EN 61069-5:2016

Industrial-process measurement, control and automation - Evaluation of system properties for the purpose of system assessment - Part 5: Assessment of system dependability

Describes in detail the method to systematically assess the dependability of industrial-process measurement and control systems. Uses the assessment methodology given in EN 61069-2.

Leittechnik für industrielle Prozesse - Ermittlung der Systemeigenschaften zum Zweck der Eignungsbeurteilung eines Systems - Teil 5: Eignungsbeurteilung der Systemverlässlichkeit

Mesure, commande et automation dans les processus industriels - Appréciation des propriétés d'un système en vue de son évaluation - Partie 5: Evaluation de la sûreté de fonctionnement d'un système

L'IEC 61069-2016:2016 spécifie la méthode d'évaluation détaillée de la sûreté de fonctionnement d'un système de commande de base (BCS) reposant sur les principes de base de l'IEC 61069-1 et la méthodologie de l'IEC 61069-2; définit la classification de base des propriétés de la sûreté de fonctionnement; décrit les facteurs ayant une influence sur la sûreté de fonctionnement et dont il faut tenir compte lors de l'appréciation de la fonctionnalité, et donne des lignes directrices concernant les techniques de sélection à partir d'un ensemble d'options (avec références) pour l'appréciation de la sûreté de fonctionnement. Cette deuxième édition annule et remplace la première édition parue en 1994. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: - réorganisation des informations contenues dans l'IEC 61069-5:1994 visant à mieux organiser l'ensemble complet de normes et à le rendre plus cohérent; - l'IEC TS 62603-1 a été incorporée dans cette édition.

Meritve, krmiljenje in avtomatizacija v industrijskih procesih - Ocenjevanje lastnosti sistema zaradi njegovega vrednotenja - 5. del: Vrednotenje zagotovljivosti sistema (IEC 61069-5:2016)

Podrobno opisuje metodo za sistematično vrednotenje zagotovljivosti meritev in krmiljenja v industrijskih procesih. Uporablja metodologijo vrednotenja, podano v standardu EN 61069-2.

General Information

• Status: Published
• Publication Date: 29-Sep-2016
• Withdrawal Date: 19-Jul-2019
• ICS: 25.040.40 - Industrial process measurement and control
• Technical Committee: CLC/TC 65X - Industrial-process measurement, control and automation
• Drafting Committee: IEC/SC 65A - IEC_SC_65A
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 30-Sep-2016
• Completion Date: 30-Sep-2016
• Ref Project: SIST EN 61069-5:2017 - Industrial-process measurement, control and automation - Evaluation of system properties for the purpose of system assessment - Part 5: Assessment of system dependability (IEC 61069-5:2016)

Relations

• Replaces: EN 61069-5:1995 - Industrial-process measurement and control - Evaluation of system properties for the purpose of system assessment - Part 5: Assessment of system dependability
• Effective Date: 23-Jan-2023

Overview

EN 61069-5:2016 (CLC) - Industrial-process measurement, control and automation - Part 5: Assessment of system dependability - defines a systematic method to assess the dependability of industrial-process measurement and control systems. Aligned with the IEC 61069 series, it uses the assessment methodology given in EN 61069-2 and is intended for designers, integrators and assessors who need to evaluate availability, reliability, maintainability, credibility, security and integrity of automation systems.

Key topics and requirements

• Dependability properties: clear definition and assessment scope for availability, reliability, maintainability, credibility, security and integrity as applied to control and measurement systems.
• Assessment lifecycle: steps for defining objectives, designing assessment layout, planning programs, executing assessments and reporting results.
• Evaluation techniques:
  • Analytical: inductive (e.g., FMEA-style), deductive (e.g., FTA-style) and predictive analyses.
  • Empirical: fault-injection tests, environmental perturbation tests and field-data collection.
• Practical checklists and artefacts: example System Requirements Documents (SRD) and System Specification Documents (SSD) tailored to dependability topics (Annexes A–C).
• Credibility and security tests: prescribed approaches for credibility testing, injected faults, observation and interpretation of results (Annexes D and F).
• Use of data and standards: references to failure-rate databases and related standards for reliability data and cybersecurity practices.

