OIML/TC11/SC3/N5
ORGANISATION INTERNATIONAL DE METROLOGIE LEGALE
International Recommendation
Fifth Commitee Draft of Recommendation
Blackbody Radiators for Calibration of Radiation Thermometers
Calibration and Verification Procedures
Subcommittee: TC11/SC3 “Radiation Thermometers”
P-Members:
Czech Republic, Germany, Japan,
Korea (R.), Netherlands, Russian Federation,
Slovakia, United Kingdom, United States
O-Members:
Austria, Bulgaria, Egypt,
Finland, Hungary, Iran,
Korea (D.P.R.), Norway, Poland,
Serbia, Spain, Sri Lanka
Liaisons:
CIE, International Commission on Illumination
ISO, International Standardization Organization
2013
OIML/TC11/SC3/N5
Contents
Explanatory Note .................................................................................................................3
1
Scope ..........................................................................................................................3
2
Terms, Definitions, Units and References ...................................................................3
3
Technical Requirements for the Blackbody Radiators (BBR) ......................................5
4
Metrological requirements and tested characteristics of the BBR ...............................6
5
Calibration and verification conditions .........................................................................7
6
Methods for calibration and verification of the BBR. Form of report. ...........................7
7
Annex A.....................................................................................................................24
Recommended forms of the calibration and verification certificates ..................................24
1 Results of the evaluation of the blackbody radiator cavity geometry...........................24
2 Results of the evaluation of the warm-up time, temperature drift and transition time for
the blackbody radiator to pass from a stationary mode to another.................................24
3 Results of the evaluation of the blackbody radiator temperature control uncertainty ..24
4 Results of the correction evaluation during sighting along the blackbody radiator axis.........24
8
Annex B.....................................................................................................................26
References ........................................................................................................................26
2
OIML/TC11/SC3/N5
Explanatory Note
This Draft Recommendation deals with the metrological control in manufacturing
and operating of blackbody radiator (further named BBR) with controlled
temperature in the OIML member-states. The Recommendation can be a basis for
calibration, verification, and certification of these instruments.
Currently the majority of manufactured radiation thermometers are verified and
calibrated using blackbody radiators. With the growth of the number of radiation
thermometers, the number of manufactured blackbody radiators has increased.
However, no international documents describing calibration and verification of such
blackbody radiators are available. Therefore the present Recommendation has
utmost importance.
1
Scope
The present Recommendation applies to BBR intended for calibration, verification
and engineering work in production, maintenance and adjustment of reference and
working radiation thermometers, thermal imaging instruments and radiometers in
the temperature range from minus 50 °C to plus 2500 °C; it sets up methods and
procedures for their calibration and verification.
2
Terms, Definitions, Units and References
2.1
The Recommendation uses the following general terms and definitions:
2.1.1 Calibration (OIML VIM-2010; 2.39 [1]1)
operation that, under specified conditions, in a first step, establishes a relation
between the quantity values with measurement uncertainties provided by
measurement standards and corresponding indications with associated
measurement uncertainties and, in a second step, uses this information to establish
a relation for obtaining a measurement result from an indication.
2.1.2 Verification (OIML VIM-2010; 2.44 [1])
provision of objective evidence that a given item fulfils specified requirement.
Confirmation that performance properties or legal requirements of a measuring
system are achieved.
2.1.3 Certification (OIML VIML-2000; 3.2 – 3.4 [2])
operation leading to the issue of a document certifying that the verification of the
measuring instrument was carried out with a satisfactory result
2.1.4 Maximum permissible (measurement) error (OIML VIM-2010; 4.26 [1])
extreme value of measurement error, with respect to a known reference quantity
value, permitted by specifications or regulations for a given measurement,
measuring instrument, or measuring system
1
See bibliography in Annex B
3
OIML/TC11/SC3/N5
2.2
The Recommendation uses the following specific terms and definitions:
2.2.1
Blackbody radiator (BBR) – a source of thermal radiation with an effective
emissivity ε close to 1 (as a rule, ε ≥ 0,95 for the radiators with radiating cavity, and
ε ≥ 0,9, for the radiators with extended flat surface.).
2.2.2 Permissible uncertainty UpBB – expanded uncertainty at a specified confidence
level (p=0,95 or p=0,99) declared in the technical documentation, at which the BBR
is considered fit for its intended use. The standard uncertainty upBB = UpBB/k(p) is
calculated from either k(p=0.95) = 2 or k(p=0.99)=3.
2.2.3 Temperature instability, Tki – instability of the BBR temperature maintained [or
‘controlled’]in a specified stationery temperature mode.
2.2.4 Temperature drift, Td – temperature drift of the BBR during its operation in a
specified stationary temperature mode.
2.2.5 Transition time, tt – the required time for the BBR to pass from one stationary
temperature mode to another.
2.2.6 Warm-up time, tw – time elapsed from the moment of turning on the BBR untill it
reaches the specified working stationary temperature mode when it is allowed to
determine the metrological characteristics of the BBR.
2.2.7 Demountable contact sensor – the contact thermometric sensor, which can be
removed from the BBR without its dismantling for the purpose of a separate
calibration and/or verification.
2.2.8 Permanent jointed contact sensor – the contact sensor of an internal or external
thermometer that cannot be removed from the BBR without the dismantling of the
latter.
2.2.9 BBR own thermometer – built-in sensor connected to an internal or external
device having an output signal (showing device, or interface, or transmitter
transforming a signal of the sensor to a normal electric signal) correlated with
temperature of the BBR radiation.
2.2.10 Pyrometer – a thermometer using the optical radiation of a source and indicating
temperature values which are calibrated traceable to (inter)national standards2
2.2.11 Pyrometer-comparator – a device using the optical radiation of sources and
indicating their temperature differences and no traceability needed (see 2.1.10).
2.2.12 Emissivity – the ratio of the radiance of a substance to the radiance of a blackbody
at the same temperature as that of the substance.
2.2.13 Effective emissivity – an apparent emissivity of a blackbody cavity or a surface of
a planar blackbody radiator. That should be taking into account of an intrinsic
emissivity of surface, a geometrical factor, a temperature distribution, and an
ambient thermal radiation.
2.2.14 Spectral selectivity - is the wavelength range over which the BBR specifications
are valid
2.3
Units
Celsius degrees (ºC) or kelvins (K) are used in this Recommendation as units for
temperature or temperature difference (drift, instability etc.).
2
Term ‘pyrometer’ is synonym of term ‘radiation thermometer’ in this document
4
OIML/TC11/SC3/N5
3
Technical Requirements for the Blackbody Radiators
(BBR)
3.1
Types of BBRs
3.1.1 The BBRs have a radiating area that is composed of a cavity or a flat surface.
3.1.2 The BBRs can be intended for working with temperature fixed points (Fixed- PointsBlackbody) or for the variable temperature range (Variable-Temperature-Blackbody)
and shall have a temperature adjustment system.
3.1.3 The BBRs are subdivided with respect to the method of the radiance temperature
measurement into the following types:
-
BBRs with demountable contact sensors;
-
BBRs with permanent mounted contact sensors that are either included into the
automatic temperature adjustment system, or that are operating off-line;
-
BBRs with non-contact sensors that are either included into the automatic
temperature adjustment system, or that are operating off-line.
3.1.4 The BBRs can be portable or stationary installed.
3.1.5 Requirements to the design of BBRs.
The BBR should be equipped with a handle for temperature control, an automatic
temperature adjustment system and with a temperature display or/and with a socket
or plugs of an output signal (analogue or digital) correlated with the BBR
temperature value.
3.1.6 It is desirable (for verification - required), that characteristics of the BBR, such as:
- the working temperature range (or fixed values),
- the radiating area,
- the temperature instability,
- the drift,
- the effective emissivity,
- the spectral selectivity,
- the permissible uncertainty of the BBR temperature,
- the warm-up time,
- the transition time,
- the correction factor or value to the readings of the BBR own thermometer –
should be given in its technical documentation (hereinafter referred to as TD).
All these values are results of measurements and have to be stated
either
- the associated expanded k  2 uncertainty
or mostly
- as the interval of minimum and maximum values specifying a rectangular
probability distribution – and the one chosen has to be stated, clearly.
If any of the characteristics are not resulted in the TD, its actual value together with
the associated expanded k  2 uncertainty can be defined at calibration, and it is not
checked at verification.
5
OIML/TC11/SC3/N5
The main task during calibration of BBR temperature is the determination of the
correction factor or value to the readings of a BBR own thermometer, associated
with the appropriate expanded uncertainty and the clear statement which coverage
factor or coverage probability p  0,95 or p  0,99 was used for calculation.
Notes:
1. Among the above mentioned characteristics, the effective emissivity is the hardest to
be separately evaluated (calibrated, verified), because it considerably depends on the
BBR design, on the form of the radiating area and on the materials used.
It is therefore impossible within the framework of this Recommendation, which does not
deal with technological and constructive differences of BBRs, to regulate specific
requirements and operations which allows to calculations or measurement of this
quantity. The effective emissivity should be taken into account in the correction value
applied to the readings of the BBR’s own thermometer and determined by the
comparison with a standard BBR traceable to the International Temperature Scale.
2. The spectral selectivity of the BBR is also considerably dependent on the BBR
design, the shape of the radiating area and the materials used. This dependence is
well-defined for the BBRs with cavity-type radiating element and can be significant for
the BBRs with radiating surface with special coating to ensure a high spectral
emissivity. In the latter case it is necessary to know the spectral curve of the
dependence of emissivity (or reflectance) on the wavelength and this curve shall be
given in the specifications.
In the case of precision BBRs (devices developed for minimum fluctuation of all their
characteristics), if a separate evaluation of the effect of these characteristics is required
in the process of their subsequent use, then it is necessary to follow the main principles
and methods of their evaluation that are specified in documents [3-5] from
bibliography (subsection 8 Annex B) in this Recommendation.
3.1.7 Generally the result of the calibration of BBR temperature has to be stated for a
coverage probability p  0,95 using a coverage factor k  p  0,95  2 . For some
applications to use the BBR the regulations define a higher coverage probability
p  0,99 with a corresponding coverage factor k  p  0,99  3 . Therefore, the
appropriate expanded uncertainty is determined from the standard uncertainty by
multiplication with the related coverage factor k  p  .
3.1.8 Depending on the intended use of a BBR as standard for temperature
measurements the TD will also state the permissible uncertainty of the BBR
temperature.
4
Metrological requirements and tested characteristics of
the BBR
In the process of testing for calibration and verification the following metrological
characteristics of the BBR shall be determined:
4.1
4.2
4.3
Temperature range (or fixed values).
Size of the radiating area of the BBR.
Warm-up time required for the BBR to reach the specified stationary mode at the
lower and upper levels of the working temperature range of the BBR.
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OIML/TC11/SC3/N5
4.4
4.5
4.6
4.7
4.8
Transition time required for the BBR to pass from one stationary mode to another.
Temperature drift during the operation in specified stationary modes.
Instability of temperature control at specified levels.
Corrections to the readings of the BBR own thermometer (or output signal).
Expanded uncertainty of the BBR temperature at a specified confidence level.
5
Calibration and verification conditions
5.1
Process of verification and calibration
The process of verification and calibration should be carried out in a stable
indoor environment within the measurement conditions (a temperature range and
the relative humidity range) accepted in each country, unless the other conditions
are specified by customer; the conditions should be written down in the calibration
certificate. A BBR should not be affected by shocks, vibrations, external
electromagnetic fields, extraneous radiation sources influencing the readings of
measuring instruments.
5.2
Accreditation
The calibration shall be carried out by an accredited calibration laboratory.
6
Methods for calibration and verification of the BBR. Form
of report.
6.1
Methods
6.1.1 Methods for the calibration and verification
The actual temperature T X  c  Y X  Y X  measured by a pyrometer is calculated
from the reading Y X and a correction value Y X . The factor c  1 with a value
defined as unity converts the reading Y X from arbitrary units Y X  in the unit T X 
wanted for the temperature. Thus, the unit of the factor c   T X  Y X  is just the
ratio of the units of the temperature and the reading.
The symbols “ T X ” and “ Y X ” stand for actual temperatures and for readings of
pyrometers specified for the device by index “ X ”. The indices “ b ” and “ sb ”
replacing index “ X ” refer to the BBR to be calibrated and a standard BBR used as
reference, while the indices “ p ” and “ sp ” refer to an external pyrometer-comparator
and a standard pyrometer used for reference.
The calibration of a BBR assigns a value to the correction value Yb to the BBR
 
