ASTM G167-05(2010)
(Test Method)Standard Test Method for Calibration of a Pyranometer Using a Pyrheliometer
Standard Test Method for Calibration of a Pyranometer Using a Pyrheliometer
SIGNIFICANCE AND USE
The pyranometer is a radiometer designed to measure the sum of directly solar radiation and sky radiation in such proportions as solar altitude, atmospheric conditions and cloud cover may produce. When tilted to the equator, by an angle β, pyranometers measure only hemispherical radiation falling in the plane of the radiation receptor.
This test method represents the only practical means for calibration of a reference pyranometer. While the sun-trackers, the shading disk, the number of instantaneous readings, and the electronic display equipment used will vary from laboratory to laboratory, the method provides for the minimum acceptable conditions, procedures and techniques required.
While, in theory, the choice of tilt angle (β) is unlimited, in practice, satisfactory precision is achieved over a range of tilt angles close to the zenith angles used in the field.
The at-tilt calibration as performed in the tilted position relates to a specific tilted position and in this position requires no tilt correction. However, a tilt correction may be required to relate the calibration to other orientations, including axis vertical.
Note 1—WMO Fist Class pyranometers, or better, generally exhibit tilt errors of less than 1 % to tilts of 50° from the horizontal.
Traceability of calibrations to the World Radiometric Reference (WRR) is achieved through comparison to a reference absolute pyrheliometer that is itself traceable to the WRR through one of the following:
One of the International Pyrheliometric Comparisons (IPC) held in Davos, Switzerland since 1980 (IPC IV). See Refs (3-7).
Any like intercomparison held in the United States, Canada or Mexico and sanctioned by the World Meteorological Organization as a Regional Intercomparison of Absolute Cavity Pyrheliometers.
Intercomparison with any absolute cavity pyrheliometer that has participated in either and IPC or a WMO-sanctioned intercomparison within the past five years and which was found to be within ±0....
SCOPE
1.1 This test method covers an integration of previous Test Method E913 dealing with the calibration of pyranometers with axis vertical and previous Test Method E941 on calibration of pyranometers with axis tilted. This amalgamation of the two methods essentially harmonizes the methodology with ISO 9846.
1.2 This test method is applicable to all pyranometers regardless of the radiation receptor employed, and is applicable to pyranometers in horizontal as well as tilted positions.
1.3 This test method is mandatory for the calibration of all secondary standard pyranometers as defined by the World Meteorological Organization (WMO) and ISO 9060, and for any pyranometer used as a reference pyranometer in the transfer of calibration using Test Method E842.
1.4 Two types of calibrations are covered: Type I calibrations employ a self-calibrating, absolute pyrheliometer, and Type II calibrations employ a secondary reference pyrheliometer as the reference standard (secondary reference pyrheliometers are defined by WMO and ISO 9060).
1.5 Calibrations of reference pyranometers may be performed by a method that makes use of either an altazimuth or equatorial tracking mount in which the axis of the radiometer's radiation receptor is aligned with the sun during the shading disk test.
1.6 The determination of the dependence of the calibration factor (calibration function) on variable parameters is called characterization. The characterization of pyranometers is not specifically covered by this method.
1.7 This test method is applicable only to calibration procedures using the sun as the light source.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: G167 − 05(Reapproved 2010)
Standard Test Method for
Calibration of a Pyranometer Using a Pyrheliometer
This standard is issued under the fixed designation G167; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Accurate and precise measurements of total global (hemispherical) solar irradiance are required in
the assessment of irradiance and radiant exposure in the testing of exposed materials, determination
of the energy available to solar collection devices, and assessment of global and hemispherical solar
radiation for meteorological purposes.
This test method requires calibrations traceable to theWorld Radiometric Reference (WRR), which
represents the SI units of irradiance. The WRR is determined by a group of selected absolute
pyrheliometers maintained by theWorld Meteorological Organization (WMO) in Davos, Switzerland.
Realization of the WRR in the United States, and other countries, is accomplished by the
intercomparison of absolute pyrheliometers with the World Radiometric Group (WRG) through a
series of intercomparisons that include the International Pyrheliometric Conferences held every five
years in Davos. The intercomparison of absolute pyrheliometers is covered by procedures adopted by
WMO and is not covered by this test method.