Practical applications and who uses it

EN 61069-5:2016 is used to:

• Assess dependability during system design reviews and procurement evaluations.
• Support commissioning and acceptance testing with structured dependability tests (fault injection, environmental tests).
• Inform maintenance planning and spare-part strategies by quantifying maintainability and reliability.
• Integrate security and integrity considerations (physical and cyber) into dependability assessments.
• Provide evidence for compliance and risk management in industrial automation projects.

Typical users:

• Control systems engineers and architects
• System integrators and OEMs
• Reliability, maintainability and safety engineers
• Asset owners, plant operators and maintenance managers
• Certification bodies and functional safety assessors

Related standards

• EN/IEC 61069-1, EN/IEC 61069-2 (series foundation and methodology)
• IEC 60300-3-2 (dependability data)
• IEC 61508 (functional safety considerations)
• IEC 62443 (industrial cybersecurity)
• ISO/IEC 25010, ISO/IEC 27001 (quality and information security)

Keywords: EN 61069-5:2016, system dependability, industrial-process measurement, control and automation, dependability assessment, availability, reliability, maintainability, credibility, cybersecurity.

Standards Content (Sample)

SLOVENSKI STANDARD
01-marec-2017
1DGRPHãþD
SIST EN 61069-5:1998
Meritve, krmiljenje in avtomatizacija v industrijskih procesih - Ocenjevanje
lastnosti sistema zaradi njegovega vrednotenja - 5. del: Vrednotenje
zagotovljivosti sistema (IEC 61069-5:2016)
Industrial-process measurement, control and automation - Evaluation of system
properties for the purpose of system assessment - Part 5: Assessment of system
dependability (IEC 61069-5:2016)
Leittechnik für industrielle Prozesse - Ermittlung der Systemeigenschaften zum Zweck
der Eignungsbeurteilung eines Systems - Teil 5: Eignungsbeurteilung der
Systemzuverlässigkeit (IEC 61069-5:2016)
Mesure, commande et automation dans les processus industriels - Appréciation des
propriétés d'un sytème en vue de son évaluation - Partie 5: Evaluation de la sûreté de
fonctionnement d'un système (IEC 61069-5:2016)
Ta slovenski standard je istoveten z: EN 61069-5:2016
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 61069-5
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2016
ICS 25.040.40 Supersedes EN 61069-5:1995
English Version
Industrial-process measurement, control and automation -
Evaluation of system properties for the purpose of system
assessment - Part 5: Assessment of system dependability
(IEC 61069-5:2016)
Mesure, commande et automation dans les processus Leittechnik für industrielle Prozesse - Ermittlung der
industriels - Appréciation des propriétés d'un sytème en vue Systemeigenschaften zum Zweck der Eignungsbeurteilung
de son évaluation - Partie 5: Evaluation de la sûreté de eines Systems - Teil 5: Eignungsbeurteilung der
fonctionnement d'un système Systemzuverlässigkeit
(IEC 61069-5:2016) (IEC 61069-5:2016)
This European Standard was approved by CENELEC on 2016-07-20. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 61069-5:2016 E
European foreword
The text of document 65A/793/FDIS, future edition 2 of IEC 61069-5, prepared by SC 65A "System
aspects", of IEC/TC 65 "Industrial-process measurement, control and automation" was submitted to
the IEC-CENELEC parallel vote and approved by CENELEC as EN 61069-5:2016.
The following dates are fixed:
(dop) 2017-04-20
• latest date by which the document has to be implemented at
national level by publication of an identical national
standard or by endorsement
(dow) 2019-07-20
• latest date by which the national standards conflicting with
the document have to be withdrawn

This document supersedes EN 61069-5:1995.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 61069-5:2016 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 standards indicated:
IEC 60300-3-1:2003 NOTE Harmonized as EN 60300-3-1:2004 (not modified).
IEC 60068 NOTE Harmonized in EN 60068 series.
IEC 60812:2006 NOTE Harmonized as EN 60812:2006 (not modified).
IEC 61000 NOTE Harmonized in EN 61000 series.
IEC 61025:2006 NOTE Harmonized as EN 61025:2007 (not modified).
IEC 61069-6 NOTE Harmonized as EN 61069-6.
IEC 61078 NOTE Harmonized as EN 61078.
IEC 61165 NOTE Harmonized as EN 61165.
IEC 61326 NOTE Harmonized in EN 61326 series.
IEC 61508 NOTE Harmonized in EN 61508 series.
1)
IEC 62443 NOTE Harmonized in EN 62443 series .
IEC/TS 62603-1 NOTE Harmonized as CLC/TS 62603-1.

