Sunshine duration is determined by CSD3. Sunshine duration is defined by WMO as the time during which the direct solar radiation exceeds the level of 120W/m². It does not have any moving components and makes use of three photo-diodes with specially designed diffusers to make an analogue calculation of sun exposure.
The switching of the output is done to high or low in order to indicate sunny or not sunny conditions. The calculated direct irradiance value is also available. CSD 3 operates from 12VDC power and has built-in heaters to dissipate rain, snow and frost. These are normally switched externally but an optional internal thermostat control is available. It can be observed from the humidity indicator when a change of drying cartridge is required.
A waterproof plug-and-socket cable connection is provided for easy installation and servicing. The larger screw on drying cartridge is easier to change at extended intervals.