own thermometer with associated combined standard uncertainty u Yb . Finally,
the standard uncertainty is converted in an expanded uncertainty
U Yb   k  uYb  by multiplication with the coverage factor k with values either
k  2 or k  3 depending on the fraction p of probability defined for the application.
There are two fundamental methods to determine this correction value:
7
OIML/TC11/SC3/N5
- Direct measurement with an external standard pyrometer as reference
- Comparison with a standard BBR as reference and using an external pyrometercomparator.

6.1.2 Direct measurement: The BBR temperature Tb  c  Yb  Y b

indicated by
readings Yb of the BBR-own-thermometer is measured by an external standard
 
  

pyrometer T sp Tb  c  Y sp Tb  Y sp , which is certified with the correction
value Y sp . Then the correction value Yb of the BBR-thermometer reads:
Yb  Tsp Tb  c  Yb
where
with
 T T   c  Y T   Y 
sp
b
sp
b
(1)
sp
Yb , Yb
- reading, correction value for BBR-own-thermometer;
Tb , T sp Tb 
- BBR temperature, indicated by standard pyrometer;
c1
- factor to match the units;
Y sp Tb  , Y sp - reading, correction value of standard pyrometer.

 indicated by its own
T   c  Y T   Y .
6.1.3 Substitution method: The BBR temperature Tb  c  Yb  Y b
thermometer is measured by the pyrometer-comparator T p

b
p
b
p

The temperature T sb  c  Y sb  Y sb of a standard BBR indicated by its own
thermometer
is
also
measured
by
the
pyrometer-comparator
T p Tsb  c  Y p T sb  Y p
. A combination of the two equations cancels out the
Y p
correction value
and the correction value Yb of the BBR-thermometer reads:
  
 

