IEC 60751:2022

IEC 60751 ®
Edition 3.0 2022-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial platinum resistance thermometers and platinum temperature sensors

Thermomètres à résistance de platine et capteurs hermométriques de platine
industriels
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IEC 60751 ®
Edition 3.0 2022-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial platinum resistance thermometers and platinum temperature sensors

Thermomètres à résistance de platine et capteurs hermométriques de platine

industriels
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.200.20 ISBN 978-2-8322-1069-2

– 2 – IEC 60751:2022 © IEC 2022
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Characteristics . 8
4.1 General . 8
4.2 Nominal resistance versus temperature relationship . 9
4.3 Numerical table of resistance values . 9
5 Compliance and requirements . 9
5.1 Compliance . 9
5.2 Tolerance classes . 10
5.2.1 Tolerance class and its temperature range of validity . 10
5.2.2 Tolerance class of platinum resistors . 10
5.2.3 Tolerance classes and marking of thermometers . 10
5.3 Measuring current . 12
5.4 Electrical supply . 12
5.5 Connecting wire configuration . 12
6 Tests . 13
6.1 General . 13
6.1.1 Test categories . 13
6.1.2 Routine production tests . 13
6.1.3 Type tests . 13
6.1.4 Additional type tests for thermometers . 14
6.1.5 Summary of the tests . 14
6.2 Routine production tests for platinum resistors . 14
6.2.1 Tolerance acceptance test . 14
6.3 Routine production tests for thermometers . 15
6.3.1 Tolerance acceptance test . 15
6.3.2 Insulation resistance at ambient temperature . 16
6.3.3 Sheath integrity test . 16
6.3.4 Dimensional test . 16
6.4 Type tests for platinum resistors . 16
6.4.1 Tolerances . 16
6.4.2 Stability at upper temperature limit . 17
6.4.3 Self-heating . 17
6.5 Type tests for thermometers . 17
6.5.1 Tolerances . 17
6.5.2 Stability at upper temperature limit . 17
6.5.3 Self-heating . 17
6.5.4 Insulation resistance at elevated temperature . 17
6.5.5 Thermal response time . 18
6.5.6 Thermoelectric effect . 18
6.5.7 Effect of temperature cycling . 18
6.5.8 Effect of hysteresis . 18
6.5.9 Minimum immersion depth . 18

6.6 Additional type tests for thermometers . 19
6.6.1 General . 19
6.6.2 Capacitance . 19
6.6.3 Inductance . 19
6.6.4 Dielectric strength . 19
6.6.5 Vibration test . 19
6.6.6 Drop test . 19
6.6.7 Cold seal . 19
7 Information to be made available by the supplier . 19
7.1 General . 19
7.2 Applicable to resistors . 20
7.3 Applicable to thermometers . 20
Annex A (informative) Numerical table . 21
Bibliography . 25

Figure 1 – Example of connecting configurations . 13
Figure 2 – Examples of test results for selecting or rejecting platinum resistors . 15

Table 1 – Tolerance class of platinum resistors. 10
Table 2 – Tolerance class of thermometers . 11
Table 3 – Table of tests specified in this document . 14
Table 4 – Minimum insulation resistance of thermometers at the maximum temperature . 17
Table A.1 – Temperature versus resistance relationship below 0 °C; R = 100,00 Ω . 21
Table A.2 – Temperature versus resistance relationship above 0 °C; R = 100,00 Ω . 22
– 4 – IEC 60751:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL PLATINUM RESISTANCE THERMOMETERS
AND PLATINUM TEMPERATURE SENSORS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC Publication(s)"). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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.
IEC 60751 has been prepared by subcommittee 65B: Measurement and control devices, of IEC
technical committee 65: Industrial-process measurement, control and automation. It is an
International Standard.
This third edition cancels and replaces the second edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) formula of resistance versus temperature relationship become the standard specification
and the numerical table ceases to be the standard,
b) new clause "Compliance and requirement" is introduced,
c) tolerance acceptance test is modified,
d) an expanded marking system is introduced to accommodate special valid temperature
range,
e) vibration test method is revised,
f) cold seal is introduced as an additional type test,

g) numerical table of resistance versus temperature is included in Annex A as information.
The text of this International Standard is based on the following documents:
Draft Report on voting
65B/1210/FDIS 65B/1214/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60751:2022 © IEC 2022
INDUSTRIAL PLATINUM RESISTANCE THERMOMETERS
AND PLATINUM TEMPERATURE SENSORS

