ASTM E2758-10
(Guide)Standard Guide for Selection and Use of Wideband, Low Temperature Infrared Thermometers
Standard Guide for Selection and Use of Wideband, Low Temperature Infrared Thermometers
SIGNIFICANCE AND USE
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 and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
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Designation: E2758 − 10
StandardGuide 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 E1256Test Methods for Radiation Thermometers (Single
Waveband Type)
1.1 This guide covers electronic instruments intended for
E1862Test Methods for Measuring and Compensating for
measurement of temperature by detecting intensity of thermal
Reflected Temperature Using Infrared Imaging Radiom-
radiation exchanged between the subject of measurement and
eters
the sensor.
E1897Test Methods for Measuring and Compensating for
1.2 The devices covered by this guide are referred to as IR
Transmittance of an Attenuating Medium Using Infrared
thermometers.
Imaging Radiometers
1.3 The IR thermometers covered in this guide are instru- E1933Test Methods for Measuring and Compensating for
Emissivity Using Infrared Imaging Radiometers
ments that are intended to measure temperatures below 1000
°Candmeasureawidebandofthermalradiationintheinfrared 2.2 IEC Standards:
IEC 62942-1 TS Industrial process control devices—
region.
Radiationthermometers—Part1:Technicaldataforradia-
1.4 This guide covers best practice in using IR thermom-
tion thermometers
eters. It addresses concerns that will help the user make better
measurements. It also provides graphical tables to help deter-
3. Terminology
mine the accuracy of measurements.
3.1 Definitions:
1.5 Details on the design and construction of IR thermom-
3.1.1 absolute zero, n—a temperature of 0 K (-273.15 °C).
eters are not covered in this guide.
3.1.2 atmospheric attenuation, n—a ratio showing how
1.6 This guide does not cover medium- and high-
muchthermalradiationinagivenspectralrangeisabsorbedor
temperature IR thermometry (above 1000 °C). It does not
scattered in air over a given distance.
address the use of narrowband IR thermometers.
3.1.3 atmospheric transmission, n—a ratio showing how
1.7 The values of quantities stated in SI units are to be
well thermal radiation in a given spectral range at a given
regarded as the standard. The values of quantities in parenthe- distance travels through a certain distance of air.
ses are not in SI and are optional.
3.1.4 attenuating medium, n—a semi-transparent solid, liq-
1.8 This standard does not purport to address all of the uid or gas, such as a window, filter, external optics and/or an
safety concerns, if any, associated with its use. It is the
atmosphere that reduces thermal radiation.
responsibility of the user of this standard to establish appro-
3.1.5 background radiation—see reflected radiation.
priate safety and health practices and determine the applica-
3.1.6 blackbody, n—the perfect or ideal source of thermal
bility of regulatory limitations prior to use.
radiant power having a spectral distribution described by
Planck’s Law.
2. Referenced Documents
2 3.1.7 blackbody simulator, n—a device with an emissivity
2.1 ASTM Standards:
close to unity that can be heated or cooled to a stable
temperature.
This guide is under the jurisdiction ofASTM Committee E20 on Temperature
3.1.8 calibration adjustment, n—the correction to an IR
Measurement and is the direct responsibility of Subcommittee E20.02 on Radiation
thermometer based on its calibration.
Thermometry.
Current edition approved May 1, 2010. Published June 2010. DOI:10.1520/ 3.1.9 center wavelength, n—thesimpleaverageofthelower
E2758-10.
and upper spectral range limits.
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
Standards volume information, refer to the standard’s Document Summary page on Available from International Electrotechnical Commission (IEC), 3, rue de
the ASTM website. Varembé, CH-1211 Geneva 20, Switzerland, www.iec.ch.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2758 − 10
3.1.10 celestial radiation, n—flux coming from the sky. mometer for handheld radiation thermometers. In general,
these devices are wideband and use a thermopile detector.
3.1.11 contact thermometer, n—an instrument that is
adapted for measuring temperature by means of thermal
3.1.25 IR thermometry, n—the use of IR thermometers to
conductance by determining the temperature at the moment
determine temperature by measuring thermal radiation.
when negligible thermal energy flows between the thermom-
3.1.26 irradiance (E), n—the radiant flux (power) per unit
eter and the object of measurement. 2
area incident on a given surface in units of W/m .
