IEC 62397:2007

INTERNATIONAL IEC
STANDARD
CEI
NORME
First edition
INTERNATIONALE
Première édition
2007-05
Nuclear power plants –
Instrumentation and control important to safety –
Resistance temperature detectors

Centrales nucléaires de puissance –
Instrumentation et contrôle-commande
importants pour la sûreté –
Sondes à résistance
Reference number
Numéro de référence
IEC/CEI 62397:2007
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de
référence, texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou
remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
INTERNATIONAL IEC
STANDARD
CEI
NORME
First edition
INTERNATIONALE
Première édition
2007-05
Nuclear power plants –
Instrumentation and control important to safety –
Resistance temperature detectors

Centrales nucléaires de puissance –
Instrumentation et contrôle-commande
importants pour la sûreté –
Sondes à résistance
PRICE CODE
T
CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
Pour prix, voir catalogue en vigueur

– 2 – 62397 © IEC:2007
CONTENTS
FOREWORD.4
INTRODUCTION.6

1 Scope.8
2 Normative references .8
3 Terms and definitions .8
4 Design and construction requirements.10
4.1 General .10
4.2 Reliability .10
4.3 Materials .10
4.3.1 Radiation dose to materials .10
4.3.2 Resistance element material.11
4.3.3 Seals and adhesives.11
4.4 Connections .11
4.4.1 Electrical connection .11
4.4.2 Mechanical connection .14
4.5 Workmanship .14
4.6 Ambient conditions (normal and accident operations) .15
4.7 RTD performance .15
4.7.1 Accuracy .15
4.7.2 Resistance temperature calibration.16
4.7.3 Self-heating error .16
4.7.4 Thermal response time .16
4.7.5 Interchangeability .17
4.7.6 Electrical insulation resistance .17
4.7.7 Repeatability (thermal shock) .17
4.7.8 Vibration.18
4.7.9 Steam test .18
4.7.10 Insulation resistance after storage .18
4.7.11 In situ response time testing .19
4.8 Identification.19
4.9 Failure mode and effects analysis .19
5 Inspection and tests .20
5.1 General .20
5.2 Inspection and test failure .20
5.3 Inspection and test reports .20
5.4 Qualification tests.20
5.4.1 Calibration procedure .21
5.4.2 Thermal cycling .22
5.4.3 Insulation breakdown test .22
5.4.4 Examination .22
5.5 Production tests .22
6 Technical information required .23

Bibliography.24

62397 © IEC:2007 – 3 –
Figure 1 – Form and dimensions of an RTD .12
Figure 2 – Installation of a rigid RTD (Type I).12
Figure 3 – Installation of a rigid RTD (Type II) long insertion.13
Figure 4 – Installation of a rigid RTD (Type II) short insertion .13

– 4 – 62397 © IEC:2007
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
RESISTANCE TEMPERATURE DETECTORS

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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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.
International Standard IEC 62397 has been prepared by subcommittee 45A: Instrumentation
and control of nuclear facilities, of IEC technical committee 45: Nuclear instrumentation.
The text of this standard is based on the following documents:
FDIS Report on voting
45A/650/FDIS 45A/656/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

