ASTM E639-78(2002)
(Test Method)Standard Test Method for Measuring Total-Radiance Temperature of Heated Surfaces Using a Radiation Pyrometer (Withdrawn 2011)
Standard Test Method for Measuring Total-Radiance Temperature of Heated Surfaces Using a Radiation Pyrometer (Withdrawn 2011)
SCOPE
1.1 This test method covers the measurement of the total-radiance temperature (see section 2.1.20) of surfaces using a radiation pyrometer that is not in contact with the surface. The measured total-radiance temperature is then converted to the "true" surface temperature using an assumed or measured value of the surface emittance.
1.2 This test method includes those pyrometers which respond to a wide band of radiant energy (heat), that is, total radiation pyrometers, as well as those which respond to a relatively narrow band of radiant energy, that is, monochromatic or pseudomonochromatic radiation pyrometers. The latter are often referred to as "optical" pyrometers. The visual optical pyrometer, sometimes referred to as a "disappearing-filament" or "brightness" pyrometer, is not covered by this test method.
1.3 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.
WITHDRAWN RATIONALE
This test method covers the measurement of the total-radiance temperature of surfaces using a radiation pyrometer that is not in contact with the surface. The measured total-radiance temperature is then converted to the “true” surface temperature using an assumed or measured value of the surface emittance.
Formerly under the jurisdiction of Committee E21 on Space Simulation and Applications of Space Technology, this test method was withdrawn in May 2011. This standard is being withdrawn without replacement due to its limited use by industry.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:E639–78 (Reapproved 2002)
Standard Test Method for
Measuring Total-Radiance Temperature of Heated Surfaces
Using a Radiation Pyrometer
This standard is issued under the fixed designation E639; 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
´l = spectral emissivity of that surface at the same
temperature,
1.1 This test method covers the measurement of the total-
L ,l = spectral radiance of a blackbody radiator at
radiance temperature (see section 2.1.20) of surfaces using a e
that temperature, and
radiation pyrometer that is not in contact with the surface. The
l and l = limits of the spectral band involved.
measured total-radiance temperature is then converted to the 1 2
For a pyrometer in which the spectral response varies over
“true” surface temperature using an assumed or measured
its wavelength range of sensitivity, the band emissivity should
value of the surface emittance.
also be weighted by the relative spectral responsivity, R (l), of
1.2 This test method includes those pyrometers which
the pyrometer. The equation then becomes:
respond to a wide band of radiant energy (heat), that is, total
l2
radiation pyrometers, as well as those which respond to a
´l L R~l!dl
* e,l
l1
relatively narrow band of radiant energy, that is, monochro-
´ 5 (2)
b l2
matic or pseudomonochromatic radiation pyrometers. The
L R~l!dl
* e,l
l1
latter are often referred to as “optical” pyrometers. The visual
Eq 2 is required only when both the spectral emissivity, ´ ,
optical pyrometer, sometimes referred to as a “disappearing-
l
and the relative spectral responsivity, R (l), vary over the
filament” or “brightness” pyrometer, is not covered by this test
wavelength band of interest. If ´ is constant, its value is used,
method.
l
and neither equation is required. If R (l) is constant, but ´
1.3 This standard does not purport to address all of the
l
varies, Eq 1 is used.
safety concerns, if any, associated with its use. It is the
It should be noted that ´ is a function of temperature even
responsibility of the user of this standard to establish appro-
b
for those materials whose spectral emissivity is independent of
priate safety and health practices and determine the applica-
temperature, since the relative distribution of L ,lvaries mark-
bility of regulatory limitations prior to use.
e
edly with temperature.
2. Terminology
2.1.2 blackbody—a thermal radiator that completely ab-
2.1 Definitions: sorbs all incident radiation, whatever the wavelength or direc-
tion of incidence. This radiator has the maximum spectral
2.1.1 band emissivity—the weighted average spectral emis-
sivity of a given surface at a given temperature and over a concentration of radiant emittance at a given temperature (1) ;
that is, blackbody is an ideal thermal radiator. Devices can be
specified wavelength band, with the spectral radiance of a
blackbody radiator at the given temperature as the weighting constructed which approximate an ideal blackbody by provid-
ing an opaque-walled heated cavity with a small opening (for
function. Expressed mathematically:
example, 2, 3) and are commonly called laboratory blackbod-
l2
´l L dl
* e,l
ies.
l1
´ 5 (1)
b l2
2.1.3 directional—in a given direction from a surface. For
L dl
* e,l
l1
isotropic surfaces this may be designated by the polar angle, u,
from the normal to the surface to the given direction. For
where:
nonisometric surfaces, the azimuth angle, f, measured from a
´b = band emissivity of a surface at some known
fiducialmarkonthesampletotheplaneofincidence,mustalso
temperature,
be given. Directional is indicated in the general case by the
symbol (u)or(u,f) following the symbol for the quantity or
property, as L (u,f)or ´(u). For a specific case the angle in
This test method is under the jurisdiction of ASTM Committee E21 on Space
degrees is substituted for u and f.