1 Scope
This International Standard specifies the requirements, in addition to the resistance versus
temperature relationship, for both industrial platinum resistance thermometers (later referred to
as "thermometers") and industrial platinum resistance temperature sensors (later referred to as
"platinum resistors") whose electrical resistance is derived from defined functions of
temperature.
Values of temperature in this document are in terms of the International Temperature Scale of
1990, ITS-90. A temperature in the unit °C of this scale is denoted by the symbol t, except in
Table A.1 where the full nomenclature t /°C is used.
This document applies to platinum resistors whose temperature coefficient α, defined as
RR−
100 0
α = ,
R ⋅°100 C
-3 -1
is conventionally written as α = 3,851⋅10 °C , where R is the resistance at t = 100 °C and
R is the resistance at t = 0 °C.
This document covers platinum resistors and thermometers for the temperature range −200 °C
to +850 °C with different tolerance classes. It can also cover particular platinum resistors or
thermometers for a part of this temperature range.
For resistance versus temperature relationships with uncertainties less than 0,1 °C, which are
possible only for platinum resistors or thermometers with exceptionally high stability and
individual calibration, a more complex interpolation equation than is presented in this document
can be necessary. The specification of such equations is outside the scope of this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 61152, Dimensions of metal-sheathed thermometer elements
IEC 61515:2016, Mineral insulated metal-sheathed thermocouple cables and thermocouples

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
platinum resistor
resistor made from a platinum wire or film with defined electrical characteristics, embedded in
an insulator (in most cases glass or ceramic), designed to be assembled into a platinum
resistance thermometer or into an integrated circuit
3.2
platinum resistance thermometer
thermometer
PRT
temperature-responsive device consisting of one or more sensing platinum resistors within a
protective sheath, internal connecting wires, and external terminals to permit connection of
electrical measurement instruments
Note 1 to entry: Mounting means and connection heads can be included. Not included is any separable protection
tube or thermowell.
3.3
nominal resistance
expected resistance R of a platinum resistor or thermometer at 0 °C, declared by the supplier
and shown in the thermometer marking, usually rounded to the nearest ohm
Note 1 to entry: Platinum resistors are often characterized by their nominal resistance. For example, a platinum
resistor with R = 100 Ω is often referred to as a Pt100
3.4
terminals
termination of the connections supplied with the platinum resistance thermometer
Note 1 to entry: Typical types of terminals are:
• screws or clamps on the terminal socket,
• pins of fixed connectors,
• open ends of fixed cables or equivalents.
3.5
temperature-sensitive length
length of the thermometer whose temperature directly influences the resistance measured
Note 1 to entry: Usually, the temperature-sensitive length is related to the length of the platinum resistor.
3.6
minimum immersion depth
immersion depth at which the change from the calibration at full immersion does not exceed
0,1 °C
3.7
tolerance
maximum allowable deviation of R(t) measured at temperature t from the nominal resistance
versus temperature relationship expressed as Δt(t) in °C

– 8 – IEC 60751:2022 © IEC 2022
3.8
dielectric strength
maximum voltage between all parts of the electric circuit and the sheath of the thermometer or,
in the case of a thermometer with two or more sensing circuits, between two individual circuits
that the thermometer can withstand without damage
3.9
insulation resistance
electrical resistance measured between any part of the electric circuit and the sheath at ambient
or elevated temperatures and with a specified measuring voltage (AC or DC)
3.10
self-heating
increase of the temperature of the platinum resistor or of the platinum resistor in a thermometer
caused by the dissipated energy of the measuring current
3.11
self-heating coefficient
temperature rise due to dissipated energy by measuring current in a resistor expressed with the
unit °C/mW
3.12
thermal response time
time a thermometer takes to reach a specified percentage of a step change in temperature
3.13
thermoelectric effect
effect of inducing electro-motive force (abbreviated by e.m.f hereafter) caused by different
metals used in the electric circuit of the thermometer and by thermoelectric inhomogeneity of
the internal leads at the conditions of temperature gradients along the leads
3.14
hysteresis
resistance difference at the middle of the temperature range between before and after exposing
the thermometer to the lower and upper limit of the temperature range
3.15
expanded uncertainty
quantity defining an interval about the result of a measurement that can be expected to
encompass a large fraction of the distribution of values that could reasonably be attributed to
the measurand
Note 1 to entry: For reference, see 3.16.
3.16
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an
expanded uncertainty
Note 1 to entry: Coverage factor, k, is typically in the range 2 to 3. In this document, k = 2 is chosen, the confidence
level of which is 95 %. Refer to Bibliography [1].
4 Characteristics
4.1 General
The nominal resistance versus temperature relationship for platinum resistors and
thermometers and their tolerance class are standardized. This specification is applied to a
sensing platinum resistor at its connecting points and to a complete thermometer at its terminals.