1) At draft stage.
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
NOTE 1 When 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.cenelec.eu.

Publication Year Title EN/HD Year
IEC 60300-3-2 -  Dependability management - EN 60300-3-2 -
Part 3-2: Application guide - Collection of
dependability data from the field
IEC 60319 -  Presentation and specification of reliability - -
data for electronic components
2)
IEC 61069-1 2016 Industrial-process measurement, control EN 61069-1 201X
and automation - Evaluation of system
properties for the purpose of system
assessment -
Part 1: Terminology and basic concepts
2)
EN 61069-2 201X
IEC 61069-2 2016 Industrial-process measurement, control
and automation - Evaluation of system
properties for the purpose of system
assessment -
Part 2: Assessment methodology
IEC 61070 -  Compliance test procedures for steady- - -
state availability
IEC 61709 2011 Electric components - Reliability - EN 61709 2011
Reference conditions for failure rates and
stress models for conversion
ISO/IEC 25010 -  Systems and software engineering - - -
Systems and software Quality
Requirements and Evaluation (SQuaRE) -
System and software quality models
ISO/IEC 27001 2013 Information technology - Security - -
techniques - Information security
management systems - Requirements
ISO/IEC 27002 -  Information technology - Security - -
techniques - Code of practice for
information security controls
2) To be published.
IEC 61069-5 ®
Edition 2.0 2016-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial-process measurement, control and automation – Evaluation of system

properties for the purpose of system assessment –

Part 5: Assessment of system dependability

Mesure, commande et automation dans les processus industriels – Appréciation

des propriétés d'un système en vue de son évaluation –

Partie 5: Évaluation de la sûreté de fonctionnement d’un système

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40 ISBN 978-2-8322-3447-1

– 2 – IEC 61069-5:2016  IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references. 8
3 Terms, definitions, abbreviated terms, acronyms, conventions and symbols . 9
3.1 Terms and definitions . 9
3.2 Abbreviated terms, acronyms, conventions and symbols . 9
4 Basis of assessment specific to dependability . 9
4.1 Dependability properties . 9
4.1.1 General . 9
4.1.2 Availability . 10
4.1.3 Reliability . 10
4.1.4 Maintainability . 10
4.1.5 Credibility . 11
4.1.6 Security . 11
4.1.7 Integrity . 12
4.2 Factors influencing dependability . 12
5 Assessment method . 12
5.1 General . 12
5.2 Defining the objective of the assessment . 12
5.3 Design and layout of the assessment . 13
5.4 Planning of the assessment program . 13
5.5 Execution of the assessment . 13
5.6 Reporting of the assessment . 13
6 Evaluation techniques . 13
6.1 General . 13
6.2 Analytical evaluation techniques . 14
6.2.1 Overview . 14
6.2.2 Inductive analysis . 15
6.2.3 Deductive analysis . 15
6.2.4 Predictive evaluation . 15
6.3 Empirical evaluation techniques. 16
6.3.1 Overview . 16
6.3.2 Tests by fault-injection techniques . 16
6.3.3 Tests by environmental perturbations . 17
6.4 Additional topics for evaluation techniques . 17
Annex A (informative) Checklist and/or example of SRD for system dependability . 18
Annex B (informative) Checklist and/or example of SSD for system dependability . 19
B.1 SSD information . 19
B.2 Check points for system dependability . 19
Annex C (informative) An example of a list of assessment items (information from
IEC TS 62603-1) . 20
C.1 Overview. 20
C.2 Dependability . 20
C.3 Availability . 20

