IEC TS 62492-2:2013
(Main)Industrial process control devices - Radiation thermometers - Part 2: Determination of the technical data for radiation thermometers
Industrial process control devices - Radiation thermometers - Part 2: Determination of the technical data for radiation thermometers
IEC/TS 62492-2:2013(E) applies to radiation thermometry and addresses all technical data specified in IEC/TS 62492-1. It defines standard test methods which can be used by the end user of radiation thermometers to determine or confirm the fundamental metrological data of radiation thermometers with one wavelength range and one measurement field. It facilitates comparability and testability. Therefore, unambiguous test methods are stipulated for determining technical data, under standardised measuring conditions that can be performed by a sufficiently skilled end user to serve as standard performance criteria for instrument evaluation or selection.
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IEC/TS 62492-2 ®
Edition 1.0 2013-04
TECHNICAL
SPECIFICATION
colour
inside
Industrial process control devices – Radiation thermometers –
Part 2: Determination of the technical data for radiation thermometers
IEC/TS 62492-2:2013(E)
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IEC/TS 62492-2 ®
Edition 1.0 2013-04
TECHNICAL
SPECIFICATION
colour
inside
Industrial process control devices – Radiation thermometers –
Part 2: Determination of the technical data for radiation thermometers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
U
ICS 17.200.20; 25.040.40 ISBN 978-2-83220-737-6
– 2 – TS 62492-2 © IEC:2013(E)
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations . 9
4 Measurement conditions . 9
5 Determination of technical data . 9
5.1 Measuring temperature range . 9
5.1.1 General . 9
5.1.2 Test method . 10
5.2 Measurement uncertainty . 10
5.2.1 General . 10
5.2.2 Test method . 10
5.3 Noise equivalent temperature difference (NETD) . 11
5.3.1 General . 11
5.3.2 Test method . 11
5.4 Measuring distance . 12
5.5 Field-of-view (target size) . 12
5.5.1 General . 12
5.5.2 Test method . 13
5.6 Distance ratio . 14
5.7 Size-of-source effect (SSE) . 14
5.7.1 General . 14
5.7.2 Test method . 14
5.8 Emissivity setting . 15
5.9 Spectral range . 15
5.10 Influence of the internal instrument or ambient temperature (temperature
parameter) . 15
5.10.1 General . 15
5.10.2 Test method . 16
5.11 Influence of air humidity (humidity parameter) . 17
5.12 Long-term stability . 17
5.12.1 General . 17
5.12.2 Test method . 17
5.13 Short-term stability . 18
5.13.1 General . 18
5.13.2 Test method . 18
5.14 Repeatability . 18
5.14.1 General . 18
5.14.2 Test method . 19
5.15 Interchangeability . 19
5.15.1 General . 19
5.15.2 Test method . 19
5.16 Response time . 20
5.16.1 General . 20
5.16.2 Test method . 21
TS 62492-2 © IEC:2013(E) – 3 –
5.17 Exposure time . 22
5.17.1 General . 22
5.17.2 Test method . 23
5.18 Warm-up time . 24
5.18.1 General . 24
5.18.2 Test method . 24
5.19 Operating temperature and air humidity range . 25
5.19.1 General . 25
5.19.2 Test method . 25
5.20 Storage and transport temperature and air humidity range . 26
5.20.1 General . 26
5.20.2 Test method . 26
6 Safety requirement . 27
Annex A (informative) Change in indicated temperature of a radiation thermometer
corresponding to a change in the radiation exchange . 28
Bibliography . 29
Figure 1 – Relative signal to a signal at a defined aperture size (source size) of
100 mm in diameter for two infrared radiation thermometers A and B versus the source
diameter . 12
Figure 2 – Demonstration of the response time to a rising temperature step . 20
Figure 3 – Possible arrangement for determining the response time with two reference
sources . 22
Figure 4 – Demonstration of the exposure time . 22
Figure 5 – Example of warm-up time . 25
Table A.1 – The change in indicated temperature corresponding to a 1 % change in the
radiation exchange with a radiation thermometer at 23 °C (Example) . 28
– 4 – TS 62492-2 © IEC:2013(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL PROCESS CONTROL DEVICES –
RADIATION THERMOMETERS –
Part 2: Determination of the technical data
for radiation thermometers
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 62492-2, which is a technical specification, has been prepared by subcommittee 65B:
Measurement and control devices, of IEC technical committee 65: Industrial-process
measurement, control and automation.
