The DigitalFlow GC868 clamp-on gas flowmeter is a complete ultrasonic flow metering system for measurement of most gases, including Natural gas, Compressed air, Fuel gases, Erosive gases, Corrosive gases,Toxic gases, High-purity gases, Air separation gases and Steam.
Historically, clamp-on flow metering was limited to liquids because existing methods could not work on metal pipes containing gases. Several years ago GE developed a new technology that extends all the benefits of clamp-on flow metering to gas measurement. This breakthrough clamp-on gas flowmeter technology has continued to improve, resulting in the second generation of the DigitalFlow GC868 flowmeter. This remarkable ultrasonic flowmeter works with gases at high or low pressure in pipes made of metal and most other materials. The Panametrics Ultrasonic Clamp-on DigitalFlow GC868 flowmeter can be used to measure the flow of any gas. It is especially useful for metering erosive, corrosive, toxic, high-purity or sterile gases, or in any application where penetrating the pipe wall is undesirable. Since no tapping or cutting of the pipe is required, permanent installation costs are significantly reduced. The meter has no wetted or moving parts, rarely requires maintenance, causes no pressure drop and has very wide rangeability. The new meter was tested extensively on metal tubes with diameters as small as 0.75 in (20 mm) and pipes as large as 24 in (600 mm). Suitable applications for this meter include flow measurements of air, hydrogen, natural gas, steam and many other gases. Using patented Correlation Transit-Time™ detection techniques, demonstrated accuracy is superb at better than ±2 percent of reading with ±0.5 percent repeatability. A DigitalFlow GC868 system comprises the DigitalFlow GC868 electronics, a pair of advanced clamp-on gas ultrasonic transducers, a preamplifier, and a clamping fixture for mounting the transducers on the pipe.
One of the biggest challenges in developing clamp-on ultrasonic transducers for gas applications is the difficulty in transmitting a coded ultrasonic signal through a metal pipe wall, through the gas, and then back through the pipe wall to the second transducer that is waiting to receive the signal. In gas systems, only 4.9×10–7 percent of the transmitted sound energy is actually received by traditional ultrasonic transducers. This simply isn’t enough to produce reliable measurements. The new line of clamp-on gas transducers produces signals that are five to ten times more powerful than those of traditional ultrasonic transducers. The new transducers produce clean, coded signals with very minimal background noise. The result is that the DigitalFlow GC868 flowmeter system performs well even with low-density gas applications.
Because the transducers clamp onto the outside of the pipe, they do not obstruct the flow inside the pipe. This prevents the pressure drops typically caused by other types of flowmeters. The DigitalFlow GC868 has no components that will foul or collect debris, and there are no moving parts to wear out. As a result, it requires no lubrication and little or no routine maintenance. Wide Range of Clamping Fixtures Available Transducer alignment is crucial in obtaining accurate measurements in clamp-on gas installations. GE offers a wide range of clamping fixtures to help ensure proper alignment of transducers with minimal effort.
Straightforward installation is another advantage of the DigitalFlow GC868 flowmeter. The system consists of one pair of transducers per channel, a clamping fixture, a preamplifier, and an electronics console. The transducers are clamped onto the outside of the existing pipe. The electronics console can be located up to 500 ft (150 m) from the transducers. Set-up and output options allow the DigitalFlow GC868 flowmeter to be customized for any process. For maximum accuracy, use a two-channel meter to average flow measurement along two different paths at the same location or to measure at two different places in the same pipe. A two-channel meter can also measure the flow in two separate pipes.
New technology also allows clamp-on measurement of steam mass flow. Conventional steam flowmeters, such as vortex shedding meters, orifice plates or turbines, cause permanent pressure drop. This robs steam of its energy and slows down the process until more steam can be generated. Often, more than one meter may be needed to handle low and high loads separately due to the limited turndown capability of these kinds of meters. The DigitalFlow GC868 flowmeter eliminates both of these problems. The process does not need to be shut down to install the meter and there’s no pressure drop, saving time and money. The DigitalFlow GC868’s high turndown capability allows measurement of both low- and high-flow conditions with a single meter. The new transducers are available for process temperature as high as 230°C (446°F), covering a wide range of steam applications. The DigitalFlow GC868 is equipped with steam flow tables for calculating steam mass flow when the meter is configured with appropriate (process dependent) auxiliary inputs for temperature and pressure.