ASTM E2847-11

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Designation:E2847 −11
StandardPractice for
Calibration and Accuracy Verification of Wideband Infrared
Thermometers
This standard is issued under the fixed designation E2847; 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.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This guide covers electronic instruments intended for
E344 Terminology Relating to Thermometry and Hydrom-
measurement of temperature by detecting the intensity of
etry
thermal radiation exchanged between the subject of measure-
E1256 Test Methods for Radiation Thermometers (Single
ment and the sensor.
Waveband Type)
1.2 The devices covered by this guide are referred to as
E2758 Guide for Selection and Use of Wideband, Low
infrared thermometers in this document.
Temperature Infrared Thermometers
1.3 The infrared thermometers covered in this guide are
3. Terminology
instruments that are intended to measure temperatures below
1000°C, measure thermal radiation over a wide bandwidth in 3.1 Definitions of Terms Specific to This Standard:
the infrared region, and are direct-reading in temperature.
3.1.1 cavity bottom, n—the portion of the cavity radiation
source forming the end of the cavity.
1.4 This guide covers best practice in calibrating infrared
3.1.1.1 Discussion—The cavity bottom is the primary area
thermometers. It addresses concerns that will help the user
where an infrared thermometer being calibrated measures
perform more accurate calibrations. It also provides a structure
radiation.
for calculation of uncertainties and reporting of calibration
3.1.2 cavity radiation source, n—a concave shaped geom-
results to include uncertainty.
etry approximating a perfect blackbody of controlled tempera-
1.5 Details on the design and construction of infrared
ture and defined emissivity used for calibration of radiation
thermometers are not covered in this guide.
thermometers.
1.6 This guide does not cover infrared thermometry above
3.1.2.1 Discussion—Acavity radiation source is a subset of
1000°C. It does not address the use of narrowband infrared
thermal radiation sources.
thermometers or infrared thermometers that do not indicate
3.1.2.2 Discussion—To be a cavity radiation source of
temperature directly.
practicalvalueforcalibration,atleast90 %ofthefield-of-view
of a radiation thermometer is expected to be incident on the
1.7 The values stated in SI units are to be regarded as the
cavity bottom. In addition, the ratio of the length of the cavity
standard. The values given in parentheses are for information
versus the cavity diameter is expected to be greater than or
only.
equal to 5:1.
1.8 The values stated in inch-pound units are to be regarded
3.1.3 cavity walls, n—the inside surfaces of the concave
as standard. The values given in parentheses are mathematical
shape forming a cavity radiation source.
conversions to SI units that are provided for information only
and are not considered standard. 3.1.4 customer, n—the individual or institution to whom the
calibration or accuracy verification is being provided.
3.1.5 distance-to-size ratio (D:S), n—see field-of-view.
ThispracticeisunderthejurisdictionofASTMCommitteeE20onTemperature
Measurement and is the direct responsibility of Subcommittee E20.02 on Radiation For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Thermometry. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Nov. 1, 2011. Published April 2012. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E2847–11. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2847−11
3.1.6 effective emissivity, n—the ratio of the amount of 5. Significance and Use
energy over a given spectral band exiting a thermal radiation
5.1 This guide provides guidelines and basic test methods
source to that predicted by Planck’s Law at a given tempera-
for the accuracy verification of infrared thermometers. It
ture.
includes test set-up and calculation of uncertainties. It is
3.1.7 field-of-view, n—a usually circular, flat surface of a
intended to provide the user with a consistent method, while
measured object from which the radiation thermometer re-
remaining flexible in the choice of calibration equipment. It is
ceives radiation. (1)
understood that the uncertainty obtained depends in large part
3.1.7.1 Discussion—Many handheld infrared thermometers
upon the apparatus and instrumentation used. Therefore, since
manufacturers include distance-to-size ratio (D:S) in their
this guide is not prescriptive in approach, it provides detailed
specifications. Distance-to-size ratio relates to the following
instruction in uncertainty evaluation to accommodate the
physical situation: at a given distance (D), the infrared ther-
variety of apparatus and instrumentation that may be em-
mometer measures a size (S) or diameter, and a certain
ployed.
percentage of the thermal radiation received by the infrared
5.2 Thisguideisintendedprimarilyforcalibratinghandheld
thermometer is within this size. Field-of-view is a measure of
infrared thermometers. However, the techniques described in
the property described by distance-to-size ratio. (1)
this guide may also be appropriate for calibrating other classes
3.1.8 flat-plate radiation source, n—a planar surface of
of radiation thermometers. It may also be of help to those
controlled temperature and defined emissivity used for calibra-
calibrating thermal imagers.
tions of radiation thermometers.