TS 62492-2 © IEC:2013(E) – 5 –
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
65B/844/DTS 65B/859/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62492 series, published under the general title Industrial process
control devices – Radiation thermometers, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International Standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – TS 62492-2 © IEC:2013(E)
INDUSTRIAL PROCESS CONTROL DEVICES –
RADIATION THERMOMETERS –
Part 2: Determination of the technical data
for radiation thermometers
1 Scope
This part of IEC 62492, which is a Technical Specification, applies to radiation thermometry
and addresses all technical data specified in IEC/TS 62492-1. It defines standard test
methods which can be used by the end user of radiation thermometers to determine or
confirm the fundamental metrological data of radiation thermometers with one wavelength
range and one measurement field.
The purpose of this specification is to facilitate comparability and testability. Therefore,
unambiguous test methods are stipulated for determining technical data, under standardised
measuring conditions that can be performed by a sufficiently skilled end user to serve as
standard performance criteria for instrument evaluation or selection.
It is not compulsory for manufacturers and sellers of radiation thermometers to include all
technical data given in this document in the data sheets for a specific type of radiation
thermometer. Only the relevant data should be stated and should comply with this
specification and IEC/TS 62492-1.
NOTE Infrared ear thermometers are excluded from this Technical Specification.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC/TS 62492-1:2008, Industrial process control devices – Radiation thermometers – Part 1:
Technical data for radiation thermometers
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document the following terms and definitions apply.
NOTE The terms and definitions listed below comply with IEC/TS 62492-1.
3.1.1
measuring temperature range
temperature range for which the radiation thermometer is designed
3.1.2
measurement uncertainty
parameter, associated with the result of a measurement, that characterises the dispersion of
the values that could reasonably be attributed to the measurand
TS 62492-2 © IEC:2013(E) – 7 –
3.1.3
noise equivalent temperature difference
parameter which indicates the contribution of the measurement uncertainty in °C, which is due
to instrument noise
3.1.4
measuring distance
distance or distance range between the radiation thermometer and the target (measured
object) for which the radiation thermometer is designed
3.1.5
field-of-view
a usually circular, flat surface of a measured object from which the radiation thermometer
receives radiation
3.1.6
distance ratio
the ratio of the measuring distance to the diameter of the field-of-view, when the target is in
focus
3.1.7
size-of-source effect
the difference in the radiance or temperature reading of the radiation thermometer when
changing the size of the radiating area of the observed source
3.1.8
emissivity setting
ratio between the radiation emitted from this surface and the radiation from a blackbody at the
same temperature
Note 1 to entry: In most measuring situations a radiation thermometer is used on a surface with an emissivity
significantly lower than 1. For this purpose most thermometers have the possibility of adjusting the emissivity
setting. The temperature reading is then automatically corrected.
3.1.9
spectral range
parameter which gives the lower and upper limits of the wavelength range over which the
radiation thermometer collects radiation from a source
3.1.10
influence of the internal instrument temperature
influence of the ambient temperature
temperature parameter
parameter which gives the additional uncertainty of the measured temperature value
depending on the deviation of the temperature of the radiation thermometer from the value for
which the technical data is valid after warm-up time and under stable ambient conditions
3.1.11
influence of air humidity
humidity parameter
parameter which gives the additional uncertainty of the measured temperature value
depending on the relative air humidity at a defined ambient temperature
3.1.12
long-term stability
the reproducibility of measurements repeated over a long time period
Note 1 to entry: The time period is typically three months or one year.
– 8 – TS 62492-2 © IEC:2013(E)
3.1.13
short-term stability
the reproducibility of measurements repeated over a short time period
Note 1 to entry: The time period is several hours.
3.1.14
repeatability
twice the standard deviation of measurements repeated under the same conditions within a
very short time span
Note 1 to entry: The time span is several minutes.
3.1.15
interchangeability
the maximum deviation between the readings of two instruments of the same type operating
under identical conditions divided by two
3.1.16
response time
time interval between the instant of an abrupt change in the value of the input parameter and
the instant from which the measured value of the radiation thermometer remains within
specified limits of its final value
Note 1 to entry: The input parameter is an object temperature or an object radiation, and the output value is an
output parameter.
