ASTM E2758-15a(2021)

Standard Guide for Selection and Use of Wideband, Low Temperature Infrared Thermometers

SIGNIFICANCE AND USE
4.1 This guide provides guidelines and basic test methods for the use of infrared thermometers. The purpose of this guide is to provide a basis for users of IR thermometers to make more accurate measurements, to understand the error in measurements, and reduce the error in measurements.
SCOPE
1.1 This guide covers electronic instruments intended for measurement of temperature by detecting intensity of thermal radiation exchanged between the subject of measurement and the sensor.  
1.2 The devices covered by this guide are referred to as IR thermometers.  
1.3 The IR thermometers covered in this guide are instruments that are intended to measure temperatures below 1000 °C and measure a wide band of thermal radiation in the infrared region.  
1.4 This guide covers best practice in using IR thermometers. It addresses concerns that will help the user make better measurements. It also provides graphical tables to help determine the accuracy of measurements.  
1.5 Details on the design and construction of IR thermometers are not covered in this guide.  
1.6 This guide does not cover medium- and high-temperature IR thermometry (above 1000 °C). It does not address the use of narrowband IR thermometers.  
1.7 The values of quantities stated in SI units are to be regarded as the standard. The values of quantities in parentheses are not in SI and are optional.  
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 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.

General Information

• Status: Historical
• Publication Date: 30-Apr-2021
• ICS: 17.200.20 - Temperature-measuring instruments
• Technical Committee: E20 - Temperature Measurement
• Drafting Committee: E20.02 - Radiation Thermometry

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2758 − 15a (Reapproved 2021)
Standard Guide for
Selection and Use of Wideband, Low Temperature Infrared
Thermometers
This standard is issued under the fixed designation E2758; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber 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
1.1 This guide covers electronic instruments intended for 2.1 ASTM Standards:
measurement of temperature by detecting intensity of thermal E1256Test Methods for Radiation Thermometers (Single
radiation exchanged between the subject of measurement and Waveband Type)
the sensor. E1862Practice for Measuring and Compensating for Re-
flected Temperature Using Infrared Imaging Radiometers
1.2 The devices covered by this guide are referred to as IR
E1897Practice for Measuring and Compensating for Trans-
thermometers.
mittance of anAttenuating Medium Using Infrared Imag-
1.3 The IR thermometers covered in this guide are instru-
ing Radiometers
ments that are intended to measure temperatures below 1000
E1933Practice for Measuring and Compensating for Emis-
°Candmeasureawidebandofthermalradiationintheinfrared
sivity Using Infrared Imaging Radiometers
region.
2.2 IEC Standards:
1.4 This guide covers best practice in using IR thermom-
IEC 62492-1 TS Industrial Process Control Devices—
eters. It addresses concerns that will help the user make better
Radiation Thermometers—Part 1: Technical Data for
measurements. It also provides graphical tables to help deter-
Radiation Thermometers
mine the accuracy of measurements.
2.3 BIPM Standards:
1.5 Details on the design and construction of IR thermom-
JCGM 200:2012International Vocabulary of Metrology—
eters are not covered in this guide.
Basic and General Concepts andAssociatedTerms (VIM)
1.6 This guide does not cover medium- and high-
3. Terminology
temperature IR thermometry (above 1000 °C). It does not
address the use of narrowband IR thermometers. 3.1 Definitions:
3.1.1 absolute zero, n—a temperature of 0 K (–273.15 °C).
1.7 The values of quantities stated in SI units are to be
3.1.2 atmospheric attenuation, n—a ratio showing how
regarded as the standard. The values of quantities in parenthe-
ses are not in SI and are optional. muchthermalradiationinagivenspectralrangeisabsorbedor
scattered in air over a given distance.
1.8 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3.1.3 atmospheric transmission, n—a ratio showing how
well thermal radiation in a given spectral range at a given
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- distance travels through a certain distance of air.
mine the applicability of regulatory limitations prior to use.
3.1.4 attenuating medium, n—a semi-transparent solid, liq-
1.9 This international standard was developed in accor-
uid or gas, such as a window, filter, external optics, or an
dance with internationally recognized principles on standard-
atmosphere that reduces thermal radiation, or combinations
ization established in the Decision on Principles for the
thereof.
