Hukseflux SR05 series - Appendix On Definition of Pyranometer Specifications

SR05-D1A3-PV manual v1801 73/83
9.8 Appendix on definition of pyranometer specifications
Table 9.8.1 Definition of pyranometer specifications
SPECIFICATION DEFINITION SOURCE
Response time
(95 %)
time for 95 % response. The time interval between the instant
when a stimulus is subjected to a specified abrupt change and the
instant when the response reaches and remains within specified
limits around its final steady value.The response time is a measure
of the thermal inertia inherent in the stabilization period for a final
reading.
ISO
9060-
1990
WMO
1.6.3
Zero offset a:
(200 W/m
2
net
thermal
radiation )
response to 200 W/m
2
net thermal radiation (ventilated).
Hukseflux assumes that unventilated instruments have to specify
the zero-offset in unventilated – worst case – conditions.
Zero offsets are a measure of the stability of the zero-point.
Zero offset a is visible at night as a negative offset, the instrument
dome irradiates in the far infra red to the relatively cold sky. This
causes the dome to cool down. The pyranometer sensor irradiates
to the relatively cool dome, causing a negative offset. Zero offset
a is also assumed to be present during daytime.
ISO
9060-
1990
Zero offset b:
(5 K/h in ambient
temperature)
response to 5 K/h change in ambient temperature.
Zero offsets are a measure of the stability of the zero-point.
ISO
9060-
1990
Non-stability
(change per
year)
percentage change in sensitivity per year. The dependence of
sensitivity resulting from ageing effects which is a measure of the
long-term stability.
ISO
9060-
1990
Non-linearity
(100 to 1000
W/m
2
)
percentage deviation from the sensitivity at 500 W/m
2
due to the
change in irradiance within the range of 100 W/m
2
to 1000 W/m
2
.
Non-linearity has an overlap with directional response, and
therefore should be handled with care in uncertainty evaluation.
ISO
9060-
1990
Directional
response
the range of errors caused by assuming that the normal incidence
sensitivity is valid for all directions when measuring from any
direction a beam radiation whose normal incidence irradiance is
1000 W/m
2
. Directional response is a measure of the deviations
from the ideal “cosine behaviour” and its azimuthal variation.
ISO
9060-
1990
Spectral
selectivity (350
to 1500 x 10
-9
m)
(WMO 300 to
3000 x 10
-9
m)
percentage deviation of the product of spectral absorptance and
spectral transmittance from the corresponding mean within 350 x
10
-9
m to 1500 x 10
-9
m and the spectral distribution of irradiance.
Spectral selectivity is a measure of the spectral selectivity of the
sensitivity.
ISO
9060-
1990
Temperature
response
(interval of 50 K)
percentage deviation of the sensitivity due to change in ambient
temperature within an interval of 50 K the temperature of the
pyranometer body.
ISO
9060-
1990
Tilt response
(0° to 90° at
1000 W/m
2
)
percentage deviation from the sensitivity at 0° tilt (horizontal) due
to change in tilt from 0° to 90° at 1000 W/m
2
irradiance. Tilt
response describes changes of the sensitivity due to changes of
the tilt angle of the receiving surface.
ISO
9060-
1990
Sensitivity
the change in the response of a measuring instrument divided by
the corresponding change in the stimulus.
WMO
1.6.3
Spectral range the spectral range of radiation to which the instrument is
sensitive. For a normal pyranometer this should be in the 0.3 to 3
x 10
-6
m range. Some pyranometers with coloured glass domes
have a limited spectral range.
Hukseflux