EN 60706-5:2007

SLOVENSKI STANDARD
01-januar-2008
9]GUåHYDOQRVWRSUHPHGHO3UHVNXVQRVWLQGLDJQRVWLþQRSUHVNXãDQMH,(&

Maintainability of equipment -- Part 5: Testability and diagnostic testing
Instandhaltbarkeit von Geräten -- Teil 5: Prüfbarkeit und diagnostisches Prüfen
Maintenabilité de matériel -- Partie 5: Testabilité et tests pour diagnostic
Ta slovenski standard je istoveten z: EN 60706-5:2007
ICS:
03.100.40 Raziskave in razvoj Research and development
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60706-5
NORME EUROPÉENNE
October 2007
EUROPÄISCHE NORM
ICS 03.120.01; 03.120.30; 21.020

English version
Maintainability of equipment -
Part 5: Testability and diagnostic testing
(IEC 60706-5:2007)
Maintenabilité de matériel -  Instandhaltbarkeit von Geräten -
Partie 5: Testabilité et tests Teil 5: Prüfbarkeit und
pour diagnostic diagnostisches Prüfen
(CEI 60706-5:2007) (IEC 60706-5:2007)

This European Standard was approved by CENELEC on 2007-10-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60706-5:2007 E
Foreword
The text of document 56/1211/FDIS, future edition 2 of IEC 60706-5, prepared by IEC TC 56,
Dependability, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 60706-5 on 2007-10-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2008-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-10-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60706-5:2007 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 60300-1 NOTE  Harmonized as EN 60300-1:2003 (not modified).
IEC 60300-2 NOTE  Harmonized as EN 60300-2:2004 (not modified).
IEC 60300-3-2 NOTE  Harmonized as EN 60300-3-2:2005 (not modified).
IEC 60300-3-3 NOTE  Harmonized as EN 60300-3-3:2004 (not modified).
IEC 60300-3-12 NOTE  Harmonized as EN 60300-3-12:2004 (not modified).
IEC 60300-3-14 NOTE  Harmonized as EN 60300-3-14:2004 (not modified).
__________
- 3 - EN 60706-5:2007
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

1)
IEC 60050-191 - International Electrotechnical Vocabulary - -
(IEV) -
Chapter 191: Dependability and quality of
service
1)
IEC 60300-3-10 - Dependability management - - -
Part 3-10: Application guide - Maintainability

1) 2)
IEC 60706-2 - Maintainability of equipment - EN 60706-2 2006
Part 2: Maintainability requirements and
studies during the design and development
phase
1) 2)
IEC 60706-3 - Maintainability of equipment - EN 60706-3 2006
Part 3: Verification and collection, analysis
and presentation of data
1)
Undated reference.
2)
Valid edition at date of issue.

IEC 60706-5
Edition 2.0 2007-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Maintainability of equipment –
Part 5: Testability and diagnostic testing

Maintenabilité de matériel –
Partie 5: Testabilité et tests pour diagnostic

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XB
CODE PRIX
ICS 03.120.01; 03.120.30; 21.020 ISBN 2-8318-9295-3

– 2 – 60706-5 © IEC:2007
CONTENTS
FOREWORD.5
INTRODUCTION.7

1 Scope.8
2 Normative references.8
3 Terms, definitions and acronyms.8
3.1 Terms and definitions .8
3.2 Acronyms .13
4 Description of testability and diagnostic testing.13
4.1 General .13
4.2 Objectives of testability.15
4.3 Objectives of diagnostic testing.16
4.4 Methods used for diagnostic testing .17
4.5 Methods used for condition monitoring .17
4.6 Concept of testability .17
5 Testability specification.18
5.1 General .18
5.2 Statement of work.19
5.3 Specification.19
5.4 Characteristics of testability .23
5.4.1 Testability features .23
5.4.2 Operational context.23
5.4.3 Test tasks.23
5.5 Characteristic values for assessing testability .25
5.6 Criteria for evaluation of alternative diagnostic designs .25
6 Testability in the development process.26
6.1 General .26
6.2 Functional assignment .27
6.3 Testability engineering.27
6.3.1 Design criteria for testability.27
6.3.2 Design for testability .28
6.3.3 Use of commercial off-the-shelf products (COTS).28
6.4 Testability development process .29
6.4.1 Logistic support .29
6.4.2 Availability and diagnostic testing .30
7 Assessment of testability .30
7.1 General .30
7.2 Verification by analysis .30
7.3 Verification by tests .30
8 Testability documentation .31