3.1.17
exposure time
time interval between an abrupt rise and an abrupt fall in the value of the input parameter,
such that the output value of the radiation thermometer reaches a given measurement value
Note 1 to entry: The input parameter is an object temperature or an object radiation.
3.1.18
warm-up time
time period needed for the radiation thermometer, after switching on, before it operates
according to its specifications
3.1.19
operating temperature
the permissible temperature range within which the radiation thermometer may be operated
Note 1 to entry: For this temperature the specifications are valid.
3.1.20
operating air humidity range
the permissible humidity range within which the radiation thermometer may be operated
Note 1 to entry: For this humidity range the specifications are valid.
3.1.21
storage and transport temperature
the permissible ambient temperature range within which the radiation thermometer may be
stored and transported without suffering permanent change
3.1.22
storage and transport air humidity range
the permissible humidity range within which the radiation thermometer may be stored and
transported without suffering permanent change
TS 62492-2 © IEC:2013(E) – 9 –
3.1.23
safety
freedom from unacceptable risk
3.1.24
risk
combination of the probability of the occurrence of harm and the severity of that harm
3.1.25
harm
physical injury or damage to the health of people, or damage to property or the environment
3.1.26
tolerable risk
risk which is accepted in a given context based on the current values of society
3.2 Abbreviations
FWHM Full width at half maximum
NETD Noise equivalent temperature difference
SSE Size-of-source effect
4 Measurement conditions
The following test conditions apply for all measurements, if not stated otherwise:
a) laboratory ambient temperature range from 18 °C to 28 °C;
b) any special ambient conditions (e.g. humidity range, maximum ambient temperature
change per time) and measurement conditions (e.g. measuring distance, radiating area
diameter, response time) given by the manufacturer for the specific radiation thermometer
to be adhered to;
c) the radiation thermometer to be connected to a power supply in accordance to the
manufacturer’s instructions;
d) the warm-up time specified by the manufacturer to be adhered to;
e) internal standardization check (initial self-test) to be carried out, if available;
f) emissivity setting set to 1 (one), if available;
g) the reference temperature source shall have a radiating area diameter as large as
possible and in any case greater than the radiation thermometer field-of-view (target area)
diameter;
h) all tests have to be performed with the reference temperature source set to a temperature
that is significantly different from ambient temperature and the internal temperature of the
radiation thermometer.
NOTE The reference temperature source is a radiation source of known radiation temperature in the spectral
range of the radiation thermometer. Usually it is a blackbody source realised by a cavity radiator of known
temperature. It will be called “reference source” throughout this document.
5 Determination of technical data
5.1 Measuring temperature range
5.1.1 General
The purpose of this test is to determine the measuring temperature range. For this
temperature range, the measurement uncertainty remains within the specified limits.
– 10 – TS 62492-2 © IEC:2013(E)
Measurement temperature range (5.1), as well as Measurement uncertainty (5.2) and Noise
equivalent temperature difference (5.3), are the most important parameters that specify a
radiation thermometer. These three parameters are correlated with each other and in general
noise equivalent temperature difference is larger at the lower limit of the measuring
temperature range where uncertainty is larger. This relation is demonstrated in Table A.1 and
the equation of Annex A.
NOTE Sometimes it is useful to determine additionally a wider indicating temperature range over which the
thermometer will display a temperature but its specifications are not guaranteed.
5.1.2 Test method
5.1.2.1 The determination of the measuring temperature range is performed in accordance
with 5.2.2 at the top and the bottom temperature of the specified measuring temperature
range.
Determination of the indicating temperature range:
5.1.2.2 Sight the radiation thermometer at the centre of the radiating area of the reference
source.
5.1.2.3 The temperature of the reference source is sequentially adjusted and stabilised at
temperatures around the minimum temperature and the maximum temperature of the
indicating temperature range given by the manufacturer, to determine the minimum and
maximum temperatures for which the radiation thermometer is still indicating.
5.1.2.4 These two temperatures give the indicating temperature range.
5.2 Measurement uncertainty
5.2.1 General
A detailed description of the different methods to determine the measurement uncertainty and
its confidence level is beyond the scope of this technical specification. In this technical
specification terms, concept and definition of uncertainty is based on ISO/IEC Guide 98-3 and
ISO/IEC Guide 99.
