ISO 9847:1992
(Main)Solar energy — Calibration of field pyranometers by comparison to a reference pyranometer
Solar energy — Calibration of field pyranometers by comparison to a reference pyranometer
Specifies two preferred methods: the outdoor calibration (with the pyranometer in a horizontal position, in a tilted position, or at normal incidence) and the indoor calibration (using an integrating sphere with shaded or unshaded lamp, or at normal incidence). Applicable to most types of field pyranometers regardless of the type of radiation receptor employed.
Énergie solaire — Étalonnage des pyranomètres de terrain par comparaison à un pyranomètre de référence
General Information
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Standards Content (Sample)
INTERNATIONAL
STANDARD
First edition
1992-07-01
-------Pp_-------
Solar energy - Calibration of field pyranometers
by comparison to a reference pyranometer
- Etalonnage des pyranometres de terrain par
Energie solaire
comparaison ZI un pyranometre de rbf&-ence
Reference number
ISO 9847: 1992(E)
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ISO 9847:1992(E)
Contents
Page
-.*.-. 1
l Scope . . . . . . . . . . . . . . . . . . . . . . . . .- - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-.
. . . . .*.*. L. . . . . . . . . . . . . . . . . . .v. 1
2 Normative references
1
3 Definitions . . . . . . . . . . . . . . . . .L.-.-.-.
................ ......... ................................. .......................... 2
4 Apparatus
......................................................... ........ 3
5 Calibration procedure
. 7
6 Certificate of calibratiori . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~._._._.
7 Preckion and srccuracy . .-. . . . . . . . .s. 7
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Annexes
8
A Calibration devices using artificial sources .,.
B Interferences and precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
C Computation of daily average solar angle . 13
D Procedure to deterrnine the ratio of the directional response 14
........................... ................................................... 15
E Bibliography
0 ISO 1992
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permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Genhve 20 9 Switzerland
Printed in Switzerland
ii
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ISO 9847:1992(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide
federation of national Standards bodies (ISO member bodies). The work
of preparing International Standards is normally carried out through ISO
technical committees. Esch mernber body interested in a subject for
which a technical cornmittee has been established has the right to be
International organizations, govern-
represented on that cornmittee.
mental and non-governmental, in liaison with ISO, also take part in the
work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an Inter-
national Standard requires approval by at least 75 Oh of the rnember
bodies casting a vote.
International Standard ISO 9847 was prepared by Technical Committee
ISO/TC 180, Solar energy, Sub-Committee SC 1, Climate -- Measurement
and data.
Annexes A, B, C, D and E of this International Standard are for in-
formation only.
. . .
Ill
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ISO 9847:1992(E)
Introduction
Accurate and precise measurements of the irradiance of the global
(hemispheric4) solar radiation are required in
a) the determi nation of the energy available to flat-plate solar collec-
tors,
the a sses sment of i rf-a diance and radiant exposure
in the testing of
W
solar and non-sola r-rei ated m ateri als tech nologies, and
c) the assessment of the direct versus diffuse solar components for
energy budget analysis, geographic mapping of solar energy, and
as an aid in the determination of the concentration of aerosol and
particulate pollution and the effects of water vapour.
Although meteoroiogical and resource assessment measurements gen-
erally require pyranometers oriented with their axis vertical, appli-
cations associated with flat-plate collectors and the study of the solar
exposure of related materials require calibrations of instruments tilted
at a predetermined non-vertical orientation. Calibrations at fixed tilt an-
gles have applications which seek state-of-the-art accuracy, requiring
corrections for cosine, tilt and azimuth.
iv
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ISO 9847:1992(E)
INTERNATIONAL STANDARD
Calibration of field pyranometers by
Solar energy -
comparison to a reference pyranometer
described methods, provided that the reference
1 Scope
pyranorneter has been calibrated at essentially the
Same tilt from horizontal as the tilt employed in the
1.1 This International Standard specifies two pre-
calibration.
ferred methods for the calibration of field pyrano-
meters using reference pyranometers.