Annex A (informative) Calculation of characteristics of fault recognition and fault
localization.32
Annex B (informative) Development process for testable products .38

60706-5 © IEC:2007 – 3 –
Bibliography .63

Figure 1 – Testability and diagnostic testing during the life cycle.15
Figure 2 – Operational context .23
Figure 3 – Development process in the V-model .26
Figure 4 – Design levels and their logistic assignment, taking an aircraft as an example .29
Figure B.1 – Example of how to determine the basic data .38
Figure B.2 – Modelling of sub-functions and terminals .40
Figure B.3 – Functional model showing the functional terminals between the sub-
functions .40
Figure B.4 – Functional model with inserted hardware units .42
Figure B.5 – Functional model showing stimulation and measuring points .43
Figure B.6 – Functional model showing test paths .44
Figure B.7 – Portions of the test task.45
Figure B.8 – Functional model showing the test paths of portion A .47
Figure B.9 – Functional model showing the test paths of portions A + B + C + D .49
Figure B.10 – Functional model of case study 1.51
Figure B.11 – Functional model of case study 2.52
Figure B.12 – Fault localization portions .54
Figure B.13 – Functional model with additional stimulation and measuring points.56
Figure B.14 – Selection criteria for verification.59
Figure B.15 – Functional model shown in the form of an extended block diagram.61

Table 1 – Elements of the operational concept .21
Table 2 – Elements of the maintenance concept.22
Table 3 – Test task .24
Table 4 – Example of logistic assignment .30
Table B.1 – Data for the document “system specification".39
Table B.2 – Data for the document "test specification" (assignment of function to
parameter) .
Table B.3 – Database with hardware units and logistic assignment added.42
Table B.4 – Database expanded to include the test steps .43
Table B.5 – Database expanded to include the test paths .44
Table B.6 – Database expanded to include the test task portions .45
Table B.7 – Determination of how many terminals and hardware units there are.46
Table B.8 – Matrix showing coverage of terminals and paths .46
Table B.9 – Determination of the characteristic value for the quality of the fault
recognition (FR) during operation (section A).47
Table B.10 – Determination of the characteristic value for the quality of the fault
recognition (FR) under test conditions (Portions A+B+C+D) .49
Table B.11 – Coverage matrix .50
Table B.12 – Coding of terminals.51

– 4 – 60706-5 © IEC:2007
Table B.13 – Sum field .51
Table B.14 – Fault localization matrix of case study 1 .52
Table B.15 – Fault localization matrix of case study 2 .52
Table B.16 – Determining the characteristic value for the quality of fault localization (FL).53
Table B.17 – Determination of the locatability of the hardware units .55
Table B.18 – Data table expanded to include test path PP 5 .56
Table B.19 – Determination of the locatability of the hardware units, including additional
test path 5.57
Table B.20 – Verification record .59
Table B.21 – Example of the document "system specification" .60
Table B.22 – Example of the document "test specification" .61
Table B.23 – Verification record .62

60706-5 © IEC:2007 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
MAINTAINABILITY OF EQUIPMENT –

Part 5: Testability and diagnostic testing

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 60706-5 has been prepared by IEC technical committee 56:
Dependability.
This second edition cancels and replaces the first edition published in 1994. This second
edition constitutes a technical revision. It expands and provides more detail on the techniques and
systems broadly outlined in the first edition.
The text of this standard is based on the following documents:
FDIS Report on voting
56/1211/FDIS 56/1231/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.