The described method is a basic test of the measurement uncertainty across the measuring
temperature range.
5.2.2 Test method
5.2.2.1 Sight the radiation thermometer at the centre of the radiating area of the reference
source.
5.2.2.2 The temperature of the reference source is sequentially stabilised at, at least, three
temperatures distributed at the top, the bottom and an intermediate temperature of the
measuring temperature range (see Note 1 of 5.2.2.5).
5.2.2.3 The temperature of the reference source and the temperature indicated by the
radiation thermometer are recorded. The difference between these two values is calculated
and recorded.
5.2.2.4 The test sequence is performed three times for the same three calibration points. An
average temperature difference is calculated and recorded for each calibration temperature
point.
5.2.2.5 The value of the measurement uncertainty of the radiation thermometer at each
calibration temperature is taken to be the average difference determined in 5.2.2.4 plus the
TS 62492-2 © IEC:2013(E) – 11 –
temperature uncertainty of the reference source in respect to the current International
Temperature Scale.
NOTE 1 The number of temperature points depends on the requirements of the specific thermometer and its
application.
NOTE 2 For radiation thermometers with more than one measuring temperature range each range is calibrated as
if it were a separate instrument.
Due to the small number of observations care shall be taken not to infer too much significance
from this basic test (i.e. no confidence level can be given).
In order to use this method to test for compliance of measuring temperature range and
measurement uncertainty with the data provided by the manufacturer, the temperature
uncertainty of the reference source shall be significantly smaller than the uncertainty of the
radiation thermometer.
5.3 Noise equivalent temperature difference (NETD)
5.3.1 General
The purpose of this method is to determine the NETD. The measured temperature and the
response time of the radiation thermometer are to be stated with the NETD. For some
instruments the NETD depends on the instrument or ambient temperature. For these
instruments the instrument or ambient temperature also has to be stated. For low cost
instruments the NETD may be limited by their resolution.
The NETD is generally largest at the lowest temperature of the measuring temperature range.
When using electronic measuring equipment, its bandwidth shall be noted or set accordingly.
In particular, the bandwidth of the radiation thermometer shall not be limited by the bandwidth
of the external measuring equipment. In contrast to the other metrological data, the
confidence level in this case is 68,3 % (standard uncertainty, k = 1).
5.3.2 Test method
5.3.2.1 Sight the radiation thermometer at the centre of the radiating area of the reference
source.
5.3.2.2 The temperature of the reference source is stabilised at a temperature within the
measuring temperature range of the radiation thermometer. The greatest expected noise
amplitudes may not exceed the limits of the measuring temperature range.
5.3.2.3 The total measurement time is at least 100 times the set response time of the
radiation thermometer with at least 100 measured values taken.
5.3.2.4 The NETD of the radiation thermometer is calculated as the standard deviation of the
measured values, and stated together with the reference source temperature and the set
response time.
Noise caused by the temperature stability of the reference source and additional
measurement equipment shall be significantly lower than the noise of the radiation
thermometer.
According to 5.3.1 the NETD is expected to vary across the measuring temperature range.
Therefore, for completeness, the NETD should be determined at a minimum of two
temperatures, one of which is the lowest measuring temperature.
– 12 – TS 62492-2 © IEC:2013(E)
5.4 Measuring distance
For this distance or distance range the specifications are valid, if not stated otherwise. No
specific test method is needed.
NOTE The calibration of a radiation thermometer, with respect to a reference source of the same area, gives
different results at different distances due to the SSE of the instrument.
5.5 Field-of-view (target size)
5.5.1 General
Its magnitude is determined by the optical components in the radiation thermometer. As the
field-of-view is not sharply defined, it is necessary to state the diameter of the field-of-view at
which the radiation signal has dropped to a certain fraction of its total integrated value
(hemispherical value or the value for an infinitely extended source). The fraction value should
be at least 90 %; typical values are 90 %, 95 % and 99 %.
For some radiation thermometers, especially for high temperature instruments, it is
impracticable to relate the field-of-view to a hemispherical value. In this case it is allowed to
relate the given field-of-view to a larger source (e.g. twice as large in area as the field-of-
view).
As the field-of-view value depends on the measuring distance, it is necessary to state the
measuring distance in addition to the fraction.