62397 © IEC:2007 – 5 –
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
– 6 – 62397 © IEC:2007
INTRODUCTION
a) Technical background, main issues and organisation of the standard
This standard describes the requirements for the design, material selection, procurement,
construction, and testing of resistance temperature detectors (RTDs) being used in nuclear
power plants (NPPs). These RTDs may be used in both the nuclear safety I&C systems
and/or in the non-safety-related instrumentation systems.
When the project was proposed in October 2002 during the SC 45A meeting held in Beijing,
China, there was no other known IEC standard currently available on this subject.
b) Situation of the current standard in the structure of the SC 45A standard series
IEC 62397 is not directly referenced by IEC 61513 and is the third-level SC 45A document
tackling the issue of RTDs.
For more details on the structure of the SC 45A series of standards, see item d) of this
introduction.
c) Recommendations and limitations regarding the application of this standard
There is no particular recommendation or limitation regarding the application of this standard.
d) Description of the structure of the SC 45A standard series and relationships with
other IEC documents and other bodies documents (IAEA, ISO)
The top-level document of the IEC SC 45A standard series is IEC 61513. It provides general
requirements for I&C systems and equipment that are used to perform functions important to
safety in NPPs. IEC 61513 structures the IEC SC 45A standard series.
IEC 61513 refers directly to other IEC SC 45A standards for general topics related to
categorization of functions and classification of systems, qualification, separation of systems,
defence against common-cause failure, software aspects of computer-based systems,
hardware aspects of computer-based systems, and control room design. The standards
referenced directly at this second level should be considered together with IEC 61513 as a
consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 are standards
related to specific equipment, technical methods, or specific activities. Usually these
documents, which make reference to second-level documents for general topics, can be used
on their own.
A fourth level extending the IEC SC 45A standard series corresponds to technical reports,
which are not normative.
IEC 61513 has adopted a presentation format similar to the basic safety publication
IEC 61508 with an overall safety life-cycle framework and a system life-cycle framework and
provides an interpretation of the general requirements of IEC 61508-1, IEC 61508-2 and
IEC 61508-4, for the nuclear application sector. Compliance with IEC 61513 will facilitate
consistency with the requirements of IEC 61508 as they have been interpreted for the nuclear
industry. In this framework, IEC 60880 and IEC 62138 correspond to IEC 61508-3 for the
nuclear application sector.
62397 © IEC:2007 – 7 –
IEC 61513 refers to ISO as well as to IAEA 50-C-QA (now replaced by IAEA 50-C/SG-Q) for
topics related to quality assurance (QA).
The IEC SC 45A series of standards consistently implements and details the principles and
basic safety aspects provided in the IAEA code on the safety of NPPs and in the IAEA safety
series, in particular the requirements NS-R-1 establishing safety requirements related to the
design of NPPs, and safety guide NS-G-1.3 dealing with instrumentation and control systems
important to safety in NPPs. The terminology and definitions used by SC 45A standards are
consistent with those used by the IAEA.

– 8 – 62397 © IEC:2007
NUCLEAR POWER PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
RESISTANCE TEMPERATURE DETECTORS