Development of International Standards, Guides and Recom-
3.1.5 background radiation—see reflected radiation.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This guide is under the jurisdiction ofASTM Committee E20 on Temperature contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Measurement and is the direct responsibility of Subcommittee E20.02 on Radiation Standards volume information, refer to the standard’s Document Summary page on
Thermometry. the ASTM website.
Current edition approved May 1, 2021. Published June 2021. Originally Available from International Electrotechnical Commission (IEC), 3, rue de
approved in 1910. Last previous edition approved in 2015 as E2758–15A. Varembé, 1st floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, https://
DOI:10.1520 ⁄E2758-15AR21. www.iec.ch.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2758 − 15a (2021)
3.1.6 blackbody, n—the perfect or ideal source of thermal 3.1.23 infrared sensing device, n—one of a wide class of
radiant power having a spectral distribution described by instruments used to display or record (or both) information
Planck’s Law. related to the thermal radiation received from any object
surfaces viewed by the instrument.
3.1.7 blackbody simulator, n—a device with an emissivity
close to unity that can be heated or cooled to a stable 3.1.24 infrared (IR) thermometer, n—optoelectronic instru-
temperature. ment adapted for noncontact measurement of temperature of a
subject by utilizing thermal radiation exchange between the
3.1.8 calibration adjustment, n—the correction to an IR
subject and the sensor.
thermometer based on its calibration.
3.1.24.1 Discussion—IRthermometersareasubsetofradia-
3.1.9 celestial radiation, n—flux coming from the sky.
tion thermometers. Most manufacturers use the term IR ther-
3.1.10 center wavelength, n—the simple average of the
mometer for handheld radiation thermometers. In general,
lower and upper spectral range limits.
these devices are wideband and use a thermopile detector.
3.1.11 contact thermometer, n—an instrument that is
3.1.25 IR thermometry, n—the use of IR thermometers to
adapted for measuring temperature by means of thermal
determine temperature by measuring thermal radiation.
conductance by determining the temperature at the moment
3.1.26 irradiance (E), n—the radiant flux (power) per unit
when negligible thermal energy flows between the thermom-
area incident on a given surface in units of W/m .
eter and the object of measurement.
3.1.27 limit of error, n—the extreme value of measurement
3.1.12 dew point, n—the temperature at which water vapor
error of an infrared thermometer reading, relative to reference
condenses into liquid water.
temperature standards, as permitted by a specification.
3.1.13 diffuse reflector, n—a surface that produces a diffuse
3.1.27.1 Discussion—Manufacturers sometimes use the
image of a reflected source.
term accuracy in their specifications to represent limit of error.
3.1.27.2 Discussion—A manufacturer’s accuracy specifica-
3.1.14 distance ratio, n—theratioofthemeasuringdistance
to the diameter of the field-of-view, when the target is in tion may apply only to well defined conditions.
focus.
3.1.28 low-temperature, adj—for radiation and IR
3.1.15 electromagnetic radiation, n—physically occurring thermometry, referring to any temperature below 660 °C.
radiant flux classified according to wavelength or frequency.
3.1.29 measurement uncertainty (accuracy), n—non-
3.1.16 emissivity (ε), n—the emissivity of a surface is the negative parameter, characterizing the dispersion of the values
that could reasonably be attributed to the measurement of the
ratio between the radiation emitted from this surface and the
radiation from a blackbody at the same temperature. quantity values being attributed to a measurand, based on the
4,5
information used.
3.1.16.1 Discussion—The emissivity describes a thermo-
physical material characteristic, which in addition to the
3.1.30 measuring distance, n—distance or distance range
chemical composition of the material may also be dependent
between the radiation thermometer and the target (measured
onthesurfacestructure(rough,smooth),theemissiondirection
object) for which the radiation thermometer is designed.
as well as on the observed wavelength and the temperature of
3.1.31 measuring temperature range, n—temperature range
the measured object.
for which the radiation thermometer is designed.
3.1.17 emissivity setting, n—an adjustment on an IR ther-
3.1.32 noise equivalent temperature difference (NETD),
mometer to compensate for an emissivity of non-unity.
n—parameter which indicates the contribution of the measure-
3.1.17.1 Discussion—In most measuring situations a radia-
ment uncertainty in °C, which is due to instrument noise.
tion thermometer is used on a surface with an emissivity
3.1.33 opaque, adj—referring to the property of a material
significantly lower than one. For this purpose most thermom-
whose transmittance is zero for a given spectral range.
eters have the possibility of adjusting the emissivity setting.
