The Sunshine Duration sensor LPSD18 measures sunshine status and duration. The WMO (World Meteorological Organization) defines the sunshine duration as the time during which the direct solar radiation exceeds the level of 120 W/m².
The LPSD18 performs the measure of radiation with an array of photodiodes arranged in a particular geometry which allows to obtain an accurate measurement in any weather conditions. This solution avoids the use of mechanical moving parts and ensures high reliability in the time.
The instrument, besides indicating the presence of sun as required by WMO, measures also direct radiation (SRD), therefore it can be used as a low cost alternative to a pyrheliometer, which use is bound to a solar tracker.
The instrument is available in three versions, which difference depends on the type of output:
- LPSD18.1 – RS485 MODBUSRTU output and volt-free contact output (contact closed = SRD ≥ 120 W/m2, contact open = SRD < 120 W/m²)
- LPSD18.2 – RS485 MODBUSRTU output, analog voltage output 0…1 Vdc, which corresponds to 0…2000 W/m² of direct radiation, and digital output voltage (digital voltage output: 1V = SRD ≥ 120 W/m², 0V = SRD < 120 W/m²)
- LP SD18.3 SDI12 output and volt-free contact output (contact closed = SRD ≥ 120 W/m², contact open = SRD < 120 W/m²)
The LPSD18 is equipped with a heating element separately powered and galvanically isolated, which prevents the formation of condensation on the glass surface onto which the sensitive elements are.
For cold climates, the above-mentioned versions are available with a second heating element (option R, LP SD18.xR), which prevents the formation of ice and prevents snow from settling.