SIST EN IEC 62541-15:2025

SLOVENSKI STANDARD
01-julij-2025
Enotna arhitektura OPC - 15. del: Varnost
OPC Unified Architecture - Part 15: Safety
OPC Unified Architecture - Teil 15: Sicherheit
Architecture unifiée OPC - Partie 15: Sécurité fonctionnelle
Ta slovenski standard je istoveten z: EN IEC 62541-15:2025
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
35.240.50 Uporabniške rešitve IT v IT applications in industry
industriji
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 62541-15

NORME EUROPÉENNE
EUROPÄISCHE NORM April 2025
ICS 25.040.40
English Version
OPC Unified Architecture - Part 15: Safety
(IEC 62541-15:2025)
Architecture unifiée OPC - Partie 15: Sécurité OPC Unified Architecture - Teil 15: Sicherheit
(IEC 62541-15:2025) (IEC 62541-15:2025)
This European Standard was approved by CENELEC on 2025-04-03. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 62541-15:2025 E

European foreword
The text of document 65C/1334/FDIS, future edition 1 of IEC 62541-15, prepared by SC 65C
"Industrial networks" of IEC/TC 65 "Industrial-process measurement, control and automation" was
submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN IEC 62541-15:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-04-30
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-04-30
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 62541-15:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 61000-6-7 NOTE Approved as EN 61000-6-7
IEC 61511 series NOTE Approved as EN 61511 series
IEC 62061 NOTE Approved as EN IEC 62061
ISO 13849 series NOTE Approved as EN ISO 13849 series
ISO 13849-1 NOTE Approved as EN ISO 13849-1
ISO 13849-2 NOTE Approved as EN ISO 13849-2
IEC 62541-7 NOTE Approved as EN IEC 62541-7
IEC 62541-8 NOTE Approved as EN IEC 62541-8
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 61508 series Functional safety of EN 61508 series
electrical/electronic/programmable
electronic safety-related systems - Part 1:
General requirements (see Functional
Safety and IEC 61508)
IEC 61784-3 2021 Industrial communication networks - EN IEC 61784-3 2021
Profiles - Part 3: Functional safety
fieldbuses - General rules and profile
definitions
IEC 62443 series Security for industrial automation and EN IEC 62443 series
control systems
IEC/TR 62541-1 2020 OPC Unified Architecture - Part 1: CLC IEC/TR 2021
Overview and concepts 62541-1
IEC 62541-3 2020 OPC Unified Architecture - Part 3: Address EN IEC 62541-3 2020
Space Model
IEC 62541-4 2020 OPC Unified Architecture - Part 4: Services EN IEC 62541-4 2020
IEC 62541-5 2020 OPC Unified Architecture - Part 5: EN IEC 62541-5 2020
Information Model
IEC 62541-6 2020 OPC Unified Architecture - Part 6: EN IEC 62541-6 2020
Mappings
IEC 62541-14 - OPC unified architecture - Part 14: PubSub EN IEC 62541-14 -
ISO/IEC 9834-8 2014 Information technology - Procedures for - -
the operation of object identifier registration
authorities - Part 8: Generation of
universally unique identifiers (UUIDs) and
their use in object identifiers

IEC 62541-15 ®
Edition 1.0 2025-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
OPC Unified Architecture –
Part 15: Safety
Architecture unifiée OPC –
Partie 15: Sécurité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40  ISBN 978-2-8327-0212-3

– 2 – IEC 62541-15:2025 © IEC 2025
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references. 9
3 Terms, definitions, symbols, abbreviated terms and conventions. 10
3.1 Terms and definitions . 10
3.1.1 Common terms and definitions . 10
3.1.2 Additional terms and definitions . 12
3.2 Symbols and abbreviated terms . 14
3.2.1 Abbreviated terms from IEC 61784-3 . 14
3.2.2 Additional symbols and abbreviated terms . 15
3.3 Conventions . 15
3.3.1 General conventions . 15
3.3.2 Conventions for requirements numbering . 15
3.3.3 Conventions in state machines . 16
4 Overview of OPC UA Safety . 16
4.1 General . 16
4.2 Implementation aspects . 16
4.3 Features . 17
4.4 Security policy . 17
5 General . 18
5.1 External documents providing specifications for the profile . 18
5.2 Safety functional requirements . 18
5.3 Safety measures . 18
5.4 Safety communication layer structure . 19
5.5 Requirements for CRC calculation . 21
6 Safety communication layer services . 21
6.1 General . 21
6.2 Information models . 22
6.2.1 General . 22
6.2.2 Object and ObjectType Definitions . 22
6.2.3 DataType definition . 34
6.2.4 SafetyProvider version . 38
6.2.5 DataTypes and length of SafetyData . 38
6.2.6 Connection establishment . 38
6.3 Service interfaces . 38
6.3.1 Overview . 38
6.3.2 OPC UA Platform interface (OPC UA PI) . 39
6.3.3 SafetyProvider interfaces . 39
6.3.4 SafetyConsumer interfaces . 46
6.3.5 Cyclic and acyclic safety communication . 53
6.3.6 Principle for "application variables with qualifier" . 53
6.4 Diagnostics . 53
6.4.1 General . 53
6.4.2 Diagnostics messages of the SafetyConsumer . 54
6.4.3 Method ReadSafetyDiagnostics of the SafetyProvider . 56

