Ultrasonic Flow Meters: Principles, Types, Advantages, and Applications

An ultrasonic flow meter determines a liquid's or gas's flow rate via ultrasonic waves across a pipe, going both with and against the flow. 

The meter then ascertains the flow rate by evaluating differences in wave travel times. It uses two transmitters, as well as two receivers, located on opposite pipe sides at a precise separation for correct readings.

These meters offer high accuracy, about ±1%, which is critical for fiscal transfers. A clamp-on model offers ease of installation because it attaches to a pipe's exterior. 

Moreover, these meters have no moving parts, offer versatility, and permit measurement in both directions.

How Ultrasonic Flow Meters Work

Ultrasonic flow meters operate without any intrusion and use sound waves to gauge volumes and flow rates. Installation is external, simplifying setup and saving time. Other flow devices may require hazardous cutting into the pipe.

The transducer assesses the flow rate, which can be set parallel or at an angle on the pipe. Two ultrasonic transmitters send brief ultrasonic pulses that two receivers capture as they pass through fluid. 

One transmitter, called the preferred one, emits sound waves along the flow, strengthening its signal with fluid speed. The other transmitter emits sound waves against the flow. Its signal diminishes because of its counterflow direction.

Types of Ultrasonic Flow Meters

A suitable flow meter exists for every use, from gauging gas consistency to measuring fluid amounts a customer ordered. 

Flow meter types offer precise data on volume, flow rate, mass, and quantity based on application needs. They are popular due to exceptional precision and operation that's noninvasive, since they don't need direct contact with what's flowing. 

Sensor placement, pipe attachment methods, and materials being checked dictate ultrasonic flow meter types.

• Hybrid Ultrasonic Flow Meters: These can measure any fluid, and are "hybrid" given their combination of both Doppler and transit time methods. Depending on fluid traits, users choose between these methods. For fluids containing particulate matter, Doppler is used, whereas the transit time is good for fluids lacking particulate matter.
• Totalization Ultrasonic Flow Meters: A meter of this type constantly tracks and documents the total volume of liquid, gas, or steam moving through a pipe. They handle pipes containing at minimum 100 parts per million (ppm) of suspended particles or bubbles 100 microns (μm) or larger. Regular ultrasonic flow meters might experience signal interruptions from particles or bubbles, yet totalization excels in difficult conditions. They are suited for measuring the flow of substances like wastewater, reactivated sludge, slurries, phosphates, lime slurries, waste-activated sludge, and pulp stock. The Doppler ultrasonic method considers particulate matter and bubbles. Styles include clamp-on types.
• Open Channel Ultrasonic Flow Meters: As opposed to closed pipe flow meters, these require channel geometry details, including depth with width. Based on the water height, the flow meter calculates the flow rate. The greatest precision exists in channels absent of sediment buildup, as sediment greatly impacts readings.
• Multi-Channel Ultrasonic Flow Meters: A typical challenge with ultrasonic flow meters involves precisely measuring flow rates when the Reynolds number changes unexpectedly. Using one ultrasonic beam may cause constant variance in the flow rate with Reynolds number alterations. A multi-channel ultrasonic flow meter addresses this issue.
• In-Line Ultrasonic Flow Meters: If the meter is an inline version, it'll need to fit into the piping via connections that are well-sealed. When installing this type, paying attention to upstream and downstream distance needs is a must. Ample space ought to exist around ultrasonic flow meters, keeping away from whatever might throw off the flow profile. While installation as close as five times the meter length in the pipe may happen, it risks causing extra inaccuracies. Always consult the installation manual for your specific flow meter model, as needs may vary. One model requires 10x both upstream and downstream.
• Biopharmaceutical Ultrasonic Flow Meters: These measure flow rates in laboratories. These clamp-on meters easily attach to flexible tubes and are media contact-free, which fulfills the critical needs of lab tests. Measuring flow rate relies on the transit time method. A calibration table exists for precise monitoring, and customer customization of controls is allowed.

Advantages of Ultrasonic Flow Meters

Since being introduced for industrial applications during the 1960s, ultrasonic flow meters are increasingly preferred for checking and measuring fluid flow. 

Their fame comes from key benefits: no moving parts and little need to adjust pipes during setup.

