Kipp & Zonen CSD1, Instruction Manual

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18
The electronics of CSD 1 first determines whether D2 or D3 is receiving
direct radiation (maximum signal). It chooses the detector with the smallest
signal, and assumes that this output represents approximately
1
/
3
of the
diffuse radiation. Some corrections, C, for geometry are made, (see the
formula below).
The value of D1 is reduced by the estimated value of the diffuse radiation to
result in the direct radiation.
Direct radiation = D1 - C * (smallest of D2 and D3)
Where D1, D2, D3 are the signals of detectors D1, D2, D3. C is a geometry correction.
This direct radiation signal can be monitored at one of the instrument outputs
and is compared internally with a voltage reference equivalent to the 120
W/m² level recommended by WMO, in order to switch the sunny/not sunny
output signal for sunshine duration.
Sunshine Duration output high (sunny) if direct radiation > 120 W/m².