In the case of two-wire connections (see 5.5), the resistance values of the leads between the
connecting point of the platinum resistor and the terminals shall be considered. They shall be
subtracted from measured resistances. In some cases, it is also advisable to consider the
temperature coefficient of the lead wires, the geometrical characteristics of the wires, and the
temperature distribution along their length. This information may be supplied to users as
additional information (refer to Clause 7).
4.2 Nominal resistance versus temperature relationship
The resistance versus temperature relationships used in this document are as follows:
For the range −200 °C to 0 °C:
2 3
R = R [1 + At + Bt + C(t − 100 °C) t ]
t 0
For the range of 0 °C to 850 °C:
R = R (1 + At + Bt )
t 0
where
R is the resistance at the temperature t,
t
R is the resistance at t = 0 °C.
The constants in these equations are,
−3 −1
A = 3,908 3 × 10 °C
−7 −2
B = −5,775 × 10 °C
−12 −4
C = −4,183 × 10 °C .
4.3 Numerical table of resistance values
Table A.1 and Table A.2 are derived from the equations and coefficients specified in 4.2 for a
thermometer or platinum resistor of nominal resistance R of 100 Ω.
Table A.1 and Table A.2 are applicable to any thermometer and platinum resistor having any
value of R .
In this case, the resistance values in Table A.1 and Table A.2 shall be multiplied by the factor
R / 100 Ω.
NOTE 1 In this edition, the numerical tables given in Annex A cease to be normative; they are now informative. The
specification of this document is the formula described in 4.2 with which user can calculate numerical value of R .
t
NOTE 2 The most frequently used device has R of 100 Ω. Devices with R of 10 Ω, 500 Ω or 1000 Ω are used
0 0
frequently as well.
5 Compliance and requirements
5.1 Compliance
In order for a thermometer to be compliant with this document, it shall be made from a platinum
resistor which is compliant with this document.

– 10 – IEC 60751:2022 © IEC 2022
Platinum resistors and thermometers shall be tested to prove that the device meets all the
applicable requirements specified in this document. Suppliers shall be responsible for
conducting the tests and for proving that the device conforms to this document before
transferring the device to the user. The test method and evaluation are specified in this
document.
5.2 Tolerance classes
5.2.1 Tolerance class and its temperature range of validity
Tolerance classes are given in Table 1 for a platinum resistor and in Table 2 for a thermometer
for any value of R .
These tolerance classes are closely related to the operable temperature range. Therefore, the
temperature ranges of validity of a tolerance class are shown in the adjacent column in the
table. Temperature ranges of validity are based on the working experience with film and wire
platinum resistors.
A thermometer that has a modified tolerance or temperature range of validity can still be
compliant with this document provided it satisfies all the applicable requirements, other than
the tolerance or the temperature range of validity, and the modification is notified to the user.
Details on this are described in 5.2.3.2.
Thermometers or platinum resistors without the specified temperature range of validity for the
tolerance are not permitted in this document.
5.2.2 Tolerance class of platinum resistors
Table 1 specifies the tolerance class for platinum resistors. Tolerances and ranges of validity
that differ from values given in Table 1 shall be agreed between the supplier and the user.
Table 1 – Tolerance class of platinum resistors
Wire wound platinum resistors Film platinum resistors
Tolerance
Tolerance Temperature range of Tolerance Temperature range of
(°C)
class validity (°C) class validity (°C)
−100 to +350 0 to +150
W 0,1 F 0,1 ±(0,1 + 0,001 7 | t |)
W 0,15 −100 to +450 F 0,15 −30 to +300 ±(0,15 + 0,002 | t |)
W 0,3 −196 to +660 F 0,3 −50 to +500 ±(0,3 + 0,005 | t |)
W 0,6 −196 to +660 F 0,6 −50 to +600
±(0,6 + 0,01 | t |)
NOTE The symbol | t | denotes modulus of temperature in °C without regard to the sign.