 Tsb  c  Y sb  Y sb 
Yb  Tsb c  Yb  Y p Tb  with 
 Y p Tb   Y p Tb   Y p Tsb 
where Yb , Yb
(2)
- reading, correction value of BBR-own-thermometer;
Tsp
- temperature of standard BBR;
c1
- factor to match the units;
Ysb , Ysb
Y p Tb 
- reading, correction value of standard BBR-own-thermometer;
- difference of indications of external pyrometer–comparator;
Y p Tb  , Y p Tsb  - indication of pyrometer-comparator for BBR, standard BBR.
6.2
Operations and means for calibration and verification of BBRs
6.2.1 The operations and measuring instruments to be used for calibration and
verification are listed in Table 1.
8
OIML/TC11/SC3/N5
Table 1
Operations and Measuring Instruments
No.
Operation
Item
in the
text
Verification
instruments and
their characteristics
1
2
3
4
1 External examination
2 Testing
Evaluation of the BBR
3 radiating geometry
Evaluation of the
warm-up time,
temperature drift and
transition time of BBR
from one stationary
mode to another
4
Evaluation of the BBR
5 temperature keeping
instability
Evaluation of the
correction to the
6 readings of the sensor
of the BBR to be
calibrated (verified)
Calculation of the
7 expanded uncertainty of
the BBR temperature
Obligation of a
verification procedure
Initial
Periodical
5
6
- Linear (length) measuring instrument with the
6.5 scale factor, provided measurement of size of the
radiating area with uncertainty less than 5%.
- chronometer;
- pyrometer-comparator with a temperature
measuring range corresponding to that of the BBR
and with the combined uncertainty up1 from
contributions of instability and limited resolution of
the thermometer has to be valid up1  upBB 3 (less
than1/3 of the permissible standard uncertainty of
the tested BBR),
6.6
- the field of view has to be smaller than the output apertures
of both, the standard BBR and the tested BBRs;
- a device to measure the BBR thermometer
output signal (if necessary) the uncertainty
contribution up2
of limited resolution of the thermometer
has to be valid up2  upBB 3 (less than1/3 of the
permissible standard uncertainty of the tested BBR)
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
6.7
Equipment from item 4 in this Table
Yes
Yes
- standard BBR with variable temperature in a
corresponding measurement temperature range
or with temperatures of the fixed points (depends
on tested BBR), the combined uncertainty of all
characteristics specified in lines 3 – 7 of this Table
shall be valid up3  upBB 3 (less than 1/3 of the
permissible standard uncertainty of the tested BBR),
- emissivity has to be   0,99 ,
- pyrometer-comparator with a corresponding
temperature measurement range; its combined
uncertainty up4 from contributions of instability and
Yes
Yes
Yes
Yes
6.3
6.4
6.8 temperature resolution has to be valid u  u
p4
pBB 3
(less than 1/3 of the permissible standard
uncertainty of the tested BBR); its field of view has
to be smaller than the output apertures of both,
the standard BBR and the tested BBR; the size-ofsource effect of the pyrometer-comparator should
be sufficiently small so that either the effect of
different aperture sizes can either be neglected
- a device to measure or decode an output signal
(if necessary) with resolution Y  upBB 3 (in a
temperature equivalent) less than 1/3 of the
permissible standard uncertainty of the tested BBR)
6.9
Calculation of the uncertainty should carried out
according to [3-5]
9
OIML/TC11/SC3/N5
6.2.2
6.2.3
6.2.4
6.2.5
Measuring instruments specified in Table 1 should be calibrated traceable to
national standards and provided with the corresponding legal documents about
their verification or calibration.
Standard BBRs shall be calibrated traceable to national standards and the
International Temperature Scale (the ITS-90).
Measuring instruments are prepared for operation in accordance with their valid
documentation.
Demountable BBR own thermometers shall have valid calibration or verification
certificates.
6.3
External examination
During external examination the following points shall be checked:
6.3.1
6.3.2
6.3.3
6.3.4
6.4
6.4.1
6.4.2
6.5
6.5.1
6.5.2
6.5.3
6.5.4
3
Correspondence of the completeness of BBR and associated equipment to the
requirements of its valid documentation;
Correspondence of the BBR to the safety requirements specified in the TD;
Absence of external damage of the calibrated (verified) BBR and associated
equipment that may adversely affect its metrological performance and main
functions.
BBR that does not comply with the requirements of item 6.3.3 is not subject to
calibration or verification.
Testing for serviceability
The BBR is connected to a power supply and its serviceability is tested in
compliance with the valid documentation.
A BBR in which a defect was found during the testing (for example: inability to look
some of the display readout, apparent instability, etc.) is rejected for a further
calibration (verification).
Evaluation of the BBR radiating geometry
The outlet diameter of the BBR radiating size and the cavity depth (in case of a
cavity BBR)3 shall be measured once. The difference between the measured
values and the values specified in the TD shall not exceed the limits ± 5 % with
reference to the declared values.
If relative differences calculated according to 6.5.1 exceed the limits ± 5 %, the
calibration (verification) certificate shall specify the actual dimensions and the
recommendation to the customer to amend the TD and to update (verify) the
emissivity value.
Evaluation of the warm-up time, temperature drift and transition time for the BBR
to pass from one stationary mode to another
The warm-up time of the BBR is interrelated with its temperature drift. Therefore
these parameters shall be determined simultaneously.
It must be kept in mind that it is impossible to insert any instruments into the blackbody cavity which could
damage the coating
10
OIML/TC11/SC3/N5
6.5.5
6.5.6
6.5.7
6.5.8
6.5.9
6.5.10
6.5.11
6.5.12
6.5.13
6.5.14
The warm-up time of the BBR at the lower temperature limit is determined by
setting the value corresponding to the lower temperature limit on the temperature
control device of the BBR control unit. The BBR is turned on and entered in the
specified stationary mode in compliance with TD.
When the BBR reaches the stationary mode after the time tW , its radiance
temperature is determined every (10 to 15) seconds during fifteen minutes by the
readings of the radiance temperature measuring device having a sufficient
resolution (see Table. 1). Simultaneously the indicated reading of the BBR own
thermometer is also recorded.
The average temperature values are determined in accordance with the
measurement results during the first five minutes, second five minutes and third
five minutes. The difference between the average temperature values shall not
exceed the temperature drift value specified in the TD.
The calculation is carried out for the radiance temperature values and for the
indicated temperatures of the BBR own thermometer.
If in the process of verification the maximum difference between the average
temperature values of the BBR is bigger than the temperature drift value, the BBR
is rejected as defective.
In the process of calibration the warm-up time of the BBR is determined with more
precision through additional measurements. With this purpose, the operations of
items 6.6.3 – 6.6.4 are repeated until the measured temperature drift becomes
equal to the value specified in the TD.
If the measured temperature drift value agrees with the value specified in the TD,
the BBR warm-up time being less than 2tW , a new value of the BBR warm-up time
is indicated in the TD.
If the measured drift value exceeds the value specified in the TD at the BBR
warm-up time being equal to 2 tW , the BBR is rejected as defective.
The BBR transition time from one stationary mode to another (tt) is determined by
setting, on the temperature control device of the BBR unit, the value
corresponding to the next temperature mode of the BBR, and, after the time
specified in the TD as the transition time from one stationary mode to another
expires, the operations mentioned in items 6.6.2 – 6.6.6 are repeated.
The transition time of the BBR to the stationary mode at the upper temperature
limit is determined after disconnecting the BBR from the power supply and cooling
down to the room temperature. Then the value corresponding to the upper
temperature limit is set on the temperature control device of the BBR unit. The
BBR is turned on again and, when the transition time of the BBR to the stationary