5.3 This guide specifies the necessary elements of the report
3.1.8.1 Discussion—Aflat-plate radiation source is a subset
of calibration for an infrared thermometer. The required
of thermal radiation sources.
elements are intended as a communication tool to help the end
3.1.9 measuring temperature range, n—temperature range
user of these instruments make accurate measurements. The
for which the radiation thermometer is designed. (1)
elementsalsoprovideenoughinformation,sothattheresultsof
3.1.10 purge, n—a process that uses a dry gas to remove the the calibration can be reproduced in a separate laboratory.
possibility of vapor on a measuring surface.
6. Sources of Uncertainty
3.1.11 radiance temperature, n—temperature of an ideal (or
6.1 Uncertainties are present in all calibrations. Uncertain-
perfect) blackbody radiator having the same radiance over a
ties are underestimated when their effects are underestimated
given spectral band as that of the surface being measured. (2)
or omitted. The predominant sources of uncertainty are de-
3.1.12 thermal radiation source, n—a geometrically shaped
scribed in Section 10 and are listed in Table 1 and Table X1.1
object of controlled temperature and defined emissivity used
of Appendix X1.
for calibration of radiation thermometers.
6.2 Typically, the most prevalent sources of uncertainties in
3.1.13 usage temperature range, n—temperature range for
this method of calibration are: (1) emissivity estimation of the
which a radiation thermometer is designed to be utilized by the
calibration source, (2) size-of-source of the infrared thermom-
end user.
eter, (3) temperature gradients on the radiation source, (4)
improperalignmentoftheinfraredthermometerwithrespectto
4. Summary of Practice
the radiation source, (5) calibration temperature of the radia-
4.1 The practice consists of comparing the readout tempera-
tion source, (6) ambient temperature and (7) reflected tempera-
ture of an infrared thermometer to the radiance temperature of
ture. The order of prevalence of these uncertainties may vary,
a radiation source. The radiance temperature shall correspond
depending on use of proper procedure and the type of thermal
to the spectral range of the infrared thermometer under test.
radiation source used. Depending on the temperature of the
4.2 The radiation source may be of two types. Ideally, the radiationsource,thecalibrationmethodoftheradiationsource,
source will be a cavity source having an emissivity close to
the optical characteristics of the infrared thermometer and the
unity (1.00). However, because the field-of-view of some detector and filter characteristics of the infrared thermometer,
infrared thermometers is larger than typical blackbody cavity
apertures, a large-area flat-plate source may be used for these
TABLE 1 Components of Uncertainty
calibrations. In either case, the traceable measurement of the
Uncertainty Component Discussion Evaluation Method
radiance temperature of the source shall be known, along with
Source Uncertainties
calculated uncertainties.
U Calibration Temperature 10.4 10.4.1
U Source Emissivity 10.5 10.2.3, X2.4 (example)
4.3 The radiance temperature of the source shall be trace-
U Reflected Ambient Radiation 10.6 10.2.2, X2.5 (example)
able to a national metrology institute such as the National
U Source Heat Exchange 10.7 10.7.1
Institute of Standards and Technology (NIST) in Gaithersburg, U Ambient Conditions 10.8 10.8.1
U Source Uniformity 10.9 10.9.1
Maryland or the National Research Council (NRC) in Ottawa,
Infrared Thermometer Uncertainties
Ontario, Canada.
U Size-of-Source Effect 10.11 Test Methods E1256
U Ambient Temperature 10.12 Appendix X3
U Atmospheric Absorption 10.13 X2.3
U Noise 10.14 10.14.1
The boldface numbers in parentheses refer to a list of references at the end of U Display Resolution 10.15 10.15.2
this standard.