5.2.3 Tolerance classes and marking of thermometers
5.2.3.1 Tolerance classes of thermometers
Table 2 specifies the tolerance class for thermometers.

Table 2 – Tolerance class of thermometers
Temperature range of validity (°C) for thermometers Tolerance
made using
(°C)
Tolerance class
Wire wound platinum Film platinum resistors
resistors
AA −50 to +250  0 to +150 ±(0,1 + 0,0017 | t |)
A −100 to +450 −30 to +300
±(0,15 + 0,002 | t |)
−50 to +500
B −196 to +600 ±(0,3 + 0,005 | t |)
C −196 to +600 −50 to +600 ±(0,6 + 0,01 | t |)
NOTE The symbol | t | denotes modulus of temperature in °C without regard to the sign.

5.2.3.2 Special tolerance classes of thermometers
Tolerances and ranges of validity that differ from the values given in Table 2 shall be agreed
between the supplier and the user. These special thermometers shall be clearly distinguished
from a standard device by the "-sp" marking as is specified in 5.2.3.3. Recommended special
tolerance classes may be constructed as multiples or fractions of class B tolerance. Example 1
in 5.2.3.3 demonstrates this case.
It is also left to the suppliers and the users to establish a special class for their thermometers
with a temperature range different from the ranges in Table 2. Special temperature ranges of
validity may be defined for restricted or extended temperature ranges. Example 2 in 5.2.3.3
demonstrates this case.
5.2.3.3 Marking of thermometers
Each thermometer shall be marked or labelled accordingly so that the user can confirm, either
directly or indirectly, the number of platinum resistors, connecting wire configuration, tolerance
class, and its temperature range of validity.
Marking Example1: 2 × Pt100 / (2/3B) –F-sp / 3 / −50 / +250
This means:
• Two platinum resistor construction,
• Nominal resistance: R = 100 Ω,
• Tolerance class: 2/3B [Tolerance value ±(0,2 + 0,0033 | t |)],
• Platinum resistor type: F (film),
• Special tolerance class [(2/3)B]: suffix –sp of F is the notification. It means that the tolerance
class is different from Table 2 and range of validity differs also,
• Wire configuration: 3 wire configuration (see Figure 1),
• Range of validity: −50 °C to +250 °C,
• Lower temperature limit of the thermometer: −50 °C,
• Upper temperature limit of the thermometer: +250 °C.
Marking Example 2: 1 × Pt100 / AA-W-sp / 4 / −50 / +300
This means:
• One platinum resistor construction,
• Nominal resistance: R = 100 Ω,
– 12 – IEC 60751:2022 © IEC 2022
• Tolerance class: AA,
• Platinum resistor type: W (wire wound),
• Special range of validity; suffix -sp of W means that range of validity is different from
Table 2,
• Wire configuration: 4 wire configuration (see Figure 1),
• Range of validity: −50 °C to +300 °C,
• Lower temperature limit of the thermometer: −50 °C,
• Upper temperature limit of the thermometer: +300 °C.
5.3 Measuring current
The measuring current of a platinum resistor or thermometer shall be limited to a value at which
the self-heating of the thermometer under conditions specified in 6.4.3 does not exceed 25 %
of the tolerance value of the declared tolerance class. The measuring current is usually not
more than 1 mA for a 100 Ω wire wound platinum resistor.
5.4 Electrical supply
Platinum resistors and thermometers shall be constructed so that they are suitable for use in
measuring systems using direct current or alternating current at frequencies up to 100 Hz. Some
measuring systems may require operation at higher frequencies.
5.5 Connecting wire configuration
Thermometers of tolerance class better than class B shall have 3-wire or 4-wire configuration
with 4-wire configuration being recommended.
Thermometers may be constructed with one or more platinum resistors and a variety of internal
connecting wire configurations. A typical example of identification and designation of the
terminals is shown in Figure 1.

