ASTM G167-15(2023)
(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
4.1 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.
4.2 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.
4.3 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.
4.4 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 High Quality pyranometers generally exhibit tilt errors of less than 0.5 %. Tilt error is the percentage deviation from the responsivity at 0° tilt (horizontal) due to change in tilt from 0° to 90° at 1000 W·m23.
4.5 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:
4.5.1 One of the International Pyrheliometric Comparisons (IPC) held in Davos, Switzerland since 1980 (IPC IV). See Refs (3-7).
4.5.2 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.
4.5.3 Intercomparison with any absolute cavity pyrheliometer t...
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.9 This interna...
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G167 − 15 (Reapproved 2023)
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 the World Radiometric Reference (WRR), which
represents the SI units of irradiance. The WRR is determined by a group of selected absolute
pyrheliometers maintained by the World 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 eter as the reference standard (secondary reference pyrheliom-
eters are defined by WMO and ISO 9060).
1.1 This test method covers an integration of previous Test
Method E913 dealing with the calibration of pyranometers
1.5 Calibrations of reference pyranometers may be per-
with axis vertical and previous Test Method E941 on calibra-
formed by a method that makes use of either an altazimuth or
tion of pyranometers with axis tilted. This amalgamation of the
equatorial tracking mount in which the axis of the radiometer’s
two methods essentially harmonizes the methodology with ISO radiation receptor is aligned with the sun during the shading
9846.
disk test.
1.2 This test method is applicable to all pyranometers
1.6 The determination of the dependence of the calibration
regardless of the radiation receptor employed, and is applicable
factor (calibration function) on variable parameters is called
to pyranometers in horizontal as well as tilted positions.
characterization. The characterization of pyranometers is not
specifically covered by this method.
1.3 This test method is mandatory for the calibration of all
secondary standard pyranometers as defined by the World
1.7 This test method is applicable only to calibration pro-
Meteorological Organization (WMO) and ISO 9060, and for
cedures using the sun as the light source.
any pyranometer used as a reference pyranometer in the
1.8 This standard does not purport to address all of the
transfer of calibration using Test Method E842.
safety concerns, if any, associated with its use. It is the
1.4 Two types of calibrations are covered: Type I calibra-
responsibility of the user of this standard to establish appro-
tions employ a self-calibrating, absolute pyrheliometer, and
priate safety, health, and environmental practices and deter-
Type II calibrations employ a secondary reference pyrheliom-
mine the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This test method is under the jurisdiction of ASTM Committee G03 on
Weathering and Durability and is the direct responsibility of Subcommittee G03.09
ization established in the Decision on Principles for the
on Radiometry.
Development of International Standards, Guides and Recom-
Current edition approved Feb. 1, 2023. Published February 2023. Originally
mendations issued by the World Trade Organization Technical
approved in 2000. Last previous edition approved in 2015 as G167 – 15. DOI:
10.1520/G0167-15R23. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G167 − 15 (2023)
2. Referenced Documents 3.2.8 hemispherical radiation, n—combined direct and dif-
2 fuse solar radiation incident from a virtual hemisphere, or from
2.1 ASTM Standards:
2π Sr, on any inclined surface.
E772 Terminology of Solar Energy Conversion
3.2.8.1 Discussion—The case of a horizontal surface is
E824 Test Method for Transfer of Calibration From Refer-
denoted global solar radiation (3.2.7).
ence to Field Radiometers
3 3.2.9 pyranometer, n—see Terminology E772.
2.2 WMO Document:
3.2.10 pyranometer, field, n—a pyranometer meeting WMO
World Meteorological Organization (WMO), “Measurement
Good Quality or better (that is, High Quality) appropriate to
of Radiation” Guide to Meteorological Instruments and
field use and typically exposed continuously.