– 6 – 60706-5 © IEC:2007
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60706 series, under the general title Maintainability of
equipment, can be found on the IEC website.
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.
60706-5 © IEC:2007 – 7 –
INTRODUCTION
Testability is an important feature in the operation and maintenance of a system or equipment
and has a significant effect on its availability and maintainability. Diagnostic testing may be
carried out manually or with test equipment which may contain various levels of automation.
Optimum design for testability requires close cooperation between design, operation and
maintenance organizations. This standard is intended to highlight the various aspects of
testability and diagnostic testing and to assist in their timely coordination.
In this standard, items to be considered in respect of their testability design may be systems,
equipment or functional units which are the objects of a contract, and will be referred to as
"products". Each product has to perform its required functions which should be verified during
the development and production phases and should be retained over the whole life cycle. For a
product to retain its functionality, the functional status of each sub-function should be known at
any time while the product is in its operating condition. If a failure occurs, action should be
taken to ensure that the fault is recognized and the faulty item localized. This requirement
placed on the testability of a product might appear to be quite simple, but if it is not considered
at the start of product development, subsequent realization will result in increased work and
significantly increased cost. If all requirements are available at the start of development, the
development engineer can specify the functional characteristic "testability" without much
additional effort and therefore achieve considerable cost savings e.g. by minimizing the number
of test steps for verifying the development results. Experience has shown that the extra cost
and effort in the development phase can be recovered for example in the production phase
since available test equipment can be used. Reliable fault recognition and low in-service
maintenance costs increase the market value of a testable product considerably.
As the technologies which are applied in the products covered by this standard are wide-
ranging, this document has been written in a neutral manner with regard to technologies and
techniques. This standard therefore only provides an assessment basis for making calculations
and the basic approach for achieving the required testability of a product. The technical
realization of fault recognition and fault localization in the product is the task of the product
development engineer and has to be achieved according to the state of the art at the time when
the product is being developed. It is therefore not of great importance whether the required test
task is realized in hardware or software form, but it is essential that all functions are checked
via test paths and that the characteristic values established for testability correspond to the
specified target values. If there are deviations from the target values, action should be taken to
ensure that the target values are met. These actions should take place at an early stage of
development before freezing the design.

– 8 – 60706-5 © IEC:2007
MAINTAINABILITY OF EQUIPMENT –

Part 5: Testability and diagnostic testing

1 Scope
The purpose of this part of IEC 60706 is to
– provide guidance for the early consideration of testability aspects in design and
development;
– assist in determining effective test procedures as an integral part of operation and
maintenance.
This International Standard can be applied to all types of products which may include
commercial off-the-shelf (COTS) items. In this respect, it does not matter whether the product
belongs to mechanical, hydraulic, electrical or some other technology. In addition, this
International Standard applies to the development of any products, with the aim of designing
the product characteristics so that they are verifiable (testable).
The objective of this International standard is to ensure that prerequisites relating to the
testability of products are defined in the preliminary phases of development, laid down by the
customer, implemented, documented and verified during development.
This International Standard also provides methods to implement and assess testability as an
integral part of the product design. It recommends that the product testability documentation
should be continually updated over the product's life cycle.
2 Normative references
The following 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 60050-191, International Electrotechnical Vocabulary – Chapter 191: Dependability and
quality of service
IEC 60706-2, Maintainability of equipment – Part 2: Maintainability requirements and studies
during the design and development phase
IEC 60706-3, Maintainability of equipment – Part 3: Verification and collection, analysis and
presentation of data
IEC 60300-3-10, Dependability management – Part 3-10: Application guide – Maintainability
3 Terms, definitions and acronyms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions of IEC 60050-191 apply together
with the following:
60706-5 © IEC:2007 – 9 –
3.1.1
built-in test
BIT
integrated capability of a test item enabling automatic fault recognition and fault localization
3.1.2
built-in test equipment
BITE
hardware and/or software assigned to the built-in test
3.1.3
commercial off-the-shelf
COTS
designates items readily available commercially
3.1.4
criticality
significance attached to a malfunction
NOTE Criticality is expressed in grades: the higher the grade, the more severe the consequences to be expected
from the malfunction.
3.1.5
depth of test
specification of the level to which the unit or sub-unit is to be identified
3.1.6
design level
level to which the design elements (functional and/or physical units), when they already exist,
are assigned within the product breakdown structure
NOTE In some cases “design level” is known as “indenture level”.
3.1.7
diagnosis correctness
proportion of faults of an item that can be correctly diagnosed under given conditions
3.1.8
diagnostic testing
test procedure carried out in order to make a diagnosis
3.1.9
false alarm
indication of failure which, after carrying out failure finding activities, is not found
3.1.10
false alarm rate
the percentage of false alarms in the total number of failure indications
3.1.11
fault recognition time
period of time between the instant of failure and fault recognition

