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How Do Flow Meters Work - Flowmeter Types And Principles |
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Written by Adrian Fletcher
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Wednesday, 06 August 2008 |
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Liquids and gases passing through a tube or pipe often need to be measured to determine the rate at which they are moving. They are generally measured in terms of their volume or their mass. A volumetric flow rate reading is meters to the power of three divided by time. The mass flow rate is kg's divided by time.
by AdrianFletcher
Liquids and gases passing through a tube or pipe often need to be measured to determine the rate at which they are moving. They are generally measured in terms of their volume or their mass. A volumetric flow rate reading is meters to the power of three divided by time. The mass flow rate is kg's divided by time.
There is a diverse range of uses for flow meters. They have applications for individuals, a common one being to help people with asthma. A peak flow meter measures the lung capacity when someone exhales. This can help to predict an imminent asthma attack.
Other than that, flow meters are used in many industries, like the food processing industry, water management, semi conductor fabrication and many others. This article will give a brief overview of how flow meters work.
Flow meters are generally classified by the principal that governs their operation or possibly by their applications. For instance, mass flow meters measure the flow rate of a medium in terms of it's mass.
The Coriolis flow meter in an example of the principle determining the name. The Coriolis effect is the force that a liquid experiences in a circular motion. In the flow meter, vibrating pipes cause the liquid to move in a circular motion. If the wave motion of the vibrating pipes is known before the liquid passes through the pipes then the flow rate of the liquid can be determined.
The ultrasonic flow meter and Doppler shift flow meter also use wave mechanics to determine the flow rate of the medium passing through a pipe or tube.
For an ultrasonic flow meter, flow rate is measured by contrasting the measurements of two ultrasonic waves. These two waves are set off at the same time as each other but from different directions.
The transmitters also act as a receiver of the wave sent by the other transmitter. One pulse of sound is sent in the direction of the flow and the other is sent against the flow.
If various constants are known about the metal of the pipe and the liquid or gas passing through the pipe, a rate of flow can be derived from the time it takes each sound wave to reach the receiver.
Doppler shift meters use a sound wave that bounces off matter in the medium passing through the pipe. Due to the Doppler effect, the frequency of the waves changes when it strikes a moving object. This change in the frequency can be used to determine the flow rate of the medium passing through the pipe.
A more traditional type of flow meter is the variable area flow meter that uses a float in a calibrated tube. When a substance passes through the tube, the float is displaced by the flow.
By taking the reading from the calibrated tube an indication of the flow rate can be determined. This is the principle of the peak flow meter used for lung capacity and asthma.
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