attach to the outside of the pipe) and inline (the meter is inserted into the pipe). Both use the same underlying physics but suit very different applications.
All ultrasonic flow meters work on the transit-time principle: two ultrasonic transducers positioned at an angle to the flow alternately send and receive ultrasonic pulses through the fluid. When a pulse travels in the direction of flow, it arrives faster than when it travels against the flow. The difference in transit time between the two directions is proportional to the average fluid velocity, which the transmitter converts to volumetric flow rate.
The transit-time method works for clean, homogeneous fluids, water, process fluids, and gases. For fluids with high suspended solids, Doppler ultrasonic meters can be used, though accuracy is generally lower.
Clamp-on meters use transducers that attach to the outside of the pipe, no pipe penetration required. The signal is transmitted through the pipe wall into the fluid, with acoustic coupling gel ensuring good signal transmission.
Inline ultrasonic meters are installed directly into the pipe like a mag meter, with transducers at a known fixed position. Modern inline meters use multiple measurement paths (2–4) to average the velocity profile across the pipe, improving accuracy.
Advantages: higher accuracy (±0.5% or better), stable installation, lower signal loss, suitable for custody transfer, no electrodes in contact with fluid. Limitations: requires pipe penetration and process shutdown for installation, expensive for large diameter pipes, limited suitability for dirty fluids.
NZ Flow Group uses the Flexim Fluxus F601 portable clamp-on ultrasonic meter for all flow meter verifications in Canterbury. ECan specifies the Ultrasonic Clamp-On method for all verifications in the region, and the Flexim Fluxus is the leading instrument for this application. Our units are IANZ-calibrated annually against an accredited flow rig.
Works on most common materials, steel, stainless steel, ductile iron, cast iron, PVC, and HDPE. Heavily corroded pipes, concrete, or pipes with thick internal linings can affect performance.
Transit-time ultrasonic meters work best with clean fluids. For high-solids wastewater, mag flow meters are generally preferred.
Yes, permanent clamp-on installations are common on large diameter pipes where inline installation is cost-prohibitive. Transducer mounting systems are available for long-term outdoor installation.
It allows verification without removing the meter from service or interrupting the process. Using a portable calibrated reference meter (Flexim Fluxus F601) alongside the installed meter gives an accurate, traceable comparison under real operating conditions.
Canterbury-based flow meter specialists. Blue Tick accredited. IANZ-calibrated equipment.
Get in touchWe supply inline ultrasonic meters for high-accuracy applications and use the Flexim Fluxus F601 for Canterbury flow meter verification. We can advise on whether ultrasonic or mag technology is right for your application.