1 Scope
This International Standard describes the requirements for resistance temperature detectors
(RTDs) suitable for nuclear power plant (NPP) services. The requirements of RTDs include
design, materials, manufacturing, testing, calibration, procurement, and inspection. In nuclear
application, both “direct-immersion” and “thermowell-mounted” RTD are commonly used;
however, this standard does not exclude any other design of RTD which may be required for
certain special applications in various types of reactors.
RTDs can be supplied in different internal constructions, which depend on the manufacture,
qualifications, and applications. For RTD being used in an NPP, the design and structure of
the RTD should consider the environmental conditions in which the detector is being used
under normal operating and under design basis accident conditions, as well as the
qualification tests specified by the user . The use of a flexible mineral-insulated (MI) cable
between the RTD and the connector is commonly adopted, and the user may also adopt any
other construction. A variation of this design may include a rigid exterior sheath over the MI
cable between the RTD and the connector, these being welded to each other.
The scope of this standard does not cover the design, material selection, and construction of
the thermowell, the guide tube, the extension cable, and the temperature transmitter or bridge
which may be associated with the RTD.
2 Normative references
The following referenced documents are indispensable for the application 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 60780:1998, Nuclear power plants – Electrical equipment of the safety system –
Qualification
IEC 60980:1989, Recommended practices for seismic qualification of electrical equipment of
the safety system for nuclear generating stations
IEC 61224, Nuclear reactors – Response time in resistance temperature detectors (RTD) – In
situ measurements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
———————
The user corresponds to the party or the company that uses the RTD in a NPP for measuring the temperature
in a safety or a non-safety system. The term user may also refer to the purchaser or the buyer, or the operator
of the RTD.
62397 © IEC:2007 – 9 –
3.1
accuracy of measurement
closeness of the agreement between the result of a measurement and the conventional true
value of the measurand
[IEV 394-40-35]
3.2
calibration
set of operations that establish, under specified conditions, the relationship between values of
quantities indicated by measuring instrument or measuring system, or values represented by
material measure or a reference material, and the corresponding values realized by standards
[IEV 394-40-43]
3.3
drift
variation in sensor or instrument channel output that may occur between calibrations that
cannot be related to changes in the process variable or environmental conditions
[IEC 62385, definition 3.6]
3.4
performance monitoring
process of demonstrating that an installed instrument channel continues to perform its
intended function of monitoring the process variable with the expected accuracy, response
time, and stability
[IEC 62385, definition 3.14]
3.5
resistance temperature detector (RTD)
detector generally made up of a stainless steel cylindrical barrel protecting a platinum resistor
whose resistance varies with temperature. This detector is placed in the piping containing the
fluid whose temperature is measured in this way. It can be directly immersed in the fluid or
protected by an intermediate casing called the thermowell
NOTE 1 Mounting means or connection heads may be included. The temperature-sensing resistor can be made of
platinum, nickel tungsten, copper, or other metals. However, a platinum sensor is commonly used in the RTD in an
NPP; therefore, a platinum resistance thermometer is referred to in this standard.
NOTE 2 In this standard, the term “sensor” describes the RTD unit with all its associated protection, for example,
barrel or thermowell. For most applications of measuring process fluid temperature in an NPP, the platinum resistor
sensor is installed inside a stainless steel thermowell. For air temperature measurement, a direct sensor may be
used.
3.6
response time
the time required for the output signal of a component to reach a specified fraction (generally
90 %) of its final variation after a step change of its input signal
3.7
self-heating error
rise in the indicated temperature due to the power dissipated in the sensor

– 10 – 62397 © IEC:2007
3.8
thermowell
protective jacket for RTDs, thermocouples, and other temperature sensors. The thermowell is
also used to facilitate replacement of the temperature sensor
[IEC 62385, definition 3.21]
3.9
time constant
in the case of a first order system, the time required for the output signal of a system to reach
63,2 % of its final variation after a step change of its input signal.
If the system is not first order system, the term “time constant” is not appropriate. For a
system of a higher order, the term “response time” should be used.
4 Design and construction requirements
4.1 General
The RTD and its associated devices shall meet the requirements described in this standard
but shall not necessarily be limited to these requirements.
4.2 Reliability
The design philosophy for RTDs in an NPP requires a device which is capable of continuous
successful operation at rated service conditions throughout the design life of the plant. The
–3
equipment should have a failure rate less than 5 × 10 failures per year.
RTDs operated in safety systems should have their design lives defined. For RTD whose
design life is less than the design life of the NPP or the safety system, then arrangement shall
be made for the RTD to be replaced or re-assessed before its design life is reached.
4.3 Materials
Materials, processes and standard parts which are not specifically designated herein and
which are necessary for the manufacturing and installation of the RTD shall be of high quality
and in accordance with the highest calibration practice pertinent to the manufacture and
application of instrumentation equipment.
All equipment, material, and articles incorporated in the products covered by this standard
shall be new but may be fabricated using components produced from recycled materials to the
maximum extent practicable without jeopardizing the intended use.
4.3.1 Radiation dose to materials
The maximum radiation dose may be about 900 kGy (90 Mrad) depending on the application
and the mission time after a design basis accident.
Some devices may be exposed to neutron fluxes. The user shall review and approve the use
of the materials, which may be subject to activation.

