ASTM E1256-95
(Test Method)Standard Test Methods for Radiation Thermometers (Single Waveband Type)
Standard Test Methods for Radiation Thermometers (Single Waveband Type)
SCOPE
1.1 The test methods described in these test methods can be utilized to evaluate the following six basic operational parameters of a radiation thermometer (single waveband type):SectionCalibration Accuracy7Repeatability8Target Size9Response Time10Warm-Up Time11Long-Term Drift12
1.2 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.
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Designation: E 1256 – 95
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Methods for
Radiation Thermometers (Single Waveband Type)
This standard is issued under the fixed designation E 1256; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope radiant power of known temperature or emissivity, or both,
used in the testing of radiation thermometers.
1.1 The test methods described in these test methods can be
2.2.2 target size, n—the diameter of a circle in the target
utilized to evaluate the following six basic operational param-
plane of a radiation thermometer that is centered on its line of
eters of a radiation thermometer (single waveband type):
sight and contains 99 % of the input radiant power received by
Section
that instrument.
Calibration Accuracy 7
Repeatability 8
2.2.3 temperature resolution, n—the minimum simulated or
Target Size 9
actual change in target temperature that gives a usable change
Response Time 10
in output or indication, or both.
Warm-Up Time 11
Long-Term Drift 12
3. Significance and Use
1.2 This standard does not purport to address all of the
3.1 The purpose of these test methods is to establish
safety concerns, if any, associated with its use. It is the
consensus test methods by which both manufacturers and end
responsibility of the user of this standard to establish appro-
users may make tests to establish the validity of the readings of
priate safety and health practices and determine the applica-
their radiation thermometers. The test results can also serve as
bility of regulatory limitations prior to use.
standard performance criteria for instrument evaluation or
2. Terminology
selection, or both.
3.2 The goal is to provide test methods that are reliable and
2.1 Definitions:
can be performed by a sufficiently skilled end user or manu-
2.1.1 blackbody, n—the perfect or ideal source of thermal
facturer in the hope that it will result in a better understanding
radiant power having a spectral distribution described by the
of the operation of radiation thermometers and also promote
Planck equation.
improved communication between the manufacturers and the
2.1.1.1 Discussion—The term blackbody is often used to
end users. A user without sufficient knowledge and experience
describe a furnace or other source of radiant power which
should seek assistance from the equipment makers or other
approximates the ideal.
expert sources, such as those found at the National Institute of
2.1.2 center wavelength, n—a wavelength, usually near the
Standards and Technology in Gaithersburg, Maryland.
middle of the band of radiant power over which a radiation
3.3 Use these test methods with the awareness that there are
thermometer responds, that is used to characterize its perfor-
other parameters, particularly spectral response limits and
mance.
temperature resolution, which impact the use and characteriza-
2.1.2.1 Discussion—The value of the center wavelength is
tion of radiation thermometers for which test methods have not
usually specified by the manufacturer of the instrument.
yet been developed.
2.1.3 radiation thermometer, n—a radiometer calibrated to
3.3.1 Temperature resolution is the minimum simulated or
indicate the temperature of a blackbody.
actual change in target temperature that results in a usable
2.1.4 radiometer, n—a device for measuring radiant power
change in output or indication, or both. It is usually expressed
that has an output proportional to the intensity of the input
as a temperature differential or a percent of fullscale value, or
power.
both, and usually applies to value measured. The magnitude of
2.1.5 target plane, n—the plane, perpendicular to the line of
the temperature resolution depends upon a combination of four
sight of a radiation thermometer, that is in focus for that
factors: detector noise equivalent power (NEP) or noise
instrument.
equivalent temperature, electronic signal processing, signal-to-
2.2 Definitions of Terms Specific to This Standard:
noise characteristics (including amplification noise), and
2.2.1 reference temperature source, n—a source of thermal
analog-to-digital conversion “granularity.”
3.3.2 Spectral response limits are the upper and lower limits
These test methods are under the jurisdiction of ASTM Committee E-20 on
to the wavelength band of radiant energy to which the
Temperature Measurement and are the direct responsibility of Subcommittee E20.02
on Radiation Thermometry.
instrument responds. These limits are generally expressed in
Current edition approved Oct. 10, 1995. Published January 1996. Originally
micrometers (μm) and include the effects of all elements in the
published as E 1256 – 88. Last previous edition E 1256 – 88.
