The need to measure the flow rate in a pipe or tube has many aaplications for individuals and in
business. Generally, gases and liquids need to be measured. there are two ways to do this. The
volumetric flow rate is a measure of the volume of the medium by time. The mass flow rate is a
measure of the mass of the medium 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.
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 touch on
how flow meters work in industry and for individuals.
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.
One example of a principle governing the name of a meter is the Coriolis flow meter. It uses the
Coriolis effect to determine the mass of a fluid passing through two vibrating tubes or pipes. The
idea being that by understanding the change in the characteristics of the wave patterns in the
vibrating tubes, you can correlate the flow rate of the substance passing through.
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 meter and the Doppler shift flow meter.
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.
Receivers at opposite ends of the pipe record the sound waves. One pulse of ultrasonic wave is sent
off in the direction of the flow while the other is in the opposite direction.
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 flow meters also use waves to determine the flow rate. They work on the principle that
a sound wave that bounces off a moving particle in the medium has it's frequency and amplitude
changed. By determining the change in these dimensions, the flow rate of the medium can be
determined.
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.
The float indicates a measurement on the calibrated tube. This is a correlation of the flow rate of
the substance that has just passed through the tube. An example of such a device is the peak flow
meter that is used to measure lung capacity. Peak flow meters help people with asthma determine if
they are likely to have an asthma attack.
