LPS10
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V1.0
3 MEASURING PRINCIPLE
PYRAsense series pyranometers are based on a thermopile sensor. The thermopile
sensitive surface is coated with a black matt paint, which allows the pyranometer not
to be selective at different wavelengths.
Radiant energy is absorbed by the thermopile black surface, thus creating a difference
of temperature between the center of the thermopile (hot junction) and the pyranom-
eter body (cold junction). Thanks to the Seebeck effect, the difference of temperature
between hot and cold junction is converted into a difference of potential.
The pyranometer spectral range is determined by the transmission of the two concen-
tric glass domes, with 50 and 30 mm outer diameters, which also grant the thermopile
a proper thermal insulation from the wind and reduce the sensitivity to thermal irradi-
ance. Furthermore, the domes protect the thermopile from the dust which, depositing
on the blackened part, could change its spectral sensitivity.
The special material used to manufacture the domes allows the spectral range to be
extended to short wavelengths starting from 283 nm.
Considering a standard solar spectrum, the portion of solar irradiation detected by the
pyranometer is greater than 99.8%. Figure 3.1 shows the relative spectral sensitivity of
the LPS10… pyranometers (blue line) and the standard solar spectrum (red line).
Fig. 3.1: LPS10… relative spectral sensitivity and standard solar spectrum
An internal compensation circuit minimizes the change of sensitivity with temperature.
To prevent condensation from forming on the internal side of the dome under certain
climatic conditions, silica-gel is inserted inside the pyranometer to absorb moisture.
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