KANOMAX 6036 Multi-function thermal anemometer User Manual - Manual (Page 31)

30 Air Velocity Compensation
§ 10 Air Velocity Compensation
When the heated air velocity sensor of the instrument is exposed to
airflow, the heat is drawn from the sensor. The instrument obtains
air velocity readings by using this relationship between the amount
of heat removed (heat dissipation) and 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 is 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).
Influence of Air Temperature
The instrument is a hot-wire anemometer, which measures the air
velocity by using heat dissipation amount. Thus if temperature
compensation is not provided, air velocity readings will be affected
by the ambient air temperature change even the air velocity is
consistent. In order to prevent such influence, the instrument is
equipped with a temperature compensation circuit for measuring
and compensating the air temperature in the range of 5°C to 60°C
Influence of Atmospheric Pressure
The instrument is calibrated under atmospheric pressure of 1013
hPa. 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.
Uc
Pm
Um
 
1013
Where; Um: Actual Air Velocity [m/s]
Uc: Indicating Value
Pm: Atmospheric Pressure at the Measuring Point [hPa]
Influence of Air Composition
Compensation if required if 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.