Methods of Observation, seventh ed., WMO-No. 8, Ge-
neva
3.2.11 pyranometer, reference, n—a pyranometer (see also
ISO 9060), used as a reference to calibrate other pyranometers,
2.3 ISO Standards:
which is well-maintained and carefully selected to possess
ISO 9060:1990 Solar Energy—Specification and Classifica-
relatively high stability and has been calibrated using a
tion of Instruments for Measuring Hemispherical Solar
pyrheliometer.
and Direct Solar Radiation
ISO 9846:1993 Solar Energy—Calibration of a Pyranometer
3.2.12 pyrheliometer, n—see Terminology E772 and ISO
Using a Pyrheliometer
9060.
3.2.13 pyrheliometer, absolute (self-calibrating), n—a solar
3. Terminology
radiometer with a limited field of view configuration. The field
3.1 Definitions:
of view should be approximately 5.0° and have a slope angle of
3.1.1 See Terminology E772. from 0.75° to 0.8°, with a blackened conical cavity receiver for
absorption of the incident radiation. The measured electrical
3.2 Definitions of Terms Specific to This Standard:
power to a heater wound around the cavity receiver constitutes
3.2.1 altazimuth mount, n—a tracking mount capable of
the method of self-calibration from first principles and trace-
rotation about orthogonal altitude and azimuth axes; tracking
ability to absolute SI units. The self-calibration principle
may be manual or by a follow-the-sun servomechanism.
relates to the sensing of the temperature rise of the receiving
3.2.2 calibration of a radiometer, v—determination of the
cavity by an associated thermopile when first the sun is
responsivity (or the calibration factor, the reciprocal of the
incident upon the receiver and subsequently when the same
responsivity) of a radiometer under well-defined measurement
thermopile signal is induced by applying precisely measured
conditions.
power to the heater with the pyrheliometer shuttered from the
3.2.3 direct solar radiation, n—that component of solar
sun.
radiation within a specified solid angle (usually 5.0° or 5.7°)
3.2.14 shading-disk device, n—a device which allows
subtended at the observer by the sun’s solar disk, including a
movement of a disk in such a way that the receiver of the
portion of the circumsolar radiation.
pyranometer to which it is affixed, or associated, is shaded
3.2.4 diffuse solar radiation, n—that component of solar
from the sun. The cone formed between the origin of the
radiation scattered by the air molecules, aerosol particles, cloud
receiver and the disk subtends an angle that closely matches the
and other particles in the hemisphere defined by the sky dome.
field of view of the pyrheliometer against which it is compared.
Alternatively, and increasingly preferred, a sphere rather than a
3.2.5 equatorial mount, n—see Terminology E772.
disk eliminates the need to continuously ensure the proper
3.2.6 field of view angle of a pyrheliometer, n—full angle of
alignment of the disk normal to the sun. See Appendix X1.
the cone which is defined by the center of the receiver surface
3.2.15 slope angle, n—the angle defined by the difference in
(see ISO 9060, 5.1) and the border of the limiting aperture, if
radii of the view limiting aperture (radius = R) and the receiver
the latter are circular and concentric to the receiver surface; if
radius (= r) in a pyrheliometer. The slope angle, s, is the
not, effective angles may be calculated (1, 2).
arctangent of R minus r divided by the distance between the
3.2.7 global solar radiation, n—combined direct and diffuse
limiting aperture and the receiver surface, denoted by L:
solar radiation falling on a horizontal surface; solar radiation
-1
s = Tan (R – r)/L. See Ref (1).
incident on a horizontal surface from the hemispherical sky
3.2.16 thermal offset, n—a non-zero signal generated by a
dome, or from 2π Steradian (Sr).
radiometer when blocked from all sources of radiation. Be-
lieved to be the result of infrared (thermal) radiation exchanges
between elements of the radiometer and the environment.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.3 Acronyms:
Standards volume information, refer to the standard’s Document Summary page on
3.3.1 ACR—Absolute Cavity Radiometer
the ASTM website.
Available from World Meterological Organization, 7bis, avenue de la Paix,
3.3.2 ANSI—American National Standards Institute
CP2300, CH-1211 Geneva 2, Switzerland, http://www.wmo.int.