Figure 1 – Example of connecting configurations
6 Tests
6.1 General
6.1.1 Test categories
Tests shall be performed to prove that platinum resistors or thermometers conform to the
requirements of this document. The tests are categorised as routine production test, type test,
and additional type test. It is not intended or recommended that all tests be performed on every
platinum resistor or thermometer supplied. Different kinds of tests are therefore described from
6.1.2 to 6.1.5.
6.1.2 Routine production tests
The routine production test shall be performed on every platinum resistor or thermometer
manufactured in accordance with this document. This routine production test can be replaced
by a sampling test provided that technically established control procedures are in place to
demonstrate that the statistical sampling test is sufficient. If the routine production test is
replaced by a sampling test, the user shall be informed.
6.1.3 Type tests
Type tests shall be carried out on a platinum resistor or a thermometer of each particular design
and temperature range of operation. The routine production test items shall also be performed
on the type tests. These tests are subdivided into tests for all forms of platinum resistors or
thermometers.
– 14 – IEC 60751:2022 © IEC 2022
6.1.4 Additional type tests for thermometers
Additional type tests may be required by other regulations or by agreement between the supplier
and the user for special applications. If not stated otherwise, there are no fixed specifications
for these test items. The results of the tests shall be made available on request.
6.1.5 Summary of the tests
All the tests specified in this document are summarized in Table 3 with reference to the clause
in which details of the test are given.
Table 3 – Table of tests specified in this document

Routine production tests Type tests
Additional type
tests for
Platinum Thermometers Platinum Thermometers
thermometers
resistors resistors
Tolerance acceptance test 6.2.1 6.3.1 6.3.1
Insulation resistance at 6.3.2 6.3.2
ambient temperature
Sheath integrity test 6.3.3 6.3.3
Dimensional test 6.3.4 6.3.4
Tolerances  6.4.1 6.5.1
Stability at upper  6.4.2 6.5.2
temperature limit
Self-heating  6.4.3 6.5.3
Insulation resistance at  6.5.4
elevated temperature
Thermal response time  6.5.5
Thermoelectric effect  6.5.6
Effect of temperature  6.5.7
cycling
Effect of hysteresis  6.5.8
Minimum immersion depth  6.5.9
Capacitance   6.6.2
Inductance   6.6.3
Dielectric strength   6.6.4
Vibration test   6.6.5
Drop test   6.6.6
Cold seal   6.6.7
6.2 Routine production tests for platinum resistors
6.2.1 Tolerance acceptance test
All types of platinum resistors shall be tested at one temperature at least. The test temperature
shall be in the range from −5 °C to +30 °C, preferably 0 °C. Estimation of measurement
uncertainty for the test shall be done with coverage factor k = 2.
Platinum resistors of the tolerance classes W0,1, F0,1, W0,15 and F0,15 shall be tested at one
additional temperature at least. This test temperature shall be the upper or lower temperature
limit of the platinum resistor, or spaced from the first test temperature by 90 °C, whichever is
less.
For selection of the platinum resistor, the supplier shall perform a measurement with expanded
uncertainty of less than 1/3 of the tolerance band. However, the supplier shall also be allowed
to select a measurement with an alternative expanded uncertainty to respond to demands,
provided that the uncertainty is notified to the user.
As a typical example, the resistors numbered 1 to 4 in Figure 2 illustrate resistance deviation
of tolerance class 0,1 resistors.
The selection criteria for the supplier are: the equivalent temperature deviation calculated by
resistance deviation from the nominal resistance versus the temperature function plus the
expanded uncertainty of the measurement shall be completely within the corresponding
tolerance band which is exemplified by resistor 1 in Figure 2.
The rejection criteria for the user are: at the entrance, check the tolerance value is not met. It
is judged by the measurement result that the deviation plus expanded uncertainty of the
measurement is completely outside the tolerance band which is exemplified by resistor 4 in
Figure 2.
Regarding resistors 2 and 3, of which part of the expanded uncertainty interval lies outside the
tolerance band, the user can ask the supplier for information about the test measurement of the
particular platinum resistor.
NOTE For the selection guidelines, refer to the Bibliography [2].

