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Quick Answer: A clamp on flow meter measures liquid flow from outside the pipe. It uses ultrasonic transit time technology to track velocity without cutting pipe or stopping production. The method works best on clean liquids with low solids or gas content for pipe sizes from DN15 to DN600, and Silver Instruments supplies these meters with 4-20 mA HART and Modbus outputs.
A clamp on ultrasonic flow meter does not require a process shutdown. You mount a pair of transducers on the outside of a pipe. The meter sends ultrasonic signals through the pipe wall and into the liquid. One transducer acts as transmitter. The other acts as receiver. The system compares upstream and downstream transit time. The difference gives flow velocity. This is transit time measurement. It is not Doppler. Doppler devices rely on particles or bubbles. Transit time devices perform better with clean or lightly loaded liquids.
In practice, we have supplied clamp on meters for a chilled water plant in Manila. Pipe size was DN150 schedule 40 carbon steel. Flow range was 80 to 400 m3/h. Water temperature was 6 °C. Pipe outer diameter was 168.3 mm. The customer could not cut the line because the HVAC shutdown window was only two hours. We selected SIL-CL-DN150-S with a PT100 input for heat metering. Installation took one technician about 45 minutes.
Clamp on meters are not universal. Pipe material matters first. Carbon steel and stainless steel are fine. Copper and PVC also work. Concrete lined pipe causes too much signal loss. Internal scale or heavy fouling is another common problem. A thick layer of rust changes acoustic coupling. Then check the liquid itself. Slurries with more than 3 percent solids reduce accuracy. Liquids with gas bubbles are also problematic. We recommend a minimum back pressure of 0.5 bar on pump discharge lines to keep gas in solution. For dirty water or sludge, a magnetic flow meter is usually a better fit. For viscous oil above 100 cP, a Coriolis mass flow meter gives direct mass output.
Most engineers skip this part. They enter nominal bore instead of measured outer diameter and wall thickness. A DN50 schedule 40 pipe and a DN50 schedule 80 pipe share the same outer diameter, but wall thickness is different. Transducer spacing depends on those dimensions. If the input is wrong, the meter may show 2 to 4 percent error. That is why we ask for actual pipe OD and wall thickness before quoting.
In water and wastewater plants, clamp on meters are used for pump verification and balancing. One customer in Dammam used a portable clamp on meter to check flow on a DN200 cooling water line. The permanently installed magnetic meter was reading 12 percent high. The portable meter showed the offset within four hours. This avoided a plant shutdown and a calibration call.
In chemical plants, clamp on meters serve dosing lines and acid transfer lines. PTFE lined pipe is common there. PTFE liner can work if the pipe is fully filled and the liner is bonded without air gaps. In food and beverage, stainless steel pipe with a polished OD works well. Use couplant gel suitable for food areas. For marine engine cooling lines, a clamp on meter gives quick verification without cutting seawater pipe. In desalination plants, a seawater clamp on flow meter can track brine reject flow after the acoustic coupling is verified on site.
For a quote, send us liquid type, pipe outer diameter, wall thickness, pipe material, flow range, temperature, and output signal. Do not send nominal bore alone. Pipe OD matters more for transducer spacing. State if the pipe is always full. If the line drains between batches, the meter may lose signal. We often quote the SIL-CL series with local display, 4-20 mA, pulse, and RS485 Modbus RTU. Options include ATEX Zone 1, Zone 2, a portable handheld model, and a wall mounted remote transmitter.
Send your pressure in bar, temperature in degrees Celsius, pipe size in DN, and flow range in m3/h or kg/h. This allows us to confirm the right transducer type and mounting kit. We also need the pipe schedule or exact wall thickness. For heat metering, mention whether you need a PT100 temperature sensor.
Clamp on flow meter price depends on pipe size, transmitter type, and mounting method. Small DN15 to DN50 clamp on meters often cost less than inline meters at the same size. Large pipe above DN300 needs more transducer power and better coupling. A DN400 clamp on meter can cost more than a magnetic flow meter because of signal attenuation. Budget portable clamp on meters exist but they may drift when pipe surface is rough. Silver Instruments focuses on industrial grade transit time units rather than low cost master meter substitutes. We give a full quote with freight to Jakarta, Dubai, Lima, Lagos, or Auckland. We also supply installation videos and remote startup support via WhatsApp.
Q: What liquids work with a clamp on ultrasonic flow meter?
Clean water, chilled water, hot water, light chemicals, fuel oil, and glycol mixes. The liquid should have less than 3 percent solids. Avoid liquids with free gas bubbles unless you can increase line pressure. For dirty water or sludge, select a magnetic flow meter.
Q: What pipe sizes can a clamp on flow meter handle?
Standard industrial models cover DN15 to DN600. Some portable units go up to DN2000 with special transducers. The key dimension is pipe outer diameter, not nominal bore. Pipe material must conduct ultrasonic energy. Carbon steel, stainless steel, copper, and PVC are common.
Q: How accurate is a clamp on flow meter?
A properly installed transit time clamp on meter typically achieves 1 percent of reading or better on clean liquid. Installation quality matters. Pipe wall measurement must be accurate. Transducer spacing and couplant application affect repeatability. We have seen accuracy drop to 3 percent when users input wrong pipe wall thickness.
Q: Does a clamp on meter work on old pipes?
It depends on internal pipe condition. Thin rust or scale is often acceptable. Heavy lamination and air gaps reflect the ultrasonic signal. For old buried pipe or unknown wall thickness, we suggest a site audit first. We can supply a portable clamp on flow meter rental unit for one week to test signal strength. We have seen this on customer sites many times.
Q: What output signals are available?
Standard outputs are 4-20 mA, pulse, and RS485 Modbus RTU. Optional outputs include HART, two relay alarms, and a PT100 input for energy measurement. Tell us if you need ATEX Zone 2 or battery powered portable logging.
Get a clamp on flow meter quote from Silver Automation Instruments. Send us your liquid, pipe outer diameter, wall thickness, pipe material, flow range, temperature, and output signal. We reply within 12 hours on working days. Contact us on Tel: +86-25-68650347, WhatsApp: +86-25-52155837, WeChat: +86 15365082610. For product specifications and installation drawings, ask our team for the SIL-CL series datasheet.