IEC 62541-15:2025 © IEC 2025 – 3 –
7 Safety communication layer protocol . 56
7.1 General . 56
7.2 SafetyProvider and SafetyConsumer . 56
7.2.1 SPDU formats . 56
7.2.2 Behaviour . 58
7.2.3 Subroutines . 76
8 Safety communication layer management . 82
8.1 General . 82
8.2 Safety function response time part of communication . 82
9 System requirements (SafetyProvider and SafetyConsumer) . 84
9.1 Constraints on the SPDU parameters . 84
9.1.1 SafetyBaseID and SafetyProviderID . 84
9.1.2 SafetyConsumerID . 85
9.2 Initialization of the MNR in the SafetyConsumer . 86
9.3 Constraints on the calculation of system characteristics . 86
9.3.1 Probabilistic considerations (informative) . 86
9.3.2 Safety related assumptions (informative) . 88
9.4 PFH and PFD values of a logical safety communication link . 88
9.5 Safety manual . 89
9.6 Indicators and displays . 90
10 Assessment . 90
10.1 Safety policy . 90
10.2 Obligations. 91
10.3 Index of requirements (informative) . 91
11 Profiles and conformance units . 94
12 Namespaces . 94
12.1 Namespace metadata . 94
12.2 Handling of IEC 62541 namespaces . 95
Annex A (normative) Safety namespace and mappings . 96
Annex B (informative) Additional information . 97
B.1 CRC calculation using tables, for the polynomial 0xF4ACFB13 . 97
B.2 Use cases . 98
B.2.1 Unidirectional communication . 98
B.2.2 Bidirectional communication . 99
B.2.3 Safety multicast . 99
B.3 Use cases for operator acknowledgment . 100
B.3.1 Explanation . 100
B.3.2 Use case 1: unidirectional communication and OA on the
SafetyConsumer side . 100
B.3.3 Use case 2: bidirectional communication and dual OA . 101
B.3.4 Use case 3: bidirectional communication and single, one-sided OA . 101
B.3.5 Use case 4: bidirectional communication and single, two-sided OA . 102
Annex C (informative) Information for assessment . 103
Bibliography . 104

Figure 1 – Relationships of OPC UA safety with other standards . 8
Figure 2 – Safety layer architecture . 20

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Figure 3 – Server Objects for OPC UA Safety . 24
Figure 4 – Instances of Server Objects for this document . 25
Figure 5 – Safety multicast with three recipients using IEC 62541 PubSub . 31
Figure 6 – Safety parameters for the SafetyProvider and the SafetyConsumer . 32
Figure 7 – Safety communication layer overview. 39
Figure 8 – SafetyProvider interfaces . 40
Figure 9 – Example combinations of SIL capabilities . 46
Figure 10 – SafetyConsumer interfaces . 47
Figure 11 – RequestSPDU . 56
Figure 12 – ResponseSPDU . 57
Figure 13 – Sequence diagram for requests and responses (Client/Server) . 59
Figure 14 – Sequence diagram for requests and responses (PubSub) . 60
Figure 15 – Duration of demand example for missed demand value in case of currently
available SafetyData not being provided until second change of MNR . 61
Figure 16 – Duration of demand example for received demand value in case of
currently available SafetyData being provided . 62
Figure 17 – Simplified representation of the state diagram for the SafetyProvider . 62
Figure 18 – Principle state diagram for SafetyConsumer . 65
Figure 19 – Sequence diagram for OA . 75
Figure 20 – Overview of task for SafetyProvider . 76
Figure 21 – Calculation of the SPDU_ID . 77
Figure 22 – Example for the calculation of SPDU_ID_1, SPDU_ID_2 and SPDU_ID_3. 78
Figure 23 – Calculation of the CRC (on little-endian machines, CRC32_Backward) . 81
Figure 24 – Calculation of the CRC (on big-endian machines, CRC32_Forward) . 82
Figure 25 – Overview of delay times and watchdogs . 83
Figure 26 – Conditional residual error probability of the CRC check . 87
Figure 27 – Counter example: data lengths not supported by OPC Safety . 88
Figure 28 – Facets and ConformanceUnits . 94
Figure B.1 – Unidirectional communication . 99
Figure B.2 – Bidirectional communication . 99
Figure B.3 – Safety multicast . 99
Figure B.4 – OA in unidirectional safety communication . 100
Figure B.5 – Two-sided OA in bidirectional safety communication . 101
Figure B.6 – One sided OA in bidirectional safety communication . 101
Figure B.7 – One sided OA on each side is possible . 102