The temperature reading is then automatically corrected. 3.1.34 operating temperature range and air humidity range,
n—the permissible temperature range and humidity range
3.1.18 emissivity tables, n—a list of objects and their mea-
within which the radiation thermometer may be operated. For
sured emissivity for a particular IR thermometer.
this temperature range and humidity range the specifications
3.1.19 field-of-view (FOV), n—a usually circular, flat sur-
are valid.
face of a measured object from which the radiation thermom-
3.1.34.1 Discussion—This is the range of ambient tempera-
eter receives radiation.
ture and humidity the instrument may operate within and be
3.1.20 frost point, n—the temperature at which water vapor
expected to meet its specification. It may be thought of as the
condenses into solid water or ice.
ambientoperatingtemperaturerangeandtheambientoperating
3.1.21 infrared (IR), adj—referring to electromagnetic ra- humidity range.
diation with a wavelength from approximately 0.7 to 30 µm.
3.1.35 radiance (L), n—the flux per unit projected area per
unit solid angle leaving a source or, in general, any reference
3.1.22 infrared reflector, n—a material with a reflectance in
the infrared region as close as possible to unity. surface.
4 5
See IEC62492-1. See BIPM JCGM 200:2012.
E2758 − 15a (2021)
3.1.35.1 Discussion—If ∂ Φ is the flux emitted into a solid 3.1.48 thermal radiation, n—electromagnetic radiation
angle ∂ω by a source element of projected area ∂Acos(θ), the which is caused by an object’s temperature and is predicted by
radiance is defined as: Planck’s Law.
] Φ 3.1.49 thermal shock, n—subjecting an IR thermometer to a
L 5
rapid temperature change.
]ω]Acos θ
~ !
3.1.50 thermopile detector, n—a thermopile detector’s out-
where:
put is voltage. Incident radiation heats the disk. When the disk
θ = theanglebetweentheoutwardsurfacenormalofthearea
is heated, its temperature rises above the sensor’s reference
element ∂ A and the direction of observation (unit =
temperature (ambient temperature) producing a temperature
W/sr•m ).
difference(∆T).Thepotentialofthethermopileisrelatedtothe
3.1.36 radiant power density (M), n—the radiant flux per
temperature difference based on the Seebeck Effect.
unit area leaving a surface that is,
3.1.51 transmittance (t), n—the ratio of the radiant flux
]Φ
transmitted through a body to that incident upon it.
M 5
]A
3.1.52 true temperature, n—temperature attributed to a
particular site of a subject or object of measurement and
where:
accepted as having a specified uncertainty.
∂Φ = flux leaving a surface element ∂A (unit = W/m ).
3.1.53 wideband, adj—referring to the situation where the
3.1.37 reflectance, n—the ratio of the radiant flux reflected
spectral range of an instrument is at least ⁄10 of its center
from a surface to that incident upon it.
wavelength.
3.1.38 reflected radiation, n—the thermal radiation incident
upon and reflected from the measurement surface of the
4. Significance and Use
specimen.
4.1 This guide provides guidelines and basic test methods
3.1.39 reflected temperature, n—the temperature of the
fortheuseofinfraredthermometers.Thepurposeofthisguide
radiant flux incident upon and reflected from the measurement
istoprovideabasisforusersofIRthermometerstomakemore
surface of a specimen.
accurate measurements, to understand the error in
measurements, and reduce the error in measurements.
3.1.40 response time, n—time interval between the instant
of an abrupt change in the value of the input parameter (object
5. Basic Use of IR Thermometry
temperature or object radiation) and the instant from which the
measured value of the radiation thermometer (output param- 5.1 General Considerations:
5.1.1 An IR thermometer can be used in a number of
eter) remains within specified limits of its final value.
applications. Although they are generally not as accurate as
3.1.41 sensor, n—devicedesignedtorespondtoIRradiation
contact thermometers, their quickness of measurement and
and convert that response into electrical signals.
their ability to measure the temperature of an opaque surface
3.1.42 size-of-source effect, n—the difference in the
without contacting it make them desirable instruments for
radiance- or temperature reading of the radiation thermometer
some temperature measurements.
when changing the size of the radiating area of the observed
5.1.2 Most handheld IR thermometers are equipped with a
source.
trigger to start and stop the measurements.