• Accurate Measurement: Measurements remain unaffected by the fluid's pressure, density, conductivity, temperature, or viscosity.
• No Moving Parts: This removes any demand for replacements or repairs. Once set, the flow meter stays still, continuously providing readings that are accurate and reliable.
• Rapid Installation: They install rapidly, often operating within 30 minutes. This ease of quick installation explains their popularity for monitoring flow.
• Precision and Rangeability: Ultrasonic flow meters possess rangeability that's exceptional, precisely measuring conditions from low to high with dependability over the long term. Extreme temperatures don't stop them from giving repeatable, precise measurements.
• Environmental Awareness: Once installed, an ultrasonic flow meter calibrates to its location's specific environment and conditions. It detects and adapts to any changes or shifts.
• Measurements that are Sanitary, Safe, and Nonintrusive: Ultrasonic flow meters never get in a fluid's or material's way, regardless of setup. Since material contact never occurs, neither the flow nor the material's integrity is affected. With this, measurements are both sanitary and safe.
• Low-Pressure Drop: Ultrasonic clamps on flow meters provide a benefit in that they cause pressure to drop negligibly across the meter. Unlike other types, like vortex or magnetic ones, ultrasonic meters lack obstructions or moving parts in the flow path. This creates low-pressure loss, which is advantageous in sectors where pressure maintenance is critical.
• Versatile Fluid Conditions: They can function across a range of fluid states, making them suited to uses from the oil sector to wastewater management. As an illustration, transit time flow meters offer effectiveness in single-phase fluids that are clean, like water or oils. Doppler meters work with liquids that are aerated or dirty, bouncing signals off suspended particles.
• Cost-Effective: For sizable bore uses where clamp-on models work, ultrasonic flow meters can be cost-effective. Clamp-on models also provide value by eliminating system shutdown for setup, and avoiding the high expenses tied to installation, since they simply strap onto the outside.

Applications of Ultrasonic Flow Meters

Industries rely on ultrasonic flow meters to receive information that's accurate and exact regarding fluid flow.

• Custody Transfer: Accuracy is vital during the exchange of fluids or gas from seller to buyer. This fiscal metering hinges on correct volume and amount recording; even small mistakes add up and affect transaction accuracy.
• Biopharmaceutical: These are made to gauge flow rates inside labs. These clamp-on models attach without problems to tubes that are flexible and don't contact media, meeting crucial lab testing needs.

Factors to Consider

• Fluid Characteristics: A fluid free of obstructions that could scatter sound waves promotes signal transit across a fluid. High concentrations of solid particles or bubbles within the fluid might disrupt ultrasonic waves.
• Flow Path: The route the signal takes through the liquid influences measurement accuracy. Signal diffusion from turbulence leads to readings that are not correct. Meters frequently include a straight line, or lengths of pipe, on each side of the sensor body so flow remains regular and smooth.
• Pipe Material and Size: Pipe material and size considerably affect an ultrasonic flow meter's function. Inner surfaces ought to be smooth for the easy propagation of ultrasonic signals. Typical industrial pipes made of steel, copper, or PVC assist with this. Pipe diameter also matters in the selection of an ultrasonic meter. Certain flow meters can handle numerous sizes, while others match specific diameters.

Installation Guidelines

• Always refer to your product manual.
• Keep the flow meter free from extreme loads like strong pipe movements, vibrations near centrifugal pumps, high-temperature media, or pressure surges.
• Take out all packing and transport retainers, checking that none remains in the device.
• Orient the flow body to the direction of flow, if there's an arrow.
• Avoid pressure and tensile load, as well as valves, or large pipe reduction on the inlet side.
• Don't go above torque recommendations during meter installation.
• Make certain the pipe material that transducers affix to can carry ultrasonic waves for clamp-on types.
• Transducers must keep a particular separation. This may happen through a factory-made spacer bar or measurement.
• A small amount of coupling grease ought to be applied between the transducer and pipe if coupling foil isn't already present.
• Attachment chains/straps need minimal transducer pressure. Overtightening straps risk compromising the transducer.
• The installation area must have sufficient straight piping run before, as well as after, the transducers.
• For piping that's horizontal, position transducers at the 2 or 10 o’clock spot on the pipe so gas bubbles at the top, and sedimentation at the bottom, don't interfere.
• Follow your meter's wiring diagram during electronics commissioning.

Ultrasonic vs. Magnetic Flow Meters

The advantage that ultrasonic flow meters hold involves measuring media that's non-conductive, although pricing may be similar.

To work correctly, magnetic flow meters must-have media with a minimum amount of conductivity. This makes many media types not suited to magnetic flow meter technology, yet suited to ultrasonic technology.

Both ultrasonic and magnetic rely on principles not needing moving parts, so maintenance is lower, plus the service life is potentially longer when compared to mechanical flow meters.

Conclusion

Ultrasonic flow meters serve as a remarkable device, demonstrating advances made technologically regarding liquid and steam flow measurement that's precise and non-intrusive.

They have cemented themselves in many industries, as a favored choice, through their ability to provide accurate flow measurements, low maintenance requirements, and negligible pressure drop.

Optimize your operations with precise ultrasonic flow measurement. Request a free demo now!