CSD3 measures daily sunshine duration according to WMO definition. Sunshine duration is calculated as the time during which direct solar radiation exceeds 120 W/m2.
CSD3 has no moving parts, making it almost maintenance free and very weather-tolerant. It uses 3 photodiodes to calculate the sunshine duration.
CSD3 includes a replaceable drying cartridge. A humidity indicator indicates when the cartridge should be changed.