1 Instruments for Measurement of Air Flow
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1 Instruments for Measurement of Air Flow

 Although alternative techniques, such as the pilot traverse method are available, anemometers are generally employed for low velocity air flow measurements. There are two general types of anemometers:

  • (a) The direct-reading anemometer of the electronic type which registers the air velocity almost instantaneously. This has a distinct advantage when measuring at terminals where there is unstable or non-uniform airflow as any instability or random changes of velocity are immediately seen and the true mean of the velocity at a point can be judged. It is also very quick to use.

  • (b) The mechanical type of direct reading anemometer with a rotating vane. The movement is a rotary deflection against the action of a spring.

These types of anemometer are small and compact, easy to read and use, give reasonably steady readings and any fault or inconsistency developing is usually quite apparent. Where a correction chart is supplied with an anemometer the correction factors should be applied to the measured velocities before comparing them. With a good quality instrument in proper repair used by an experienced operator, the probable error on the comparative value obtained will range from a maximum of ±2% when comparing similar velocities to a maximum of ±5% when comparing widely differing velocities.

Parent topic: Appendix 2 - Measurement of Air Flow
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