Over the past decade, ultrasonic flow meters have undergone a remarkable transformation. Once a niche technology, they are now among the fastest-growing flow measurement systems in the market.
Early prototypes of this technology date back to the 1960s. Fuji Electric pioneered the development of ultrasonic flowmeters with the launch of its first model FLH in 1975.
Despite being commercially available for several decades, it is only recently that ultrasonic flow meters have gained widespread acceptance.
There are several reasons why ultrasonic flow meters are gaining popularity. Signal processing advancements have improved noise filtering leading to increased accuracy and efficiency in flow metering.
Enhancements in signal processing technology have resulted in superior noise reduction, ultimately boosting the precision of flow metering measurements. This improvement contributes to the growing popularity of ultrasonic flow meters and their widespread adoption across various industries.
Compared to mechanical-type flow meters, ultrasonic flow meters require minimal maintenance, and failure rates are significantly lower. Vendors, like Fuji Electric, have also developed products tailored to specific industries and applications, including the ability to measure not only liquids but also gases and steam.
This targeted product development has helped to revolutionize flow metering and made ultrasonic flow meters an increasingly preferred choice across multiple industries for businesses around the world.
To fully comprehend clamp-on ultrasonic flow metering, it's essential, to begin with the underlying principles of ultrasonic flow meters.
The term "ultrasonic" refers to the frequency of the sound waves utilized by these devices, which are above 20 kHz and thus inaudible to human ears.
Ultrasonic flow meters measure flow rate through these high-frequency sound waves, generated by transducers that employ piezoelectric crystals to convert electrical signals into sound wave signals.
There are two main categories of ultrasonic flow meters: in-line flow meters and non-intrusive clamp-on flow meters.
The distinction lies in how the sound wave signals are transmitted, received, and processed for flow rate measurement.
Inline meters feature transducers in direct contact with the process fluid, usually mounted on a pre-built spool piece with a standard length to ensure proper angle and ease of installation.
Inline meters have a longer history and tend to offer greater accuracy due to the absence of signal degradation caused by pipe walls, scaling, and installation inconsistencies found in clamp-on meters.
As a result, inline ultrasonic flow meters are often the preferred choice for custody transfer applications. Custody transfer, also known as fiscal metering, involves flow metering applications in which the ownership of the metered fluid is transferred between parties.
Although these applications constitute a small portion of all suitable ultrasonic flow metering scenarios, they play a crucial role.
Contrary to inline meters, clamp-on meters attach externally to the pipe, without coming into direct contact with the process fluid.
These clamp-on meters have experienced substantial technological advancements, making them the faster-growing type among the two. Additionally, clamp-on meters provide exclusive advantages that contribute to their increasing popularity.
Although all ultrasonic flow meters operate using sound wave signals, they don't function in the same manner.
There are two main types of clamp-on ultrasonic flow meters: transit-time and Doppler, each differing in the transmission, reception, and processing of sound wave signals.
Transit-time meters utilize a pair of transducers that act as both transmitters and receivers of the sound wave signals. The speed of sound waves in a fluid is faster when traveling downstream and slower when going upstream.
By measuring the time difference between these scenarios, the meter can calculate fluid velocity and, subsequently, volumetric flow rate. When combined with the known density of the fluid, mass flow rate can also be determined.
Transit time ultrasonic flow meters are more versatile, capable of measuring liquids and steam, but typically only work with one fluid type at a time. They require liquids with minimal particulate solids or entrained bubbles to avoid interference with the sound wave signal.
Doppler flow meters, on the other hand, measure the frequency shift of the sound wave signal, which is proportional to the fluid's velocity.
These meters rely on the presence of particulate solids or air bubbles in the flow stream to deflect sound wave signals back to the meter.
As a result, Doppler meters are limited to metering liquids containing particulate solids or entrained bubbles, such as dirty or aerated liquids and slurries.
Thermal energy meters, also known as BTU meters, measure the energy of hydronic-based heating and cooling systems by utilizing volumetric flow sensors, temperature sensors, and a flow computer.
With growing emphasis on environmental regulations and financial incentives, thermal energy metering is becoming increasingly crucial for optimizing HVAC systems in district energy systems and commercial facilities.
Clamp-on ultrasonic thermal energy meters are ideal for retrofitting older systems, as they eliminate the need for expensive and time-consuming piping modifications.
For transit-time liquid meters to function accurately, it is essential that the liquid contains minimal particulate solids or entrained air bubbles, as these can disrupt the sound wave signal and compromise measurement precision.
