Directional Response; Maximum Irradiance; Non-Stability; Spectral Selectivity - Kipp & Zonen SMP series Instruction Manual

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B.11 Directional response

Radiation incident on a flat horizontal surface originating from a point source with a defined zenith position (such as the sun)
will have an intensity value proportional to the cosine of the zenith angle of incidence. This is sometimes called the 'cosine-law'
or 'cosine-response' and is illustrated below.
α = 45 ° α = 0 °
Ideally a pyranometer has a directional response which is exactly the same as the cosine-law. However, in a pyranometer the
directional response is influenced by the detector and by the quality, dimensions and construction of the dome(s). The maximum
deviation from the ideal cosine-response of the pyranometer is given up to 80 ° angle of incidence with respect to 1000 W/m²
irradiance at normal incidence (0 ° zenith angle).
B.12 Maximum irradiance
The maximum irradiance is defined as the total irradiance level beyond which the output is no longer linear and out of specifications.
The analogue output for the SMP's is set to 2000 W/m², which is su cient under normal atmospheric conditions. For special
applications (environmental test rooms) the SMP's can be set higher, up to 4000 W/².
B.13 Non-stability
This is the percentage change in sensitivity over a period of one year. This e ect is mostly due to degradation by UV radiation
of the black absorber coating on the thermopile surface.
Kipp & Zonen recommends recalibration every two years. However, for quality assurance purposes some institutes, companies or
networks may require more or less frequent recalibration. Please read the chapter on the calibration procedure for pyranometers
for more information.
B.14 Spectral selectivity
Spectral selectivity is the variation of the dome transmittance and absorption coe cient of the black detector coating with
wavelength and is commonly specified as % of the mean value.
B.15 Environmental
The SMP series are intended for outdoor use under all expected weather conditions. The radiometers comply with IP 67 and
their solid mechanical construction is suitable to be used under all environmental conditions within the specified ranges.
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