IEC 61069-5:2016  IEC 2016 – 3 –
C.3.1 System self-diagnostics . 20
C.3.2 Single component fault tolerance and redundancy . 20
C.3.3 Redundancy methods . 21
C.4 Reliability . 22
C.5 Maintainability . 23
C.5.1 General . 23
C.5.2 Generation of maintenance requests . 23
C.5.3 Strategies for maintenance . 23
C.5.4 System software maintenance . 23
C.6 Credibility . 23
C.7 Security . 24
C.8 Integrity . 24
C.8.1 General . 24
C.8.2 Hot-swap . 24
C.8.3 Module diagnostic . 24
C.8.4 Input validation . 24
C.8.5 Read-back function . 24
C.8.6 Forced output . 24
C.8.7 Monitoring functions . 24
C.8.8 Controllers . 24
C.8.9 Networks . 25
C.8.10 Workstations and servers . 25
Annex D (informative) Credibility tests . 26
D.1 Overview. 26
D.2 Injected faults . 27
D.2.1 General . 27
D.2.2 System failures due to a faulty module, element or component . 27
D.2.3 System failures due to human errors . 27
D.2.4 System failures resulting from incorrect or unauthorized inputs into the
system through the man-machine interface . 27
D.3 Observations . 28
D.4 Interpretation of the results . 28
Annex E (informative) Available failure rate databases . 29
E.1 Databases . 29
E.2 Helpful standards concerning component failure . 30
Annex F (informative) Security considerations . 31
F.1 Physical security . 31
F.2 Cyber-security . 31
F.2.1 General . 31
F.2.2 Security policy . 31
F.2.3 Other considerations . 31
Bibliography . 33

Figure 1 – General layout of IEC 61069 . 7
Figure 2 – Dependability . 9

– 4 – IEC 61069-5:2016  IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL-PROCESS MEASUREMENT, CONTROL AND AUTOMATION –
EVALUATION OF SYSTEM PROPERTIES FOR
THE PURPOSE OF SYSTEM ASSESSMENT –

Part 5: Assessment of system dependability

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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61069-5 has been prepared by subcommittee 65A: System
aspects, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This second edition cancels and replaces the first edition published in 1994. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) reorganization of the material of IEC 61069-5:1994 to make the overall set of standards
more organized and consistent;
b) IEC TS 62603-1 has been incorporated into this edition.

IEC 61069-5:2016  IEC 2016 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
65A/793/FDIS 65A/803/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.
A list of all parts in the IEC 61069 series, published under the general title Industrial-process
measurement, control and automation – Evaluation of system properties for the purpose of
system assessment, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 61069-5:2016  IEC 2016
INTRODUCTION
IEC 61069 deals with the method which should be used to assess system properties of a
basic control system (BCS). IEC 61069 consists of the following parts.
Part 1: Terminology and basic concepts
Part 2: Assessment methodology
Part 3: Assessment of system functionality
Part 4: Assessment of system performance
Part 5: Assessment of system dependability
Part 6: Assessment of system operability
Part 7: Assessment of system safety
Part 8: Assessment of other system properties
Assessment of a system is the judgement, based on evidence, of the suitability of the system
for a specific mission or class of missions.
To obtain total evidence would require complete evaluation (for example under all influencing
factors) of all system properties relevant to the specific mission or class of missions.
Since this is rarely practical, the rationale on which an assessment of a system should be
based is:
– the identification of the importance of each of the relevant system properties,
– the planning for evaluation of the relevant system properties with a cost-effective
dedication of effort to the various system properties.
In conducting an assessment of a system, it is crucial to bear in mind the need to gain a
maximum increase in confidence in the suitability of a system within practical cost and time
constraints.
An assessment can only be carried out if a mission has been stated (or given), or if any
mission can be hypothesized. In the absence of a mission, no assessment can be made;
however, evaluations can still be specified and carried out for use in assessments performed
by others. In such cases, IEC 61069 can be used as a guide for planning an evaluation and it
provides methods for performing evaluations, since evaluations are an integral part of
assessment.
In preparing the assessment, it can be discovered that the definition of the system is too
narrow. For example, a facility with two or more revisions of the control systems sharing
resources, for example a network, should consider issues of co-existence and inter-operability.
In this case, the system to be investigated should not be limited to the “new” BCS; it should
include both. That is, it should change the boundaries of the system to include enough of the
other system to address these concerns.
The series structure and the relationship among the parts of IEC 61069 are shown in Figure 1.