62397 © IEC:2007 – 11 –
4.3.2 Resistance element material
Platinum is used extensively for resistance thermometers in an NPP for both safety- and non-
safety-related instrument applications. Platinum is a noble metal, relatively stable and
unaffected by its surrounding environment. It resists corrosion, oxidation, and other forms of
chemical attack. It is easily workable and can be drawn into fine wires. Platinum has a high
melting- point, which shows little volatilization below 1 000 °C. Platinum can be obtained to a
high degree of purity, which has a reproducible electrical and chemical characteristic over a
wide range of temperatures. All this is evidenced by a simple linear and stable resistance
temperature relationship that characterizes the platinum sensor. However, the electrical
resistance of platinum wire is extremely sensitive to minute quantities of contaminating
impurities and to strains; both of these characteristics may alter the simple resistance-
temperature relationship.
Other metals may also be used for resistance thermometers provided their accuracy,
repeatability, response time, and reliability comply with the requirements of the applications.
The sensing wire shall be mounted so as to be almost free of strains to avoid the strain gauge
effect from causing extraneous changes in resistance. Furthermore, the thermometer shall be
manufactured with the resistance element free of contaminants.
4.3.3 Seals and adhesives
The RTD shall be hermetically sealed. The connector may or may not be an integral part of
the RTD assembly. RTD used in a harsh environment, such as under high-temperature and/or
radiation areas, shall be designed without organic material. The use of ceramic material is
recommended. The tightness of the insulating termination shall be tested according to an
adequate and proven procedure. Commonly suggested seals of the connector are
–8
cm /s leak rate when
glass-to-metal or ceramic-to-metal, which should have less than 10
tested with helium at an atmospheric differential pressure.
All cements, adhesives, or seals used internally in the device shall be capable of withstanding
the service conditions without functional deterioration and without emitting gases. All non-
metallic materials, when used for seals, protective finishes, and so forth, shall be moisture-
and flame-resistant. These non-metallic materials shall not support fungus growth and shall
not be adversely affected by the ambient environments specified in the performance
requirements of this standard.
4.4 Connections
4.4.1 Electrical connection
RTDs shall have lead wires terminated through a qualified hermetic seal.
There are two common types of electrical connections used in an NPP. Figure 1 provides the
general form and dimensions of an RTD without any thermowell. Figure 2 is a rigid RTD
without a quick disconnect and is referred to as Type I (standard). Figures 3 and 4 are rigid
RTDs with quick disconnectors, and are referred to as Type II with long insertion and short
insertion, respectively. A user may specify any other form of RTD and construction, depending
on its particular applications.

– 12 – 62397 © IEC:2007
Type I (standard): The electrical connection is made within a metallic housing (connection
head) and is achieved by screw-type terminals. The housing shall be waterproof when closed
and shall permit ready withdrawal of the RTD when open. The removable cap shall be joined
to the body by a corrosion-resistant chain. The nipple and the extension may be specified as
part of the application or recommended by the temperature-sensor manufacturer .
Type II (quick disconnect): The electrical connection is achieved by using a multi-pin
connector. The connector need not be a hermetic type, but it shall be splash-proof when
mated and shall meet the insulation resistance requirements in 4.7.6. In addition, the contact
resistance across a mated connector shall not exceed 0,25 Ω. For high-accuracy application,
the user may consider gold or silver plating for the pins and sockets of the connector.

Overall length
406 mm
Installed length
(spring compressed)
195 mm min.
∅6,35 ± 0,127 mm
Spring
Slot for bayonet pin
Spring gap
Connection head or connector
IEC  620/07
NOTE Spring may be enclosed inside connection head.
Figure 1 – Form and dimensions of an RTD

Bayonet pin
RTD spring Thermowell
Connector
Extension tube
RTD
Adaptor
Hex. nut
IEC  621/07
Figure 2 – Installation of a rigid RTD (Type I)

———————
The manufacturer corresponds to the party or the company that manufactures the RTD. The term manufacturer
may also refer to the supplier or the vendor of the RTD.