The examples shown are for tolerance class 0,1. Limits are part of the tolerance band.
Figure 2 – Examples of test results for selecting or rejecting platinum resistors
6.3 Routine production tests for thermometers
6.3.1 Tolerance acceptance test
The suppliers shall ensure that platinum resistors of the appropriate tolerance class have been
used for their thermometers. Thermometers of tolerance classes A and better (see 5.2) shall be
tested for resistance accuracy at one temperature point in the range of −5 °C to +30 °C. All the
selection criteria are the same as those described in 6.2.1.

– 16 – IEC 60751:2022 © IEC 2022
6.3.2 Insulation resistance at ambient temperature
The insulation resistance between each terminal and the sheath shall be tested with a test
voltage of a minimum of 100 V DC.
The insulation resistance shall be not less than 100 MΩ.
For thermometers with two or more measuring circuits, the same test shall be made between
the individual circuits.
6.3.3 Sheath integrity test
6.3.3.1 General
The integrity of the sheath and all closure welding shall be tested in general by suitable means:
either by a suitable test method not mentioned in this document, or with such a method given
in this document. For particular applications, sheath integrity tests may be agreed between the
user and the supplier. Examples of commonly accepted suitable integrity tests are given in
6.3.3.2 to 6.3.3.5.
6.3.3.2 Water quench test
The thermometer shall be subjected to a minimum temperature of 300 °C for a minimum time
of 5 min and then immediately plunged into water at room temperature. Then the insulation
resistance shall be measured while the thermometer is immersed. The insulation resistance
shall meet the requirements of 6.3.2.
6.3.3.3 Nitrogen pressure test
The thermometer shall be externally pressurized for approximately 30 s at a minimum pressure
of 2,5 MPa in a nitrogen gas, after which the thermometer shall be immediately immersed in
water or alcohol. There shall be no bubbling from the weld.
6.3.3.4 Liquid nitrogen test
The thermometer shall be immersed in liquid nitrogen until the temperature is stabilized, after
which the thermometer shall be immediately immersed in water or alcohol. There shall be no
bubbling from the weld. This test is only recommended for thermometers that can be used at a
temperature down to −196 °C or −200 °C.
6.3.3.5 Helium leakage test
The helium leakage test shall be mentioned as a further means of integrity test. The details of
this test may be determined by agreement between the supplier and the user.
6.3.4 Dimensional test
If the manufactured thermometer is covered by the scope of IEC 61152, the outside diameter
and the straightness shall be tested to be in accordance with the requirements of IEC 61152.
6.4 Type tests for platinum resistors
6.4.1 Tolerances
The tolerance values for the specified tolerance class shall be met for the whole temperature
range of validity. The number of necessary measurements for this test depends on the
temperature range and the tolerance class and shall include temperatures close to the upper
and lower limits of the declared temperature range. To consider uncertainty, refer to 6.2.1.

6.4.2 Stability at upper temperature limit
The platinum resistor shall be subjected to its declared upper temperature limit in air for
1 000 hours. The drift in resistance (R − R ) shall be converted to
0, End of test 0, Start of test
temperature and it shall not be more than the tolerance value at 0 °C for the respective tolerance
class.
6.4.3 Self-heating
The self-heating coefficient shall be evaluated at a temperature between 0 °C and 30 °C in
flowing air with a velocity of (3 ± 0,3) m/s or in flowing water with a velocity (0,3 ± 0,1) m/s. The
self-heating under the above mentioned conditions shall not exceed 25 % of the tolerance value
of the declared tolerance class at the declared maximum measuring current. Applied test
conditions shall be declared.
6.5 Type tests for thermometers
6.5.1 Tolerances
The tolerance values for the specified tolerance class shall be met for the whole temperature
range of validity. The number of necessary measurements for this test depends on the
temperature range and the tolerance class, and shall include temperatures close to the upper
and lower limits of the declared temperature range.
NOTE Tolerance is closely related to the acceptance test. Acceptance criteria are described in 6.2.1 of this
document.
6.5.2 Stability at upper temperature limit
The thermometer shall be subjected to its declared upper temperature limit in air for a minimum
of 4 weeks (672 h) continuously. The drift in resistance (R − R ) is to be
0, End of test 0, Start of test
converted to temperature, and it shall be within the tolerance band of the declared tolerance
class. The insulation resistance specif
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