IEC 61069-5:2016  IEC 2016 – 7 –

IEC 61069: Industrial-process measurement, control and automation –
Evaluation of system properties for the purpose of system assessment
Part 1: Terminology and basic concepts
• Basic concept
• Terminology ‐ Objective
‐ Common terms ‐ Description of system
‐ Terms for particular part
‐ System properties
‐ Influencing factors
Part 2: Assessment methodology
• Generic requirements of procedure of assessment
‐ Overview, approach and phases
‐ Requirements for each phase
‐ General description of evaluation techniques
Parts 3 to 8: Assessment of each system property
• Basics of assessment specific to each property
‐ Properties and influencing factors
• Assessment method for each property
• Evaluation techniques for each property

IEC
Figure 1 – General layout of IEC 61069
Some example assessment items are integrated in Annex C.

– 8 – IEC 61069-5:2016  IEC 2016
INDUSTRIAL-PROCESS MEASUREMENT, CONTROL AND AUTOMATION –
EVALUATION OF SYSTEM PROPERTIES FOR
THE PURPOSE OF SYSTEM ASSESSMENT –

Part 5: Assessment of system dependability

1 Scope
This part of IEC 61069:
– specifies the detailed method of the assessment of dependability of a basic control system
(BCS) based on the basic concepts of IEC 61069-1 and methodology of IEC 61069-2,
– defines basic categorization of dependability properties,
– describes the factors that influence dependability and which need to be taken into account
when evaluating dependability, and
– provides guidance in selecting techniques from a set of options (with references) for
evaluating the dependability.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60300-3-2, Dependability management – Part 3-2: Application guide – Collection of
dependability data from the field
IEC 60319, Presentation and specification of reliability data for electronic components
IEC 61069-1:2016, Industrial-process measurement, control and automation – Evaluation of
system properties for the purpose of system assessment – Part 1: Terminology and basic
concepts
IEC 61069-2:2016, Industrial-process measurement, control and automation – Evaluation of
system properties for the purpose of system assessment – Part 2: Assessment methodology
IEC 61070, Compliance test procedures tor steady-state availability
IEC 61709:2011, Electric components – Reliability – Reference conditions for failure rates and
stress models for conversion
ISO IEC 25010, Systems and software engineering – Systems and software Quality
Requirements and Evaluation (SQuaRE) – System and software quality models
ISO IEC 27001:2013, Information technology – Security techniques – Information security
management systems – Requirements
ISO IEC 27002, Information technology – Security techniques – Code of practice for
information security controls
IEC 61069-5:2016  IEC 2016 – 9 –
3 Terms, definitions, abbreviated terms, acronyms, conventions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61069-1 apply.
3.2 Abbreviated terms, acronyms, conventions and symbols
For the purposes of this document, the abbreviated terms, acronyms, conventions and
symbols given in IEC 61069-1 apply.
4 Basis of assessment specific to dependability
4.1 Dependability properties
4.1.1 General
To fully assess the dependability, the system properties are categorised in a hierarchical way.
For a system to be dependable it is necessary that it is ready to perform its functions.
However, in practice, when the system is ready to perform its function, this does not mean
that it is sure that the functions are performed correctly. In order to cover these two aspects,
dependability properties are categorised into the groups and subgroups shown in Figure 2.
Dependability
Availability Credibility
Reliability Maintainability Integrity Security
IEC
Figure 2 – Dependability
Dependability cannot be assessed directly and cannot be described by a single property.
Dependability can only be determined by analysis and testing of each of its properties
individually.
The relationship between the dependability properties of the system and its modules is
sometimes very complex.
For example:
– if the system configuration includes redundancy, availability property of the system is
dependent upon the integrity properties of the redundant modules;
– if the system configuration includes system security mechanisms, security property of the
system is dependent upon the availability properties of modules that perform the security
mechanism;
– if the system configuration includes modules that check data transferred internally from
other parts of the system, then integrity property of the system is dependent upon the
security properties of these modules.
When a system performs several tasks of the system, its dependability can vary across those
tasks. For each of these tasks, a separate analysis is required.