3.1.43 spectral range, n—parameter which gives the lower 5.1.3 As objects vary in temperature, they emit a varying
and upper limits of the wavelength range over which the
amount of thermal radiation. This amount of thermal radiation
radiation thermometer operates. ispredictablebasedontheobject’stemperature,emissivityand
reflected temperature.
3.1.43.1 Discussion—Spectral range is sometimes referred
to as bandwidth. 5.1.4 Handheld IR thermometers measure thermal radiation
in a given spectral range and determine the relationship
3.1.43.2 Discussion—These limits are generally defined as
between the measured thermal radiation and temperature. The
the wavelengths where the power or signal is attenuated by a
sensor mainly used in these instruments is a thermopile.
defined amount.
5.2 Basic IR Measurement:
3.1.44 spectral response, n—the numerical quantity of a
5.2.1 Before making a measurement, the emissivity setting
given phenomenon at a specific wavelength in the electromag-
netic spectrum. of the IR thermometer should be set to the object’s effective
emissivity in the instrument’s spectral range. Some IR ther-
3.1.45 standard atmosphere, n—a model of how electro-
mometersdonotallowtheusertoadjusttheemissivitybecause
magneticradiationistransmittedthroughtheatmospherebased
their emissivity is fixed. In these cases there are mathematical
on variations in pressure, temperature and humidity.
compensations that can be made.
3.1.46 surface-modifying material, n—any material that is
5.2.2 To make a measurement, the IR thermometer’s lens
used to change the emissivity of the specimen su
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2758 − 15a E2758 − 15a (Reapproved 2021)
Standard Guide for
Selection and Use of Wideband, Low Temperature Infrared
Thermometers
This standard is issued under the fixed designation E2758; 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
1.1 This guide covers electronic instruments intended for measurement of temperature by detecting intensity of thermal radiation
exchanged between the subject of measurement and the sensor.
1.2 The devices covered by this guide are referred to as IR thermometers.
1.3 The IR thermometers covered in this guide are instruments that are intended to measure temperatures below 1000°C 1000 °C
and measure a wide band of thermal radiation in the infrared region.
1.4 This guide covers best practice in using IR thermometers. It addresses concerns that will help the user make better
measurements. It also provides graphical tables to help determine the accuracy of measurements.
1.5 Details on the design and construction of IR thermometers are not covered in this guide.
1.6 This guide does not cover medium- and high-temperature IR thermometry (above 1000°C).1000 °C). It does not address the
use of narrowband IR thermometers.
1.7 The values of quantities stated in SI units are to be regarded as the standard. The values of quantities in parentheses are not
in SI and are optional.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.9 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.
2. Referenced Documents
2.1 ASTM Standards:
This guide is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.02 on Radiation
Thermometry.
Current edition approved May 1, 2015May 1, 2021. Published May 2015June 2021. Originally approved in 1910. Last previous edition approved in 2015 as
E2758 – 15.E2758 – 15A. DOI:10.1520 ⁄E2758-15A.⁄E2758-15AR21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2758 − 15a (2021)
E1256 Test Methods for Radiation Thermometers (Single Waveband Type)
E1862 Practice for Measuring and Compensating for Reflected Temperature Using Infrared Imaging Radiometers
E1897 Practice for Measuring and Compensating for Transmittance of an Attenuating Medium Using Infrared Imaging
Radiometers
E1933 Practice for Measuring and Compensating for Emissivity Using Infrared Imaging Radiometers
2.2 IEC Standards:
IEC 62492-1 TS Industrial Process Control Devices—Radiation Thermometers—Part 1: Technical Data for Radiation Ther-
mometers
2.3 BIPM Standards:
JCGM 200:2012 International Vocabulary of Metrology—Basic and General Concepts and Associated Terms (VIM)
3. Terminology
3.1 Definitions:
3.1.1 absolute zero, n—a temperature of 0 K (-273.15°C).(–273.15 °C).
3.1.2 atmospheric attenuation, n—a ratio showing how much thermal radiation in a given spectral range is absorbed or scattered
in air over a given distance.
3.1.3 atmospheric transmission, n—a ratio showing how well thermal radiation in a given spectral range at a given distance travels
through a certain distance of air.
3.1.4 attenuating medium, n—a semi-transparent solid, liquid or gas, such as a window, filter, external optics, or an atmosphere
that reduces thermal radiation, or combinations thereof.
3.1.5 background radiation—see reflected radiation.
3.1.6 blackbody, n—the perfect or ideal source of thermal radiant power having a spectral distribution described by Planck’s Law.