3.3.3 ARM—Atmospheric Radiation Measurement Program
Available from International Organization for Standardization (ISO), 1, ch. de
la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
3.3.4 DOE—Department of Energy
The boldface numbers in parentheses refer to the list of references at the end of
this standard. 3.3.5 GUM—(ISO) Guide to Uncertainty in Measurements
G167 − 15 (2023)
3.3.6 IPC—International Pyrheliometer comparison which was found to be within 60.4 % of the mean of all
absolute pyrheliometers participating therein.
3.3.7 ISO—International Standards Organization
4.6 The calibration method employed in this test method
3.3.8 NCSL—National Council of Standards Laboratories
assumes that the accuracy of the values obtained are indepen-
3.3.9 NIST—National Institute of Standards and Technology
dent of time of year, with the constraints imposed and by the
3.3.10 NREL—National Renewable Energy Laboratory
test instrument’s temperature compensation circuit (neglecting
cosine errors).
3.3.11 PMOD—Physical Meteorological Observatory Da-
vos
5. Selection of Shade Method
3.3.12 SAC—Singapore Accreditation Council
5.1 Alternating Shade Method:
3.3.13 SINGLAS—Singapore Laboratory Accreditation Ser-
5.1.1 The alternating shade method is required for a primary
vice
calibration of the reference pyranometer used in the
3.3.14 UKAS—United Kingdom Accrediation Service
Continuous, Component-Summation Shade Method described
3.3.15 WRC—World Radiation Center in 5.2.
5.1.2 The pyranometer under test is compared with a
3.3.16 WRR—World Radiometric Reference
pyrheliometer measuring direct solar irradiance (or, optionally,
3.3.17 WMO—World Meteorological Organization
a continuously shaded control pyranometer; see Appendix X3
– Appendix X5). The voltage values from the pyranometer that
4. Significance and Use
correspond to direct solar irradiance are derived from the
4.1 The pyranometer is a radiometer designed to measure difference between the response of the pyranometer to hemi-
the sum of directly solar radiation and sky radiation in such
spherical (unshaded) solar irradiance and the diffuse (shaded)
proportions as solar altitude, atmospheric conditions and cloud solar irradiance. These response values (for example, voltages)
cover may produce. When tilted to the equator, by an angle β, are induced periodically by means of a movable sun shade
pyranometers measure only hemispherical radiation falling in disk. For the calculation of the responsivity, the difference
the plane of the radiation receptor. between the unshaded and shaded irradiance signals is divided
by the direct solar irradiance (measured by the pyrheliometer)
4.2 This test method represents the only practical means for
component that is normal to the receiver plane of the pyra-
calibration of a reference pyranometer. While the sun-trackers,
nometer.
the shading disk, the number of instantaneous readings, and the
5.1.3 For meteorological purposes, the solid angle from
electronic display equipment used will vary from laboratory to
which the scattered radiative fluxes that represent diffuse
laboratory, the method provides for the minimum acceptable
radiation are measured shall be the total sky hemisphere,
conditions, procedures and techniques required.
excluding a small solid angle around the sun’s disk.
4.3 While, in theory, the choice of tilt angle (β) is unlimited,
5.1.4 In addition to the basic method, modifications of this
in practice, satisfactory precision is achieved over a range of
method that are considered to improve the accuracy of the
tilt angles close to the zenith angles used in the field.
calibration factors, but which require more operational
4.4 The at-tilt calibration as performed in the tilted position experience, are presented in Appendix X3 – Appendix X5.
relates to a specific tilted position and in this position requires
5.2 Continuous Sun-and-Shade Method (Component Sum-
no tilt correction. However, a tilt correction may be required to
mation):
relate the calibration to other orientations, including axis
5.2.1 The pyranometer is compared with two reference
vertical.
radiometers, one of which is a pyrheliometer and the other a
well-calibrated reference pyranometer equipped with a track-
NOTE 1—WMO High Quality pyranometers generally exhibit tilt errors
of less than 0.5 %. Tilt error is the percentage deviation from the ing shade disk or sphere to measure diffuse solar radiation. The
responsivity at 0° tilt (horizontal) due to change in tilt from 0° to 90° at
reference pyranometer shall be either calibrated using the
1000 W·m .
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 t
...
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