Pwd22/52 Reports Precipitation When There Is None; Pwd22/52 Reports Frozen Precipitation During Rain - Vaisala PWD22/52 User Manual

USER'S GUIDE____________________________________________________________________
96 __________________________________________________________________ M210543EN-E
PWD22/52 Reports Precipitation When
There Is None
In temperatures under 0 °C, only the optical measurement is used in
detecting precipitation. In temperatures above 0 °C, the RAINCAP
detection is used in cross-checking the optical detection, and false
detection can only be caused by problems in both measurements.
1. Check that there are no flashing lights close to PWD22/52.
Flashing lights may cause PWD22/52 to detect peaks in the optical
signal.
2. Check that there are no foreign objects in the sample volume. Tree
branches or other moving objects may cause sudden changes in the
scatter signal.
3. Check that receiver is not facing cars passing by. If the sun beams
are reflected from the passing cars towards the receiver, this could
cause false precipitation reports especially in the winter. These
short sun beam reflections can cause short spikes to the PWD22/52
optical signal and they are interpreted as light snow. This might
even happen if there are sharp changes of the lighting condition of
the ground where the receiver is looking at. If the area where the
receiver is looking at is bright and shiny and passing cars cause
shadows to that area, it might be possible that it will cause similar
short spikes to the receiver signal.
4. If the false detection has occurred in temperatures above 0 °C,
®
RAINCAP does not function correctly. The RAINCAP
surfaces should be thoroughly cleaned.
PWD22/52 Reports Frozen Precipitation
during Rain
The ratio of optical intensity measurement to the RAINCAP
measurement is too high.
1. Check the optical calibration and RAINCAP
2. If everything else seems to be functioning correctly, change the
parameter settings.
- If possible, check the accumulated water sum against a reference
rain gauge. This will indicate how close the Rain intensity scale
is to the optimal value. Decrease the scaling factor if the
PWD22/52 rain amount is too high.
- Otherwise, increase DRD scale (the WSET command).
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sensing
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operation.