mode at the upper temperature limit (tW2) expires, the operations of items 6.6.2 –
6.6.6 are repeated, and the values tW2 and 2tW2 substitute the values tW and 2tW .
6.5.15 Evaluation of the temperature control instability of the BBR
6.5.16 The value corresponding to the lower temperature limit is set on the temperature
handle of the BBR control unit and then the BBR is adjusted to this temperature
value according to its operation manual.
6.5.17 When the BBR reaches the stationary mode, the radiance temperature value Ti is
measured every (10 to 15) seconds during (15 to 20) minutes by the readings of
the temperature measuring device with a resolution no worse than 0,1 °C
( T  0 ,1 C ).
11
OIML/TC11/SC3/N5
The average temperature value Ta during the period 15  t min  20 , the empirical
standard deviation  Ti  of the current temperature value Ti and standard
uncertainty type B u(T) are calculated using the formulae:
n
n
 Ti
Ta =
i=1
uTa  
;
n
where Ta
Ti
n
 Ti 
uTa 
-
 Ti 
with  Ti  
 T
i
 Ta 
2
i=1
,
(3)
n1
n
average temperature value;
the i-th temperature measurement result;
number of independent readings;
empirical standard deviation of readings;
standard uncertainty type B equals the empirical standard
deviation of the mean of readings.
6.5.18 Similar procedure is carried out for values of temperature which are indicated by
the BBR own thermometer.
6.5.19 For calculations of an expanded uncertainty largest of the average temperature
values obtained in item 6.7.1 - 6.7.3 is used.
6.5.20 The expanded uncertainty of the temperature keeping instability depends on the
confidence probability p, and is equal to the standard deviation multiplied by the
coverage factor k (for example, k = 2 when p = 0.95).
6.5.21 If the standard deviation exceeds half of the temperature keeping instability
specified in the TD, the BBR shall be rejected as defective.
6.5.22 Operations in items 6.7.1 – 6.7.4 are repeated for the BBR with regulated
temperature at the mid and maximum temperature values in the working range.
6.6
Evaluation of the correction to apply to the readings of the BBR own thermometer
6.6.1
The correction to the readings of the BBR own thermometer is determined by
comparing it with a standard BBR by a pyrometer-comparator, or by direct
measurement of its radiance temperature with a standard radiation thermometer.
A standard BBR and a standard radiation thermometer shall be calibrated with
radiance temperature traceable to national standards and the International
Temperature Scale (the ITS-90) by the calibration laboratory4.
The correction to the readings of the BBR own thermometer to be calibrated
(verified) in the low temperature range  50  T C  300 ) is determined by
comparing it with a standard BBR by a pyrometer-comparator working in a full
radiation or in a spectral interval 8   μm  14 , or by direct measurement of its
radiance temperature with a standard radiation thermometer working in such a
spectral interval.5
The BBR to be calibrated (verified) is placed on a test bench connected to the
power supply and adjusted to the specified lower stationary temperature mode.
Comparisons are performed by means of a comparator using the equal signals
method 6. With this method, the comparator is placed in such a way that its optical
6.6.2
6.6.3
6.6.4
4
calibration laboratories must be accredited according to the state legislation
The numerical ranges of temperature and wavelength in clauses 6.8.2, 6.8.12 and 6.8.14 are given as an
informative example.
6
Method, in which the comparator signals received from the test and standard BBR are equal
5
12
OIML/TC11/SC3/N5
6.6.5
6.6.6
6.6.7
6.6.8
6.6.9
6.6.10
6.6.11
6.6.12
6.6.13
axis lies in the axis of the standard BBR and passes through the centre of its
radiating aperture.
Then the comparator is directed at the tested BBR. The temperature of the tested
BBR is selected in such a way that the comparator signal is equal to the signal of
the standard BBR. The standard BBR temperature and the readings of the
calibrated (verified) BBR own thermometer are recorded. The measurements shall
be repeated 10 times. The average-values of temperatures of the standard BBR
and of the BBR own thermometer to be calibrated (verified) are calculated.
The correction to the readings of the BBR own thermometer to be calibrated
(verified) is determined as a difference of the average temperature values of the
standard and calibrated (verified) BBRs.
In the calibration of the variable temperature BBR, the standard BBR and the BBR
to be calibrated (verified) are entered in the next stationary temperature mode and
operations are carried out according to items 6.8.3 – 6.8.6. These operations are
repeated at all temperature modes of the BBR specified in theTD (or required by
customer).
In the verification of the variable temperature BBR the number of specified
temperature modes may be reduced to three (including minimal and maximal
temperatures).
The correction values obtained during the calibration are specified in the certificate
of calibration, if they exceed half the value of the expanded (permissible)
uncertainty of the BBR temperature.
If the correction value obtained during the verification differs from the correction
value given in the TD by more than half the value of the permissible expanded
uncertainty of the BBR temperature at one temperature mode, the correction shall
be revised at all specified temperature modes of the BBR. The obtained new
correction values are to be specified in the TD of the BBR in the same way as
during the calibration.
If the corrections are determined by means of a standard pyrometer, they are
calculated as a difference of the average readings of the standard pyrometer and
the BBR own thermometer to be calibrated (verified).
The correction to the readings of the BBR own thermometer to be calibrated
(verified) in the mid temperature range ( 300  T C  1000 ) is determined by
comparing it with a standard BBR by means of pyrometer-comparators with the
partial spectral range, or standard pyrometers with two or three partial spectral
ranges, e.g., with the ranges 2   μm  5 and 8   μm  14 . The operations
described in items 6.8.3 – 6.8.11 are carried out for each spectral intervals7.
If the correction obtained with different spectral intervals (within one temperature
mode) do not agree with each other within a half value of the permissible
expanded uncertainty U pBB , they shall be averaged over all spectral intervals and
the temperature uncertainty component, usi (one standard uncertainty), shall be
taken to be the maximum deviation of the correction from its average value..
Otherwise yields usi  U pBB .
6.6.14 The corrections to the readings of the BBR own thermometer to be calibrated
(verified) at the temperature T  800 C can be determined by comparing it with a
standard BBR by means of a spectrocomparator with a narrow spectral band
7
See footnote to Clause 6.8.2
13
OIML/TC11/SC3/N5
depending on the purpose of the BBR to be calibrated (verified). During the
verification it is allowed to use the pyrometer-comparator, or the standard radiation
thermometer with the partial spectral interval instead of the spectrocomparator8.
6.6.15 When the BBR to be calibrated (verified) is intended for calibration of radiation
thermometers of a special type, it is possible to calibrate (verify) the BBR by
means of the same calibrated radiation thermometer type, if it meets the
requirements of the Table 1, irrespective of the temperature range.
6.6.16 If the BBR to be calibrated (verified) is intended to be applicable for calibration of
radiation thermometers with wide-angle objectives, the dependence of correction
on viewing angle9 shall be determined. With this purpose, the operations from
items 6.8.2 - 6.8.15 are carried out for each viewing angle depending on the
temperature mode. The average correction value is determined for all viewing
angles. If the correction obtained is higher than half the value of the permissible
expanded uncertainty, the maximum deviation of the corrections from the average
value by all viewing angles is taken into account as the uncertainty component
uva . Otherwise yields uva  U pBB
6.6.17 The dependence of correction on the radiating surface non-uniformity of the
radiance temperature Ti shall be determined only for BBRs with the extended
radiating surface. With this purpose, the average correction value is determined as
the maximum difference between radiance temperature values Ti from 5 points of
the surface (in the center and on periphery) and their average value. It is taken


