It is often necessary to measure the flow rate in a pipe or tube both for the individual and for many industries. This is needed both by individuals or in many industries.  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 a measure of the mass of the substance with time.

Flow meters can be used in many ways. For individuals, a common flow meter is the asthma peak flow meter that measures lung capacity. For Asthmatics this can help to predict an attack and help them take preventative action.

However the most varied applications are in the manufacturing industries or water management processes where precise measurements are vital for successful operations. This article will cover flow meter types and how they work.

Flow meter principle are generally classified by the principal that governs their operation or possibly by their applications. 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 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.

Two other examples of flow meters that analyze and calculate changes in waves to reach a measure for a flow rate are the ultrasonic flow metering and the Doppler shift flow meter.

For the ultrasonic flow meter, two transmitters of low frequency sound waves are placed at the ends of a pipe where the measurement is taking place. Each transmitter sends a low frequency pulse of sound.

The transmitters will also play the role of receiver of the wave sent by the other transmitter. One sound wave is sent in the direction of the flow and the other is sent opposite 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. With this information it can work out a flow rate for the substance, particularly slurry.

A variable area flow meter is a more straightforward meter. When a substance passes through the tube, the float is displaced by the flow. 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. One example of this type of meter is the peak flow meter that measures the flow rate of the lungs when a person breathes out.