Flow meters are devices that are used to measure the flow rate of a certain liquid or gas. They can measure these substances in terms of the volumetric flow rate or the mass flow rate. The volumetric flow rate is generally given in m3/second. The mass flow rate is given in kg/second.

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.

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.

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.

The ultrasonic flow meter transmits two ultrasonic waves in opposite directions of a pipe where a liquid or gas is flowing.

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 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.