Some ultrasonic flowmeters use clamp-on transducers that can be mounted external to the pipe and do not have any wetted parts. Temporary flow measurements can be made using portable ultrasonic flowmeters with clamp-on transducers. Clamp-on transducers are especially useful when piping cannot be disturbed, such as in power and nuclear industry applications.
In addition, clamp-on transducers can be used to measure flow without regard to materials of construction, corrosion, and abrasion issues. However attractive, the use of clamp-on transducers introduces additional ultrasonic interfaces that can affect the reliability and performance of these flowmeters.
In particular, if not properly applied and maintained, attenuation of the ultrasonic signal can occur at the interfaces between the clamp-on transducers and the outside pipe walls, and between the inside pipe walls and the fluid. Ultrasonic flowmeters are commonly applied to measure the velocity of liquids that allow ultrasonic waves to pass, such as water, molten sulfur, cryogenic liquids, and chemicals.
Transit time designs are also available to measure gas and vapor flow. Be careful because fluids that do not pass ultrasonic energy, such as many types of slurry, limit the penetration of ultrasonic waves into the fluid. Transit time ultrasonic flowmeters can fail to operate when an opaque fluid weakens the ultrasonic wave to such an extent that the wave does not reach the receiver. In this application, the ultrasound is transmitted from the first transducer and travels through the pipe wall, through the liquid, then reflects off the back wall of the pipe, then travels through the pipe wall, and is picked up by the second transducer.
The same process is then repeated in reverse as the second transducer transmits the ultrasound. The angle of the ultrasound path is calculated by knowing the speed of sound of the pipe and the liquid. This angle is used in a common trigonometry equation to convert the ultrasound path into a straight line in the pipe. This will be the velocity of the liquid in the pipe.
While still requiring sections of straight pipe upstream of the measurement location, the process does not require shutting the system down to install, making maintenance and upkeep of transit-time meters much more attractive.
Low maintenance: There are no blades to wear out or bearings to replace as in turbine meters, nor are there electrodes that can foul over time as in magnetic flow meters. Let's look at the principle using direct contact diagonal mode as an example.
Each of the sensors works as a signal source and receiver. They send an ultrasonic pulse through the moving flow. When sensors send the ultrasonic pulse through the moving flow they have different travel times depending on direction. Such signal accelerates when directed along the flow upstream and slows down when directed against it downstream. Transit time flow meters is an ideal solution for pure liquids or gases. The presence of solid parts or bubbles effects on its results.
Transit time flow meters are used to measure gas, steam and vapors. There are two categories of flow meters according to the type of installation:. Inline flow meter is device that mounting inside the pipeline system this is described above.
Clamp-on flow meter also called strap on are portable compact device for measurements without interrupting in a pipeline. These flow meters are attached to the outer surface of the pipeline. The most popular mounting approach for clamp flowmeters is V method with 2 paths. Two different sensors send two signals to each other. Such signals are directed diagonally into the wall of the pipe, from which it is reflected and hits the other sensor and vice versa. One of them moves upstream with higher speed and other moves downstream with lower speed.
The trajectory of these waves looks like the letter V. Clamp on ultrasonic flow meters will be an ideal solution for temporary measurements. It doesn't require mounting inside the pipeline, so it can be used with sanitary and corrosive and abrasive materials. Open channel flow meters are created for measuring level in open vessels or channels. Such sensor is mounted on the top above the flow.
It sends high frequency ultrasonic sounds to the flow surface. To learn more about flow meters contact our experts today! Sign up for our newsletter to get industry trends, educational content, and product updates, the way you want to receive them.
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