62397 © IEC:2007 – 13 –
Ceramic terminal block
Thermowell
S.S. nipple
RTD
Coupling
Connection head IEC  622/07
Figure 3 – Installation of a rigid RTD (Type II) long insertion

Ceramic terminal block
Short insertion
Thermowell
RTD
Coupling
Connection head
IEC  623/07
Figure 4 – Installation of a rigid RTD (Type II) short insertion
The temperature rating of the connector shall be at least 150 °C or the accident temperature
specified by the user. Unless otherwise specified, the manufacturer shall supply the mating
connector half with the RTD. The adapter and the extension tube shall be supplied by the
manufacturer.
Electrical continuity
All circuits shall maintain electrical continuity throughout the normal and accident operating
conditions.
Contact resistance
Resistance in the contacts of each circuit shall not be greater than 0,25 Ω.
Lead wires
Three or four lead wires may be used depending on their applications and degree of required
accuracy. The RTD should normally be used as a three-wire device unless a four-wire device
is required for specific design reasons. The lead wires of the RTD shall be continuously
supported by an insulating material in such a manner that the completed RTD is insensitive to
vibration. The lead-wire material shall be so chosen as to reduce the resistance of the leads
to the practicable minimum.
– 14 – 62397 © IEC:2007
Installation of RTD into a thermowell
The RTD shall be installed generally as shown in Figures 2, 3, and 4. In each case, the RTD
shall be held in its thermowell by spring pressure. Where an RTD of Type I is used, the spring
cap which forms part of a dust-cap shall completely cover the end of the extension tube. In
each case, the extension nipple is considered to be part of the RTD.
4.4.2 Mechanical connection
The user shall ensure that the RTD is compatible with the design of the thermowell, the
connection head, the extension guide tube, and the end fittings shown in figure 1.
NOTE The guide tube is not part of this standard.
A spring force of the order of 1 100 kN/m ensures a satisfactory RTD to thermowell bottom
contact.
The connector assembly shall prevent moisture intrusion that may result in a leakage current,
thus deteriorating the signal and producing a false temperature indication. The cable
connector assembly shall also provide mechanical protection for the connections, thus
preventing mechanical stresses from rendering the circuit susceptible to the effects of
moisture intrusion, or breaking off the connections completely.
If fastening devices, such as screws, pins, bolts and similar, are used, these parts shall be
installed with a means for preventing loss of tightness. These parts, when subject to removal
or adjustment, shall not be swaged, peened, stacked, or otherwise permanently deformed.
X-rays of welds
All the welds shall be checked by X-ray. Any evidence of damage to components beneath the
welds or any evidence of voids, cracks, reduction of area, or incomplete fusion in the weld
should be considered as a cause for rejection.
Liquid penetrant
All the welds shall be tested by a liquid penetrant. The manufacturer and the user shall agree
on the liquid penetrant examination procedures and materials. Documented qualification of
personnel to the standard of a recognized regulatory body is required for those who are
involved in the liquid penetrant examination.
Liquid penetrant materials
Halogenated liquid penetrant products or liquid penetrant products containing halogenated
