Air flow meters are most frequently used to infer mass flow after taking various flow measurements such as absolute pressure, differential pressure, viscosity and temperature as air flows through a tube. Besides air, these flow meters can also measure many different types of gases including nitrogen, oxygen, argon, helium, hydrogen, natural gas and carbon dioxide.
Air flowmeters have many plastic or metal parts that work together to produce a reading. The parts are manufactured to very close tolerances in order to provide readings with an accuracy as low as 2%. Air flow meters come in several types. Besides variations such as size or material, they may vary in pressure range, switching technology, and the presence and type of transmitters. These variations allow air flow meters to have applications in several industries.
In the medical industry, flow meters are used to measure patients’ air intake, allowing physicians to further determine the severity of any illness. These types of flow meters are called peak flow meters and are particularly beneficial for asthma patients. Air flow meters are also common in the automotive, petroleum and gas, utility services, HVAC, food processing, and raw materials industries.
There are four main categories of air flow meters that are identified based on how they obtain a reading of the flow rate or quantity of air.
Differential pressure air flow meters are the most common type. These devices take both a primary and a secondary measurement and report the difference. The first measurement causes a change in kinetic energy by directing the air through a hole or orifice in the flow meter which is measured by the second element.
Positive displacement meters separate the air flow into specific volumes which are then counted. Vanes, gears, pistons, or diaphragms are commonly used to divide the air which is counted mechanically or electronically.
Velocity air flow meters use a depth measurement and the average air velocity of the flow to produce a reading. They have a greater range than differential pressure devices.
The last category is true mass air flow meters. They directly measure the mass of the fluid, not the volume; two common kinds are thermal meters and Coriolis flow meters.
Air flow meters vary in how they obtain and report a reading but the list of parts may include pressure ports, bellows, spindles, pinions, gear mechanisms, gauges, cell caps, magnets, sensors, pistons, nuts, seals, levers, and more.