E2847−11
thecontributionoftheseuncertaintiesmaychangesignificantly (L:D) or radius-to-diameter ratio (R:D) in the spherical case
in the overall uncertainty budget. will result in a smaller uncertainty. A smaller conical angle Φ
will also result in a smaller uncertainty.
7. Apparatus
7.1.3.2 The location of a reference or a control probe, or
both, and the thermal conductivity of the cavity walls are
7.1 Thermal Radiation Source:
important considerations in cavity source construction. In
7.1.1 There are two different classes of thermal radiation
general, a reference or control probe should be as close as
sources which can be used for infrared thermometer calibra-
practical to the center of the area where the infrared thermom-
tions: a cavity source and a flat-plate source. Some sources
eterwilltypicallymeasure,typicallythecavitybottom.Ifthere
may be considered a hybrid of both categories. Each of these
is a separation between the location of the reference probe and
sources has advantages and disadvantages. The cavity source
the cavity surface, cavity walls with a higher thermal conduc-
provides a source of radiation that has a more predictable
tivity will result in a smaller uncertainty due to temperature
emissivity. However, the flat-plate source can usually be made
gradients in this region.
less expensively, can be made with a diameter large enough to
7.1.3.3 The walls of the cavity source can be treated in
calibrate infrared thermometers with low distance to size ratios
several different ways. A painted or ceramic surface will
(D:S), and may geometrically more resemble the surface
generally result in higher emissivity than an oxidized metal
measured by the infrared thermometer when in use in the field.
surface. By the same measure an oxidized metal surface will
7.1.2 Ideally, the size of the thermal radiation source should
generally result in higher emissivity than a non-oxidized metal
be specified by the infrared thermometer manufacturer. In
many cases, this information may not be available. In these surface. In some cases, it may be impossible to paint the cavity
source surface. This is especially true at high temperatures.
cases a field-of-view test should be completed as discussed in
E1256.Theportionofsignalincidentontheinfraredthermom- 7.1.3.4 The effective emissivity of the cavity source shall be
calculated to determine the radiance temperature of the cavity.
eter that does not come from the source should be accounted
for in the uncertainty budget. Calculation of effective emissivity is beyond the scope of this
standard. Determination of effective emissivity can be math-
7.1.3 Cavity Source:
7.1.3.1 Acavity source can be constructed in several shapes ematically calculated or modeled.
as shown in Fig. 1. In general, a high length-to-diameter ratio 7.1.4 Flat-Plate Source:
FIG. 1Cavity Shapes
E2847−11
7.1.4.1 A flat-plate source is a device that consists of a 7.2.2 In Fig. 2,d is the aperture distance. The measuring
apr
painted circular or rectangular plate.The emissivity is likely to distance is shown by d .
meas
be less well defined than with a cavity source. This can be
7.3 Transfer Standard:
partially overcome by performing a radiometric transfer (see
7.3.1 The thermal radiation source shall be calibrated with a
Scheme II in 7.3.7) to the flat-plate source. However, the
transfer standard traceable to a national metrological institute
radiometric transfer should be carried out with an instrument
such as the National Institute of Standards and Technology
operating over a similar spectral band as the infrared thermom-
(NIST) or National Research Council (NRC). If a reference
eter under test.
thermometer (radiometric or contact) is used during the cali-
7.1.4.2 A cavity source is the preferred radiometric source
bration of the unit-under-test, this serves as the calibration of
for infrared thermometer calibrations. The cavity source has
the radiation source. In this case, the reference thermometer
two main advantages over a flat-plate source. First, the cavity
shall have a calibration traceable to a national metrological
source has better defined emissivity and an emissivity much
institute.
closer to unity due to its geometric shape. Second, along with
7.3.2 This calibration of the thermal radiation source may
the emissvity being closer to unity, the effects of reflected
take place in the calibration laboratory, or it may be done by a
temperature are lessened. Temperature uniformity on the flat-
third party calibration laboratory. The interval of these checks
plate source may be more of a concern as well. However, a
is determined by the calibration laboratory. The drift related to
flat-plate source has two possible advantages over a cavity
the calibration interval is part of the calibration uncertainties
source. First, the temperature controlled flat-plate surface can
for the infrared thermometer calibration.
be much larger than a typical cavity source opening, allowing
...