NOTE 1 Pyranometers used for collector tests should
be calibrated using a reference pyrheliometer (see
ISO 9846).
1.2 One method, the outdoor calibration or type I,
employs solar radiation as the Source, while the
other method, the indoor calibration or type II, em-
2 Normative references
ploys an artificial radiation Source.
The following Standards contain provisions which,
1.2.1 The outdoor calibration of field pyranometers through reference in this text, constitute provisions
may be performed with the pyranometer in a hori-
of this International Standard. At the time of publi-
zontal position (i.e. Zero tilt) (type Ia), in a tilted
cation, the editions indicated were valid. All stan-
Position (type Ib), or at normal incidence (type Ic) dards at-e subject to revision, and Parties to
maintaining the receiver surface perpendicular to agreements based on this International Standard
the sun’s beam component. are encouraged to investigate the possibility of ap-
plying the most recent editions of the Standards in-
dicated below. Mernbers of IEC and ISO maintain
1.2.2 The indoor calibration of field pyranometers
registers of currently valid International Standards.
may be performed using an integrating sphere with
shaded (type Ha) or unshaded (type Hb) lamp(s), or
ISO 9060:1990, Solar energy - SpecKcation and
at normal incidence (type HC) frequently using an
measuring
classifkation of instruments fot-
Optical bench to present the receiver surface per-
hemispherical solar and direct solar radiation.
pendicular to the beam of the lamp.
Types lla and llb correspond to an outdoor cali- Calibration of a
ISO 9846:~‘1, Solar energy -
bration under conditions of overcast and sunny sky
pyr-anometer using a reference pyrheliorneter.
with large light cloud fields, respectively. Type Ilc is
comparable with the normal incidence calibration
3 Definitions
of type lc.
For the purposes of this international Standard, the
1.3 The methods of calibration specified are
following definitions apply.
traceable to the worid radiometric reference (WRR);
traceability to the international Pyrheliometric Scale
3.1 altazimuth mount: A tracking mount capable of
of 1956 is not permitted.
rotation about orthogonal altitude and azimuth axes;
tracking may be manuai or by a follow-the-sun
servomechanism. (See also ISO 9846.)
1.4 This International Standard is applicable to
most types of field pyranometers regardless of the
type of radiation receptor employed. In general, all 3.2 global (solar) irradiance: Hemispherical solar
irradiance received by a horizontal plane surface.
pyranometers used for lang-term monitoring of inci-
(See also ISO 9060.)
dent solar irradiance may be calibrated by using the
1) To be published.
1
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ISO 9847:1992(E)
3.3 integrating sphere [hemisphere]: A sphere
4.2.1 For outdoor calibration (type 1)
[hemisphere], generally from 1 m to 4 rn in diam-
The reference pyranometer for outdoor calibration
eter, provided with a planar Segment (usually a
(type 1) should be typically of a higher class (in ac-
horizontal bottom Segment) on which to mount
cordante with the classification given in ISO 9060)
pyranometers (to be compared with an artificial light
than the test pyranometer, and should exhibit a
Source), the sphere wall of which is coated with a
particularly high long-term stability. The depen-
flat, white paint that is as iambertian as possible to
dence of its responsivity on temperature, irradiance,
provide uniform illumination.
tilt and angles of incidence shall be determined!
Within 12 months Prior to its use for calibrating field
3.4 pyranometer: Radiometer designed for meas-
pyranometers, the reference pyranometer should it-
uring the irradiance on a plane receiver sur-face
self be recalibrated outdoors by comparison to a
which results frorn the radiant fluxes incident from
pyrheliometer (see ISO 9846). This recalibration
the hemisphere above within the wavelength range
should be tat-ried out under conditions typical of
0,3 prn to 3 pm. (See also ISO 9060.)
those in which the field pyranotneter and reference
pyranometer will be used. The calibration history of
3.5 Geld pyranometer: Pyranometer usually meet-
the reference pyranometer should be weil docu-
ing second class”) specifications or first class speci-
rnented.
fications, designed for field use and (typically)
C;ontinr~orIc exposure.