materials are not recommended. Furthermore, all liquid penetrant examination consumables
(such as developers, cleaners) shall have both a restricted halogen and sulphur content
regardless of the end use.
4.5 Workmanship
Workmanship shall be in accordance with good engineering and manufacturing practice as
adopted in the nuclear industry. The RTD and its assembly should have a high degree of
excellence to ensure satisfactory operations and service life in accordance with the provisions
of this standard.
62397 © IEC:2007 – 15 –
4.6 Ambient conditions (normal and accident operations)
The RTD may be either a “directly immersed” type or a “thermowell mounted” type, when it is
exposed to the following service conditions.
a) Maximum element temperature 330 °C
b) Plant design lifetime 40 years
c) Radiation exposure
rate (normal operation) up to 3 Gy/h (300 rad/h)
rate (accident operation) up to 100 kGy/h (10 Mrad/h)
total integrated dose 2 000 kGy (200 Mrad) for 40 years
d) Air/steam environments under normal and accident
temperature 0 °C to 330 °C
humidity up to 100 % (saturated)
contaminants up to 50 ppm ozone salt laden “sea air”
steam saturated
Depending on the application of the subject RTD and the design of the reactor, the user may
specify conditions other than the conditions as listed above.
– Environmental qualification
Environment Qualification for a plant accident scenario, such as a loss of coolant accident
(LOCA) or a high-energy line break (HELB), shall be specified in the individual RTD
specification sheets. Qualification shall be done in accordance with the technical specification
as defined by the user. In the absence of any specific instruction from the user, the
qualification tests shall be performed in accordance with the methods and procedures
provided in IEC 60780.
Certain RTDs with their cable connector assemblies may be used in nuclear safety I&C
systems; they are required to perform continuously their temperature-measurement safety
functions throughout the defined mission time. If such a requirement is specified, the RTD
with the complete assembly shall be subjected to a range of qualification tests, as described
in 5.4. This is to demonstrate and to ensure that the RTD and its assembly is capable of
performing its required functions under various operating and design basis accident
conditions that may occur during the life of the plant.
For the laboratory to perform the qualification tests, the user shall define the normal operating
environments of these RTDs, harsh environments as a result of the postulated accidents or
design basis accidents, normal and accident safety functions, and the RTD performance in
4.7, their mission times, and floor-response spectrum for seismic qualification, see
IEC 60980.
4.7 RTD performance
Each RTD shall meet the performance requirements of this clause.
4.7.1 Accuracy
During normal and accident operating conditions, the error attributed to the performance of
the temperature measurement loop, including the RTD with its cable and connector, is limited
to 0,25 °C (temperature between 0 °C and 100 °C) or 0,25 % (for temperatures above 100 °C)
variance in temperature measurement. The maximum drift shall not be more than 0,2 % of full
This error includes contributions due to the resistance-temperature calibration,
scale per year.
self-heating, drift, and steam conduction, but does not include contributions due to field
extension wiring and the temperature transmitter or bridge.