– 10 – 60706-5 © IEC:2007
3.1.12
fault simulation
inclusion of faults by non-destructive interventions in the hardware units and/or, where
necessary, simulation via software in order to verify the diagnostic capability
3.1.13
function
performance required of the item
NOTE A function is always associated if realised with an item of a given level in the product breakdown structure.
3.1.14
functional model
conceptual representation of an item describing the interrelationship and dependencies
between its stimuli and measurement (response) terminals
NOTE The functional model, which arises during the development of a product, is in principle a block diagram
showing the functions of the product and supplemented to include the test paths envisaged by the developer.
3.1.15
functional test
testing of all the specified functions of hardware units to prove their functional capability
3.1.16
hardware unit
design element which represents functions and/or sub-functions in the form of hardware,
possibly including software components
3.1.17
line replaceable unit
LRU
replaceable hardware or software unit which can be replaced directly on the equipment by the
user or by a maintenance support facility
3.1.18
maintenance concept
interrelationship between the design levels and the levels of maintenance to be applied for the
maintenance of an item
3.1.19
maintenance policy
general approach to the provision of maintenance and maintenance support based on the
objectives and policies of owners, users and customers
3.1.20
monitoring
automatic supervision of the functions required for the operation in a selected operational
mode; operation should not be affected by this
3.1.21
operational context
circumstances in which an item is expected to operate
3.1.22
parameter
physical quantity that specifies a function

60706-5 © IEC:2007 – 11 –
3.1.23
product
specified deliverable goods or service
NOTE 1 In the context of dependability, a product may be simple (e.g. a device, a software algorithm) or complex
e.g. a system or an integrated network comprising of hardware, software, human elements, support facilities and
activities).
NOTE 2 Product has its own life cycle phases.
NOTE 3 Product has the same definition as item.
3.1.24
product breakdown structure
hierarchical tree visualizing the physical composition of a product by assemblies of units and
sub-units
3.1.25
shop replaceable unit
SRU
replaceable hardware or software unit which can be replaced by the user depot/workshop or by
the maintenance support facility at the same level or in the company's workshops
3.1.26
signal
variation of a physical quantity used to represent data
NOTE A signal is represented by one or several parameters.
3.1.27
specification
detailed definition of the functions of an item for a given level of the product breakdown
structure
NOTE Specifications should be derived from the systems requirements and be verifiable.
3.1.28
statement of work
SoW
document which defines goods and services to be provided.
NOTE The statement of work is prepared or accepted by the customer and defines the work for which a contract is
to be placed and which is to be provided by the contractor. It therefore forms the main technical document
according to which the bidders present their offers, the contractor performs the work and the customer accepts the
goods and services provided.
3.1.29
stimulus
input signal with defined parameters for the purpose of triggering functions
3.1.30
sub-function
sub-division of a function (see also function, 3.1.13)
3.1.31
terminal
generic term for the physical access points to the signals of a test item. Examples of physical
implementations or relevant terms for synonymous expressions are
– pin
– 12 – 60706-5 © IEC:2007
– connector
– plug/plug-type connector
– test point
– interface
– port
NOTE A terminal is generally identified by a unique identifier.
3.1.32
test concept
description of the results of the system testability requirements analysis and stipulation of the
method of how the requirements are to be met
3.1.33
test coverage
ratio of the number of faulty functions actually capable of diagnosis by the given test instruction
to the total number of functions
3.1.34
test equipment
tools (hardware and/or software) required for conducting tests
NOTE Due to the technology involved, these are divided into internal (BITE) and external test equipment.
3.1.35
test instruction
document describing how the tests required in the test specification are to be implemented
3.1.36
test path
description of the assignment of hardware units to their terminals, taking the associated test
steps into account
NOTE In addition, the test path defines the (functional) relationship between the stimulus and the response.
3.1.37
test sequence
series of test steps
3.1.38
test specification
document in which test sequences, parameters and functions are specified
3.1.39
test step
smallest unit in a test conducted on a hardware unit
3.1.40
test task
sum of all the tests necessary to meet the specifications of fault recognition and localization
3.1.41
testability
design characteristic which determines the degree to which an item can be functionally tested
under stated conditions
60706-5 © IEC:2007 – 13 –
3.2 Acronyms
ATE automatic test equipment
ATS automatic testing system
BIT built-in test
BITE built-in test equipment
COTS commercial off-the-shelf
DP data processing
FL fault localization
FM functional monitoring
FME(C)A failure mode, effects, (and criticality) analysis
FR fault recognition
FT functional test
FTA fault tree analysis
HWE hardware unit
LCC life cycle cost
LORA level of repair analysis
LRU line replaceable unit
PCB printed circuit board
SoW statement of work
SRU shop replaceable unit
SF sub-function
TS technical specification
4 Description of testability and diagnostic testing
4.1 General
The efficient and cost effective operation and maintenance of products is aided by ensuring
that testability is considered during design and also during all the phases of the life cycle.
Applicable diagnostic testing methods are then incorporated into the product as a component
of the maintenance concept. Implementation of testability and diagnostic testing is
accomplished throughout the life cycle of a product.
Life cycle cost (LCC) is an increasingly important aspect in evaluating the quality of any design.
In addition to the immediate acquisition cost, many customers demand control of the costs
associated with day to day operation, maintenance and logistic support. These costs are
primarily influenced by the product's reliability, maintainability and maintenance support
characteristics. In this context, the application of diagnostic testing techniques can be a
significant contributory factor in the reduction of certain cost elements in the LCC. Constraints
resulting from LCC optimization efforts should therefore be taken into account whenever
diagnostic testing requirements are established.
This International Standard is intended to be applicable to all phases of the life cycle, i.e. from
the time when the need for a product is identified through the design and development phase,
to the manufacturing and installation phase and finally to the operation and maintenance phase
as follows (see also Figure 1).
a) Design and development phase
From the concept down to the realization of a product, the requirements placed on a