If the rneasuring conditions dut-inq calibration devi-
ate strongly from those during the’typical use of the
3.6 reference pyranometer: Weil-maintained
field pyranometer (by more than + 5 “C and + 15”
pyranorneter, selected for its stability and quality,
azimuth angle), a reference py&nometer 07 the
used exclusively to calibrate other instruments.
Same type that has been calibrated under similar
conditions should be used.
3.7 test pyranometer: Pyranometer being cali-
brated, regardless of its classikation or its
4.2.2 For indoor calibration (type II)
photoreceptor type.
The reference pyranometer for indoor calibration
(type II) shall be of the Same type as the test
3.8 tilt angle: Angle between the vertical and the
pyranometer (to avoid errors that may be caused by
pyranometer axis (which is eq[Jal to thc angle be-
the artificial radiation employed; these errors may
tween the horizontal plane and the plane of the de-
arise mainly from imperfect homogeneity of the
tector surface).
Source beam or from an imperfect match to the solar
spectrum). In addition, the pyranometer shall meet
3.9 calibration factor: Multiplicator, used to derive
the requirements specified in 4.2.1.
the global solar irradiance from the measured out-
put (voltage). The units are those of the reciprocal
value of the responsivity (e.g. Watts per Square me- 4.3 Integrating sphere or hemisphere
tre per microvolt).
For type Ila or Ilb calibration (see 5.3.1), an inte-
grating sphere or hemisphere (see 3.3) is required.
Suitable apparatus are described in annex A for in-
4 Apparatus
formation.
4.4 Precision calibration table
4.1 Digital electronie readout device
A precision calibration table is required for all hori-
Any digital microvoltmeter having an accuracy of
zontal and fixed-angle tilt calibrations. lt shall be
better than $- 0,l % may be employed. Data loggers
level at 0” tilt (i.e. horizontal) and shall be able to
with print-out shall be capable of a measurement
be tilted over a suitable range of angles from the
frequency of at least two per minute. A data logger
horizontal with an uncertainty of less than 0,3*.
having at least a three-channel capacity may be
IJSefuI.
NOTE 2 The deviation between the tilt angle of the ref-
erence pyranometer and that of the field pyranometer
should be not more than 0,l O which means that the tilt of
4.2 Reference pyranometer
the pyranometers has to be finely adjusted. If the cali-
bration tables are mechanically and thermally stable it is
The reference pyranometer shall be specially se-
necessary to check the tilt only after periods longer than
lected, tested and maintained as follows. a week.
2) For the classification of pyr irlometers, see ISO 9060.
the dependence of
3) Test methods to determine t he responsi vi sranometer on temperature, irradiance, tilt and
tY of a PY
subject of a future
angle of incidence will form the International S tandard.
2
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ISO 9847:1992(E)
5.2.1.3 Connect the reference and test pyrano-
4.5 Sun-tracking mount
meters to their respective, or common, digital
The mount, whether power driven or manually op-
Voltmeter, using proper shielding. Check the instru-
erated, shall be capable of maintaining the refer-
ments for electrical continuity, Signal polarity, Signal
ence pyranometer and all test pyranometers normal strength and stability. Clean the domes of the
to the sun for the entire test period. The tracking
pyranometers (see [13]). Check that the radiant
precision shall be such that for all data-taking peri-
fluxes of the foreground on both instruments are
ods, deviations from the exact normal to the sun do
equai at the relevant tilt angle by transposing the
not exceed
positions of the pyranometers.
a) + 4” where the reference and test pyranometers
- cal and
5.2.2 Horizontal calibration for meteorologi
separate
are mounted on trackers;
resource nleasurements (type Ia)
whe re the reference and test pyt-ano-
b) + IO"
-
5.2.2.1 Stable cloudless sky conditions
mounted on the s a me tracke r.
