SIST EN 50402:2005
(Main)Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen - Requirements on the functional safety of fixed gas detection systems
Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen - Requirements on the functional safety of fixed gas detection systems
This European Standard is applicable to fixed gas detection systems for the detection and measurement of flammable or toxic gases or vapours or oxygen. This European Standard supplements the requirements of the European Standards for electrical apparatus for the detection and measurement of flammable gases, vapours (e.g. EN 61779 or EN 50241), toxic gases (e.g. EN 45544) or oxygen (e.g. EN 50104). NOTE 1 These European Standards will be mentioned in the text as "metrological standards". NOTE 2 The examples above show the state of the standardisation for industrial applications at the time of publishing this European Standard. There may be other metrological standards covering other application fields, for which this standard is also applicable. NOTE 3 For fixed apparatus used for safety applications with a SIL requirement up to 1 and for portable apparatus the European Standard EN 50271 may be applied instead of this European Standard. Applying the above mentioned metrological standards will ensure the measuring performance is adequate in normal operation of a gas detection system. Additionally the requirements of this European Standard address the functional safety of gas detection systems and encompass criteria for reliability, fault tolerance and avoidance of systematic faults. This European Standard will lead to the characterisation of the gas detection system by a SIL-capability and related hardware failure rate representing a hierarchical order of safety levels. This will allow the user to incorporate the gas detection system into an overall safety system according to the safety integrity levels of EN 61508 or the categories of EN ISO 13849-1 (see Annex B). This European Standard is a product standard which is based on EN 61508 and includes additional requirements of EN ISO 13849-1. It covers part of the phase 9 “realisation” of the overall safety lifecycle defined in EN 61508-1. This European Standard is applicable for gas detection systems, which may consist of the following functional units: - gas-sampling; - sensor; - signal transmission; - input to control unit; - signal processing in control unit; - output from control unit. This European Standard does not specify requirements for the installation and maintenance of gas detection systems. It also does not specify the physical positioning of sensors.. This European Standard does not specify which SIL-capability is sufficient for which application. NOTE 4 The SIL-capability required for an application will be specified by the user (see Annexes A and B).
Elektrische Geräte für die Detektion und Messung von brennbaren oder toxischen Gasen und Dämpfen oder Sauerstoff - Anforderungen an die funktionale Sicherheit von ortsfesten Gaswarnsystemen
Diese Europäische Norm gilt für ortsfeste Gaswarnsysteme zur Detektion und Messung von brennbaren oder toxischen Gasen oder Dämpfen oder Sauerstoff. Diese Europäische Norm ergänzt die Anforderungen der Europäischen Normen an elektrische Geräte zur Detektion und Messung von brennbaren Gasen, Dämpfen (z. B. EN 61779 oder EN 50241), toxischen Gasen (z. B. EN 45544) oder Sauerstoff (z. B. EN 50104). ANMERKUNG 1 Auf diese Europäischen Normen wird im Text als „messtechnische Normen“ Bezug genommen. ANMERKUNG 2 Die oben genannten Beispiele stellen den Stand der Normung für industrielle Anwendungen zum Zeitpunkt der Veröffentlichung dieser Europäischen Norm dar. Es können weitere messtechnische Normen für andere Anwendungsfelder bestehen, auf die diese Norm ebenfalls anwendbar ist. ANMERKUNG 3 Für ortsfeste Geräte zum Einsatz in sicherheitsgerichteten Anwendungen mit einer SIL-Anforderung bis Level 1 und für tragbare Geräte darf anstelle dieser Europäischen Norm die Europäische Norm EN 50271 angewendet werden. Die Anwendung der oben genannten messtechnischen Normen stellt ein angemessenes messtechnisches Betriebsverhalten im Normalbetrieb des Gaswarnsystems sicher. Die Anforderungen dieser Europäischen Norm richten sich ergänzend auf die funktionale Sicherheit von Gaswarnsystemen und umfassen Kriterien für Zuverlässigkeit, Fehlertoleranz und Vermeidung systematischer Fehler. Diese Europäische Norm führt zu einer Einstufung des Gaswarnsystems in Form einer SIL-Fähigkeit und von damit verbundenen Hardwareausfallraten. Sie spiegelt eine hierarchische Anordnung von Sicherheitsstufen wider. Dadurch wird es dem Anwender ermöglicht, das Gaswarnsystem in ein Gesamtsicherheitssystem gemäß den Sicherheits-Integritätsleveln der EN 61508 oder den Kategorien der EN ISO 13849-1 einzubinden (siehe Anhang B). Diese Europäische Norm stellt eine Produktnorm auf Grundlage der EN 61508 dar und schließt zusätzliche Anforderungen der EN ISO 13849-1 ein. Sie deckt Teile der Phase 9 „Realisierung“ des in EN 61508 1 definierten Gesamt-Sicherheitslebenszyklus ab. Diese Europäische Norm ist auf Gaswarnsysteme anwendbar, die aus folgenden funktionalen Einheiten bestehen können: Gasprobenentnahme; Sensor; Signal-Übertragung; Eingang der Auswerteeinheit; Signalverarbeitung in der Auswerteeinheit; Ausgang der Auswerteeinheit. Diese Europäische Norm legt keine Anforderungen an die Installation und Wartung von Gaswarnsystemen fest. Sie legt auch nicht die Platzierung von Sensoren fest. Diese Europäische Norm legt nicht fest, welche SIL-Fähigkeit für welche Anwendung ausreichend ist. ANMERKUNG 4 Die für eine Anwendung erforderliche SIL-Fähigkeit wird vom Anwender festgelegt (siehe Anhänge A und B).