– 14 – 60706-5 © IEC:2007
product should be adapted to the specific needs of its field of application, where necessary
passing through several pre-phases.
b) Manufacturing and installation phase
During this phase, it may be necessary to verify the diagnostic techniques using actual
equipment and assess the product’s effectiveness. Documentation can be prepared and
training can now occur for operational and maintenance personnel.
c) Operation and maintenance phase
There may be a change to tested equipment due to obsolescence. The testing function may
need to be continued and replacement or upgrading of equipment should take into account
a continuing need for diagnostic testing. In the latter case, a redesign should be carried out
in a new development phase.
By applying this International Standard, the preconditions are assumed to be fulfilled for
generating the necessary product data/information and that this can be verified and updated
over the product's complete life cycle.
Annex B gives an example of how testability is developed, documented and verified with regard
to product/system design.
Diagnostic testing can consist of
– functional testing with the purpose of verifying that a function can still be performed;
– condition monitoring which is intended to track the condition of equipment that degrades
over time.
Condition monitoring is closely related to the concepts covered by diagnostic testing, and
cannot, and should not, be dissociated from it. However, it is not the intention that full coverage
of condition monitoring should be part of this standard.

Need of product
Maintainability Maintenance support
Maintenance concept Material management
Environment Transport/storage
Mission conditions Infrastructure
Product
PrePPrerephas -- phasphaseesess
Prephases
-- alternatives
Configuration Personal skills alternatives
environment
-- studies
studies
Management Training support
-- technology
technology
analysis
Test equipment Documentation
PrPreeppaarraattioionn o off te tessttaabbilitilityy s sppeeccififiiccaattiioonn
Operation and maintenance
phase
CCContontontractractract
Manufacturing and installation phase
Design and development phase
SoSoWW
SoW
System
---  ffuncuncttiionsons
M1M1M1 M2M2
functions M3M3M3
---  tetesstatabbiilliityty
testability
---  llogiogisstticicss
logistics
TS
TS
---  LCCLCC
LCC
CECE
VeVerriifificcaatitioonn LRU
TS
TS
CECE
TS
TS
SRU
DoDocucummenenttatatiioonn
AAssssessmenessmentt Documentation
TS   Test specification ooff t testestababiilliittyy for maintenance
CE  Concurrent engineering FRFR, FL, FL support
M1  Validation of requirements
Installation phase MMainaintentenanance pce phhaasse e
Development process
M2  Verification by analysis
M3  Verification by tests
IEC  1669/07
60706-5 © IEC:2007 – 15 –
Figure 1 – Testability and diagnostic testing during the life cycle
4.2 Objectives of testability
Testability during design and development is closely aligned with maintainability, availability
and safety and the main objective of testability is to address the following questions for each of
the system functions.
a) Can the function’s failures be detected by a diagnostic test ? Certain functions cannot be
completely tested because of safety constraints or because the test may be destructive
(such as testing the overspeed mechanism on a rotor).
b) Is it practical to test? The criticality of the function’s failure, the test costs (the test
equipment cost, the test equipment maintenance costs as well as the test activity costs)
and the use of better and cheaper alternatives may result in the conclusion that it is not
cost effective to test.
NOTE For both the cases in a) and b), alternative methods should be adopted to ensure the performance of these