Table 1 – Conventions used in state machines . 16
Table 2 – Deployed safety measures to detect communication errors . 18
Table 3 – SafetyACSet definition . 22
Table 4 – SafetyObjectsType definition . 26
Table 5 – SafetyProviderType definition . 26
Table 6 – SafetyConsumerType definition . 27
Table 7 – ReadSafetyData Method arguments . 28
Table 8 – ReadSafetyData Method AddressSpace definition . 29

IEC 62541-15:2025 © IEC 2025 – 5 –
Table 9 – ReadSafetyDiagnostics Method arguments . 30
Table 10 – ReadSafetyDiagnostics Method AddressSpace definition . 30
Table 11 – SafetyPDUsType definition . 31
Table 12 – SafetyProviderParametersType definition . 33
Table 13 – SafetyConsumerParametersType definition . 34
Table 14 – InFlagsType values . 35
Table 15 – InFlagsType definition . 35
Table 16 – OutFlagsType values . 35
Table 17 – OutFlagsType definition . 36
Table 18 – RequestSPDUDataType structure . 36
Table 19 – RequestSPDUDataType definition . 36
Table 20 – ResponseSPDUDataType structure . 37
Table 21 – ResponseSPDUDataType definition . 37
Table 22 – NonSafetyDataPlaceholderDataType structure . 37
Table 23 – SAPI of the SafetyProvider . 41
Table 24 – SPI of the SafetyProvider . 42
Table 25 – SAPI of the SafetyConsumer . 47
Table 26 – SPI of the SafetyConsumer . 50
Table 27 – Example "application variables with qualifier" . 53
Table 28 – Safety layer diagnostic messages . 54
Table 29 – Symbols used for state machines . 62
Table 30 – SafetyProvider instance internal items . 63
Table 31 – States of SafetyProvider instance . 64
Table 32 – SafetyProvider transitions . 64
Table 33 – SafetyConsumer internal items . 66
Table 34 – SafetyConsumer states . 70
Table 35 – SafetyConsumer transitions . 71
Table 36 – Presentation of the SPDU_ID . 77
Table 37 – Coding for the SafetyProviderLevel_ID . 78
Table 38 – Examples for cryptographically strong random number generators . 85
Table 39 – The total residual error rate for the safety communication channel . 89
Table 40 – Information to be included in the safety manual . 89
Table 41 – Index of requirements (informative) . 92
Table 42 – NamespaceMetadata Object for this document . 95
Table 43 – Namespaces used in a safety Server . 95
Table B.1 – The CRC32 lookup table for 32-bit CRC signature calculations . 98

– 6 – IEC 62541-15:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPC UNIFIED ARCHITECTURE –
Part 15: Safety
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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 62541-15 has been prepared by subcommittee 65C: Industrial networks, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is an International
Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
65C/1334/FDIS 65C/1339/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.

IEC 62541-15:2025 © IEC 2025 – 7 –
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/publications.
Throughout this document and the referenced other parts of the IEC 62541 series, certain
document conventions are used:
Italics are used to denote a defined term or definition that appears in Clause 3 in one of the
parts of the series.
Italics are also used to denote the name of a service input or output parameter or the name of
a structure or element of a structure that are usually defined in tables.
The italicized terms and names are also, with a few exceptions, written in camel-case (the
practice of writing compound words or phrases in which the elements are joined without spaces,
with each element's initial letter capitalized within the compound). For example, the defined
term is AddressSpace instead of Address Space. This makes it easier to understand that there
is a single definition for AddressSpace, not separate definitions for Address and Space.
A list of all parts of the IEC 62541 series, published under the general title OPC Unified
Architecture, can be found on the IEC website.
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, or
• revised.
– 8 – IEC 62541-15:2025 © IEC 2025
INTRODUCTION
OPC UA safety extends OPC UA to fulfill the requirements of functional safety as defined in the
IEC 61508 series and IEC 61784-3 series of standards.
Figure 1 shows the relationship between this document and the relevant safety and OPC UA
standards in an industrial environment. An arrow from Document A to Document B means
"Document A is referenced in Document B". This reference can be either normative or
informative. Not all of these standards are applicable or required for a given product.

