The best ultrasonic flow meter for water is usually a transit-time clamp-on meter: it straps onto the outside of an existing PVC, PE, steel or cast-iron pipe, needs no shutdown or cutting, and has no wetted parts. Choose it by pipe size and material, accuracy class, output signal (4-20 mA, RS485 Modbus, pulse) and whether the installation is permanent or portable.
How an Ultrasonic Flow Meter Measures Water
A clamp-on ultrasonic flow meter uses two transducers fixed to the outside of the pipe with stainless-steel straps and couplant. One pulse travels with the flow and one against it. Water moving through the pipe makes the downstream pulse arrive slightly earlier than the upstream pulse; the transmitter converts that time difference into velocity and, using the pipe inner diameter you enter, into volume flow in m³/h or the unit you configure. This transit-time principle is the one described for liquids in closed conduits in ISO 12242 — Measurement of fluid flow in closed conduits: ultrasonic transit-time meters for liquid.
Because nothing is inserted into the pipe, there is no pressure drop, no risk of leaks at a new flange and no contact with potable water. That is why clamp-on meters are widely used for retrofit metering of water mains, pump stations and building services where the line cannot be taken out of service.
Water Applications and What Each One Needs
Water flow measurement covers very different duties. The table below matches typical water applications to the meter configuration and the points to confirm before ordering.
| Application | Typical pipe | Suggested SEGMENsensor configuration | Confirm before ordering |
|---|---|---|---|
| Water supply mains and district metering | Ductile/cast iron, steel, PE; large diameters | Fixed U10 or split-type X3, Z-mode on large pipes | Pipe OD and wall thickness, liner, straight run, RS485 to SCADA |
| Pump station and borehole discharge | Steel or PE | Fixed U10 with 4-20 mA to the pump PLC | Distance from pump outlet and valves, full pipe at all times |
| Irrigation and agricultural water | PVC, PE | Fixed U series, pulse output for volume totalizing | Pipe fully filled, air release upstream, outdoor enclosure rating |
| HVAC chilled and condenser water | Steel, copper | X3M with M-BUS / Modbus for energy metering | Liquid temperature, insulation removal at the measuring section |
| Treated effluent and process cooling water | Steel, stainless steel, PVC | Fixed U10 or X3 | Solids and air content; transit-time needs a clean single-phase liquid |
| Water audits, leak surveys and commissioning | Any of the above | U20 portable meter with data logger | Pipe size range of the transducer pair supplied |
Five Selection Steps for a Water Flow Meter
Measure the real pipe, not the nominal size
Record outer diameter, wall thickness, pipe material and any internal liner. An incorrect outer diameter becomes a systematic error in every reading, so measure it with a circumference tape or calipers.
Find a full, straight section
Transit-time meters need a pipe that is always full at the measuring point and a straight run of at least 10D upstream and 5D downstream of elbows, valves and pumps. On horizontal pipes, mount the transducers at the side (3 or 9 o'clock) to avoid air at the top and sediment at the bottom.
Choose the accuracy class
For process control and water balance, U10 and X3 meters are specified at ±1% of reading. U12 (±2%) and U13 (<3% FS) suit indication and trend monitoring. For billing or custody-transfer projects, see the higher-accuracy option in our SEGX3 vs X3M vs X5 comparison.
Match the output to your control system
Use 4-20 mA for a PLC analog input (signal levels per IEC 60381-1 analogue direct current signals), RS485 Modbus RTU for SCADA or a BMS, pulse output for totalizing and relay for low-flow alarms.
Decide between fixed and portable
Permanent metering uses a wall-mount transmitter powered from 85–265 VAC or 10–36 VDC. Surveys, leak checks and verification of existing meters use the battery-powered U20 portable clamp-on flow meter.
Send us your pipe data for a water flow meter quotation
Tell us the pipe OD, wall thickness and material, liner, water temperature, available straight run, output signal and quantity. MOQ 1 pc · samples 1–5 pcs in 5–7 days · production 3–5 weeks · quotation within 24 hours.
