Vaisala PWD22 - Page 65

Chapter 5 ________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 63
where
Light rain limit
=
The maximum rain intensity (mm/h), when
the intensity is reported as light. If rain
intensity is between the above heavy and
light limits, it is reported as moderate.
Snow limit
=
The minimum ratio of optical precipitation
intensity to surface sensor (
RAINCAP
®
)
precipitation intensity, when precipitation is
snow.
A typical value for
Snow limit is 5. Smaller
value directs
PWD22/52 to report more wet
precipitation as snow.
Heavy snow limit
=
The maximum visibility (m) of two-minute
average in heavy snow.
Light snow limit
=
The minimum visibility (m) of two-minute
average in light snow. If snow is detected
and the two
-minute average visibility is
between the above heavy and light limits,
snow intensity is reported as moderate.
DRD scale
=
The scaling factor for the calculated
intensity of the RAINCAP
®
surface sensor.
A typical value for this parameter is 1.0.
To calibrate the precipitation measurement, compare the PWD22/52 rain
amount to measurements made with a suitable reference rain gauge.
Make the comparison after a few rain events with 5 mm or more of total
accumulated rain. Calculate a new scaling factor using the following
formula:
NEWSCALE = OLDSCALE * (REF_AMOUNT / PWD_AMOUNT)
where
OLDSCALE
=
The old value of rain intensity scale.
REF_AMOUNT
=
The amount measured with the reference rain
gauge.
PWD_AMOUNT
=
The corresponding amount measured by
PWD22/52.