tneters are
For stable cloudless sky conditions, simulZaneously
NOTE 3 An altazimuth mount is preferred for pyrano-
take instantaneous voltage readings on both instru-
meters with a responsivity dependent on tfre aftazimuth
ments for a minimum of fifteen 10 min to 20 min
angle of the tifted receiver. The requirements for tracking
measurement series, each consisting of 21 or more
a pyranometer at normal incidence are less stringent than
instantaneous readings. Take these measurement
those for tracking a pyrheliorneter. For example, the
series over a 2 day to 3 day period, or over a longer
cosine of 4O is 0,997 6, and only an insignificant uncer-
tainty in normal incident calibration will resrrlt from a de- period to cover a larger range of environmental
viation of this magnitude.
conditions. Obtain data from early morning, through
and including solar noon, to late afternoon to ensure
that data are taken during the period that the solar
elevation angle exceeds 20”.
5 Calibratian procedure
5.2.2.2 Unstable sky conditions with some cloud
5.1 General considerations
For unstable sky conditions, with clouds at a dis-
tance from the sun of greater than 30” (see S.2),
A nurnber of possible interferences and precautions
simultaneously take instantaneous voltage readings
relating directly to the methods specified in this In-
on both instruments continuously at from 1 min to
ternational Standard are given for information in
5 min intervals from sunrise to sunset for a mini-
annex B.
mum of 5 days (and for as long as 2 weeks). The
length of time should be Chosen such that a rnini-
Particular care shall be taken to correct for Zero
nium of fifteen series of 21 or more measurements
Off-Sets. The off-set of Signals of the reference and
are obtained that represent steady radiation span-
test pyranometers shall be checked, as a minimum,
ning a period from forenoon to afternoon (with sun
at the Start and the end of a measurement series.
elevation angle > 20).
Alternatively, take a minimum of fifteen measure-
5.2 Outdoor calibration (type 1)
ment series integrated over 1 min to 5 min intervals
in such a manner that data are spread over the pe-
riod from forenoon to afternoon, including solar
5.2.1 General (types Ia, Ib and Ic)
noon.
5.2.1.1 Mount the reference pyranometer and the 5.2.2.3 Cloudy sky conditions
test pyranometer outdoors on a common calibration
table for horizontal calibration (type Ia) and cali- For cloudy sky conditions take simultaneous
bration at tilt (type Ib) and on an altazimuth or sun- readings integrated over more than fifty 1 h intervals
pointing mount for normal-incidence calibration on both instruments. Take this hourly data for a
(type tc). Adjust both instruments to a common el- minimum of IO days at different solar elevation an-
evation facing the equator. Ensure that the azimuth gles, and different types of cloudiness if the hourly
reference marks Point in a common direction. mean of global irradiance is greater than
100 W-m-- *.
NOTE 4 Convention is to use the electrical connector
as the azimuth reference and to Point it towards the
5.2.3 Calihration at tilt (type Ib)
equator and downwards.
Calibration at tilt shall be carried out only under
clear sky conditions with clouds at a distance from
5.2.1.2 Adjust the calibration table to the required
tilt (which may be 0°) from the horizontal. the sun of greater than 30”. Use as the tilt from
3
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ISO 9847:1992(E)
horizontal, that tilt which will be employed in testing
(about 8 min) to ensure an accuracy sf 0,25 %
solar collectors. Care should be taken that the
and a precision of + 0,2!? %.
-
albedo from the ground is approximately the Same
at both receivers.
5.3.1.5 Measure the temperature of tF
te pyrano-
meter bodies and of the wall of the integrating
Take data in accordance with 5.2.2.1.
sphere.
52.4 Calibration at normal incidence (type Ic)
5.3.1.6 Apply the general mathematica treatment
described in 5.4.1.