1 5
into account as the uncertainty component urs  max  Ti   T j  .
1 i  5 
5 j  1 

These measurements are made according to items 6.8.2 – 6.8.13. In this case the
dependence of correction on the viewing angle is not determined. Such correction,
as a rule in practice, is most powerful at a temperature T  300 C .
6.7
Evaluation of the uncertainty of the BBR temperature
The basic components of the uncertainty budget in calibration (verification) of a
BBR temperature are listed below and grouped for the two methods. The
uncertainty contribution from the reading of the BBR own thermometer is
independent of the method of calibration (verification) and reads:
Uncertainty contribution due to reading of the BBR-own-thermometer
The uncertainty contribution from the readings Yb of the BBR-own-thermometer is
determined as the maximum from either resolution  Yb or empirical standard
deviation  Yb  of a number n of independent readings.
 

u Yb  max Yb
where
 
3 ,  Yb
n

(4)
  - standard uncertainty of BBR-own-thermometer reading;
u Yb
 Yb
- resolution of BBR-own-thermometer;
 Yb  - empirical standard deviation of reading;
n
- number of independent readings.
8
9
See footnote to Clause 6.8.2
viewing angle is the angle between the line of observation and the normal line to the radiating area
14
OIML/TC11/SC3/N5
The readings are modified by a possible difference Ta , b  Ta , b  Ta , b, 0 between
the actual value Ta , b of the ambient temperature and the value Ta , b, 0 stated in the
certificate. The small correction
 b  Ta , b  1 is the product of ambient
temperature difference Ta , b and a relative temperature coefficient  b . In the TD
of the BBR the value  b is given with associated expanded uncertainty U  b  and
coverage factor k  p  . Thus, the standard uncertainty u b   U  b  k  p  can be

calculated. The corrected readings Y b  1   b  Ta , b
correction factor.



 

  

are the product with a
 

u b  c  u Yb  1   b  Ta , b  c  u 2 Yb  Yb2  u 2 Yb  Ta2, b   b2  u 2  b  u 2 Ta , b
where

(5)
ub
- standard uncertainty of BBR temperature by own thermometer;
c  1 - factor to match the units;
Yb
- reading of BBR-own-thermometer;
b
- relative temperature coefficient;
Ta , b - ambient temperature difference.
Provided the ambient temperature difference is less than the associated
uncertainty Ta , b  u Ta , b , than the higher order term in brackets has to be


used.
6.7.1
Uncertainty contribution of the standard measuring instruments
a) Calibration (verification) option by comparison with a standard BBR as
reference using a pyrometer-comparator and described by the following model of
evaluation:
Yb  Tsb c  Yb  Y p Tb 
1 2
u Tsb   u 2 Yb   u 2 Y p Tb 
2
c

uYb  
where Yb , Yb
Tsb
c1
u Yb
Y p Tb 
 
-

(6)
reading, correction value of BBR-own-thermometer;
temperature of standard BBR;
factor to match the units;
standard uncertainty associated with Yb ;
difference of indications from external pyrometer-comparator.
Uncertainty of temperature relating to the standard BBR as reference
usb = u(Tsb) – includes the uncertainty of its calibration; its instability; uncertainty
due to its positioning against the optical axis of the comparator; uncertainty of
measuring instruments used to maintain the conditions of its operation; uncertainty
dues to the effect of the ambient conditions.
It is evaluated using the following models:
The temperature Tsb of the standard BBR is evaluated from the reading Ysb and
15
OIML/TC11/SC3/N5
the correction value Ysb modified for small effects of ambient temperature
1  
sb



 Ta , sb and ageing 1   sb  t sb , respectively.




  sb  Ta , sb  1

with 
  sb  t sb  1
(7)
  sb2  u 2 t sb 
Tsb  c  Ysb  1   sb  Ta , sb  Y sb  1   sb  t sb
u sb  uTsb   c 
where



 

Y   Y  T
 
   
u 2 Ysb  Y sb2  t sb2  u 2  sb
u2
2
sb
sb
Tsb
Ysb
с≡1
Ysb
sb
Ta,sb
sb
tsb
-
2
a , sb
 u2

sb
2
sb
 
 u    u T 
2
2
sb
a , sb
temperature of standard BBR;
reading of standard BBR;
factor to match the units;
correction value standard BBR;
relative temperature coefficient standard BBR;
ambient temperature difference;
relative ageing coefficient standard BBR;
time since calibration, standard uncertainty.

u Ysb  U Ysb k  p  is the uncertainty associated with the correction value of the
standard BBR from calibration, certified as expanded uncertainty U Ysb  with
coverage factor k  p  . For long term stability the uncertainty contribution
Ysb2  tsb2  u 2  sb   sb2  u 2 tsb  is evaluated from the relative ageing coefficient  sb with
associated uncertainty u sb   U  sb  k  p  and coverage factor k  p  given in the TD.
The period of time tsb since last calibration is determined from the certificate and
usually the associated uncertainty utsb  is negligible.
 

u Ysb  max Ysb
 
3 ,  Ysb
n
 is the uncertainty from the readings of standard BBR-
own-thermometer. It is determined as the maximum from either resolution  Ysb or
the empirical standard deviation  Ysb  of a number n of independent readings.
The uncertainty contribution from ambient conditions e.g. the ambient
temperature Ysb2  Ta2, sb  u 2  sb    sb2  u 2  sb  u 2 Ta , sb  is determined from the difference
Ta , sb  Ta , sb  Ta , sb0 between the actual ambient temperature Ta , sb near the standard
BBR and the value Ta , sb0 defined for its operation. Provided the temperature
difference Ta , sb is less than the uncertainty uTa , sb  , then the higher order term (in
brackets) have to be regarded. The relative temperature coefficient  sb with
associated uncertainty u sb   U  sb  k and coverage factor k is given in the TD.
The nominal effective geometric extend Gsb   sb  Asb  Щsb of the standard BBR has
to be stated in the certificate of the standard BBR with individual values of
emittance  sb of the radiating area Asb , the size and location of this area and the
solid angle Щsb to be collected. During the measurement with a radiation
thermometer a geometric extend Gp, sb   p, sb  Ap, sb  Щp, sb is used and the reading has to
be corrected by a factor 1   p  Gp, sb  . It is combined from the imperfect match
Gp, sb  Gp, sb  Gsb between the effective geometric extends and a relative weighting
coefficient  p . The value  p and associated standard uncertainty u p   U  p  k  p 
are found in the TD or the latter is determined from the expanded uncertainty U  p 
and the related coverage factor k  p  .
16
OIML/TC11/SC3/N5
 
usb  u Tsb
the uncertainty associated with the temperature of the standard BBR
and modeled in equ. (7) shall be specified in the calibration certificate. It
(uncertainty) shall be expressed in terms of expanded uncertainty with the
confidence level of p  0,95 . If it is expressed as standard uncertainty, its value
should be adjusted to correspond to the expanded value by multiplying by the
coverage factor k  p  0,95  2 determined by this probability10.
Uncertainty due to pyrometer-comparator.
For the pyrometer-comparator the model of evaluation with the sources of
uncertainty shall be known. It contains the readings Yp Tb , Yp Tsb  for the
temperatures Tb , Tsb of the BBR and the standard BBR, respectively. In case of fine
adjustment their difference Yp Tb   Yp Tsb   1 will be negligible and the associated
uncertainty can be evaluated in a simplified formula.
The readings have to be corrected for fluctuations in ambient temperature
Ta , p  Ta , p, b  Ta , p, sb , possible effects of ageing t p  t p, b  t p, sb (usually, negligible),
and differences in the effective geometric extend Gp, b, sb  Gp, b  Gp, sb . All these
corrections are small and determined as products with relative coefficients for
temperature  p , ageing  p and geometry  p .