Simulation andApplications of Space Technology and is the direct responsibility of
Subcommittee E21.08 on Thermal Protection.
Current edition approved May 10, 2002. Published May 2002. Originally
´1 2
approved in 1978. Last previous edition approved in 1996 as E639 – 78 (1996) . The boldface numbers in parentheses refer to the list of references appended to
DOI: 10.1520/E0639-78R02. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E639–78 (2002)
2.1.4 emissivity, ´—the ratio of the radiant existance of the property, as L or ´. It generally refers to quantities of
t t
thermalradiatortothatofablackbodyatthesametemperature. backbody radiation, or properties involving blackbody radia-
The emissivity is a measure of the extent to which a surface tion, and is precisely indicated by giving the temperature of the
deviates from an ideal radiative surface. blackbody source, in kelvins, as L(300K) or ´(300K).
t t
2.1.5 hemispherical—in all directions from a surface, and
2.1.16 total directional emissivity, ´(u,f,T)—is the emis-
t
generally refers only to properties. It is indicated by the sivity in direction u averaged over all wavelengths, or the ratio
subscript h as ´ , and means properly weighted averaged over
of the radiance of a given surface at a given temperature in a
h
all directions. given direction to that of a blackbody radiator at the same
2.1.6 irradiance, E =dF /dA—the ratio of the radiant flux
temperature.
e e
incident on an infinitesimal surface element, to the area of that
2.1.17 total emissivity, ´ (T)—the weighted average spec-
t
element (4).
tral emissivity, ´(l,T) in which the weighting function is the
2.1.7 irradiation—theexposureofanobjecttoradiation(1).
spectral radiance of a blackbody radiator at temperature T, and
2.1.8 radiance, L =dF /dv dA cos u,(in a given direction,
e e the average is taken over all wavelengths at which significant
at a point on a surface)—quotient of the radiant flux leaving,
emission occurs.
arriving at, or passing through an element of area surrounding
2.1.18 total hemispherical emissivity, ´ (T)—emissivity
t,h
the point and propagated in direction s, u, v, defined by an
averaged over all wavelengths and all directions, or the ratio of
elementary cone containing the direction, by the product of the
the total exitance from a given surface at a given temperature,
solid angle of the cone, dv, and the area of the orthogonal
T, to the blackbody radiator at the same temperature.
projectionoftheelementofsurfaceonaplaneperpendicularto
2.1.18.1 Discussion—A true blackbody radiator is lamber-
the given direction, dA cos u. See Fig. 1.
tain; that is, its radiance is independent of direction. However,
2.1.9 radiant energy, Q —the quantity of energy transferred
e
laboratory blackbodies (heated cavities) are usually lambertian
by radiation (4).
over only a relatively small solid angle about the normal to the
2.1.10 radiant exitance, M =dF /dA—the ratio of the ra-
e e
plane of the aperture of the cavity.
diant flux emitted by an infinitesimal surface element to the °
2.1.19 total normal emissivity, ´ (0 ,T)—the total direc-
t
areaofthatelement(4).Notethatthisahemisphericalquantity.
tional emissivity normal to the surface.
2.1.11 radiant flux, F —the energy per unit time (power)
e
2.1.20 total-radiance temperature—the temperature of a
emited, transmitted, or incident in the form of radiation (4).
blackbody that has the same total-radiance as the body consid-
2.1.12 responsivity (of the pyrometer)—the ratio of detector
ered. The radiance of the body must be averaged over the solid
output to radiance input. It may vary with wavelength.
angle subtended by the entrance window of the pyrometer used
2.1.13 spectral—for a radiometeric quantity (energy, flux,
for the measurement, from the surface of the body (4).
radiance, exitance), the spectral concentration of the quantity
2.1.20.1 Discussion—No radiation pyrometer can collect
perunitwavelengthintervalatagivenwavelength, l,indicated
the radiant flux emitted by a body into a complete hemisphere,
by the subscript l following the symbol for the property, as L .
l
and most radiation pyrometers collect the radiant flux emitted
For a radiometric property (absorptance, emissivity, etc.), it is
into a very small solid angle. Since for many materials the
thevalueofthepropertyataspecifiedwavelength, l,indicated
directional emissivity varies markedly with direction, signifi-
by the symbol (l) following the symbol for the property, as
cant errors can result if total hemispherical emissivity is used
´(l). For precise indication, the symbol l is replaced by the
for the emissivity correction instead of total directional emis-
value of the wavelength, usually in micrometres.
sivity in the direction of viewing.
