11. Air Velocity Compensation
The air velocity sensor of this instrument is heated. The air flowing past the heated sensor removes heat from the
sensor. The instrument uses the relation between how much heat removed (dissipation heat) and air velocity to
indicate the air velocity.
Since the instrument is calibrated with clean airflow with normal temperature and pressure, when the condition of air
to be measured is different from that of the air used for calibration, the heat dissipation amount will differ even when
the velocity is consistent (i.e. velocity reading is influenced by the condition of air).
11.1 Influence of Air Temperature
The instrument is a hot-wire anemometer, which measures air velocity using a heat dissipation method. Thus, if
temperature compensation is not provided, air velocity readings will be affected by ambient air temperature changes
even when the air velocity is consistent. In order to prevent such influence, the instrument is equipped with a
temperature compensation circuit for measuring and compensating for air temperature in the range of 5
℃
to 60
℃
.
11.2 Influence of Atmospheric Pressure
The instrument is calibrated under atmospheric pressure of 1013hPa. Since change in the atmospheric pressure will
influence the heat dissipation amount, compensation of the atmospheric pressure is required. Compensation can be
provided by using the following formula.
Where, Um: Actual Air Velocity [m/s]
Uc: Air Velocity Reading
Pm: Atmospheric Pressure at the Time of Sampling [hPa]
11.3 Influence of Air Composition
Compensation is required when the measurement is to be performed in an environment including any gas other than
air. Compensation shall be performed by calculating the heat dissipation amount from the physical properties of the
gas, and comparing it with the heat dissipation amount of the air.
11. Air Velocity Compensation
35
Uc
Pm
Um
×
=
1013
