Coriolis flowmeters – what you need to know
Flowmeters come in a variety of forms and operate on a range of different principles. Choosing the correct flowmeter for your application is vital for ensuring both accuracy, efficiency and value for money.
Coriolis flowmeters are one of the most popular for measuring mass flow – that is, the movement of fluid down a pressure or thermal gradient.
How do Coriolis flowmeters work?
The first question to ask is: What is the Coriolis Effect? Named after French mathematician Gaspard Gustave de Coriolis, it relates to the perceived motion of an object when moving in a straight line over a rotating body or frame of reference.
“One common example given to illustrate the Coriolis Effect is that of a ball propelled through the air a long distance in a straight line from the North Pole toward a target on the equator. By the time the ball arrives at the equator, it will not land at its apparent target, because the earth will have rotated sufficiently underneath the moving ball so that it will land some distance away from the perceived target on the equator. From the perspective of the person standing where the ball is “thrown,” the ball will appear to have curved.”
A Coriolis flowmeter works around this principle. When the fluid enters the sensor, it is split into two tubes and “a drive coil stimulates the tubes to oscillate in opposition at the natural resonant frequency.” Flowmeter manufacturer Emerson explains on its website.
“As the tubes oscillate, the voltage generated from each pickoff creates a sine wave. This indicates the motion of one tube relative to the other. The time delay between the two sine waves is called Delta-T, which is directly proportional to the mass flow rate,” Emerson’s explanation continues. The information is fed into a sensor, and translated into information on flow.
Coriolis flowmeter pros and cons
Coriolis flowmeters are used in a variety of industries, including oil and gas, water and wastewater, power, chemical, food and beverage, and life sciences. They are particularly well suited to measuring corrosive fluids, for instance in chemical processes.
Because Coriolis flowmeters are relatively insensitive to density when compared to other flowmeters, they are a good solution for applications where the physical properties of the fluid are not well known. They are mass flowmeters, meaning they can be useful for measuring gases, which are more affected by pressure and temperature than liquids.
Coriolis flowmeters are approved for custody transfer applications, and can achieve a relatively high accuracy of 0.1%, making them a particularly popular choice.
The major downside of Coriolis flowmeters is the price, which is high compared to most other types of flowmeter.
Coriolis flowmeter manufacturers
There are a number of companies who manufacture Coriolis flowmeters. Some specialise in Coriolis principled devices, while others include them as part of a broader portfolio. Some major Coriolis flowmeter manufacturers include: