An Ultrasonic Flow Meter – Basic Principles

Having data on a liquid or gas is needed in many industries where these substances are created or used in the manufacturing of other items. Sensors or meters are needed to determine the mass, volume or velocity of a liquid or gas. In the case of velocity, an ultrasonic flow meter is used. Determining the velocity of a liquid that passes through some form of machinery, for instance, could help to determine if the machine is malfunctioning or if the liquid is not right. This article will cover some of the features of an ultrasonic flow meter so that you can be sure you have what you need.

There are two types of ultrasonic flow meter. The most common type is the transit time flowmeter. This effectively works by having two ultrasonic pulses of 20 kilohertz emitted from different transducers. One pulse is with the flow of the liquid and the other is against the flow. By sensing when each pulse strikes a receiver or sensor, the velocity of the liquid can be determined. The differential transit time of the signals is proportional to the flow rate of the fluid.

In the case of the transit time flow meter, also known as "time of flight" meter, clean liquids are best, although most should be able to tolerate less than five percent solids.

The second type of ultrasonic flow meter utilizes the change in the frequency and wavelength of a sound wave through any medium to determine the velocity of this medium. This is known as the Doppler effect. A sound wave is passed through a pipe containing any liquid that has particulate matter in it. The Doppler shift is measured when the sound wave reflects off the particulate matter. This change can be measured against the original frequency and wavelength to determine the flow velocity.

Doppler shift flowmeters, also known as reflection flow meters, are generally used in liquids that are not considered clean as they need things in the liquid to reflect off.

Some of the features of these types of flow meters include the fact that they are non intrusive. There are no moving parts of the device that come into contact with the liquid or gas. This means that the meters can give highly accurate readings.

Normally, the flowmeter is installed by clamping onto the outside of the pipe and will not interrupt the flow inside the pipe. This helps to get the most accurate measurement and assure that the meter is not affecting the flow.

The flow meter should be able to measure pipe sizes from ten to seven thousand millimeters in diameter. It is also important to make sure that the flow meter can measure hazardous materials. Depending on your needs, you should make sure that the flow meter can measure both gas and liquids.

One of the most important parts of an ultrasonic flow meter is the inputs. You need to have both analogue and digital inputs that are capable of multiple processes for measuring temperature, relays and pressure. In addition these models should be able to log the data without any external help.

A portable non contact ultrasonic flow meter featuring a clamp on design will be able to measure the flow of material through clamp on transducers that attach to the outside of the pipe work.

As you can see, ultrasonic flow meters use the change in the dimensions of a sound wave to determine relevant details in the medium that the sound wave is flowing through. By correlating the changes in the sound wave, determining important data, like the velocity of the medium, is possible.

Go to Gas Ultrasonic Flow Meter for more on how ultrasonic waves are used to measure the mass flow rate of gases.