Drd12 signal processing, Figure 28, Optical signal amplitude distribution (in rain) – Vaisala FD12P User Manual
Page 104: Figure 29, Drd12 surface signal (heavy rain beginning)

User's Guide _______________________________________________________________________
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Figure 28
Optical Signal Amplitude Distribution (in Rain)
DRD12 Signal Processing
The DRD12 output voltage is measured once a second by the DRI21
interface board. With dry surfaces, the voltage is approximately 3 V
and drops when the sensing elements become wet (Figure 29 below).
0110-186
Figure 29
DRD12 Surface Signal (Heavy Rain Beginning)