How ultrasonic flow meters work?
There are several types of ultrasonic flow meter technologies available on the market. This information was designed to help users understand some basic differences between the technologies so that it will be easier to select the correct type for their application.
Ultrasonic flow meters are advanced devices that use sound waves to measure the flow of liquids or gases in a pipe. They are popular because they offer non-invasive, accurate flow measurement without the need to cut into pipes or disrupt the process. Instead, ultrasonic flow meters attach to the outside of the pipe and use sound waves to calculate flow rates.
What is an Ultrasonic Flow Meter?
An ultrasonic flow meter is a device that measures the flow rate of a fluid by using high-frequency sound waves, beyond the range of human hearing (typically above 20 kHz). These sound waves travel through the fluid in the pipe, providing precise flow measurement without needing to penetrate or alter the pipe structure.
Ultrasonic flow meters work by sending high-frequency sound pulses through the fluid. When these sound waves pass through a moving fluid, their speed and path are slightly altered, depending on the direction and velocity of the flow. By calculating these changes, the meter determines the fluid’s flow rate accurately and in real time.
This method is inspired by natural ultrasonic detection found in animals like bats, which use echolocation by emitting high-frequency sounds and listening for their echoes to navigate. Similarly, elephants use subsonic frequencies to communicate over long distances, proving how sound waves can travel through air or even solid structures over vast ranges. In an ultrasonic flow meter, the sound waves bounce within the pipe, but with precise sensors and calculations, the meter can determine flow rates with great accuracy.
The animation shows a device that is both a wave emitter and receiver. This is how high frequency transducers are able to measure distance. If the sonic velocity of the media (in this case air) is fixed and known, then the time taken for the wave to transmit and bounce back to the source will be directly proportional to the level or distance.
Even though the sound waves are above the hearing level, we can understand how the meters work by observing how sound waves act at the audible level. By visualizing this phenomena, it is easier to comprehend how ultrasonics are used in industry using transit-time technology.
Lets take for example how transit-time ultrasonic technology is used in flow measurement. In this case, the distance is now fixed and transducers are placed upstream and downstream of the flow. The variable is now the flow rate of the fluid.
Understanding Transit-Time Flow Meters
Most transit-time flow meters use a simple technique to measure flow. If this technique is combined with cross-correlation and advanced signal processing, it is possible to measure liquids with some amount of solids and aeration. EESIFLO design and manufacture transit-time cross-correlation flow meters which vastly improve accuracy, repeatability as well as user experience. Sometimes it is helpful to visualize the speed at which these things happen. The following animation produced for a University in Houston TX gives us an idea of just how many signals are constantly being sent to.
Accuracy and repeatability will depend on how well the initial and subsequent signals are interpreted and the need for cross-correlation techniques and advanced signal processing. The processor capability becomes an issue that needs careful consideration.
The clamp on ultrasonic flow meters have some unique advantages over traditional flowmeters such as the Coriolis, turbine, vortex, magnetic and positive displacement types. Of course, each technology has it it’s own plus and minuses but unlike fixed flow meters (where the pipe must be cut and the process halted to install a meter) the clamp on ultrasonic flow meter can be tested in the field without having to shut down anything. In fact, since there are so many manufacturers of clamp on ultrasonic flow meters, it is possible to test them all on site to see which technology works best. This takes the pressure off the buyer who is able to “kick the tyres” before deciding to make a larger capital investment in the clamp ons.
What is the difference between Transit-time and Doppler flow meters?
Doppler flow meters come in handy in situations that are often impossible for transit time flow meters to work well. This is because we are measuring the doppler shift. A continuous wave is sent through the pipe into the liquid which will reflect off particles or undissolved gas or air bubbles. The return signal will be a different frequency (doppler shift) which is proportional to the flow velocity of the liquid. This technology assumes that the particles or air bubbles are moving at a speed close to the flow velocity, hence the need for a minimum velocity in order to obtain the required accuracy.
PRODUCT
Doppler Flow Meters
Choosing the Right Meter
When deciding between transit-time and Doppler flow meters, it’s essential to consider the specific characteristics of the fluid being measured and the application requirements. Transit-time meters are preferable for clean fluids, while Doppler meters offer a reliable solution for more challenging conditions where the flow may contain particulates or gases.
In Rayville, we test our flow meters before shipping them to you. We want to make sure that you receive exactly the kind of flow meter you need.
For expert guidance on selecting the right flow meter for your needs, don’t hesitate to