SEGMENsensor Clamp-On Flow Meter Specifications for Water
The values below are taken from the SEGMENsensor ultrasonic flow meter product page and datasheet.
| Parameter | U series (fixed) | X3 / X3M split-type | U20 portable |
|---|---|---|---|
| Measuring principle | Transit-time | Transit-time | Transit-time |
| Pipe size | DN15–DN6000 | DN25–DN6000 (X3M: DN32–DN6000) | DN15–DN6000 |
| Accuracy | ±1% (U10) · ±2% (U12) · <3% FS (U13) | ±1% of reading | ±1% of reading |
| Repeatability | ±0.2% | ±0.2% | ±0.2% |
| Velocity range | ±0.01–±15 m/s | ±0.01–±15 m/s | ±0.01–±15 m/s |
| Liquid temperature | -40 °C to +90 °C | -40 °C to +160 °C (high-temp version) | -40 °C to +90 °C |
| Pipe materials | Steel, stainless steel, copper, cast iron, PVC, PE and most plastics | ||
| Outputs | 4-20 mA, RS485 Modbus RTU, pulse, relay | 4-20 mA, RS485 Modbus RTU, pulse, M-BUS (X3M) | 4-20 mA, RS232, USB data logger, SD card |
| Power supply | 85–265 VAC or 10–36 VDC | 85–265 VAC or 10–36 VDC | Rechargeable Li-ion battery, 3,000 mAh |
| Protection rating | IP67 | IP67 / IP68 (transducers) | IP54 |
| MOQ / lead time | 1 pc / 3–5 weeks | 1 pc / 3–5 weeks | 1 pc / 3–5 weeks |
Protection ratings follow the IP code defined in IEC 60529 — Degrees of protection provided by enclosures (IP Code). For pits and chambers that can flood, specify IP68 transducers and route the cable to a transmitter mounted above the flood level.
Download the one-page datasheet (PDF)
Pipe size ranges, accuracy, transducer types and temperature ratings, outputs, power supply, enclosure ratings and ordering code for the SEGMENsensor clamp-on ultrasonic flow meter range. No registration required.
Portable Meters for Water Audits and Leak Surveys
Utilities and facility teams often need to check a flow reading before deciding where a permanent meter belongs. A portable clamp-on meter does this in minutes: strap on the transducers, enter the pipe data, and log flow over a full demand cycle to compare night flow with day flow or to verify an existing inline meter. The U20 stores data on an SD card for reporting.
Common Mistakes on Water Pipes
- Measuring right after a pump or valve. Swirl and turbulence make readings unstable; keep at least 10D upstream and 5D downstream.
- Partially filled pipes. Gravity lines and high points can run partly full; a transit-time meter needs a full pipe at the measuring point.
- Ignoring the liner. Cement or thick rubber linings change the acoustic path; enter liner material and thickness or choose a different section.
- Wrong pipe data. A nominal size from a drawing is not the actual outer diameter; measure it on site.
The full mounting procedure, including V-, Z- and W-mode spacing, is in our clamp-on flow meter installation guide. If your water carries solids or air, read transit-time vs Doppler ultrasonic flow meters first.
What Affects the Cost of an Ultrasonic Water Flow Meter
We do not publish list prices because the configuration drives the quotation. The main factors are the pipe size range and transducer type, the accuracy class, the output and communication options, the enclosure and transducer protection rating, any certification required by your project, and order quantity. Quotations are FOB China and exclude international freight and import duties or taxes; payment is 100% T/T in advance, and meters carry a 12-month warranty.
Get a clamp-on ultrasonic flow meter for your water project
Fixed or portable, DN15 to DN6000, with 4-20 mA, RS485 Modbus RTU or pulse output. MOQ 1 pc · samples 1–5 pcs in 5–7 days · production 3–5 weeks · quotation within 24 hours. Download the clamp-on flow meter datasheet (PDF).
Frequently Asked Questions
Yes. A clamp-on meter measures drinking water from outside the pipe, so no part of the meter touches the water and the line does not need to be cut or drained. SEGMENsensor U series and X3 meters cover DN15 to DN6000 with ±1% of reading on U10 and X3 models.
SEGMENsensor U10, X3 and U20 meters are specified at ±1% of reading with ±0.2% repeatability, U12 at ±2% and U13 at less than 3% FS. These values assume a full pipe, correct pipe data entry and at least 10D straight run upstream and 5D downstream.
Yes. Transit-time clamp-on meters work on steel, stainless steel, copper, cast iron, PVC, PE and most plastics. Thick internal linings and heavily corroded or scaled pipe walls weaken the ultrasonic signal, so state the pipe material and any liner in your inquiry.
A transit-time meter works on clean, single-phase water such as treated effluent, cooling water and irrigation water. Raw sewage or slurry with a high solids or air content scatters the ultrasonic signal; for those liquids, describe the medium in your inquiry so the suitable measuring principle can be confirmed.
Fixed SEGMENsensor meters provide 4-20 mA for a PLC analog input, RS485 Modbus RTU for SCADA or BMS, a pulse output for totalizing and a relay output for alarms. The X3M version adds M-BUS for heat and chilled-water energy metering.
MOQ is 1 piece. Samples of 1–5 pieces ship in 5–7 days and production orders take 3–5 weeks. Quotations are FOB China, sent within 24 hours on working days, and depend on pipe size range, output, transducer type, certification and quantity.