Yp Tb   Yp Tb  1   p  Ta , p, b   p  t p, b   p  Gp, b
 Yp Tsb   1   p  Ta , p, sb   p  t p, sb   p  Gp, sb

uY T   u Y T   u Y T   u 
2
p
b
2
p
2
b
p
sb
p



2
with

Y T   Y T
p

b
2

p
sb
  1
 Ta,p  u  p  t p  u  p  Gp, b, sb
(8)

where Yp Tb 
Tb , Tsb
- difference indications of pyrometer-comparator for BBR temperature;
- BBR temperature, standard BBR temperature;
Yp Tb 
- indication pyrometer-comparator for BBR temperature;
Yp Tsb 
- indication pyrometer-comparator for standard BBR temperature;
 p ,  p ,  p - relative coefficients for ambient temperature, ageing, geometry;
Ta,p , tp , Gp, b, sb - fluctuation ambient temperature, time since calibration,
difference in geometry;


- uncertainty component caused by the effect of ambient
temperature fluctuations during the calibration. The tested BBR and the standard
BBR are measured sequentially by the radiation thermometer. In between the
radiation thermometer ambient temperature fluctuates from Ta , p, b to Ta , p, sb .
u1  u  p  Ta,p
  

  

is the related uncertainty and
a part of equ. (7) with differences Ta , p,b  Ta , p,b  Ta, p0 and Ta , p,sb  Ta , sp,b  Ta , p0 .
Provided, the adjustment of the BBR is such, that differences between the
comparator readings Yp Tb   Yp Tsb   1 are negligibly, then the simplification
u1  Yp2 Tb  u 2  p  Ta, p, b  Yp2 Tsb  u 2  p  Ta , p, sb
10
Sources of uncertainties that were not considered in the calibration certificate shall be estimated
separately by the user of the reference standard BBR. Especially it concerns of uncertainty due to
difference in dimensions of the compared BBRs
17
OIML/TC11/SC3/N5
   
u  Y T 
 is valid and with the higher order term in brackets yields:
    u   u T  T 
(9)
u   T
T
u1  Yp Tb  u  p  Ta , p, b  Ta , p, sb
1
p
2
2
b
p
where Yp Tb 
Ta , p, b , Ta , p, sb

2
p
2
2
p
a , p, sb
a , p, b
- indication of pyrometer-comparator for BBR temperature;
- relative temperature coefficient pyrometer;
- ambient temperature for pyrometer when measuring the
tested BBR, the standard BBR;
- standard uncertainty of the ambient temperature difference.
p
u Ta , p, b  Ta , p, sb
a , p, sb
a , p, b

The values  p of the relative temperature coefficient with associated uncertainty
u  p   U  p  k  p  and coverage factor k  p  are given in the TD of the pyrometercomparator. The ambient temperatures Ta , p, b and Ta , p, sb are measured with a
thermometer not necessarily certified. The uncertainty of the ambient temperature
readings is found from either the resolution  Ta, p or the empirical standard
deviation  Ta, p  . The latter is not affected by the type of BBR and one gets:



u Ta , p, b  Ta , p, sb  2  max Ta, p

 
3 ,  Ta, p
n
.

u2  u  p  t p – uncertainty component due to instability of the measurement
transducer efficiency. The stability of the pyrometer between the sequential
measurements is also part of equ. (7) and with comparator readings
Yp Tb   Yp Tsb   1 one gets:


 
 

2

u2  u  p  t p  Yp Tb  u 2  p  t p, b  tp, sb   p2  u 2 tp, b  t p, sb
where Yp Tb 
p
t p, b , t p, sb
BBR,

u t p, b  t p, sb


(10)
- indication pyrometer-comparator for BBR temperature;
- relative ageing coefficient of pyrometer;
- time since calibration of pyrometer when measuring the tested
the standard BBR;
- standard uncertainty of difference of ambient times.
u3  u Yp Tb   Yp Tsb  – uncertainty component due to resolution Yp
of the
instrument measuring the comparator output signal and the empirical standard
deviations  Yp Tb  and  Yp Tsb  for a number of n readings for the BBR Yp Tb  and
for the standard BBR Yp Tsb  , respectively:

   n  maxY
u3  u Yp Tb   Yp Tsb   max Yp2 3 ,  2 Yp Tb
where Yp Tb  , Yp Tsb 
Tb , Tsb
temperature;
Yp
 Yp Tb  ,  Yp Tsb 

2
p
   n 
3 ,  2 Yp Tsb
(11)
- indications of pyrometer-comparator for BBR temperature;
- the tested BBR temperature, the standard BBR
- resolution of indication of pyrometer-comparator;
- empirical standard deviation of pyrometer indication.

– uncertainty component due to the difference in the
dimensions of the reference radiation source Asb and the radiation source under
u4  u  p  Gp, b, sb
18
OIML/TC11/SC3/N5
calibration Ab (size-of-source effect) 11. Their emittance  sb ,  b and solid angles
Ω sb ,Ω b forming the differences in the effective geometric extends measured by
the
pyrometer-comparator
have
to
be
regarded,
additionally
u p  Gp, b, sb   Yp Tb   1   p  Gp, b   Yp Tsb  1   p  Gp, sb  . If the adjustment of the tested
BBR is such, that Yp Tb   Yp Tsb   1 the comparator readings are (nearly) equal,


then simplification Y p Tb   Y p Tb   1   p   b  Ab  Ω b   sb  Asb  Ω sb  is valid and
one gets:




 


u4  u  p  G p, b, sb  Y p Tb   u 2 Y p Tb   u 2  p   2p  u 2  b  Ab  Ω b   u 2  sb  Asb  Ω sb  (12)
where Yp Tb 
-
indication of pyrometer-comparator for BBR temperature;
p
relative geometry coefficient of pyrometer;
Tb , Tsb
the tested BBR temperature, the standard BBR temperature;
Gp, b, sb
effective geometric extents, the tested BBR minus the standard BBR;
 Yp Tb  ,  Yp Tsb  - the empirical standard deviation of the pyrometer indication.
The combined uncertainty ust for the temperature is compiled from the
contributions of equ. (4) to equ. (11) of the standard measuring instruments and
shall be calculated by the formula:

ust = usb2  ub2  c 2  u12 + u22 + u32 + u42

(13)
b) Calibration (verification) option by direct measurement of the tested BBR
temperature using the reference pyrometer is described by the following model:
Yb  Ysp Tb   Yb  Ysp
uYb   u 2 Ysp Tb   u 2 Yb   u 2 Ysp 
where
Yb Ysp Tb  Ysp Yb
(14)
reading of BBR-own-thermometer;
correction value for the tested BBR;
reading of the standard pyrometer;
correction value of the standard pyrometer.
11
Usually, in the process of calibration in the conditions of laboratory the fluctuations of
the ambient temperature are negligibly small; the requirements for instability and resolution of the
instrument measuring the output signal of the comparator given in Table 1 also allow to ignore
these uncertainty components. What is important to be taken into account is the uncertainty due to
the difference in the dimensions of the compared BBRs. According to the estimates of [4] and [5]
the normal standard value of this uncertainty in the case of different dimensions of the compared
BBRs varies between 0.1 and 0.2 %. If it is necessary to calibrate BBRs with an uncertainty below
0.5 %, one shall be guided by the rules and estimates given in [3-5].
19
OIML/TC11/SC3/N5
Uncertainty of temperature related with the reference pyrometer (the
standard radiation thermometer).
usp – is the uncertainty of a BBR temperature Tb indicated by a standard
pyrometer used as reference. It includes: the uncertainty of its calibration; its
instability; uncertainty due to its positioning against the optical axis of the BBR;
uncertainty due to the effect of ambient conditions.
The temperature Tb of a BBR is evaluated from the reading Ysp(Tb) of the
standard pyrometer corrected by a factor 1   sp  Ta , sp   sp  G sp, b for effects


of ambient temperature Ta , sp and effective geometric extend Gsp, b and from the
correction value Ysp modified by a correction factor 1  sp  tsp  for ageing during
the period of time tsp since calibration. The small corrections are products of
variations in ambient temperature Ta , sp , differences in effective geometric extents
Gsp, b and due to ageing time Ta , sp with the related relative coefficients  sp ,  sp ,  sp .




Tb  c  Y sp Tb   1   sp  Ta , sp   sp  G sp, b  Y sp  1   sp  t sp



 

 
     u    u T   
     u    u G  
u 2 Y sp  Y sp2  t sp2  u 2  sp   sp2  u 2 t sp 
u sp  uTb   c 


u 2 Y sp Tb 
 Ta2, sp  u 2
2
 Y sp Tb   
 G 2  u 2
sp, b

where Tb
Ysp Tb 
Ysp
 sp ,  sp ,  sp



-
sp
2
sp
sp
2
sp
2
(15)
2
sp
2
a , sp
2
sp
sp, b
indication of the tested BBR temperature;
reading of the standard pyrometer;
correction value of the standard pyrometer;
relative coefficients of the standard pyrometer for
temperature, ageing and geometry.

u Y sp  U Y sp k  p  is the uncertainty of the pyrometer correction value
assigned by the calibration of the pyrometer, and certified as expanded uncertainty
U Ysp  with coverage factor k  p  .
For
long
term
stability
the
uncertainty
contribution
2
2
2
2
2
Y sp  t sp  u  sp   sp  u t sp is evaluated from the relative ageing coefficient

 


 
  k  p and a coverage factor k  p 
 sp with the associated uncertainty u  sp  U  sp
given in the TD for the standard pyrometer. The period of time tsp since last
calibration is determined from the certificate and usually the uncertainty utsp  is
negligible.



u Y sp Tb   max Y sp
 
3 , Y sp
n

from the readings is determined as the
maximum from either resolution  Y sp Tb  or the empirical standard deviation
 Y sp Tb  of a number n of independent readings.

  
 

The uncertainty contribution Y sp2 Tb   Ta2, sp  u 2  sp   sp2  u 2  sp  u 2 Ta , sp

from ambient conditions e.g. the variation of the ambient temperature is
determined from the difference Ta , sp  Ta , sp  Ta , sp0 between the actual ambient
20
OIML/TC11/SC3/N5
temperature Ta , sp near the standard pyrometer and the value Ta , sp0 defined for its
operation. Provided the temperature difference Ta , sp is negligible, then the higher
order term (in brackets) have to be regarded. The relative temperature coefficient
 sp with associated uncertainty u  sp  U  sp k  p  and coverage factor k  p  is
 
 
given in the TD of the standard pyrometer.
The effective geometric extend G b, 0   b,0  Ab,0  Ω b,0 for the tested BBR is stated
in the certificate with nominal values of emittance  b, 0 of the radiating area Ab, 0 , the
size and location of this area and the collected solid angle Ω b, 0 . It is compared
with the measured geometric extend G sp, b   sp, b  Asp, b  Ω sp, b of the standard
pyrometer with individual values of emittance  sp, b of the radiating area Asp, b , the
size and location of this area and the collected solid angle Ω sp, b . The correction


factor 1   sp  G sp, b is product of the relative coefficient  sp and the difference
G sp, b  G sp, 0  G b, 0 .
  
  

2
2
2
2
2
The uncertainty contribution G sp,
during
b  u  sp   sp  u  sp  u G sp, b
the calibration of the tested BBR due to an imperfect match between these
effective geometric extends has to be accounted for.
The uncertainty usp of the standard pyrometer shall be specified in its
calibration certificate. In the same way as mentioned in the previous section, this
uncertainty shall be expressed in terms of the expanded uncertainty with the
probability level of p = 0,95. If it is expressed as standard uncertainty (k = 1) , its
value shall be adjusted to correspond to the expanded value with multiplying by
the coverage factor k  p  0 ,95   2 determined by this probability.
The uncertainty due to the difference between (dimensions) effective geometric
extent of the BBR used in calibration of the reference pyrometer and the
dimensions of the BBR to be calibrated is explained in Note to Section 6.9.1 and
taken into account in equ. (15). In this case the uncertainty of the standard
measuring instruments u st from equ. (13) in this case shall be equal to usp.
The standard uncertainty estimated repeated readings are obtained in
accordance of 6.7.2.
21
OIML/TC11/SC3/N5
Uncertainty in the calibration of the tested BBR
6.7.2
The tested BBR temperature is determined from the average Yb of repeated
readings of the tested BBR own thermometer obtained in accordance of 6.7.2 and
the correction value Yb evaluated either from equ. (7) or equ. (15) and stated in




the certificate as expanded uncertainty U Yb  k  p   u Y b
with specified
coverage factor k  p  . The related standard uncertainties are determined from
equ. (4) and either equ. (7) or equ. (15).

Tb  c  Y b  Y b
where Tb
c 1 Yb
Yb -

(16)
the tested BBR temperature;
factor to match the units;
reading of the tested BBR-own-thermometer;
correction value for the tested BBR-own-thermometer.
6.7.3 The maximum standard uncertainty of the tested BBR temperature for verification is
calculated by the following formula using the correction value form equ. (7) or
equ. (15) and the limiting intervals (rectangular probability distribution) in the TD
estimated by Type B – u (Tb) – is calculated by the formula:
u( Tb ) = u st2 + ( uci2 + u si2 + uva2 + u rs2 ) / 3
where
(17)
Tb
-
the tested BBR temperature;
c 1
ust
-
factor to match the units;
standard uncertainty form equ. (7) or equ. (15);
uci
-
usi
-
uva
-
urs
-
standard interval from instability of the tested BBR-ownthermometer given as limits in the TD;
standard interval from calibration (verification) for spectral
intervals, limits of uncertainty according to 6.7.15;
standard interval from calibration (verification) for viewing angle
limits of uncertainty according to 6.7.16;
standard interval from calibration (verification) for inhomogen
radiating surface, limits of uncertainty according to 6.7.16.
All components of the budget have to be expressed as standard uncertainties
determined from the limits of permissible values taking into account the
recommended coverage factor.
6.7.4
The combined standard uncertainty of a temperature measurement of a BBR to be
calibrated (verified) – uΣ ( T ) – is calculated by the formula:
 
uΣ ( T ) = c 2  u 2 Yb + u 2 ( Tb )
where
uΣ ( T )
-
the measured BBR temperature;
c1
-
factor to match the units;
u Yb
 