It should be emphasized that “calibration of a pyranometer” essentially means the transfer of the
WRR scale from a pyrheliometer to a pyranometer under specific experimental procedures.
1. Scope 1.5 Calibrations of reference pyranometers may be per-
formed by a method that makes use of either an altazimuth or
1.1 This test method covers an integration of previous Test
equatorial tracking mount in which the axis of the radiometer’s
Method E913 dealing with the calibration of pyranometers
radiation receptor is aligned with the sun during the shading
with axis vertical and previous Test Method E941 on calibra-
disk test.
tion of pyranometers with axis tilted.This amalgamation of the
twomethodsessentiallyharmonizesthemethodologywithISO 1.6 The determination of the dependence of the calibration
9846. factor (calibration function) on variable parameters is called
characterization. The characterization of pyranometers is not
1.2 This test method is applicable to all pyranometers
specifically covered by this method.
regardlessoftheradiationreceptoremployed,andisapplicable
to pyranometers in horizontal as well as tilted positions. 1.7 This test method is applicable only to calibration pro-
cedures using the sun as the light source.
1.3 This test method is mandatory for the calibration of all
1.8 This standard does not purport to address all of the
secondary standard pyranometers as defined by the World
safety concerns, if any, associated with its use. It is the
Meteorological Organization (WMO) and ISO 9060, and for
responsibility of the user of this standard to establish appro-
any pyranometer used as a reference pyranometer in the
priate safety and health practices and determine the applica-
transfer of calibration using Test Method E842.
bility of regulatory limitations prior to use.
1.4 Two types of calibrations are covered: Type I calibra-
tions employ a self-calibrating, absolute pyrheliometer, and
2. Referenced Documents
Type II calibrations employ a secondary reference pyrheliom-
2.1 ASTM Standards:
eter as the reference standard (secondary reference pyrheliom-
E772 Terminology of Solar Energy Conversion
eters are defined by WMO and ISO 9060).
E824 Test Method for Transfer of Calibration From Refer-
ence to Field Radiometers
This test method is under the jurisdiction of ASTM Committee G03 on
Weathering and Durability and is the direct responsibility of Subcommittee G03.09
on Radiometry. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2010. Published December 2010. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2000. Last previous edition approved in 2005 as G167 – 05. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0167-05R10. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G167 − 05 (2010)
2.2 WMO Document: which is well-maintained and carefully selected to possess
World Meteorological Organization (WMO), “Measurement relatively high stability and has been calibrated using a
of Radiation” Guide to Meteorological Instruments and pyrheliometer.
Methods of Observation, fifth ed., WMO-No. 8, Geneva
3.2.12 pyrheliometer, n—see Terminology E772 and ISO
2.3 ISO Standards: 9060.
ISO 9060:1990 Solar Energy—Specification and Classifica-
3.2.13 pyrheliometer, absolute (self-calibrating), n—a solar
tion of Instruments for Measuring Hemispherical Solar
radiometer with a limited field of view configuration. The field
and Direct Solar Radiation
ofviewshouldbeapproximately5.0°andhaveaslopeangleof
ISO 9846:1993 Solar Energy—Calibration of a Pyranometer
from 0.75 to 0.8°, with a blackened conical cavity receiver for
Using a Pyrheliometer
absorption of the incident radiation. The measured electrical
power to a heater wound around the cavity receiver constitutes
3. Terminology
the method of self-calibration from first principles and trace-
3.1 Definitions: ability to absolute SI units. The self-calibration principle
3.1.1 See Terminology E772. relates to the sensing of the temperature rise of the receiving
cavity by an associated thermopile when first the sun is
3.2 Definitions of Terms Specific to This Standard:
incident upon the receiver and subsequently when the same
3.2.1 altazimuth mount, n—a tracking mount capable of
thermopile signal is induced by applying precisely measured
rotation about orthogonal altitude and azimuth axes; tracking
power to the heater with the pyrheliometer shuttered from the
may be manual or by a follow-the-sun servomechanism.
sun.
