Panametrics Large-Pipe, High-Velocity, Clamp-On Gas Flowmeter

The DigitalFlow™ CTF878 clamp-on gas flowmeter utilizes a new technology called correlation tag (patented) to determine gas flow rate. This technique is very different from traditional ultrasonic transit-time measurement and is well-suited for gas applications. The DigitalFlow™ CTF878 can measure a wide range of velocities in small to large pipes up to 46 m/s, giving it broad applicability in gas flow measurement. It is used on plastic and metal pipes from 150 to 750 mm in diameter. Accuracy is excellent – better than ±2 percent of reading – with repeatability of ±0.6 percent of reading. The turndown ratio is 43-to-1.

The DigitalFlow™ CTF878 flowmeter can be used in applications where penetrating the pipe wall is undesirable, making it ideal for erosive, corrosive, toxic, high-purity or sterile gases. Because the pipe is not tapped or cut, the cost for permanent installation is considerably lower than with other meters. There are no wetted or moving parts, there is no pressure drop, and maintenance is seldom required.

A complete system comprises the DigitalFlow™ CTF878 electronics, two pairs of advanced clamp-on gas ultrasonic transducers, two preamplifiers for the receiving transducers and a clamping fixture to mount the transducers on the pipe.

The DigitalFlow™ CTF878 uses an ultrasonic signal pattern recognition technology, called correlation tag, for flow measurement. Correlation tag technology utilizes a total of four clamp-on transducers externally mounted on a pipe. The transducers are arranged in two pairs, one upstream and one downstream. Each pair includes one transmitter sending ultrasound in a continuous wave mode through the fluid to its receiver, forming an upstream and downstream interrogation path. The continuous wave signal is modulated by turbulence and local density variations that are characteristic of a moving gas. Thus, both sets of the received signal contain a unique turbulence signature of the flowing gas. The received ultrasonic signals are demodulated and processed through a correlation algorithm. With turbulent flow conditions, a distinct correlation peak is recorded, which reflects the time it took for the unique turbulence signature to travel past each ultrasonic interrogation path. Since the distance between each interrogation path is defined in the transducer set-up, the flow velocity is determined by dividing distance by the time it took for the turbulence signature to pass between each interrogation path.

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