E 1256
measuring optical path. At the spectral response limits, the which accurately displays the temperature of the reference
transmission of the measuring optics is 5 % of peak transmis- temperature source.
sion (see Fig. 1). 4.1.3 Shutter Mechanism—Of sufficient size so as to com-
pletely block the opening of the reference temperature source
from the field of view of the test instrument. The shutter
mechanism shall activate in a time interval that is short when
compared with the response time of the test instrument.
4.1.4 Iris Diaphragm—Of sufficient size so that when fully
open the iris diameter is greater than the opening of the
reference temperature source. It shall be located with its
opening concentric with and perpendicular to the line of sight
of the radiation thermometer.
4.1.4.1 The side of the diaphragm facing the radiation
thermometer should be blackened (nearly nonreflective) so as
to minimize the effect of radiation reflected from the surround-
ing environment. In addition the iris should be shaded from
sources of intense extraneous radiation. (See Note 9).
4.1.5 Aperture Set—If an iris diaphragm is not available, an
aperture disc set of appropriate diameters can be used. Each
aperture should be blackened and also mounted and protected
FIG. 1 Spectral Response Limits
from extraneous sources of radiation as discussed in 4.1.4.1.
4.1.6 Data Acquisition Systems—Of appropriate speed and
4. Apparatus
storage capacity to measure and record the output signal of the
4.1 The following apparatus, set up as illustrated in Fig. 2,
FIG. 2 Test Method Apparatus
can be used to perform the standard tests for all six parameters. radiation thermometer in the Response Time Test Method,
4.1.1 Reference Temperature Source—A blackbody (or Section 9.
other stable isothermal radiant source of high and known
4.1.7 Power Supply—Capable of supplying the proper volt-
emissivity) with an opening diameter at least as large as that age and frequency, if necessary, to the radiation thermometer.
specified in these test methods.
5. Calibration Accuracy Test Method
NOTE 1—Typical examples include nearly isothermal furnaces with
internal geometries, such as a sphere with an opening small relative to its 5.1 Summary—This test method outlines the procedure to
radius, or a right circular cylinder with one end closed having a radius
be used to evaluate the maximum deviation between the
small relative to its length. Consult footnote for greater detail.
temperature indicated by the radiation thermometer and the
known temperature of a reference temperature source, includ-
4.1.2 Temperature Indicator—Either contact or radiometric,
ing the uncertainty of the reference temperature source relative
to the current International Temperature Scale.
2 5.2 Test Conditions:
DeWitt, D. P., and Nutter, G. D., eds., “Theory and Practice of Radiation
Thermometry,” John Wiley and Sons, New York, NY. 5.2.1 Rated supply voltage and frequency.
E 1256
NOTE 4—If the reference temperature source is measured with other
5.2.2 Prescribed warm-up period.
than a calibrated reference or secondary standard radiation thermometer,
5.2.3 After execution of internal standardization check (if
then the emissivity of the source enters into the calibration of the test
available).
radiation thermometer.
5.2.4 Emissivity compensation set to one (1).
5.2.5 Minimum opening of the reference temperature source
6. Procedure
shall not obstruct the field of view of the radiation thermometer
6.1 Detailed directions for evaluation of each parameter
with the test aperture as specified by the manufacturer.
listed in 1.1 are included in each parameter test method.
5.2.6 Laboratory ambient temperature range (20 to 25°C).
6.2 Each parameter test method is organized by: parameter
5.2.7 Manufacturer shall specify any special conditions
term, summary, test conditions, test method, test result, and
such as atmospheric absorption effects, target distance, etc.
applicable notes.
5.2.8 Manufacturer shall specify the output for determining
7. Repeatability Test Method
the indicated temperature.
5.3 Test Method:
7.1 Summary—This test method outlines the procedure to
5.3.1 The radiation thermometer is sighted at the reference
be used to evaluate the repeatability of the temperature
temperature source whose temperature is sequentially stabi-
indication of a radiation thermometer for a number of consecu-
lized at three calibration points distributed uniformly over the
tive measurements made under the same conditions over a
measurement range of the instrument.
specified interval of time.