3.1.12 dew point, n—the temperature at which water vapor
3.1.27 limit of error, n—the extreme value of measurement
condenses into liquid water.
error of an infrared thermometer reading, relative to reference
3.1.13 diffuse reflector, n—a surface that produces a diffuse
temperature standards, as permitted by a specification.
image of a reflected source.
3.1.27.1 Discussion—Manufacturers sometimes use the
3.1.14 distance ratio, n—theratioofthemeasuringdistance
term accuracy in their specifications to represent limit of error.
to the diameter of the field-of-view, when the target is in
3.1.27.2 Discussion—A manufacturer’s accuracy specifica-
focus.
tion may apply only to well defined conditions.
3.1.15 electromagnetic radiation, n—physically occurring
3.1.28 low-temperature, adj—for radiation and IR
radiant flux classified according to wavelength or frequency.
thermometry, referring to any temperature below 660 °C.
3.1.16 emissivity (ε), n—the emissivity of a surface is the
3.1.29 measurement uncertainty (accuracy), n—parameter,
ratio between the radiation emitted from this surface and the
associated with the result of a measurement, that characterizes
radiation from a blackbody at the same temperature.
the dispersion of the values that could reasonably be attributed
3.1.16.1 Discussion—The emissivity describes a thermo-
to the measurand.
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
the measured object. 3.1.31 measuring temperature range, n—temperature range
for which the radiation thermometer is designed.
3.1.17 emissivity setting, n—an adjustment on an IR ther-
mometer to compensate for an emissivity of non-unity.
3.1.32 noise equivalent temperature difference (NETD),
3.1.17.1 Discussion—In most measuring situations a radia-
n—parameter which indicates the contribution of the measure-
tion thermometer is used on a surface with an emissivity
ment uncertainty in °C, which is due to instrument noise.
significantly lower than one. For this purpose most thermom-
3.1.33 opaque, adj—referring to the property of a material
eters have the possibility of adjusting the emissivity setting.
whose transmittance is zero for a given spectral range.
The temperature reading is then automatically corrected.
3.1.34 operating temperature range and air humidity range,
3.1.18 emissivity tables, n—a list of objects and their mea-
n—the permissible temperature range and humidity range
sured emissivity for a particular IR thermometer.
within which the radiation thermometer may be operated. For
3.1.19 field-of-view (FOV), n—a usually circular, flat sur-
this temperature range and humidity range the specifications
face of a measured object from which the radiation thermom-
are valid.
eter receives radiation.
3.1.35 radiance (L), n—the flux per unit projected area per
3.1.20 frost point, n—the temperature at which water vapor
unit solid angle leaving a source or, in general, any reference
condenses into solid water or ice.
surface.
3.1.21 infrared (IR), adj—referring to electromagnetic ra-
3.1.35.1 Discussion—If ∂ Φ is the flux emitted into a solid
diation with a wavelength from approximately 0.7 to 30 µm.
angle ∂ω by a source element of projected area ∂Acos(θ), the
radiance is defined as:
3.1.22 infrared reflector, n—a material with a reflectance in
the infrared region as close as possible to unity. 2
] Φ
L 5
3.1.23 infrared sensing device, n—one of a wide class of ]ω]Acos θ
~ !
instruments used to display or record or both information
where:
related to the thermal radiation received from any object
θ = theanglebetweentheoutwardsurfacenormalofthearea
surfaces viewed by the instrument.
element ∂ A and the direction of observation (unit =
3.1.24 infrared (IR) thermometer, n—optoelectronic instru- 2
W/sr•m ).
ment adapted for noncontact measurement of temperature of a
3.1.36 radiant power density (M), n—the radiant flux per
subject by utilizing thermal radiation exchange between the
unit area leaving a surface that is,
subject and the sensor.
3.1.24.1 Discussion—IRthermometersareasubsetofradia-
]Φ
M 5
tion thermometers. Most manufacturers use the term IR ther-
]A
where:
∂Φ = flux leaving a surface element ∂A (unit = W/m ).
See IEC62942-1.
E2758 − 10
3.1.37 reflectance, n—the ratio of the radiant flux reflected 5. Basic Use of IR Thermometry
from a surface to that incident upon it.
5.1 General Considerations
3.1.38 reflected radiation, n—the thermal radiation incident
5.1.1 An IR thermometer can be used in a number of
upon and reflected from the measurement surface of the
applications. Although they are generally not as accurate as
specimen.
contact thermometers, their quickness of measurement and
their ability to measure the temperature of an opaque surface
3.1.39 reflected temperature, n—the temperature of the
without contacting it make them desirable instruments for
radiant flux incident upon and reflected from the measurement
some temperature measurements.
surface of a specimen.