Figure 1 – Relationships of OPC UA safety with other standards
Implementing this document allows for detecting all types of communication errors encountered
in the lower network layers. In case an error is detected, this information is shared with the
safety applications in the user layer which can then act in an appropriate way, e.g. by switching
to a safe state.
The document describes the behaviour of the individual endpoints for safe communication, as
well as the OPC UA Information Model which is used to access these endpoints.
This document is application-independent and does not pose requirements on the structure and
length of the application data. Application-specific requirements are expected to be described
in appropriate companion specifications.
This document can be used for applications requiring functional safety up to the safety integrity
level (SIL) 4.
IEC 62541-15:2025 © IEC 2025 – 9 –
OPC UNIFIED ARCHITECTURE –
Part 15: Safety
1 Scope
This document describes a safety communication layer (services and a protocol) for the
exchange of SafetyData using IEC 62541 mechanisms. It identifies the principles for functional
safety communications defined in IEC 61784-3 that are relevant for this safety communication
layer. This safety communication layer is intended for implementation in safety devices only.
NOTE 1 This document targets controller-to-controller communication. However, easy expandability to other use-
cases (e.g. OPC UA field level communication) has already been considered in the design of this document.
NOTE 2 This document does not cover electrical safety and intrinsic safety aspects. Electrical safety relates to
hazards such as electrical shock. Intrinsic safety relates to hazards associated with potentially explosive
atmospheres.
This document defines mechanisms for the transmission of safety-relevant messages among
participants within a network using OPC UA technology in accordance with the requirements of
the IEC 61508 series and IEC 61784-3 for functional safety. These mechanisms can be used
in various industrial applications such as process control, manufacturing, automation, and
machinery.
This document provides guidelines for both developers and assessors of compliant devices and
systems.
NOTE 3 The resulting SIL claim of a system depends on the implementation of this document within the system –
implementation of this document in a standard device is not sufficient to qualify it as a safety device.
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 61508 (all parts), Functional safety of electrical/electronic/programmable electronic safety-
related systems
IEC 61784-3:2021, Industrial communication networks – Profiles – Part 3: Functional safety
fieldbuses – General rules and profile definitions
IEC 62443 (all parts), Industrial communication networks – Network and system security
IEC 62541-1:2020, OPC Unified Architecture – Part 1: Overview and Concepts
IEC 62541-3:2020, OPC Unified Architecture – Part 3: Address Space Model
IEC 62541-4:2020, OPC Unified Architecture – Part 4: Services
IEC 62541-5:2020, OPC Unified Architecture – Part 5: Information Model
IEC 62541-6:2020, OPC Unified Architecture – Part 6: Mappings