5.3.2 The temperature of the reference temperature source
7.2 Test Conditions:
and the temperature indicated by the radiation thermometer are
7.2.1 Rated supply of voltage and frequency.
recorded, then the difference between the two values is
7.2.2 Prescribed warm-up period.
calculated and recorded (see Fig. 3).
7.2.3 After execution of internal standardization check (if
5.3.3 The test sequence is repeated twice for the same three
available).
calibration points, and an average temperature difference is
7.2.4 Diameter of the reference temperature source opening
calculated and recorded for each calibration point.
shall be greater than the radiation thermometer target size, as
5.4 Test Result—The value for the calibration accuracy of
specified by the manufacturer.
the temperature indication of the radiation thermometer is
7.2.5 Laboratory ambient temperature range (20 to 25°C).
taken to be the largest of the three average temperature
7.2.6 Emissivity compensation, if any, set to one (1).
differences determined in 5.3.2 plus or minus the uncertainty of
7.2.7 Manufacturer shall specify any special conditions
the temperature of the reference temperature source relative to
such as response time, atmospheric absorption effects, target
the current International Temperature Scale.
distance, etc.
7.3 Test Method:
NOTE 2—The calibration accuracy is generally expressed as a tempera-
7.3.1 Once a day for twelve consecutive working days, the
ture difference or a percent of full scale value, or both.
NOTE 3—The value applies across the entire measurement range. radiation thermometer is sighted at the reference temperature
FIG. 3 Worksheet for Calibration Accuracy Test Method
E 1256
source whose temperature is stabilized at the approximate when it is sighted through an aperture that is twice the diameter
midpoint of the radiation thermometer calibration range. of the instrument’s target size at the plane of the aperture.
NOTE 5—The selected reference temperature source temperature shall NOTE 8—Some radiation thermometers have a target size so large that
be reproduced for each of the twelve consecutive tests. a commercially available reference temperature source cannot be used; a
separate test method is under preparation for use in such cases.
7.3.2 The temperature of the reference temperature source
and the temperature(s) indicated by the radiation thermometer 8.2.6 Manufacturer shall specify any special conditions
during each day’s test are recorded. such as atmospheric absorption effects, distance, how and
7.3.3 The radiation thermometer shall be switched off after when to clean the radiation thermometer lens, etc.
each series of measurements. 8.3 Test Method:
7.4 Test Result—The value for the repeatability of the 8.3.1 The temperature of the reference temperature source is
readings of the radiation thermometer is taken to be the stabilized at a value near the top of the calibration range of the
radiation thermometer.
standard deviation of the twelve recorded readings.
8.3.2 The iris is positioned in the front of and concentric
N
with the opening of the reference temperature source (as
~ X !
N N ( i
i 5 1
2 2
¯
illustrated in Fig. 2). The iris is then adjusted to a diameter
~X 2 X! X 2
( (
i i
N
i 5 1 i 5 1
˛
slightly smaller (typically 10 %) than the expected target
S.D. 5 5 !
N 2 1 N 2 1
diameter.
where:
NOTE 9—The iris should be kept cool enough so that its thermal
S.D. 5 standard deviation,
emission does not contribute significantly to the output signal. Uncovering
N 5 number of measurements,
the iris quickly can minimize heating, but this requires care. Evaluation of
X 5 value of the ith measurement, and
the error from this source requires computational procedures beyond the
i
N
¯
X 5
scope of this test method; a discussion of such procedures can be found in
X
(
i
footnote 2. In most cases, however, the error is insignificant if the iris is
i 5 1
average of the twelve measurements 5 . maintained near room temperature (20°C) and the reference temperature
N
source temperature is at or above 200°C.
NOTE 6—The repeatability of the temperature indication is generally
8.3.3 The position of the radiation thermometer is then
expressed as a temperature difference or a percent of full scale value, or
both.
adjusted vertically and horizontally and focused to produce
NOTE 7—The value for the repeatability can be applied across the entire
maximum output while also maintaining the line of sight
measurement range, or, the same test can be performed at other selected
perpendicular to the iris.
temperatures across the measurement range in order to assess the
8.3.4 The iris is then opened to the point where the
repeatability of the radiation thermometer at those temperatures.
temperature indicated by the radiation thermometer stops
increasing, but its diameter is still smaller than the reference
8. Target Size Test Method
temperature source opening.
8.1 Summary—This test method outlines the procedure to
8.3.5 The temperature indicated by the radiation
...
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