The transfer function between the measured radiation (input parameter) and temperature
(output parameter) is non-linear. As an example the change in indicated temperature
corresponding to a 1 % change in the radiation exchange with a radiation thermometer is
given in Annex A. The field-of-view is therefore either defined for the fraction of measured
radiation or, for instruments which only read directly in temperature, it is necessary to specify
a change in the measured temperature in °C at a given temperature for the field-of-view in
comparison to the total integrated value (hemispherical value or the value for an infinitely
extended source). As a minimum, these values should be given for the top, middle and bottom
of the temperature range.
The complete field-of-view information would be a graph (see Figure 1), which shows the
signal or temperature versus source size (size-of-source effect).
A
B
0 2 4 6 8 10 12 14 16 18
1,8 IEC 683/13
Source diameter (mm)
Figure 1 – Relative signal to a signal at a defined aperture size (source size) of 100 mm
in diameter for two infrared radiation thermometers A and B versus the source diameter
Relative signal (%)
TS 62492-2 © IEC:2013(E) – 13 –
Explanation of Figure 1: The field-of-view diameter (target diameter) is stated as 1,8 mm for
each of the two radiation thermometers A and B. For radiation thermometer A, this
corresponds to 95 % of the maximum measuring signal, while for radiation thermometer B it
corresponds to 90 % of the maximum measuring signal. The figure indicates the change in the
measuring signal with the change in source diameter. In order to achieve 98 % of the
maximum measuring signal, a source diameter of 4,5 mm is required for radiation
thermometer A while a source diameter of 13 mm is required for radiation thermometer B. The
maximum measuring signal in this example is determined at a source (aperture) diameter of
100 mm and is taken to be 100 % of the hemispherical value.
The following test method determines the diameter of the field-of-view at which the signal has
dropped to a 99 % fraction of the hemispherical value or is related to a 99 % fraction of the
signal at a defined aperture size of the source. The method can be adapted accordingly to
determine the field of view of radiation thermometers which relates to 95 % or 90 % of the
hemispherical value or the signal at a defined aperture size of the source.
5.5.2 Test method
5.5.2.1 Sight the radiation thermometer at the centre of the radiating area of the reference
source at the specified measuring distance. Position an iris diaphragm in front of and
concentric with the opening of the reference source. The minimum opening of the reference
source shall be large enough so as not to obstruct the optical path (i.e. the nominal field-of-
view as specified by the manufacturer) of the radiation thermometer when the thermometer is
sighted through the plane of the iris and the iris is set at a diameter of at least twice the field-
of-view of the instrument.
5.5.2.2 The temperature of the reference source is stabilised at a temperature near the top
of the measuring temperature range of the radiation thermometer.
5.5.2.3 The iris is adjusted to a diameter slightly smaller (typically 10 % less) than the
expected field-of-view.
5.5.2.4 The position of the radiation thermometer is adjusted vertically and horizontally and
focused if applicable to produce maximum output while also maintaining the line of sight
perpendicular to the iris.
5.5.2.5 The iris is opened to the point where the temperature indicated by the radiation
thermometer stops increasing, but its diameter is still smaller than the reference source
opening. In this case, the field-of-view is defined in terms of the 99 % fraction of the
hemispherical value. If the temperature indicated by the radiation thermometer does not
stabilize after exceeding the largest possible iris diameter, the field-of-view is defined in terms
of the maximum iris diameter for which the temperature source does not obstruct the optical
path of the radiation thermometer.
5.5.2.6 The iris diameter is decreased until the radiation measured by the radiation
thermometer decreases by 1 % of the original signal or the temperature indicated by the
radiation thermometer decreases by the amount appearing in Annex A.
5.5.2.7 The value for the field-of-view at the measuring distance chosen is taken to be the
diameter of the iris opening for which the radiant power received by the radiation thermometer
or the temperature indicated by the radiation thermometer has been reduced according to
5.5.2.6.
The reference source shall have a stable and homogenous radiance temperature within its
radiating area (i.e. the temperature and emissivity of the source shall not change when
changing the size of the radiating area or such changes have to be corrected).
The iris shall be kept cool enough so that its thermal emission does not contribute
significantly to the output signal. In most cases the error is insignificant if the iris is
– 14 – TS 62492-2 © IEC:2013(E)
maintained near room temperature and the temperature of the reference source is at or above
200 °C.
