USER'S GUIDE ____________________________________________________________________
24 __________________________________________________________________ M210543EN-F
As PWD22/52 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.
Temperature Sensor
The primary temperature sensor of PWD22/52 is a Pt100 thermistor. The
temperature is measured once a minute using a high resolution A/D
converter. The sensor temperature (TS) is used to select an initial default
precipitation type for the algorithm.
Possible temperature sensor locations in the PWD22/52 include:
- Inside the cross arm
The cross arm temperature sensor provides adequate performance for
most PWD22/52 applications.
- Inside an external radiation shield
In some conditions, for example in calm winds, the hood heaters can
cause a bias in the cross arm temperature measurement due to heat
conduction. The optional temperature sensor in an external radiation
shield avoids this bias.
Temperature measurement plays a role in identifying freezing conditions.
Due to the effects described above, in some applications it is beneficial to
augment the PWD temperature sensing with data from an external
temperature sensor and/or an additional ice detection sensor. Reporting
freezing conditions should be complemented with an expert familiar with
local conditions.
Background Luminance Sensor PWL111
(optional)
PWL111 is used as a day/night switch for distinguishing day and night
conditions. Its luminance measurement is rudimentary and indicative.
PWD22/52 measures the PWL111 signal every second and calculates a
new one-minute running average 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 in the same way as the other
PWD22/52 heaters.
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