3.1.7 blackbody simulator, n—a device with an emissivity close to unity that can be heated or cooled to a stable temperature.
3.1.8 calibration adjustment, n—the correction to an IR thermometer based on its calibration.
3.1.9 celestial radiation, n—flux coming from the sky.
3.1.10 center wavelength, n—the simple average of the lower and upper spectral range limits.
3.1.10 celestial radiation, n—flux coming from the sky.
3.1.11 contact thermometer, n—an instrument that is adapted for measuring temperature by means of thermal conductance by
determining the temperature at the moment when negligible thermal energy flows between the thermometer and the object of
measurement.
3.1.12 dew point, n—the temperature at which water vapor condenses into liquid water.
3.1.13 diffuse reflector, n—a surface that produces a diffuse image of a reflected source.
3.1.14 distance ratio, n—the ratio of the measuring distance to the diameter of the field-of-view, when the target is in focus.
3.1.15 electromagnetic radiation, n—physically occurring radiant flux classified according to wavelength or frequency.
Available from International Electrotechnical Commission (IEC), 3, Ruerue de Varembé, CH-1211 1st floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland,
www.iec.ch.https://www.iec.ch.
See IEC 62492-1.
E2758 − 15a (2021)
3.1.16 emissivity (ε), n—the emissivity of a surface is the ratio between the radiation emitted from this surface and the radiation
from a blackbody at the same temperature.
3.1.16.1 Discussion—
The emissivity describes a thermo-physical material characteristic, which in addition to the chemical composition of the material
may also be dependent on the surface structure (rough, smooth), the emission direction as well as on the observed wavelength and
the temperature of the measured object.
3.1.17 emissivity setting, n—an adjustment on an IR thermometer to compensate for an emissivity of non-unity.
3.1.17.1 Discussion—
In most measuring situations a radiation thermometer is used on a surface with an emissivity significantly lower than one. For this
purpose most thermometers have the possibility of adjusting the emissivity setting. The temperature reading is then automatically
corrected.
3.1.18 emissivity tables, n—a list of objects and their measured emissivity for a particular IR thermometer.
3.1.19 field-of-view (FOV), n—a usually circular, flat surface of a measured object from which the radiation thermometer receives
radiation.
3.1.20 frost point, n—the temperature at which water vapor condenses into solid water or ice.
3.1.21 infrared (IR), adj—referring to electromagnetic radiation with a wavelength from approximately 0.7 to 30 μm.
3.1.22 infrared reflector, n—a material with a reflectance in the infrared region as close as possible to unity.
3.1.23 infrared sensing device, n—one of a wide class of instruments used to display or record (or both) information related to
the thermal radiation received from any object surfaces viewed by the instrument.
3.1.24 infrared (IR) thermometer, n—optoelectronic instrument adapted for noncontact measurement of temperature of a subject
by utilizing thermal radiation exchange between the subject and the sensor.
3.1.24.1 Discussion—
IR thermometers are a subset of radiation thermometers. Most manufacturers use the term IR thermometer for handheld radiation
thermometers. In general, these devices are wideband and use a thermopile detector.
3.1.25 IR thermometry, n—the use of IR thermometers to determine temperature by measuring thermal radiation.
3.1.26 irradiance (E), n—the radiant flux (power) per unit area incident on a given surface in units of W/m .
3.1.27 limit of error, n—the extreme value of measurement error of an infrared thermometer reading, relative to reference
temperature standards, as permitted by a specification.
3.1.27.1 Discussion—
Manufacturers sometimes use the term accuracy in their specifications to represent limit of error.
3.1.27.2 Discussion—
A manufacturer’s accuracy specification may apply only to well defined conditions.
3.1.28 low-temperature, adj—for radiation and IR thermometry, referring to any temperature below 660°C.660 °C.
3.1.29 measurement uncertainty (accuracy), n—non-negative parameter, characterizing the dispersion of the values that could
reasonably be attributed to the measurement of the quantity values being attributed to a measurand, based on the information
4,5
used.
See BIPM JCGM 200:2012.
E2758 − 15a (2021)
3.1.30 measuring distance, n—distance or distance range between the radiation thermometer and the target (measured object) for
which the radiation thermometer is designed.
3.1.31 measuring temperature range, n—temperature range for which the radiation thermometer is designed.
3.1.32 noise equivalent temperature difference (NETD), n—parameter which indicates the contribution of the measurement
uncertainty in °C, which is due to instrument noise.
