User's Guide _______________________________________________________________________
22____________________________________________________________________ M210543EN-B
0008-012
Figure 4
RAINCAP
®
Block Diagram
The RAINCAP
®
sensing surface is heated by the heating element built
into the surface. The heating power varies by software control.
PWD22 is equipped with a double-plate RAINCAP
®
to improve
drizzle detection in certain conditions.
When the heating of the sensor elements is switched off, they become
very sensitive to ambient moisture. If the relative humidity of the air is
more than about 70 %, the surfaces produce a measurable signal even
with no precipitation. In PWD22 this is used as an estimated humidity
measurement. The estimated humidity is used to separate between
dust and mist.
As PWD22 can detect the beginning of precipitation from the optical
signal, RAINCAP
®
can be used as a cross-check for the detection of
above zero temperatures. This eliminates false detection of rain caused
by for example mosquitoes.
Background Luminance Sensor
PWL111 (optional)
PWL111 is used for aeronautical visibility calculations, for example,
to distinguish day and night conditions for a visibility calculation.
The PWL111 signal is measured every second by PWD22. A new
one-minute running average is calculated every 15 seconds. The one-
minute average is reported in the corresponding messages. The value
range is 4 ... 20000 cd/m
2
. The sensor heaters are controlled as the
other PWD22 heaters.