– 10 – IEC 62541-15:2025 © IEC 2025
IEC 62541-14, OPC Unified Architecture – Part 14: PubSub
ISO/IEC 9834-8:2014, Information technology – Procedures for the operation of object identifier
registration authorities – Part 8: Generation of universally unique identifiers (UUIDs) and their
use in object identifiers
3 Terms, definitions, symbols, abbreviated terms and conventions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62541-1:2020,
IEC 62541-3:2020, IEC 62541-4:2020, IEC 62541-6:2020 and the following apply.
ISO and IEC maintain terminology 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
NOTE This document uses concepts of IEC 62541 information modeling to describe the concepts in this document.
3.1.1 Common terms and definitions
3.1.1.1
Cyclic Redundancy Check
CRC
redundant data derived from, and stored or transmitted together with, a block of data
in order to detect data corruption
procedure used to calculate the redundant data
Note 1 to entry: Terms "CRC code" and "CRC signature", and labels such as CRC1, CRC2, may also be used in
this document to refer to the redundant data.
[SOURCE: IEC 61784-3:2021, 3.10]
3.1.1.2
error
discrepancy between a computed, observed or measured value or condition and the true,
specified or theoretically correct value or condition
Note 1 to entry: Errors may be due to design mistakes within hardware/software and/or corrupted information due
to electromagnetic interference and/or other effects.
Note 2 to entry: Errors do not necessarily result in a failure or a fault.
[SOURCE: IEC 60050-192:2024, 192-03-02, modified – notes added]
3.1.1.3
failure
termination of the ability of a functional unit to perform a required function or operation of a
functional unit in any way other than as required
Note 1 to entry: Failure can be due to an error (for example, problem with hardware/software design or message
disruption).
[SOURCE: IEC 61508-4:2010, 3.6.4, modified – notes and figures deleted, new note to entry
added]
IEC 62541-15:2025 © IEC 2025 – 11 –
3.1.1.4
fault
abnormal condition that may cause a reduction in, or loss of, the capability of a functional unit
to perform a required function
Note 1 to entry: IEV 191-05-01 defines "fault" as a state characterized by the inability to perform a required function,
excluding the inability during preventive maintenance or other planned actions, or due to lack of external resources.
[SOURCE: IEC 61508-4:2010, 3.6.1, modified – figure reference deleted]
message
ordered sequence of characters (usually octets)
intended to convey information
[SOURCE: ISO/IEC 2382:2015, 2123031, modified – insertion of "(usually octets)", deletion of
notes and source]
3.1.1.5
performance level
PL
discrete level used to specify the ability of safety-related parts of control systems to perform a
safety function under foreseeable conditions
[SOURCE: ISO 13849-1:2023, 3.1.5]
3.1.1.6
residual error probability
probability of an error undetected by the SCL safety measures
[SOURCE: IEC 61784-3:2021, 3.1.35]
3.1.1.7
residual error rate
statistical rate at which the SCL safety measures fail to detect errors
[SOURCE: IEC 61784-3:2021, 3.1.36]
3.1.1.8
safety communication layer
SCL
communication layer above the IEC 62541 communication stack that includes all necessary
additional measures to ensure safe transmission of data in accordance with the requirements
of IEC 61508
Note 1 to entry: The SCL provides several services, the most important ones being the SafetyProvider and the
SafetyConsumer.
[SOURCE: IEC 61784-3:2021, 3.1.39, modified – "FAL" replaced by "IEC 62541 communication
stack", note to entry added]
3.1.1.9
safety function response time
worst case elapsed time following an actuation of a safety sensor connected to a fieldbus, until
the corresponding safe state of its safety actuator(s) is achieved in the presence of errors or
failures in the safety function
Note 1 to entry: This concept is introduced in IEC 61784-3:2021, 5.2.4 and is addressed by the functional safety
communication profiles defined in the IEC 61784-3 series of documents.
[SOURCE: IEC 61784-3:2021, 3.1.44]

– 12 – IEC 62541-15:2025 © IEC 2025
3.1.1.10
safety integrity level
SIL
discrete level (one out of a possible four), corresponding to a range of safety integrity values,
where safety integrity level 4 has the highest level of safety integrity and safety integrity level 1
has the lowest
Note 1 to entry: The target failure measures (see IEC 61508-4:2010, 3.5.17) for the four safety integrity levels are
specified in Table 2 and Table 3 of IEC 61508-1:2010.
Note 2 to entry: Safety integrity levels are used for specifying the safety integrity requirements of the safety
functions to be allocated to the E/E/PE safety-related systems.
Note 3 to entry: A safety integrity level (SIL) is not a property of a system, subsystem, element or component. The
correct interpretation of the phrase "SIL n safety-related system" (where n is 1, 2, 3 or 4) is that the system is
potentially capable of supporting safety functions with a safety integrity level up to n.
[SOURCE: IEC 61508-4:2010, 3.5.8]
3.1.1.11
safety measure
measure to control possible communication errors that is designed and implemented in
compliance with the requirements of IEC 61508
Note 1 to entry: In practice, several safety measures are combined to achieve the required safety integrity level.
Note 2 to entry: Communication errors and related safety measures are detailed in IEC 61784-3:2021, 5.3 and 5.4.
[SOURCE: IEC 61784-3:2021, 3.1.46]
3.1.1.12
safety PDU
SPDU
PDU transferred through the safety communication channel
Note 1 to entry: The SPDU may include more than one copy of the SafetyData using differing coding structures and
hash functions together with explicit parts of additional protections such as a key, a sequence count, or a time stamp
mechanism.
Note 2 to entry: Redundant SCLs may provide two different versions of the SPDU for insertion into separate fields
of the IEC 62541 frame.
[SOURCE: IEC 61784-3:2021, 3.1.47]
3.1.2 Additional terms and definitions
3.1.2.1
fail-safe
ability of a system that, by adequate technical or organizational measures, prevents from
hazards either deterministically or by reducing the risk to a tolerable measure
Note 1 to entry: Equivalent to functional safety.
3.1.2.2
fail-safe substitute values
FSV
values which are issued or
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