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Ultrasonic Liquid Flow Meter: Fixed and Portable External Pipe Sensors
Quick Answer: External clamp-on ultrasonic flow meters measure liquid flow from outside the pipe without cutting or process shutdown. Fixed models suit permanent monitoring on DN15 to DN6000 lines. Portable units serve field audits, leak detection, and temporary checks. Silver Instruments supplies both types with 4-20 mA HART, Modbus output. Accuracy reaches ±1.0% of reading for clean liquids.
How External Pipe Sensors Work
The sensor pair clamps onto the pipe surface. One transducer sends an ultrasonic signal through the pipe wall and liquid. The second receives it. The system measures transit time difference between upstream and downstream signals. This difference directly corresponds to flow velocity. No pipe cutting. No pressure drop. No moving parts. The clamp-on method works on metal and plastic pipes. We have tested this on carbon steel, stainless steel, PVC, and HDPE lines up to 6000 mm diameter.
Fixed vs. Portable Ultrasonic Flow Meters
Fixed meters mount permanently in a cabinet or on a wall. They output 4-20 mA, pulse, or RS485 Modbus signals to a PLC or SCADA. Typical applications include cooling water loops, chemical transfer lines, and HVAC chilled water. Many plants in Thailand and Vietnam use fixed clamp-on meters to avoid welding on pressurized pipes.
Portable units come in a rugged carry case with a built-in battery. Technicians walk around a plant and spot-check flow rates. A water utility in Indonesia used our portable meter to audit 42 pipe sections in three days. They found two leaking bypass valves that no one knew about. The data logging function stores 100,000 points. You transfer logs via USB.
Key Selection Parameters
Pipe diameter from DN15 to DN6000. Pipe material code is critical because sound speed varies. Our transducers support carbon steel, stainless steel, cast iron, PVC, PE, and lined pipes. Liquid must be clean or contain less than 3% solids. Maximum particle size 1 mm. Temperature range: standard sensors from -30°C to 160°C. High-temperature sensors up to 250°C available on request. Viscosity up to 100 cSt is fine. For very viscous oils above 100 cSt, accuracy drops.
Provide pipe wall thickness and lining data. We need this to calculate the correct transducer spacing. Here is the thing: if you do not know the exact wall thickness, we can still measure it with an ultrasonic thickness gauge. Most engineers skip this part, but it matters for ±1% accuracy.
Typical Use Cases
Water and wastewater. External sensors monitor raw water intake, treated water discharge, and sludge return lines. No sensor contact with dirty water. A desalination plant in Saudi Arabia bought 18 fixed units for brine and permeate lines. They avoided cutting fiberglass pipes.
Oil and gas. Fixed meters measure light oil, diesel, and lube oil on carbon steel pipes. Ex-proof versions are certified ATEX Zone 1 and IECEx.
HVAC and building automation. Facility managers use portable ultrasonic meters to balance chilled water and hot water circuits. Fixed meters integrate with BMS via Modbus.
Chemical and food. Clamp-on meters suit corrosive acids, caustic soda, and demineralized water. Because the sensors never touch the fluid, there is zero contamination risk. A dairy in New Zealand uses fixed meters on CIP return lines at 85°C wash cycles.
Silver Instruments Ultrasonic Flow Meter Range
We offer fixed transmitters DTFX-UF200 and portable kits SUP-1158J. The fixed version has a wall-mount enclosure IP66, backlit LCD, and 4-20 mA HART output. The portable kit includes transducers, mounting fixtures, a signal cable, and a carrying case. Both models measure flow in both directions. Display shows flow rate (m³/h, l/min, GPM), totalizer, velocity (m/s), and diagnostics. Accuracy ±1.0% of rate for pipe sizes above DN50. For DN15 to DN50, accuracy is ±2.0% with optimized transducer mounting. In practice, most customers choose fixed meters for remote monitoring and portable units for field service. We have seen both used together in large water networks. A distributor in Mexico keeps one portable set for commissioning and sells fixed meters for each pump station.
To get a quote, send us your pipe size (DN), pipe material, wall thickness, liquid type, temperature (°C), and flow range (min and max in m³/h or l/min). Our engineers will recommend a suitable sensor and transmitter in 24 hours. Contact Silver Automation Instruments: email [email protected], tel +86-135-1213-1526, Whatsapp 86-135-12131526, WeChat +86 13512131526. Website: https://flow-meter.com.au
Frequently Asked Questions
What is the minimum pipe size for external clamp-on sensors?
We support DN15 with special small-pipe transducers. Accuracy drops slightly for very small lines.
Can I use a clamp-on meter on old concrete pipes?
Usually not. Concrete and asbestos cement scatter the ultrasonic signal too much. Use a different technology like magnetic flow meter.
How often do I need to calibrate the meter?
The sensor pair does not drift. Factory calibration is valid for five years. We recommend a field verification every two years using a reference meter or portable unit.
Does the meter work with glycol-water mixtures?
Yes. You select the fluid type in the menu. Preloaded liquid profiles include water, seawater, diesel, glycol 30% and 50%, and other oils. Provide sound speed if your liquid is not in the list.
What signal outputs are available?
Standard outputs: 4-20 mA, pulse, and RS485 Modbus RTU. Optional HART on the fixed version. Relay outputs for flow alarms or batch totals.