5.6 Distance ratio
As the distance ratio is defined as the ratio of the measuring distance to the diameter of the
field-of-view no specific test method is needed.
5.7 Size-of-source effect (SSE)
5.7.1 General
To describe the SSE the difference in the radiance or temperature reading of the radiation
thermometer when changing the size of the radiating area of the observed source shall be
stated. The complete information would be a graph, which shows the signal or temperature
reading versus source diameter (see Figure 1).
To simplify the SSE statement and make it more comparable, the following measurement
conditions shall be used as far as possible: the SSE is to be stated at a given measuring
distance, measured temperature and ambient temperature, when observing a target with the
area of the nominal field-of-view and twice the area of the nominal field-of-view or more than
twice the area of the nominal field-of-view. In the latter case, the area should be specified.
The SSE is either defined as the relative change in the observed radiance or, for instruments
which only read in temperature, as the absolute change in the measured temperature at a
given temperature, when changing the observed target area. Since the latter definition
depends on the source temperature it is necessary to state the SSE at the top, middle and
bottom temperatures of the measuring temperature range.
The following test method determines the SSE when increasing the area of the target from the
nominal field-of-view to twice the field-of-view. With the size-of-source effect it is necessary to
state the measuring distance, the measured temperature and the surrounding temperature of
the source.
5.7.2 Test method
5.7.2.1 Sight the radiation thermometer at the centre of the radiating area of the reference
source at the specified measuring distance. Position an iris diaphragm in front of and
concentric with the opening of the reference source. The minimum opening of the reference
source shall be large enough so as not to obstruct the optical path of the radiation
thermometer, i.e. the nominal field-of-view as specified by the manufacturer, when the
thermometer is sighted through the plane of the iris and the iris is set at a diameter of at least
twice the field-of-view of the instrument.
5.7.2.2 The temperature of the reference source is stabilised at a temperature near the top
of the measuring temperature range of the radiation thermometer.
5.7.2.3 The iris is adjusted to a diameter slightly smaller (typically 10 % less) than the
expected field-of-view.
5.7.2.4 The position of the radiation thermometer is adjusted vertically and horizontally and
focused if applicable to produce maximum output while also maintaining the line of sight
perpendicular to the iris.
5.7.2.5 The iris is opened to the diameter specified as the nominal field-of-view by the
manufacturer and the radiation signal or the temperature indicated by the radiation
thermometer is recorded.
TS 62492-2 © IEC:2013(E) – 15 –
5.7.2.6 The iris area is increased to an area twice the nominal field-of-view of the radiation
thermometer. The radiation signal or the temperature indicated by the radiation thermometer
is recorded.
5.7.2.7 The relative change in radiance reading or the absolute change in temperature
reading when changing the size of the iris is recorded as the SSE of the radiation
thermometer.
5.7.2.8 For radiation thermometers which indicate temperature the test method is repeated
for a temperature of the reference source stabilized near the middle and bottom of the
temperature range.
The reference source shall have a stable and homogenous radiance temperature within its
radiating area (i.e. the temperature and emissivity of the source shall not change when
changing the size of the radiating area or such changes have to be corrected).
The iris shall be kept cool enough so that its thermal emission does not contribute
significantly to the output signal. In most cases the error is insignificant if the iris is
maintained near room temperature and the temperature of the reference source is at or above
200 °C.
5.8 Emissivity setting
The range and the resolution of the emissivity setting shall be given by the manufacturer. For
information on the internal emissivity correction procedure the manufacturer has to be
contacted. A test method for the emissivity setting is beyond the scope of this technical
specification.
5.9 Spectral range
A test method for the determination of the spectral range is beyond the scope of this technical
specification.
The spectral range is given in µm or nm. The lower and upper wavelength limits at which the
spectral responsivity has reached 50 % of the peak responsivity are given as the spectral
range. Alternatively, a mean wavelength and full wavelength width at which the responsivity
has reached 50 % of the peak sensitivity (full width at half maximum (FWHM)) are given.
For some radiation thermometers, especially for narrow band or spectral radiation
thermometers, it is more useful to give lower and upper wavelength limits at which the
spectral responsivity has reached significantly less than 50 % of the peak responsivity (e.g.
10 %). In this case the criteria for the wavelength limits have to be stated.
5.10 Influence of the internal instrument or ambient temperature (temperature
parameter)
5.10.1 General
The tech
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