3.2.2 calibration of a radiometer, v—determination of the
3.2.14 shading-disk device, n—a device which allows
responsivity (or the calibration factor, the reciprocal of the
movement of a disk in such a way that the receiver of the
responsivity) of a radiometer under well-defined measurement
pyranometer to which it is affixed, or associated, is shaded
conditions.
from the sun. The cone formed between the origin of the
3.2.3 direct solar radiation, n—that component of solar
receiverandthedisksubtendsananglethatcloselymatchesthe
radiation within a specified solid angle (usually 5.0° or 5.7°)
fieldofviewofthepyrheliometeragainstwhichitiscompared.
subtended at the observer by the sun’s solar disk, including a
Alternatively, and increasingly preferred, a sphere rather than a
portion of the circumsolar radiation.
disk eliminates the need to continuously ensure the proper
3.2.4 diffuse solar radiation, n—that component of solar
alignment of the disk normal to the sun. See Appendix X1.
radiationscatteredbytheairmolecules,aerosolparticles,cloud
3.2.15 slope angle, n—the angle defined by the difference in
and other particles in the hemisphere defined by the sky dome.
radii of the view limiting aperture (radius = R) and the receiver
3.2.5 equatorial mount, n—see Terminology E772.
radius (= r) in a pyrheliometer. The slope angle, s,isthe
arctangent of R minus r divided by the distance between the
3.2.6 field of view angle of a pyrheliometer, n—full angle of
limiting aperture and the receiver surface, denoted by L:
the cone which is defined by the center of the receiver surface
-1
s=Tan (R – r)/L. See Ref (1).
(see ISO 9060, 5.1) and the border of the limiting aperture, if
the latter are circular and concentric to the receiver surface; if
3.2.16 thermal offset, n—a non-zero signal generated by a
not, effective angles may be calculated (1, 2).
radiometer when blocked from all sources of radiation. Be-
lieved to be the result of infrared (thermal) radiation exchanges
3.2.7 global solar radiation, n—combineddirectanddiffuse
between elements of the radiometer and the environment.
solar radiation falling on a horizontal surface; solar radiation
incident on a horizontal surface from the hemispherical sky
3.3 Acronyms:
dome, or from 2π Steradian (Sr).
3.3.1 ACR—Absolute Cavity Radiometer
3.2.8 hemispherical radiation, n—combined direct and dif-
3.3.2 ANSI—American National Standards Institute
fuse solar radiation incident from a virtual hemisphere, or from
3.3.3 ARM—Atmospheric RadiationMeasurement Program
2π Sr, on any inclined surface.
3.3.4 DOE—Department of Energy
3.2.8.1 Discussion—The case of a horizontal surface is
denoted global solar radiation (3.2.7).
3.3.5 GUM—(ISO) Guide to Uncertainty in Measurements
3.2.9 pyranometer, n—see Terminology E772. 3.3.6 IPC—International Pyrheliometer comparison
3.2.10 pyranometer, field, n—a pyranometer meeting WMO
3.3.7 ISO—International Standards Organization
Second Class or better (that is, First Class) appropriate to field
3.3.8 NCSL—National Council of Standards Laboratories
use and typically exposed continuously.
3.3.9 NIST—NationalInstituteofStandardsandTechnology
3.2.11 pyranometer, reference, n—a pyranometer (see also
3.3.10 NREL—National Renewable Energy Laboratory
ISO 9060), used as a reference to calibrate other pyranometers,
3.3.11 PMOD—Physical Meteorological Observatory Da-
vos
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
3.3.12 SAC—Singapore Accreditation Council
4th Floor, New York, NY 10036, http://www.ansi.org.
