Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 101)

Pyranom eters, pyrheliom eters and pyrradiometers have been categorized into three groupings depending
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upon the quality of the ins trum ent. T he ins trum ent mus t m eet all the specifications of a given c ategory
before being classified within the category. T he highest category for pyranometers is the secondary
standard because the m ost accurate determ ination of global irradiance is believed to be the sum of the
direct beam irradiance as m easured 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 Pyranom eter 27
Secondary
Standard
First Class Second
Class
Response tim e: tim e for 95% response < 15 s < 30 s < 60 s
Zero off-set:
(a) Response to 200 W m net therm al radiation (ventilated)
-2
(b) response to 5 K h change in am bient tem perature -1
+ 7 W m -2
± 2 W m -2
+ 15 W m -2
± 4 W m -2
+30 W m -2
± 8 W m -2
Resolution (sm allest detectable change) ± 1 W m ± 5 W m ± 10 W m -2 -2 -2
Stability: percentage change in responsivity per year ± 0.8 % ± 1.8 % ± 3 %
Non-linearity:
percentage deviation from the responsivity at 500 W m due
-2
to change in irradiance within 100 W m to 1000 W m -2 -2
± 0.5 % ± 1 % ± 3 %
Directional response for beam radiation (the range of errors
caused by assum ing that the norm al incidence responsivity
is valid for all directions when m easuring, from any direction,
a beam radiation whose norm al incidence irradiance is
1000 W m
-2
± 10 W m ± 20 W m ± 30 W m -2 -2 -2
Spectral selectivity:
percentage deviation of the product of the spectral
absorptance and the spectral transm ittance from the
corresponding m ean within 0.3 :m and 3.0 :m
± 2 % ± 5 % ± 10 %
Tem perature response:
total percentage deviation due to change in am bient
tem perature 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 W m
-2
irradiance
± 0.5 % ± 2 % ± 5 %
Table B 1.1. Pyranom eter specification list from ISO 9060.