Air meter is a device which is used to measure the rate at which the air flows. This means that an air meter measures the velocity of air. In addition to velocity, these can measure its pressure as well. A few among these are even capable of detecting the wind direction.
Types of Air Flow MeterBasically we found four types of air flow meter which are -
- Hot Wire Air Flow Meter
- Vane Air Flow Meter
- Cup Anemometer
- Pitot Tube Air Flow Meter
Hot Wire Air Flow MeterThese kind of air flow meters use a hot wire mass air flow sensor to measure the flow rate of air. These sensors are made of short, circular shaped platinum- or tungsten-like resistive wires which are heated in prior upto a certain degree of temperature. These sensors are then placed in central position across the air stream. The flowing air cools-off the wire which in turn causes its resistance to drop-off. This drop in resistance of the wire gives a measure of its flow rate.
Vane Air Flow MeterThese air flow meters employ vane type mass air flow sensors to measure the amount of air passing through them. Basically they comprise of a metered vane which is placed along the direction of the flowing air. This vane will be connected to a spring and usually be placed in its rest position. However once the air starts to flow, this vane will get displaced under the pressure of the spring. This deflection is converted into the voltage signal with the help of a potentiometer which is then used to determine the rate of air flow.
Cup AnemometerThis kind of air flow meter has an arrangement of vertical shaft which supports the horizontal arms carrying four hemispherical cups. At any instant of time, there would be atleast one cup facing the direction along which the air flows. As a result, flowing wind causes the shaft attached to the device to rotate. The number of turns made by the shaft over a particular interval of time would give us a measure of speed with which the wind blows across it.
Pitot Tube Air Flow MeterThese air flow meters are usually employed in aircrafts to measure the air speed. They can be either impact or cantilever or static in nature. In pitot-static type, the pitot tube will comprise of two ports - pitot and static. Generally pitot port is inserted into the duct so as to face the air flow. Here pitot port measure the dynamic pressure of air flow while the static port gives an estimate of the static pressure from the small holes present along the tube-side. The difference between these two pressures gives a measure of flow rate of air.
Applications of Air Flow Meter
- Air meters are used in many industries to achieve proper ratio of fuel to compressed air which in turn leads to efficient ignition, and hence maximum flame.
- Air meters are used as safety devices in hazardous environments like that of mining and nuclear reactors, in which people are subjective to heavy risks.
- Air flow meters when used as a component in automobiles, ensure that proper amount of air enters into their internal combustion engine.
- Ventilation installations also use air flow meters so as to monitor the air which flows through them.