ASTM E1256-95(2001)
(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:E1256–95 (Reapproved 2001)
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 2.2 Definitions of Terms Specific to This Standard:
2.2.1 reference temperature source, n—a source of thermal
1.1 The test methods described in these test methods can be
radiant power of known temperature or emissivity, or both,
utilized to evaluate the following six basic operational param-
used in the testing of radiation thermometers.
eters of a radiation thermometer (single waveband type):
2.2.2 target size, n—the diameter of a circle in the target
Section
plane of a radiation thermometer that is centered on its line of
Calibration Accuracy 7
Repeatability 8
sight and contains 99 % of the input radiant power received by
Target Size 9
that instrument.
Response Time 10
2.2.3 temperature resolution, n—the minimum simulated or
Warm-Up Time 11
Long-Term Drift 12
actual change in target temperature that gives a usable change
in output or indication, or both.
1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Significance and Use
responsibility of the user of this standard to establish appro-
3.1 The purpose of these test methods is to establish
priate safety and health practices and determine the applica-
consensus test methods by which both manufacturers and end
bility of regulatory limitations prior to use.
users may make tests to establish the validity of the readings of
2. Terminology
their radiation thermometers. The test results can also serve as
standard performance criteria for instrument evaluation or
2.1 Definitions:
selection, or both.
2.1.1 blackbody, n—the perfect or ideal source of thermal
3.2 The goal is to provide test methods that are reliable and
radiant power having a spectral distribution described by the
can be performed by a sufficiently skilled end user or manu-
Planck equation.
facturer in the hope that it will result in a better understanding
2.1.1.1 Discussion—The term blackbody is often used to
of the operation of radiation thermometers and also promote
describe a furnace or other source of radiant power which
improved communication between the manufacturers and the
approximates the ideal.
end users.Auser without sufficient knowledge and experience
2.1.2 center wavelength, n—a wavelength, usually near the
should seek assistance from the equipment makers or other
middle of the band of radiant power over which a radiation
expert sources, such as those found at the National Institute of
thermometer responds, that is used to characterize its perfor-
Standards and Technology in Gaithersburg, Maryland.
mance.
3.3 Use these test methods with the awareness that there are
2.1.2.1 Discussion—The value of the center wavelength is
other parameters, particularly spectral response limits and
usually specified by the manufacturer of the instrument.
temperature resolution, which impact the use and characteriza-
2.1.3 radiation thermometer, n—a radiometer calibrated to
tion of radiation thermometers for which test methods have not
indicate the temperature of a blackbody.
yet been developed.
2.1.4 radiometer, n—a device for measuring radiant power
3.3.1 Temperature resolution is the minimum simulated or
that has an output proportional to the intensity of the input
actual change in target temperature that results in a usable
power.
change in output or indication, or both. It is usually expressed
2.1.5 target plane, n—the plane, perpendicular to the line of
as a temperature differential or a percent of full-scale value, or
sight of a radiation thermometer, that is in focus for that
both, and usually applies to value measured. The magnitude of
instrument.
the temperature resolution depends upon a combination of four
factors: detector noise equivalent power (NEP) or noise
These test methods are under the jurisdiction of ASTM Committee E20 on
equivalent temperature, electronic signal processing, signal-to-
TemperatureMeasurementandarethedirectresponsibilityofSubcommitteeE20.02
noise characteristics (including amplification noise), and
on Radiation Thermometry.
analog-to-digital conversion “granularity.”
Current edition approved Oct. 10, 1995. Published January 1996. Originally
published as E 1256 – 88. Last previous edition E 1256 – 88.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1256
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
from extraneous sources of radiation as discussed in 4.1.4.1.
4.1.6 Data Acquisition Systems—Of appropriate speed and
storage capacity to measure and record the output signal of the
radiation thermometer in the Response Time Test Method,
Section 9.
4.1.7 Power Supply—Capable of supplying the proper volt-
age and frequency, if necessary, to the radiation thermometer.
5. Calibration Accuracy Test Method
5.1 Summary—This test method outlines the procedure to
be used to evaluate the maximum deviation between the
temperature indicated by the radiation thermometer and the
FIG. 1 Spectral Response Limits
known temperature of a reference temperature source, includ-
ing the uncertainty of the reference temperature source relative
to the current International Temperature Scale.
3.3.2 Spectral response limits are the upper and lower limits
5.2 Test Conditions:
to the wavelength band of radiant energy to which the
instrument responds. These limits are generally expressed in 5.2.1 Rated supply voltage and frequency.
micrometers (µm) and include the effects of all elements in the
5.2.2 Prescribed warm-up period.
measuring optical path. At the spectral response limits, the
5.2.3 After execution of internal standardization check (if
transmission of the measuring optics is 5 % of peak transmis-
available).
sion (see Fig. 1).
5.2.4 Emissivity compensation set to one (1).
5.2.5 Minimumopeningofthereferencetemperaturesource
4. Apparatus
shallnotobstructthefieldofviewoftheradiationthermometer
4.1 The following apparatus, set up as illustrated in Fig. 2,
with the test aperture as specified by the manufacturer.
can be used to perform the standard tests for all six parameters.
5.2.6 Laboratory ambient temperature range (20 to 25 °C).
4.1.1 Reference Temperature Source—A blackbody (or
5.2.7 Manufacturer shall specify any special conditions
other stable isothermal radiant source of high and known
such as atmospheric absorption effects, target distance, etc.
emissivity) with an opening diameter at least as large as that
5.2.8 Manufacturer shall specify the output for determining
specified in these test methods.
the indicated temperature.
