Pyranometers, pyrheliometers and pyrradiometers have been categorized into three groupings depending
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upon the quality of the instrument. The instrument must meet all the specifications of a given category
before being classified within the category. The highest category for pyranometers is the secondary
standard because the most accurate determination of global irradiance is believed to be the sum of the
direct beam irradiance as measured by an absolute cavity radiometer and the diffuse solar irradiance as
measured by a secondary standard pyranometer shaded from the sun by a disc.
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Pyranometer Specification List
Specification Class of Pyranometer
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Secondary
Standard
First Class Second
Class
Response time: time for 95% response < 15 s < 30 s < 60 s
Zero off-set:
(a) Response to 200 Wm net thermal radiation (ventilated)
-2
(b) response to 5 K h change in ambient temperature
-1
+ 7 Wm
-2
± 2 Wm
-2
+ 15 Wm
-2
± 4 Wm
-2
+30 Wm
-2
± 8 Wm
-2
Resolution (smallest detectable change) ± 1 Wm ± 5 Wm ± 10 Wm
-2 -2 -2
Stability: percentage change in responsivity per year ± 0.8 % ± 1.8 % ± 3 %
Non-linearity:
percentage deviation from the responsivity at 500 Wm due
-2
to change in irradiance within 100 Wm to 1000 Wm
-2 -2
± 0.5 % ± 1 % ± 3 %
Directional response for beam radiation (the range of errors
caused by assuming that the normal incidence responsivity
is valid for all directions when measuring, from any direction,
a beam radiation whose normal incidence irradiance is
1000 Wm
-2
± 10 Wm ± 20 Wm ± 30 Wm
-2 -2 -2
Spectral selectivity:
percentage deviation of the product of the spectral
absorptance and the spectral transmittance from the
corresponding mean within 0.3 :m and 3.0 :m
± 2 % ± 5 % ± 10 %
Temperature response:
total percentage deviation due to change in ambient
temperature within in interval of 50 K
2 % 4 % 8 %
Tilt response:
percentage deviation form the responsivity at 0° tilt
(horizontal) due to change in tilt from 0° to 90° at 1000 Wm
-2
irradiance
± 0.5 % ± 2 % ± 5 %
Table B 1.1. Pyranometer specification list from ISO 9060.
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