2.1.14 spectral emissivity, ´(l,T)—the emissivity at wave-
length l, or the ratio of the radiance or exitance at wavelength
3. Summary of Test Method
l of a given surface at a given temperature to that of a
3.1 Manysurfacesreachhightemperatureswhenexposedto
blackbody at the same temperture.
high-energy convective flows or other heating environments.
2.1.15 total—integrated (for a quantity) or averaged (for a
The hot surfaces emit radiant energy that can be used to
property) over all wavelengths. It is generally indicated by
determine surface temperature. The energy is emitted in a
adding the subscript t to the symbol for the quantity or
given direction in a known solid angle and from a known
surface area, that is, the radiance is focused on a detector that
is responsive to the incident energy. The total-radiance tem-
perature of the surface is then determined from the electrical
output of the detector, through proper calibration of the
detector using a blackbody source at a known temperature. A
measurement or estimate of the emittance of the emitting
surfaceisthenusedtoconvertthetotal-radiancetemperatureto
the “true” surface temperature. For the method to be accurate,
radiation reflected from the surface and absorption by and
emission from gaseous vapors and entrained particulates be-
tween the surface and the detector must be accurately ac-
counted for or determined to be negligible. When this criterion
FIG. 1 Illustration of Radiance is met, the method can be used with ablating surfaces. The
E639–78 (2002)
optics must be capable of transmitting energy over the wave- 4.3 Aphotosensitivedetectorhashighresponsivityandvery
lengths for which the surface emits significant amounts of rapidtimeresponse.Sometypesarebetterinbothrespectsthan
energy.Also, the detector must be capable of responding to the the best pyroelectric detectors now available. However, the
energyatthesewavelengths.Itispossibletousethemethodfor more common photosensitive materials that are useful at room
radiatively heated surfaces if the detector has a rapid response temperature are sensitive only to radiation in the visible and
time and the radiative source can be periodically “chopped” to near infrared portions of the spectrum. Those that respond at
separate emitted energy from surface reflected energy. In some wavelengths beyond about 2.5 µm are noisy, and usually
situations, the band blockage characteristic of the windows or require cryogenic cooling to achieve a satisfactory signal-to-
envelopes of the source can be used to advantage by using noise ratio. The spectral band over which these detectors
pyrometers with response limited to the blocked band; the respond is narrow compared to that of thermal detectors, and
radiant heating source is thus effectively blocked at all times. the spectral responsivity usually varies widely over that band
(2, 5).
4. Significance and Use
4.3.1 Photosensitive devices can be used, providing ad-
4.1 This test method utilizes a radiation pyrometer to
equate care has been taken in the design and calibration, to
measure the radiance of an emitting surface. Generally, radia-
properly protect the detector from overheating, to provide for
tion pyrometers are classified by the type of detector used as
temperature compensation, to verify uniform sensitivity over
either thermoelectric radiation pyrometers or photosensitive
the detector surface, and to account for wavelength sensitivity.
radiation pyrometers (2, 3). The thermoelectric radiation py-
The detector should have a known response to energy at
rometer utilizes a detector that depends upon a temperature
wavelengths in the visible and near infrared regions or at least
difference to provide a response. Included in this class are
over the bandpass of the pyrometer optics.
thermopiles, pyroelectric detectors, and bolometers. The pho-
4.4 The advantages offered by a thermoelectric radiation
tosensitive radiation pyrometer utilizes a detector where the
pyrometer make it one of the most desirable for use in the
direct effect of the radiant energy impinging on the detector
measurement of surface temperature. However, a rapid re-
material provides a response. Included in this class are photo-
sponse detector, such as photosensitive or pyroelectric, is
emissive, photoconductive, and photovoltaic materials.
mandatory if the method is to be used with a radiatively heated
4.2 Advantages of the thermoelectric radiation pyrometer
surface since the measurement of total-radiance temperature
include ruggedness, survivability in high ambient tempera-
must be obtained when the source is blocked to separate
tures, and uniform sensitivity over a wide range of wave-
reflected and emitted energy and the period of time that the
lengths. The major disadvantage is slow time response.
source is blocked should be small.
4.2.1 The thermopile detector is constructed so that one set
4.5 For the method to be accurate, emission or absorption
of thermojunctions serves as the receiver that is irradiated. The
from any high-temperature boundary layer surrounding the
other set of thermojunctions is isolated from the radiant energy
surface, that is, those containing certain gaseous vapors or
and is located to conform to the pyrometer body temperature.
entrained particulates, must either be small relative to emission
The resulting temperature difference, which depends upon the
from the surface or well known. Furthermore, the surface
magnitude of the impinging radiant energy, produces a ther-
temperature, the surface emittance, and appropriate combina-
moelectric emf that is related in a direct manner to the
tions thereof must be sufficiently large to provide adequate
total-radiance temperature of the viewed surface. The respon-
radiance from the surface. A correction must b
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