NOTE 1—Typical examples include nearly isothermal furnaces with
5.3 Test Method:
internal geometries, such as a sphere with an opening small relative to its
5.3.1 The radiation thermometer is sighted at the reference
radius, or a right circular cylinder with one end closed having a radius
2 temperature source whose temperature is sequentially stabi-
small relative to its length. Consult footnote for greater detail.
lized at three calibration points distributed uniformly over the
4.1.2 Temperature Indicator—Either contact or radiometric,
measurement range of the instrument.
which accurately displays the temperature of the reference
5.3.2 The temperature of the reference temperature source
temperature source.
and the temperature indicated by the radiation thermometer are
4.1.3 Shutter Mechanism—Of sufficient size so as to com-
recorded, then the difference between the two values is
pletely block the opening of the reference temperature source
calculated and recorded (see Fig. 3).
from the field of view of the test instrument. The shutter
5.3.3 The test sequence is repeated twice for the same three
mechanism shall activate in a time interval that is short when
calibration points, and an average temperature difference is
compared with the response time of the test instrument.
calculated and recorded for each calibration point.
4.1.4 Iris Diaphragm—Of sufficient size so that when fully
5.4 Test Result—The value for the calibration accuracy of
open the iris diameter is greater than the opening of the
the temperature indication of the radiation thermometer is
reference temperature source. It shall be located with its
taken to be the largest of the three average temperature
opening concentric with and perpendicular to the line of sight
differencesdeterminedin5.3.2plusorminustheuncertaintyof
of the radiation thermometer.
the temperature of the reference temperature source relative to
4.1.4.1 The side of the diaphragm facing the radiation
the current International Temperature Scale.
thermometer should be blackened (nearly nonreflective) so as
to minimize the effect of radiation reflected from the surround-
NOTE 2—The calibration accuracy is generally expressed as a tempera-
ing environment. In addition the iris should be shaded from ture difference or a percent of full-scale value, or both.
sources of intense extraneous radiation. (See Note 9).
NOTE 3—The value applies across the entire measurement range.
NOTE 4—If the reference temperature source is measured with other
than a calibrated reference or secondary standard radiation thermometer,
then the emissivity of the source enters into the calibration of the test
DeWitt, D. P., and Nutter, G. D., eds., “Theory and Practice of Radiation
Thermometry,” John Wiley and Sons, New York, NY. radiation thermometer.
E1256
FIG. 2 Test Method Apparatus
FIG. 3 Worksheet for Calibration Accuracy Test Method
6. Procedure 7.2 Test Conditions:
7.2.1 Rated supply of voltage and frequency.
6.1 Detailed directions for evaluation of each parameter
7.2.2 Prescribed warm-up period.
listed in 1.1 are included in each parameter test method.
7.2.3 After execution of internal standardization check (if
6.2 Each parameter test method is organized by: parameter
available).
term, summary, test conditions, test method, test result, and
7.2.4 Diameter of the reference temperature source opening
applicable notes.
shall be greater than the radiation thermometer target size, as
7. Repeatability Test Method
specified by the manufacturer.
7.2.5 Laboratory ambient temperature range (20 to 25 °C).
7.1 Summary—This test method outlines the procedure to
7.2.6 Emissivity compensation, if any, set to one (1).
be used to evaluate the repeatability of the temperature
indication of a radiation thermometer for a number of consecu- 7.2.7 Manufacturer shall specify any special conditions
tive measurements made under the same conditions over a such as response time, atmospheric absorption effects, target
specified interval of time. distance, etc.
E1256
FIG. 4 Target Diameter versus Target Distance from Instrument
7.3 Test Method: 8.2.5 Minimumopeningofthereferencetemperaturesource
7.3.1 Once a day for twelve consecutive working days, the shall be large enough so as to not obstruct the optical path of
radiation thermometer is sighted at the reference temperature the radiation thermometer, as specified by the manufacturer,
source whose temperature is stabilized at the approximate whenitissightedthroughanaperturethatistwicethediameter
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 Thetemperatureofthereferencetemperaturesourceis
readings of the radiation thermometer is taken to be the
stabilized at a value near the top of the calibration range of the
standard deviation of the twelve recorded readings.
radiation thermometer.
N
8.3.2 The iris is positioned in the front of and concentric
X !
~
N N ( i
i 5 1 with the opening of the reference temperature source (as
2 2
¯
~X 2 X! X 2
( (
i i
N
i 5 1 i 5 1 illustrated in Fig. 2). The iris is then adjusted to a diameter
Œ
S.D. 5 5!
N 2 1 N 2 1
slightly smaller (typically 10 %) than the expected target
diameter.
where:
S.D. = standard deviation,
NOTE 9—The iris should be kept cool enough so that its thermal
N = number of measurements,
emissiondoesnotcontributesignificantlytotheoutputsignal.Uncovering
X = value of the ith measurement, and the iris quickly can minimize heating, but this requires care. Evaluation of
i
N
¯
X = the error from this source requires computational procedures beyond the
X
( i scope of this test method; a discussion of such procedures can be found in
i 5 1
footnote 2. In most cases, however, the error is insignificant if the iris is
average of the twelve measurements = .
N
maintained near room temperature (20 °C) and the reference temperature
NOTE 6—The repeatability of the temperature indication is generally
source temperature is at or above 200 °C.
expressed as a temperature difference or a percent of full-scale value, or
8.3.3 The position of the radiation thermometer is then
both.
NOTE 7—Thevaluefortherepeatabilitycanbeappliedacrosstheentire adjusted vertically and horizontally and focused to produce
measurement range, or, the same test can be performed at other selected
maximum output while also maintaining the line of sight
temperatures across the measurement range in order to assess the
perpendicular to the iris.
repeatability of the radiation thermometer at those temperatures.
8.3.4 The iris is then opened to the point where the
temperature indicated by the radiation thermometer stops
8. Target Size Test Method
increasing, but its diameter is still smaller than the referen
...
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