Vaisala FD12P - Manual (Page 75)

Chapter 4 _________________________________________________________________ Operation
VAISALA ________________________________________________________________________ 75
Rain Intensity Scale
The Rain intensity scale parameter is multiplied by the measured raw
intensity, which gives the reported precipitation intensity (optical).
The rain amount is scaled with the same coefficient because the
amount is a direct integral of 15-second intensities.
The typical value for the Rain intensity scale is 0.8. as the optimal
value is complex to determine; it depends on the optical, opto-
electronic, and electronic parameters. No applicable factory
calibration method has been developed yet.
The precipitation measurement can be calibrated by comparing the
FD12P rain amount to measurements made with a suitable reference
rain gauge. Make the comparison after a few rainfalls with 5 mm or
more of total accumulated rain. A new scaling factor can be calculated
using the following formula:
Newscale = Oldscale × (Ref_Amount/FD12P_Amount)
where
Oldscale
= Old value of Rain Intensity Scale
Ref_Amount = Amount measured with the reference rain gauge
FD12P_Amount = Corresponding amount measured by the FD12P
Violent Rain Limit
The Violent rain limit parameter defines the minimum rain intensity
(mm/h), when the intensity is violent.
Heavy Rain Limit
The Heavy rain limit parameter defines the minimum rain intensity
(mm/h), when the intensity is heavy.
Light Rain Limit
The Light rain limit parameter specifies the maximum rain intensity
(mm/h), when the intensity is light. If the rain intensity is between the
above heavy and light limits, it is moderate.
Drizzle Limit
The Drizzle limit parameter refers to the maximum drop size (in
FD12P internal units), which can be detected as drizzle. The typical
value is 15, which has been found to be the optical signal from a 0.5
mm diameter droplet measured by typical FD12P hardware. The