functions is maintained during the life of the product. Together, these elements contribute to the test coverage. A
low test coverage value may be detrimental in that the system cannot be tested to confirm operational performance
during its life cycle, but it may also indicate that the maintainability and maintenance capability is such that testing
is not necessary.
c) In what stages in the life cycle should the item be tested? The ability to test should be
considered for each stage in the life cycle; testing a function at unit level may be possible,
but impractical at system level. This can best be explained by an example: consider a
washing machine and its function to discharge waste water. It would be useful, from a user
perspective, to run a pre-operation stage test to confirm that the function can be performed
prior to operation (running an operational stage test would provide little benefit). The design
for this function may not require the introduction of test equipment to test this function
because
1) the life of the pump and associated equipment well exceeds the life of the product
(other failures and the expense of their repair may define the product’s life);
2) the maintenance task to remove a possible blockage can be easily accommodated;
3) units that perform this function can be fully tested at the unit stage and at the system
level stage prior to delivery;
4) determining the stages to test can also influence the life cycle cost;
d) To what depth should it be tested? The depth of test is also an important criterion and, as
in the above example, it is closely aligned to the maintenance concept. The depth of test
specifies the level to which the unit or sub-unit is to be identified. For example, a system
test may identify the unit to be replaced, but can also identify the sub-unit that needs to be
replaced with little or no impact on the cost. This may reduce the costs associated with the
test equipment required at the unit level to identify and replace the faulty sub-unit.
It is a basic principle in the design of testability that all functions developed should be
verifiable. It should, however, be noted that test coverage of 100 % is not necessarily
desirable, as testing can create failures that manifest themselves during operation, which
may be worse than not testing, e.g. real failures introduced by testing or false alarms. Nor
is test coverage of 100 % recommended for all safety issues, as the test itself may
prejudice the safety of the system. It is more important that tests give substantial
confidence in the operation of the system. To achieve this, deviations from test coverage of
100 % should always be thoroughly substantiated.
Nevertheless, the objectives of testability should not contradict higher ranking objectives,
e.g. availability.
– 16 – 60706-5 © IEC:2007
e) How should false alarms and no fault found be managed? The system test may detect and
report a failure to the user when a failure does not truly exist. This may cause unnecessary
investigations and result in the report of a false alarm. It may also generate unnecessary
maintenance action that concludes in a No Fault Found diagnosis. False alarm rates for the
various resolutions should not exceed the defined criteria and, where possible, be reduced
to zero. Methods that are recognised to minimise these occurrences may involve feedback
systems that constantly assess the environment and recalibrate themselves to allow for
component degradation within the defined criteria. Repeating a test to eliminate a false
alarm (the scenario of the test may have changed sufficiently for the alarm not to be
generated) will increase the test time and should be avoided.
Faults can be indicated where no faults exist. This can be due to a number of reasons:
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