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.

However they are most commonly used in industry, notably in machines or processes that require precise amounts of a certain gas or liquid to be applied or added during the manufacturing of an item. This article will cover how some 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.

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.

Ultrasonic and Doppler shift flow meters also use the changes caused to sound waves to correlate a rate of flow for the medium passing through the 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.

The flow rate can be determined by the difference in the timings of each ultrasonic wave provided information on the material of the pipe and some details on the medium being measured are known.

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 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.