Background Luminance Sensor Pwl111 (Optional); Figure 4 Raincap ® Block Diagram - Vaisala PWD22/52 User Manual

Chapter 3 ______________________________________________________ Functional Description
VAISALA _______________________________________________________________________ 23
Figure 4 RAINCAP
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The RAINCAP sensing surface is heated by the heating element built
into the surface. The heating power varies by software control.
PWD22/52 is equipped with a double-plate RAINCAP
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 PWD22/52 this is used as an estimated humidity
measurement. The estimated humidity is used to separate between dust
and mist.
As PWD22/52 can detect the beginning of precipitation from the optical
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signal, RAINCAP
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 PWD22/52. 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
PWD22/52 heaters.
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Block Diagram
can be used as a cross-check for the detection of
2
. The sensor heaters are controlled as the other
0008-012
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to improve