– 16 – 62397 © IEC:2007
4.7.2 Resistance temperature calibration
The changes in resistivity with the temperature of platinum follow a definite relationship which
can be expressed as a simple mathematical formula. For a platinum resistance thermometer,
the resistance at any temperature can be represented by the following Callendar equation.
R = R (1+ AT + BT )
t 0
where
R is the resistance of thermometer at temperature T °C;
t
R is the resistance of thermometer at 0 °C;
A, B are constants, dependent on the characteristics of the platinum wire;
(constants A and B can be defined as A = α(1 + δ/100); B = α δ/10 );
α (alpha) is given on each specific calibration table, nominally = 0,00385 Ω/Ω/°C;
δ (delta) is given on each specific calibration table, nominally = 1,5.
(Alpha and delta should be provided by the manufacturer or defined by the user.)
The purity of the platinum wire and the strain free construction of the RTD element for the
alpha constant should result in a value of not less than 0,003850 Ω/Ω/°C. The nominal
resistance of the RTD element at 0 °C shall be 100 Ω. For precision temperature
measurement, the user may specify the nominal resistance of the RTD element at 0 °C to be
200 Ω. A master resistance-temperature relationship table shall be provided covering the
range between 9 °C and 330 °C at intervals of 1 °C.
Temperature range in °C Tolerances
0-150 ±0,75 °C
Above 150 ±0,50 %
The resistance shall be that measured at the connector head.
For certain applications, and where specifically required on the application specifications, an
individual calibration table of resistance versus temperature shall be supplied. It shall be
performed in accordance with the procedure described in the calibration procedure (see
5.4.1). Different calibration tables shall be provided for different resistance elements.
4.7.3 Self-heating error
The self-heating error is defined as the rise in the indicated temperature due to the power
dissipated in the sensor. The principle for the test method for evaluating the self-heating error
should be as follows.
The sensor assembly is placed in water with a stable specified temperature. Under this
condition, the sensor shall be capable of dissipating 10 mW without causing the indicated
temperature to raise more than 0,2 °C.
4.7.4 Thermal response time
The response time is defined as the time required for the temperature detector to reach
63,2 % of the total change in resistance for a step change in temperature. For NPP
applications, the response time requirements depend on the functions to be fulfilled. Typically
two kinds of RTD are considered: fast-response-time RTDs and standard-response-time
RTDs.
62397 © IEC:2007 – 17 –
The test procedure and the requirements shall be defined according to the functional needs.
IEC 61224 gives recommendations and requirements related to RTDs.
A typical test condition for determining response time is to quickly plunge the detector at
20 °C into water flowing at 1 m/s ± 0,15 m/s and at 75 °C ± 2,5 °C. Alternatively, the sensor
can be heated in the air and then plunged into room temperature water flowing at 1 m/s.
Unless otherwise specified, the time to reach 63,2 % of the step change in temperature shall
not exceed 20 s for an RTD in a thermowell or 3,0 s for an RTD alone.
For some special applications, the user may require the in situ response time to be testable
using the loop current step response (LCSR) method. The LCSR method requires currents of
40 mA to 80 mA to be applied temporarily for up to 1 min to 2 min. This test can be repeated
up to 50 times to allow averaging of the data to reduce the effect of process fluctuations on
the LCSR signal.
4.7.5 Interchangeability
Every sensor produced under the same specification shall be interchangeable with any other
of the same type, within the tolerances listed in the resistance temperature calibration (see
4.7.2) above.
4.7.6 Electrical insulation resistance
The RTD shall successfully meet acceptance criteria for the electrical insulation resistance
test as specified below.
The electrical insulation resistance of the temperature detector element, as measured
between each terminal of the element and the element sheath, shall not be less than 100 MΩ,
at 100 V d.c. at room temperature, and shall be at least 10 MΩ at 100 V d.c. at a temperature
equal to, or greater than, 200 °C.
For the purpose of the qualification test specified in the following qualification test, see 5.4,
the insulation resistance shall be continuously monitored as the element cools from
330 °C ± 10 °C to room temperature. Any drop in insulation resistance below the stated limits
shall be a cause for disqualification.
4.7.7 Repeatability (thermal shock)
The RTDs shall successfully meet the acceptance criteria stated in the repeatability (thermal
shock) test specified below.
The sensor shall be transferred between baths at 0 °C to 330 °C to 0 °C for 25 cycles. Each
transfer shall be achieved in less than 5 s and the sensor shall remain immersed in the bath
for a minimum of 60 s between transfers. The sensor may be mounted in the thermowell to be
used for this test but shall be allowed to stabilize at each temperature for a minimum period of
1 min. Following this test, the sensor shall be checked for insulation resistance and be
calibrated at 0 °C and 100 °C. The insulation resistance shall be at least 100 MΩ, and the
thermal cycling shall not shift the resistance temperature calibration more than 0,1 °C at 0 °C
or 0,15 °C at 150 °C.
The number of cycles and the procedure may be specified jointly by the user and the
manufacturer.
– 18 – 62397 © IEC:2007
4.7.8 Vibration
The RTD shall successfully meet acceptance criteria for a mechanical endurance test
(vibrations). The conditions of the test (frequency range, duration of one sweep cycle, type of
frequency sweep, vibration level, and test duration) and the acceptance criteria should be
defined according to the conditions and the application of the temperature measurement. A
typical test procedure is given as follows.
The sensor is to be mounted in a fashion similar to the installation (in particular, the spring
tension shall be identical to the installation) and heated to 330 °C ± 10 °C for the duration of
the test. The sensor is then subjected to vibration in two planes in two separate runs: one
perpendicular and one parallel to the sensor’s longitudinal axis. The vibration spectrum to be
used for each run is tabulated below.
Frequency range 10-5 000 Hz
Dur
...