5.1.2 Most handheld IR thermometers are equipped with a
3.1.40 sensor, n—devicedesignedtorespondtoIRradiation
trigger to start and stop the measurements.
and convert that response into electrical signals.
5.1.3 As objects vary in temperature, they emit a varying
3.1.41 size-of-source effect, n—The difference in the
amount of thermal radiation. This amount of thermal radiation
radiance- or temperature reading of the radiation thermometer
ispredictablebasedontheobject’stemperature,emissivityand
when changing the size of the radiating area of the observed
reflected temperature.
source.
5.1.4 Handheld IR thermometers measure thermal radiation
in a given spectral range and determine the relationship
3.1.42 spectral range, n—parameter which gives the lower
between the measured thermal radiation and temperature. The
and upper limits of the wavelength range over which the
sensor mainly used in these instruments is a thermopile.
radiation thermometer operates.
3.1.42.1 Discussion—Spectral range is sometimes referred
5.2 Basic IR Measurement
to as bandwidth.
5.2.1 Before making a measurement, the emissivity setting
3.1.42.2 Discussion—These limits are generally defined as
of the IR thermometer should be set to the object’s effective
the wavelengths where the power or signal is attenuated by a
emissivity in the instrument’s spectral range. Some IR ther-
defined amount.
mometersdonotallowtheusertoadjusttheemissivitybecause
their emissivity is fixed. In these cases there are mathematical
3.1.43 spectral response, n—the numerical quantity of a
compensations that can be made.
given phenomenon at a specific wavelength in the electromag-
5.2.2 To make a measurement, the IR thermometer’s lens
netic spectrum.
should be pointed at the object being measured. The measure-
3.1.44 standard atmosphere, n—a model of how electro-
ment should be initiated. If the IR thermometer has a trigger,
magneticradiationistransmittedthroughtheatmospherebased
thisisdonebypullingthetrigger.Thetriggershouldbeheldat
on variations in pressure, temperature and humidity.
least as long as the IR thermometer’s specified response time.
3.1.45 surface-modifying material, n—any material that is
Themeasuredtemperatureisusuallyfrozenonthedisplayafter
used to change the emissivity of the specimen surface.
the trigger is released.
5.2.3 Fig. 1 shows a diagram of how much of a surface an
3.1.46 table of offsets, n—a list of calibration points and
IR thermometer measures. Subsection 11.1 discusses spot size
calibration adjustments to be used when no internal calibration
and distance-to-size ratio.
adjustment is available.
5.2.4 Fig. 2 shows how much surface area is needed for
3.1.47 thermal radiation, n—electromagnetic radiation
temperature measurement when considering the IR thermom-
which is caused by an object’s temperature and is predicted by
eter’s spot size. The part of the figure labeled ‘poor’ shows a
Planck’s Law.
situation where the object being measured is smaller than the
3.1.48 thermal shock, n—subjecting an IR thermometer to a
spotsize.Suchsituationsareundesirable.Thepartofthefigure
rapid temperature change.
labeled ‘OK’ shows a situation where the object being mea-
sured is slightly larger than the spot size. Such situations
3.1.49 transmittance (t), n—the ratio of the radiant flux
should produce acceptable temperature measurements. The
transmitted through a body to that incident upon it.
part of the figure labeled ‘better’ shows a situation where the
3.1.50 true temperature, n—temperature attributed to a
object being measured is significantly larger than the spot size.
particular site of a subject or object of measurement and
Thissituationwillproducethebesttemperaturemeasurements.
accepted as having a specified uncertainty.
5.3 Accuracy
3.1.51 wideband, adj—referring to the situation where the
5.3.1 To make accurate measurements, many factors must
spectral range of an instrument is at least ⁄10 of its center
be considered. The first is that the IR thermometer in use
wavelength.
shouldbecalibratedwithtraceabilitytoanationalmetrological
institute such as the National Institute of Standards and
4. Significance and Use
Technology (NIST). Calibration results can be implemented in
4.1 This guide provides guidelines and basic test methods subsequent measurements in two ways. If the IR thermometer
fortheuseofinfraredthermometers.Thepurposeofthisguide has an internal calibration adjustment, the user can use the
istoprovideabasisforusersofIRthermometerstomakemore reading on the readout. Some IR thermometer
...
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