– 10 – IEC 61069-5:2016  IEC 2016
4.1.2 Availability
Availability of the system is dependent upon the availabilities of the individual modules of the
system and the way in which these modules cooperate in performing tasks of the system. The
way in which modules of the system cooperate can include functional redundancy
(homogeneous or diverse), functional fall-back and degradation. Availability is dependent in
practice upon the procedures used and the resources available for maintaining the system.
The availability of the system can differ with respect to each of its tasks.
Availability of the system for each task can be quantified in two ways:
A system’s availability can be predicted as:
Availability = mean_time_to_failure / (mean_time_to_failure + mean_time_to_restoration)
where:
• "availability" is the availability of the system for the given task;
• "mean_time_to_failure" is the mean of the time from restoration of a system into a
state of performing its given task(s) to the time the system fails to do so;
• "mean-time_to_restoration" is the mean of the total time required to restore
performance of the given task from the time the system failed to perform that task.
For a system in operation, the availability can be calculated as:
Availability = total_time_the_system_has_been_able_to_perform_the_task /
Total_time_the_system_has_been_expected_to_perform_the_task
4.1.3 Reliability
Reliability of a system is dependent upon the reliability of the individual modules of the
system and the way in which these modules cooperate in performing task(s) of the system.
The way in which these modules cooperate can include functional redundancy (homogeneous
or diverse), functional fall-back and degradation.
Reliability of the system can differ with respect to each of its tasks. Reliability can be
quantified for individual tasks, with varying degrees of predictive confidence.
The reliability of the individual elements of the system can be predicted using the parts count
method (see IEC 62380 and IEC 61069-6). Reliability of the system can then be predicted by
synthesis. It should be noted, that for the software modules of systems, there are no reliability
prediction methods available that provide high levels of confidence.
Mechanisms to analyse software reliability are described in ISO IEC 25010.
Reliability can be represented by mean time to failure (MTTF) or failure rate.
4.1.4 Maintainability
The maintainability of a system is dependent upon the maintainability of individual
elements and structure of elements and modules of the system. The physical structure
affects ease of access, replaceability, etc. The functional structure affects ease of
diagnosis, etc.
When quantifying the maintainability of a system, all actions required to restore the
system to the state where it is fully capable of performing its tasks should be included.
This should include actions such as the time necessary to detect the fault, to notify
maintenance, to diagnose and remedy the cause, to adjust and check, etc.