-
standard uncertainty form equ. (4);
u( Tb )
-
standard uncertainty from equ. (17).
(18)
22
OIML/TC11/SC3/N5
6.7.5
The expanded uncertainty of the temperature value of the BBR to be calibrated
(verified) is determined by the coverage factor k  p  depending on the confidence
probability p ( k  p  0 ,95   2 , k  p  0 ,99   3 ) and is calculated by the formula:
U = k  p   u Σ T 
(19)
6.7.6
The obtained expanded uncertainty of the temperature value of the BBR to be
verified shall not exceed the corresponding uncertainty specified in the TD.
6.7.7
The calibration interval lasts usually for one or two years in the case of BBRs with
permanent jointed thermometers or in the case of BBRs with demountable
thermometers, respectively, unless otherwise specified in the TD.
6.8
Drawing up the results
6.8.1
The calibration and verification results are entered into the protocols, the forms for
which are given in the Annex.
6.8.2
When verification or calibration results are favorable, a verification or calibration
document (certificate, report) is issued. When verification or calibration results are
unfavorable, a verification or calibration document (certificate, report) that clearly
states the unserviceability of the instrument and the reasons being identified is
issued.
6.8.3
Legal metrological control system on BBR is significantly different in each member
state. Accordingly, the practical procedure, which is used to inform a result of
verification or calibration and to grant a permission to use the instrument by issuing
a certificate or a verification mark, is specified by the national authority in each
member state
6.8.4
If appropriate, the following data and parameters shall be specified in calibration or
verification certificates:
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
radiating area dimensions of the BBR forming the effective geometric extend
(emissivity, area and solid angle, cavity dimensions in case of the cavity BBR);
warm-up time of the BBR;
transition time for the BBR to pass from one stationary mode to another;
temperature drift of the BBR;
temperature control instability of the BBR at the specified stationary mode;
correction to the BBR own thermometer indication;
expanded uncertainty of the BBR temperature value;
positions of the temperature control device (if it given) of the BBR unit
depending on temperature (in the table form);
indication about using the BBR as a reference one;
period of validity of the BBR calibration/verification.
If appropriate, the following data and parameters shall be specified in
calibration or verification certificates
23
OIML/TC11/SC3/N5
7
Annex A
Recommended forms of the calibration and verification
certificates
1
Results of the evaluation of the blackbody radiator cavity geometry
Aperture diameter, mm
Permissible value
2
Results of the evaluation of the warm-up time, temperature drift
and transition time for the blackbody radiator to pass from a
stationary mode to another
Temperature
T, oC*
3.
Measured value
Distance from the aperture to the back wall of the
BB model, mm
Permissible value
Measured value
Readings
of the BBR own
thermometer
to be calibrated
(verified), oC
Average temperature values at the
time intervals t1, t2, t3, oC
t1
(0–5 min)
t2
(5-10 min)
t3
(10-15 min)
Maximum difference of the
average temperature values at
the time intervals t, t2, t3, oC
Value
calculated
Permissible
by the
value
measurement
data
Results of the evaluation of the blackbody radiator temperature
control uncertainty
Temperature
T, oC
Readings of the
thermometer of a
BBR to be calibrated
(verified), oC
Average
temperature value,
o
C
Maximum deviation from the average
temperature value, oC
Value calculated by the
Permissible value
measurement data
4
Results of the correction evaluation during sighting along the
blackbody radiator axis
4.1
Results of the correction evaluation using full radiation comparators
Temperature
T, oC
Thermometer readings of a
BBR to be calibrated
(verified), oC
Radiance temperature
of a standard BBR, oC
Difference between the radiance
temperature of a standard BBR and
thermometer readings of a BBR to be
calibrated (verified), oC
24
OIML/TC11/SC3/N5
4.2
Results of the correction evaluation using pyrometer-comparators with a partial
spectral range
Temperature
o
T, C
Thermometer
readings of a BBR
to be calibrated
o
(verified), C
Spectral
range, μm
Radiance
temperature of a
standard BBR, oC
Difference between the radiance
temperature of a standard BBR
and thermometer readings of a
o
BBR to be calibrated (verified), C
The average temperature difference for all spectral ranges, oC…
The maximum deviation from the average temperature difference, oC…
4.3
Results of the correction evaluation depending on the viewing angle of a BBR to be
calibrated (verified)
The table is filled for each viewing angle according to 4.2. Then the results are
summarized in the following table:
Temperature
T, oC
Viewing
angle,
i ,
1 i  m ,
grad
Differences between the standard
BBR temperature and temperature
indicated by the thermometer of
the calibrated (verified) BBR
thermometer for 1  j  n spectral
bands, oC
Average by all
The j -th band
angles
Uncertainty
of correction
for each
band and
angle,
o
C
Average value* of the
temperature correction for
all spectral ranges and
angles, oC
The maximum deviation from the average temperature correction for all spectral ranges
and angles, oC…
4.4
Results of the correction evaluation depending on the location of sighting at a BBR
to be calibrated (verified)
Temperature
T,
o
C
Thermometer
readings of a
standard BBR,
o
C
Coordinates of the
location of view,
mm
The BBR
own thermometer
readings,
o
C
Difference between the
thermometer readings of a
standard BBR and a BBR to
be calibrated (verified), oC
NB. T is the temperature set measured by the own thermometer of the BBR to be
calibrated (verified)
The average temperature difference for all sighting locations, oC…
The maximum deviation from the average temperature difference, oC…
25
OIML/TC11/SC3/N5
8
Annex B
References
[1]
OIML VIM-2010 – International Vocabulary of Metrology – Basic and General
Concepts and Associated Terms (VIM). 3rd Edition (Bilingual E/F), 2010, minor
corrections 2012
[2]
OIML VIML-2000 – International vocabulary of terms in legal metrology (VIML)
(bilingual French-English) / Vocabulaire international des termes de métrologie
légale (VIML) (bilingue franзais-anglais) , edition 2000
[3]
Guide to the Expression of Uncertainty in Measurement: First edition. – ISO,
Switzerland, 1993
[4]
J. Fischer et al., «CCT-WG5 on radiation thermometry, Uncertainty budgets for
realization of scales by radiation thermometry», 2003, CIPM, CCT/03-03. Summary
in Temperature, Its Measurement and Control in Science and Industry, 2003 vol.7,
D.C.Ripple ed., Melville, New York, pp.631-638
[5]
J. Fischer et al., «CCT-WG5 on radiation thermometry, Uncertainty budgets for calibration of
radiation thermometers below the silver point», Ver. 1.71, CIPM, CCT-WG5/docs-03-2008,
(http://www.bipm.org/wg/AllowedDocuments.jsp?wg=CCT-WG5);
Int J Thermophys (2008) 29:1066–1083; DOI 10.1007/s10765-008-0385-1
26