3.3.13 SINGLAS—Singapore Laboratory Accreditation Ser-
The boldface numbers in parentheses refer to the list of references at the end of
this standard. vice
G167 − 05 (2010)
3.3.14 UKAS—United Kingdom Accrediation Service 5.1.2 The pyranometer under test is compared with a
pyrheliometer measuring direct solar irradiance (or, optionally,
3.3.15 WRC—World Radiation Center
a continuously shaded control pyranometer; see Appendix X3
3.3.16 WRR—World Radiometric Reference
– Appendix X5).The voltage values from the pyranometer that
3.3.17 WMO—World Meteorological Organization
correspond to direct solar irradiance are derived from the
difference between the response of the pyranometer to hemi-
4. Significance and Use
spherical (unshaded) solar irradiance and the diffuse (shaded)
4.1 The pyranometer is a radiometer designed to measure
solar irradiance.These response values (for example, voltages)
the sum of directly solar radiation and sky radiation in such
are induced periodically by means of a movable sun shade
proportions as solar altitude, atmospheric conditions and cloud
disk. For the calculation of the responsivity, the difference
cover may produce. When tilted to the equator, by an angle β,
between the unshaded and shaded irradiance signals is divided
pyranometers measure only hemispherical radiation falling in
by the direct solar irradiance (measured by the pyrheliometer)
the plane of the radiation receptor.
component that is normal to the receiver plane of the pyra-
nometer.
4.2 This test method represents the only practical means for
5.1.3 For meteorological purposes, the solid angle from
calibration of a reference pyranometer. While the sun-trackers,
which the scattered radiative fluxes that represent diffuse
theshadingdisk,thenumberofinstantaneousreadings,andthe
radiation are measured shall be the total sky hemisphere,
electronic display equipment used will vary from laboratory to
excluding a small solid angle around the sun’s disk.
laboratory, the method provides for the minimum acceptable
5.1.4 In addition to the basic method, modifications of this
conditions, procedures and techniques required.
method that are considered to improve the accuracy of the
4.3 While, in theory, the choice of tilt angle (β) is unlimited,
calibration factors, but which require more operational
in practice, satisfactory precision is achieved over a range of
experience, are presented in Appendix X3 – Appendix X5.
tilt angles close to the zenith angles used in the field.
5.2 Continuous Sun-and-Shade Method (Component Sum-
4.4 The at-tilt calibration as performed in the tilted position
mation):
relates to a specific tilted position and in this position requires
5.2.1 The pyranometer is compared with two reference
no tilt correction. However, a tilt correction may be required to
radiometers, one of which is a pyrheliometer and the other a
relate the calibration to other orientations, including axis
well-calibrated reference pyranometer equipped with a track-
vertical.
ing shade disk or sphere to measure diffuse solar radiation.The
NOTE 1—WMO Fist Class pyranometers, or better, generally exhibit tilt
reference pyranometer shall be either calibrated using the
errors of less than 1 % to tilts of 50° from the horizontal.
alternating sun-and shade method described in 5.1, or shall be
4.5 Traceability of calibrations to the World Radiometric compared against such a pyranometer in accordance with Test
Reference (WRR) is achieved through comparison to a refer- Method E824.
ence absolute pyrheliometer that is itself traceable to the WRR 5.2.2 Global solar irradiance (or hemispherical solar irradi-
through one of the following: ance for inclined pyranometers) is determined by the sum of
4.5.1 One of the International Pyrheliometric Comparisons the direct solar irradiance measured with a pyrheliometer
(IPC) held in Davos, Switzerland since 1980 (IPC IV). See multiplied by the cosine of the incidence angle of the beam to
Refs (3-7). thelocalhorizontal(orinclinedplaneparalleltotheradiometer
4.5.2 Any like intercomparison held in the United States, sensor), plus the diffuse solar irradiance measured with a
CanadaorMexicoandsanctionedbytheWorldMeteorological shaded reference pyranometer mounted in the same configu-
Organization as a Regional Intercomparison of Absolute Cav- ration (tilted or horizontal) as the unit under test.
ity Pyrheliometers. 5.2.3 The smallest uncertainty realized in the calibration of
4.5.3 Intercomparison with any absolute cavity pyrheliom- pyranometers will occur when the pyrheliometer is a self-
eter that has participated in either and IPC or a WMO- calibrating absolute cavity pyrheliometer and when the refer-
sanctioned intercomparison within the past five years and ence pyranometer has itself been calibrated over a range of air
which was found to be within 60.4 % of the mean of all mass (zenith angle) by the component summation (continuous
absolute pyrheliometers participating therein.
shade) metho
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