So far, we have focused on fixed-mount clamp-on flow meters, which are installed in a single location, often with the electronics enclosure mounted to a wall or pipe.
However, the clamp-on transducer design lends itself exceptionally well to portable flow metering solutions. By combining clamp-on transducers with handheld electronics, portable ultrasonic flow meters can be developed.
These portable devices typically come with handheld electronics, transducers, fixtures, and all necessary accessories in a compact carrying case.
Portable flowmeters offer unique applications that fixed-mount flowmeters cannot, such as spot checks, accuracy verification of other flowmeters and temporary replacement of fixed-mount flowmeters.
Spot checking involves taking temporary flow rate measurements where no fixed-mount meter is present, often during flow rate surveys of an entire system. These surveys help users understand flows throughout the system, establish reference baseline flow rates and identify leaks or blockages.
Portable meters can also be used to verify the accuracy of another flow meter, especially if it displays unusual or erratic readings. This verification helps determine whether there is an issue with the process or the meter itself.
In some cases, process facilities require periodic calibration of their instrumentation, which may involve removing a flow meter for calibration at an accredited facility.
During this time, a portable flow meter can serve as a temporary placeholder until the fixed-mount meter is reinstalled.
Fuji Electric's portable flowmeter offers various signal output options, such as analog output, enabling seamless integration with control systems.
By utilizing both fixed-mount and portable ultrasonic clamp-on flow meters, process operators can maximize process visibility while minimizing equipment costs.
A common strategy is to use fixed-mount meters for critical measurements and portable meters for temporary measurements, covering any potential blind spots.
Additionally, Fuji Electric offers ultrasonic portable flow meters rental programs for temporary needs.
Numerous industrial professionals employ a mix of fixed-mount and portable ultrasonic clamp-on flow meters to optimize process monitoring and maintain cost-efficiency in equipment investments.
In recent times, the progress of electricity visualization for energy-saving has played a crucial role in reducing greenhouse gas emissions.
However, efforts to save energy in steam usage have lagged behind due to the challenges associated with visualizing steam loss.
To tackle this issue, there was a need for clamp-on ultrasonic flow meter for steam that allows the identification of steam loss without cutting the pipes.
While clamp-on flow meters have been utilized for liquid measurements, developing products for steam has been difficult due to its extremely low ultrasonic transmission coefficient from pipes.
By employing noise reduction technologies, lamb wave utilization, and advanced signal processing, Fuji Electric has successfully launched in 2019 the world's first product capable of measuring low-pressure saturated steam..
The Fuji Electric FSJ ultrasonic steam flowmeter uses temperature or pressure transducers to measure thermal energy in saturated steam applications.
With their wide range of communication options, FSJ series meters enable easy integration into building automation systems.
While clamp-on ultrasonic flow metering technology offers numerous benefits, it is crucial to consider the intended application to determine its suitability.
Like any flow metering technology, clamp-on ultrasonic flow meters have their unique set of advantages and disadvantages.
The adoption of clamp-on ultrasonic flow metering is expected to expand, as the advantages supersede the limitations for a growing range of flow metering applications. While the technology is currently prevalent in certain industries, its reach will extend to other sectors.
Clamp-on ultrasonic flow meters offer numerous advantages to process operators seeking to measure liquid and steam flow rates across a wide variety of pipe sizes and materials.
The non-invasive installation eliminates the need for costly pipe modifications or regular maintenance while providing accurate readings without measurement drift over time.
Moreover, portable clamp-on ultrasonic flow meters present unique applications that fixed-mount meters cannot achieve, such as on-the-spot monitoring and verifying the accuracy of another flow meter.
With their versatility and cost-saving benefits, it is easy to understand why many industry professionals utilize both fixed-mount ultrasonic flow meters and portable clamp-on ultrasonic flow meters to optimize their processes.
When it comes to optimizing process visibility and reducing costs, clamp-on ultrasonic flow meters provide a unique set of advantages.
With non-invasive installation requiring no piping modifications or maintenance needs, these devices are highly versatile in applications such as district energy systems, industrial plants, pharmaceutical manufacturing, water treatment facilities, oil and gas operations, food and beverage processing, chemical production, HVAC systems and spot checking for flow rate surveys.
Portable models are likely to serve as an entry point for many users, given the lack of alternative commercially viable portable flow metering options.
Ultimately, the selection of any process instrumentation, including flow meters, depends on the specific application requirements and determining the most suitable technology to meet those needs.