IEC 61069-5:2016  IEC 2016 – 11 –
The quantification of maintainability should be augmented with qualitative statements by
checking the provision for and the coverage of the following items:
The quantification of maintainability should be augmented with qualitative statements by
checking the provision for and the coverage of the following items:
– notification of the occurrence of the failures: lights, alert messages, reports, etc.;
– access: ease of access for personnel and for connecting measuring instruments,
modularity, etc.;
– diagnostics: direct fault identification, diagnostic tools which have no influence on the
system by itself, remote maintenance support facilities, statistical error checking and
reporting;
– repairability/replaceability: few restrictions on the replacement of modules while
operating (“hot swap” support), modularity, unambiguous identification of modules
and elements, minimum need for special tools, minimum repercussions on other
elements or modules, when elements or modules are replaced;
– check-out: guided maintenance procedures, minimum check-out requirements.
Maintainability can be represented by mean time to repair (MTTR).
4.1.5 Credibility
The credibility of a system is dependent upon the integrity and security mechanisms
implemented as functions performed by the modules of the system.
Credibility mechanisms include:
– a check on
• correct performance of functions (for example by watchdog, using known data);
and/or
• correct data (for example validity check, parity check, readback, input validation, etc.);
– an action, such as:
• self-correction;
• confinement;
• notification of action, etc.
These mechanisms can be used to provide integrity and/or security.
To analyse the credibility mechanisms, the fault injection techniques described in 6.1
c an be used.
Credibility is deterministic and some aspects can be quantified.
4.1.6 Security
The security of a system is dependent upon mechanisms implemented at the boundary of the
system to detect and prevent incorrect inputs and unauthorized access. These boundaries
can be physical or virtual. See:
– Annex F for more considerations on security, and
– IEC 62443 series.
A security mechanism can be implemented by an element checking the inputs to other
elements.
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4.1.7 Integrity
The integrity is dependent upon mechanisms implemented at the output elements of the
system to check for correct outputs. It also depends upon mechanisms implemented within
the system to detect and prevent incorrect transitions of signals or data between parts of the
system.
An integrity mechanism is implemented by an element checking the outputs of other
elements.
4.2 Factors influencing dependability
The dependability of a system can be affected by the following influencing factors listed in
IEC 61069-1:2016, 5.3.
For each of the system properties listed in 4.1, the primary influencing factors are as
follows:
– Reliability is influenced by the influencing factors;
• utilities, the influence is partly predictable using IEC 61709,
• environment, the influence is partly predictable using IEC 61709,
• services, due to the handling, storage of parts, etc.
– Maintainability; for the purpose of this standard, maintainability is considered as an
intrinsic property of the system itself and is only affected in an indirect way, for example
restricted access due to hazardous conditions.
– Availability; when taking into account the human activities necessary to retain the
system in, or restore the system to, a state in which the system is capable of
performing task(s) of the system, availability is influenced by human behaviour and
service conditions (delays in delivery of spare parts, training, documentation, etc.).
– Credibility; the mechanisms (security and integrity) can be affected by intentional or
unintentional human actions and by infestations of pests and if these mechanisms
share common facilities, such as buses or multitasking processors, they can be
influenced by task(s) of the system, the process due to a sudden increase in process
activity (for example an alarm burst), etc. and external systems.
In general, any deviations from the reference conditions in which the system is supposed
to operate can affect the correct working of the system.
When specifying tests to evaluate the effects of influencing factors, the following
standards should be consulted:
– IEC 60068,
– IEC 60801,
– IEC 61000, and
– IEC 61326.
5 Assessment method
5.1 General
The assessment shall follow the method as laid down in IEC 61069-2:2016, Clause 5.
5.2 Defining the objective of the assessment
Defining the objective of the assessment shall follow the method as laid down in IEC 61069-
2:2016, 5.2.
IEC 61069-5:2016  IEC 2016 – 13 –
5.3 Design and layout of the assessment
Design and layout of the assessment shall follow the method as laid down in IEC 61069-
2:2016, 5.3.
Defining the scope of assessment shall follow the method laid down in IEC 61069-2:2016,
5.3.1.
Collation of documented information shall be conducted in accordance with IEC 61069-2:2016,
5.3.3.
The statements compiled in accordance with IEC 61069-2:2016, 5.3.3 should include the
following in addition to the items listed in IEC 61069-2:2016, 5.3.3.
– No additional items are noted
Documenting collated information shall follow the method in IEC 61069-2:2016, 5.3.4.
Selecting assessment items shall follow IEC 61069-2:2016, 5.3.5.
Assessment specification should be developed in accordance with IEC 61069-2:2016, 5.3.6.
Comparison of the SRD and the SSD shall follow IEC 61069-2:2016, 5.3.
NOTE 1 A checklist of SRD for system dependability is provided in Annex A.
NOTE 2 A checklist of SSD for system dependability is provided in Annex B.
5.4 Planning of the assessment program
Planning the assessment program shall follow the method as laid down in IEC 61069-2:2016,
5.4.
Assessment activities shall be developed in accordance with IEC 61069-2:2016, 5.4.2.
The final assessment program should specify points specified in IEC 61069-2:2016, 5.4.3.
5.5 Execution of the assessment
The execution of the assessment shall be in accordance with IEC 61069-2:2016, 5.5.
5.6 Reporting of the assessment
The reporting of the assessment shall be in accordance with IEC 61069-2:2016, 5.6.
The report shall include information specified in IEC 61069-2:2016, 5.6. Additionally, the
assessment report should address the following points:
– No additional items are noted.
6 Evaluation techniques
6.1 General
Within this standard, several evaluation techniques are suggested. Other methods may be
applied but, in all cases, the assessment report should provide references to documents
describing the techniques used.
Those evaluation techniques are categorized as described in IEC 61069-2:2016, Clause 6.

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Factors influencing dependability properties of the system as per 4.2 shall be taken into
account.
The techniques given in 6.2, 6.3 and 6.4 are recommended to assess dependability properties.
Quantitative evaluation can be based on a predictive analysis, calculations, or on tests.
To start the evaluation it is first necessary to analyse the functional and physical structure of
the system. Once this is accomplished an analysis of how the tasks are performed by the
system should be done.
The structure of the system can be described using functional and physical block diagrams,
signal flow diagrams, state graphs, tables, etc.
Failure modes are considered for all elements (hardware and software). Their effects on the
dependability of the task(s) of the system, together with the influence of the requirements for
maintainability, are determined.
Quantitative evaluations can be performed using one of, or a combination of, the available
methods described in 6.2 and 6.3.
The analysis shall include an examination of the manner in which alternative paths through
the system are initiated, i.e.:
– in a static manner by changing the system configuration; or
– dynamically, either automatically,
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