Take a minimum of fifteen 10 min to 20 min meas-
urement series consisting of 21 or more instan-
5.3.2 Direct beam calibration (type Ilc)
taneous voltage readings centred around solar
noon. Ensure that all data are taken while the
5.3.2.1 Check that the reference and test pyrano-
hemispherical normal-incident solar irradiance ex-
meters are of the Same type.
ceeds 600 Wem- *.
5.3.2.2 Mount the reference and test pyranometer
NOTE 5 For determining the ratio of the directional re-
sponse (see ISO 9060: 1990, table 1) of the reference horizontally on a movable support which allows an
pyranometer to that of the test pyranorneter, a special
exchange of the Position of the instruments (see
procedure which operates the mount in an azimrrth track-
A.3). Adjust the Position of the instruments and the
ing mode is given in annex D for information.
spirit level. Ensure that the reference and test
pyranometers have the Same azimuthal orientation.
5.2.5 Mathematical treatment
Optical tools should be installed above the receivers
of the pyranometers in Order to create the vertical
Apply the general mathematical treatment de-
beams’ homogeneity and divergente.
scribed in 5.4.1.
5.3.2.3 About 30 min or more before the first read-
ing, switch on the data acquisition electronics and
5.3 Indoor calibration (type II)
energize the lamp to stabilize the radiant flux of the
lamp and the field of thermal radiation around the
5.3.1 Integrating sphere calibratlon (with
bench.
pyranometer horizontal: type Ila and with
pyranometer tilted: type II b)
Connect the reference and test pyranometers to
their respective, or comrnon, digital Voltmeter, using
5.3.1.1 Mount the reference and test pyranometers
proper shielding. Check the instruments for elec-
on the common instrument support in the integrating
trical continuity, Signal polarity, Signal strength and
sphere. Ensure that the reference and test pyrano-
stability. If necessary, clean the domes of the
meters have exactly the Same orientation, and that
pyranometers.
their relationships to the Source (if type Ilb) and to
the hemisphere are geometrically symmetrical.
5.3.2.4 Take periodic readings of both pyrano-
meters (which are alternately shaded and un-
5.3.1.2 Connect the reference and test pyrano-
shaded). Follow for example the time tables of
meters to their respective, or common, digital
readings given in A.3 for the two different methods
Voltmeter, using proper shielding. Check the instru-
in use. The number of readings to be taken depends
ments for electrical continuity, Signal polarity, Signal
on the stability of the interim results.
strength and stability. If necessary, clean the domes
of the pyranometers. About 30 min before the first
5.3.2.5 If the pyranometer mount tan be tilted, re-
reading, energize the lamp (or lamps) to the power
peat the reading procedure used in 5.3.2.4 at the
level required.
desired tilt (tilt angle fl), which corresponds to an
angle of incidence of /?.
5.3.1.3 Check that the loci of both instruments re-
ceive the Same irradiance by transposing the pos-
5.3.2.6 Apply the special mathematical treatment
itions of the pyranometers.
descri bed in 5.4.3.
5.3.1.4 Either
5.4 Mathematical treatment
a) simultaneously take ten series of 21 Point in-
stantaneous voltage readings of the reference 5.4.1 Determlnatfon of the callbration factor
and test pyranometers, or (general treatment)
b) take simultaneous integrated voltage readings
The following general treatment is applicable to all
of the reference and test pyranometers over a
types of calibration except type Ilc, for which the
minimurn of five periods of sufficient Iength
spfxial treatment given in 5.4.3 applies.
4
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ISO 9847:1992(E)
5.4.1.1 First step by more than + 2 % from I;(G) [see equation (2)].
Repeat the calculation of ,FV) on the basis of the
This step applies to instantaneous readings. “clean” data. Compute the final calibration factor in
accordance with equation (4) or (5) from the “clean”
From each reading i within a measurement seriesj,
F(j) data.
calculate the ratio
4&i) r
-l . .
5.4.1.4 Statistical analysis
! E------f
. . .
