METER ATMOS 41 - 3.4 VAPOR PRESSURE;RELATIVE HUMIDITY SENSOR

14
SYSTEM
Splash
guard
Sintered
glass plate
Figure7 Anemometer
The ATMOS 41 measures wind speed every 10 s and keeps a running average of the last
10 measurements. If an instantaneous measurement is more than eight times the running
average, the instantaneous measurement is rejected. It is not reported as the maximum gust
or included in the data that are averaged over the output interval.
For normal ATMOS 41 use cases, this is an effective method for eliminating inaccuracy
resulting from spurious spikes in wind speed (e.g., bumblebee checking out the ultrasonic
path). In special use cases where data are output frequently and large step changes in wind
speed are present (e.g., turning on a wind tunnel), this spike rejection algorithm may result in
an error code being output.
3.4 VAPOR PRESSURE/RELATIVE HUMIDITY SENSOR
The vapor pressure sensor (Figure8) on the ATMOS41 is located behind the circular Teflon
®
screen in the same housing as the sonic transducers. The Teflon screen protects the sensor
from liquid water and dust while allowing water vapor to freely pass to the sensor and
equilibrate with air vapor pressure. The sensor measures relative humidity and temperature
in addition to computing vapor pressure.