3.1.33 opaque, adj—referring to the property of a material whose transmittance is zero for a given spectral range.
3.1.34 operating temperature range and air humidity range, n—the permissible temperature range and humidity range within
which the radiation thermometer may be operated. For this temperature range and humidity range the specifications are valid.
3.1.34.1 Discussion—
This is the range of ambient temperature and humidity the instrument may operate within and be expected to meet its specification.
It may be thought of as the ambient operating temperature range and the ambient operating humidity range.
3.1.35 radiance (L), n—the flux per unit projected area per unit solid angle leaving a source or, in general, any reference surface.
3.1.35.1 Discussion—
If ∂ Φ is the flux emitted into a solid angle ∂ω by a source element of projected area ∂Acos(θ), the radiance is defined as:
] Φ
L 5
]ω]Acos~θ!
where:
where:
θ = the angle between the outward surface normal of the area element ∂ A and the direction of observation (unit = W/sr•m ).
3.1.36 radiant power density (M), n—the radiant flux per unit area leaving a surface that is,
]Φ
M 5
]A
where:
where:
∂Φ = flux leaving a surface element ∂A (unit = W/m ).
3.1.37 reflectance, n—the ratio of the radiant flux reflected from a surface to that incident upon it.
3.1.38 reflected radiation, n—the thermal radiation incident upon and reflected from the measurement surface of the specimen.
3.1.39 reflected temperature, n—the temperature of the radiant flux incident upon and reflected from the measurement surface of
a specimen.
3.1.40 response time, n—time interval between the instant of an abrupt change in the value of the input parameter (object
temperature or object radiation) and the instant from which the measured value of the radiation thermometer (output parameter)
remains within specified limits of its final value.
3.1.41 sensor, n—device designed to respond to IR radiation and convert that response into electrical signals.
3.1.42 size-of-source effect, n—the difference in the radiance- or temperature reading of the radiation thermometer when changing
the size of the radiating area of the observed source.
3.1.43 spectral range, n—parameter which gives the lower and upper limits of the wavelength range over which the radiation
thermometer operates.
E2758 − 15a (2021)
3.1.43.1 Discussion—
Spectral range is sometimes referred to as bandwidth.
3.1.43.2 Discussion—
These limits are generally defined as the wavelengths where the power or signal is attenuated by a defined amount.
3.1.44 spectral response, n—the numerical quantity of a given phenomenon at a specific wavelength in the electromagnetic
spectrum.
3.1.45 standard atmosphere, n—a model of how electromagnetic radiation is transmitted through the atmosphere based on
variations in pressure, temperature and humidity.
3.1.46 surface-modifying material, n—any material that is used to change the emissivity of the specimen surface.
3.1.47 table of offsets, n—a list of calibration points and calibration adjustments to be used when no internal calibration adjustment
is available.
3.1.48 thermal radiation, n—electromagnetic radiation which is caused by an object’s temperature and is predicted by Planck’s
Law.
3.1.49 thermal shock, n—subjecting an IR thermometer to a rapid temperature change.
3.1.50 thermopile detector, n—a thermopile detector’s output is voltage. Incident radiation heats the disk. When the disk is heated,
its temperature rises above the sensor’s reference temperature (ambient temperature) producing a temperature difference (ΔT). The
potential of the thermopile is related to the temperature difference based on the Seebeck Effect.
3.1.51 transmittance (t), n—the ratio of the radiant flux transmitted through a body to that incident upon it.
3.1.52 true temperature, n—temperature attributed to a particular site of a subject or object of measurement and accepted as having
a specified uncertainty.
3.1.53 wideband, adj—referring to the situation where the spectral range of an instrument is at least ⁄10 of its center wavelength.
4. Significance and Use
4.1 This guide provides guidelines and basic test methods for the use of infrared thermometers. The purpose of this guide is to
provide a basis for users of IR thermometers to make more accurate measurements, to understand the error in measurements, and
reduce the error in measurements.
5. Basic Use of IR Thermometry
5.1 General Considerations:
5.1.1 An IR thermometer can be used in a number of applications. Although they are generally not as accurate as contact
thermometers, their quickness of measurement and their ability to measure the temperature of an opaque surface without contacting
it make them desirable instruments for some temperature measurements.
5.1.2 Most handheld IR thermometers are equipped with a trigger to start and stop the measurements.
5.1.3 A
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