1 (Ij) . (1)
V&~~ R
Determine the stability of the calibration conditions
where during a measurement series by calculating the
Standard deviation F(f/) about their mean for set
i,&(ij) and Vr(ij) are the voltages (for example in
values. (The Standard deviations of FV) around its
millivolts) measured using the reference
mean value represent the stability of the conditions
and the field pyranometers respectively,
during the entire calibration.)
with the corresponding Zero value sub-
tracted;
5.4.1.5 Determination of the temperature-corrected
is the calibration factor, Watts per Square
I
final calibration factor
?R
metre per microvolt, of the reference
pyranometer, which has beeil adjusted
If during a measurement seriesj the temperature 7’
for the typical field conditions, in the case
deviates markedly (i.e. by more than + 10 “C) from
where the field and reference pyrano-
the desired typical value 7N, and if thetemperature
meters are of the Same type and have
response of the field pyranometer is known to devi-
the type-inherent measurement specifi-
ate markedly from that of the reference pyrano-
cation (for instance in the temperature
meter-, then calculate the final temperature-
response).
corrected calibration factor Fcorr at TN as follows.
Correct the r;(i) data using the formula
Where & as defined above is not applicable, it is
replaced, for each measurement series, by a value
. . .
(3)
of &(i) which is fitted to the calibration conditions
(for instance, mean temperature) and which gives
the most accurate value of irradiance E(o) according
and calculate r;COr,. as
to the formula
m
1
I$(/)VR(ij) = E(@ fl --.
I . . .
corr - m &orr 0’1 TbJ) (4)
c
jc 1
5.4.1.2 Second step
where
Determine the series of calibration factot-s of the
during
is the mean air temperature the
field pyranometer from y2 readings of a measure-
s Celsiu
m easu ring seriesj, in degree
s;
ment seriesj using the formula
I?,-C’r((/)] and &(7h) are the responsivities of
12
the field pyranometer at 7’(j) and 7N re-
spectively, where R = l/F.
iz 1
t
=-
ro?
n
For some types of pyranometer, temperature
NOTE 6
coefficients a of the responsivity are specified; in this case
the relation R[?‘(j)] = (1 + a [7’(j) - T,J} X(T,) is appli-
cable.
. 43C vROli nt 5.4.1.6 Determination of the final calibration factor
f =
. . .
m
(2)
without temperature correction of data
C 1’7&~3i nt
In cases where it is not necessary or not possible to
where [I’G)]ir,t are integrated values (types Ila and
correct the data relative to the temperature re-
llb) .
sponse, derive the final calibration factor of the field
pyranometer from the total number m of measure-
5.4.1.3 Data rejection
ment series from the formula
m
Reject any data which have been subject to oper-
.
1
f--
-
r n2 .;’
. . .
IO>
(5)
ational Problems for both pyranometers. Also, reject
c
.i- 1
those data for which F(g) [see equation (1)] deviates
---------------------- Page: 9 ----------------------
ISO 9847:1992(E)
Seiection of caiibration factors for speciai 8 If global or hemispherical solar irradiation is deter-
5.4.2
mined for daily sums, the use of a daily average solar el-
vaiues of solar angies
evation is recommended. An expedient means for
computation of the daily average solar angle is given in
annex C for information.
In the case where
5.4.3 Speciai treatment for type iic caiibration
a) for special meteorological and resource assess-
ment purposes the calibration factor calculated
a) Simultanemus readings (see A.3.1)
by an averaging process using equation (4) is not
Calculate the measured values V from the readings
accurate enough (since within a larger range of
taken using the following formrrlae:
calibration Parameters special values of solar
elevation angles have to be considered for the
I”‘R = 1’7 u - VR s
3
end-use application of the field pyranometer),
v = r+ ” -- VT s
T I t
b) the directional response (or cosine error, see
T?
