How Do Flow Meters Work - Mass And Volumetric Flow Rates

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.

Flow meters have many applications. For individuals, a peak flow meter can measure the lung capacity. This is also used by people with asthma and can be used to determine if an asthma attack is imminent.

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.

There are a wide variety of types of flow meters. They are generally classified by what they do or how they operate. For instance, a mass flow meter is a general classification of flow meter that determines the flow rate of a medium in terms of mass even though the operating principles for each meter may be different.

The Coriolis flow meter is a point in case of a principle giving it’s name to the type of flow meter. The Coriolis effect is the force exerted on a liquid moving in a circular motion. In the flow meter this is done by vibrating the pipes that the liquid passes through. The vibrations (or waves) that are created in the pipes are changed when the liquid passes through them. By knowing the changes in the wave vibrations you can work out the flow rate of the liquid.

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.

Provided some information is known about the type of pipe used and a few constants for the liquid or gas, then the flow rate can be determined from the time difference of each wave.

Doppler shift flow meters use the changes in the frequency and amplitude of a sound wave when it bounces off particulate matter in the liquid that is being measured to determine the flow rate.

A variable area flow meter is a more straightforward meter. It consists of a calibrated tube in which a liquid or gas passes through. In the tube is a float that is displaced by the substance.

The reading on the calibrated tube is a correlation of the flow rate of the substance. The peak flow meter uses this principle to measure the flow rate of the lungs when person exhales.

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