n
p” =
ISO 9060:1990, table 1) of the field pyranometer I/ v
R R,u - R,s
is not yet known. or
i
rT = .j7’7.,u - T,s
J 1 T/
c) the directional response of the reference
Check whether the condition
pyranometer is weil-known and is used to intro-
duce cosine-error-corrected reference data in
equation (2), - < (1 -t- k)
(1 -k)< 12;2
FJ RY T
carry out the following mathematical treatment.
e k is a factor:
is fulfilled for k < 0,005, whei
Plot all F(j) values as a function of the corresponding
0 < k < 0,005
mean solar elevation y (for horizontal or fixe+tilt
instruments respectively) using the formula
cal culate the responsivity
If the condition is fulfilled,
of the test pyranometer from
sin y = sin + sin ti -t- cos + cos S cos CR)
Lt VT
. .-
R
R
T=------
R
where 17; -+ vf;
geographical latitude of the Point
is the
b) Alternate readings (see A.3.2)
ervation;
of obs
Calculate the measured values V from the readings
6 is the solar declination;
taken at time t (in minutes) for the reference
pyranometer using
is the solar hour angle, in degrees (i.e.
the angle between the hour circle of the
I/R(l) = I/rR,u(t) - 0,5[ J&(~ - 2) + VR I s(t $- 2)]
sun and the meridian at the time of ob-
servation), which tan be calculated ft-om
and for the test pyranometer using
the True Solar Time (TST) from
CU = (TST - 720)/4, where TST is in min-
‘T(l) = vT,u(f) - O,s[ J’T 9 s(t - 2) + VT , s(t +- 2)]
utes.
Check whether the means
-
Plot also a best-fit regression curve of the data.
V
R 1 = 0,5[ &(4) + 4@)]
9
Read the calibration factor from the regression
curve at the representative solar elevation angle.
-
I/ R.2 = V[ lr,(N - lr,(32)]
7 An outdoor method to determine approximately the
deviate by more than + 0,5 %, and whether the
ratio of directional response of the field pyranometer to
three V,(t> values deviate by more than + - 0,5 %
that of the reference pyranometer is described in
from their mean VT.
annex D. Recommended laboratory test procedures will
form the subject of a future International Standard. With
a given directional response function f(y, J/) the cali-
If the deviation is less than or equal to + 0,5 % in
bration factor tan be extrapolated to solar angles yO, I/F~
both cases, calculate the responsivity gf the test
(see ISO 9846:-, annex B) outside the measured range
pyranometer /?T using the formula
of =ingles by using the formula
v,
fllr (i)l 11/0’)1
R
RR
qq)’ $0) = fili) f(yIý)--- T=‘T’ -
05(1
1
‘R,l + v R,2 1
0, 0
---------------------- Page: 10 ----------------------
ISO 9847:1992(E)
d) the result of the calibration:
6 Certificate of callbration
-
responsivity (for instance in microvolts per
The certificate of calibration shall as a minimum
watt per Square metre) or calibration factor
state the following information on
(for instance in watt Square metres per milli-
Volt):
a) the test pyranometer:
-
Standard deviation;
--
manufacturer, type and serial nrrmber;
- absolute uncertainty (total uncertainty);
--.-. Position (i.e. inclination angles, azimuthal
orientation and tracking);
-
range of validity (Parameters: solar elevation
angle, temperature, etc.).
---
special remarlts on the state of the pyrano-
meter;
7 Precision and accuracy
h) the reference pyranometer:
7.1 The precision of the outdoor determination of
-
manufxturer, type and serial number;
the calibration factor of a field pyranometer is par-
ticrrlarly dependent on sky conditions and solar el-
-- hierarchy of traceability;
evation when perforrning measurements at low
angles. Repeatability within any 21 Point or more set
-
corrections applied;
of values of the Same test scan performed at or near
solar noon under stable irradiance conditions
c) the procedure:
should be such that the Standard deviation is less
than + 0,5 % of the calibration value of the instru-
-
- type of procedure (i.e. reference to this Inter-
me
...
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