Matériel électrique pour la détection et la mesure des gaz ou vapeurs combustibles ou toxiques, ou de l'oxygène - Exigences relatives à la fonction de sécurité des systèmes fixes de détection de gaz
La présente Norme Européenne s'applique aux systèmes de détection de gaz fixes utilisés pour la détection et le mesurage de gaz ou de vapeurs inflammables ou toxiques, ou de l'oxygène. La présente Norme Européenne complète les exigences des normes européennes relatives au matériel électrique pour la détection et le mesurage de gaz et des vapeurs inflammables (par exemple EN 61779 ou EN 50241), de gaz toxiques (par exemple EN 45544) ou de l'oxygène (par exemple EN 50104). NOTE 1 La présente norme qualifie ces normes européennes de ''normes métrologiques''. NOTE 2 Les exemples susmentionnés illustrent l'état réel de la normalisation relative aux applications industrielles au moment de la publication de la présente Norme Européenne. Il peut exister d'autres normes métrologiques traitant d'autres domaines d'application pour lesquels la présente norme s'applique également. NOTE 3 Pour les matériels fixes utilisés dans des applications de sécurité avec une exigence de SIL jusqu’à 1 et pour les matériels portables, l'EN 50271 peut être appliquée à la place de la présente Norme Européenne. L'application des normes métrologiques susmentionnées garantit les performances de mesure en exploitation normale du système de détection de gaz. Les exigences de la présente Norme Européenne traitent en outre de la sécurité fonctionnelle des systèmes de détection de gaz et englobent les critères de fiabilité, de tolérance aux pannes et d'évitement des pannes systématiques. La présente Norme Européenne conduit à la caractérisation du système de détection de gaz par un SIL qui représente un ordre hiérarchique des niveaux de défaillance. Ceci permet à l'utilisateur d'intégrer le système de détection de gaz à un système de sécurité globale selon les niveaux d'intégrité de sécurité définis dans l'EN 61508 ou les catégories spécifiées dans l'EN ISO 13849-1 (voir Annexe B). La présente Norme Européenne est une norme de produit fondée sur l'EN 61508, comprenant les exigences supplémentaires de l'EN ISO 13849-1. Elle traite également en partie de la phase 9 “réalisation” du cycle de vie de sécurité globale défini dans l'EN 61508-1. La présente Norme Européenne s'applique aux systèmes de détection de gaz pouvant comporter les unités fonctionnelles suivantes: - un module d'échantillonnage de gaz; - un capteur; - un module de transmission des signaux; - l'entrée vers l'unité de commande; - le traitement des signaux dans l'unité de commande; - la sortie de l'unité de commande. La présente Norme Européenne ne spécifie aucune exigence relative à l'installation et à la maintenance des systèmes de détection de gaz. Elle ne précise également pas la position physique des capteurs. De même, la présente Norme Européenne ne spécifie pas le SIL adapté à une application particulière. NOTE 4 Le SIL requis pour une application donnée est spécifié par l'utilisateur (voir Annexes A et B).
Električne naprave za odkrivanje in merjenje vnetljivih ali strupenih plinov, hlapov ali kisika - Zahteve za funkcionalno varnost vgrajenih sistemov za odkrivanje plina
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 50402:2005
01-december-2005
(OHNWULþQHQDSUDYH]DRGNULYDQMHLQPHUMHQMHYQHWOMLYLKDOLVWUXSHQLKSOLQRYKODSRY
DOLNLVLND=DKWHYH]DIXQNFLRQDOQRYDUQRVWYJUDMHQLKVLVWHPRY]DRGNULYDQMHSOLQD
Electrical apparatus for the detection and measurement of combustible or toxic gases or
vapours or of oxygen - Requirements on the functional safety of fixed gas detection
systems
Elektrische Geräte für die Detektion und Messung von brennbaren oder toxischen Gasen
und Dämpfen oder Sauerstoff - Anforderungen an die funktionale Sicherheit von
ortsfesten Gaswarnsystemen
Matériel électrique pour la détection et la mesure des gaz ou vapeurs combustibles ou
toxiques, ou de l'oxygène - Exigences relatives à la fonction de sécurité des systèmes
fixes de détection de gaz
Ta slovenski standard je istoveten z: EN 50402:2005
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
13.320 Alarmni in opozorilni sistemi Alarm and warning systems
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
SIST EN 50402:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 50402:2005
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SIST EN 50402:2005
EUROPEAN STANDARD EN 50402
NORME EUROPÉENNE
EUROPÄISCHE NORM August 2005
ICS 13.320
English version
Electrical apparatus for the detection and measurement of combustible
or toxic gases or vapours or of oxygen –
Requirements on the functional safety of fixed gas detection systems
Matériel électrique pour la détection et la Elektrische Geräte für die Detektion und
mesure des gaz ou vapeurs combustibles Messung von brennbaren oder toxischen
ou toxiques, ou de l'oxygène – Gasen und Dämpfen oder Sauerstoff –
Exigences relatives à la fonction Anforderungen an die funktionale
de sécurité des systèmes fixes Sicherheit von ortsfesten
de détection de gaz Gaswarnsystemen
This European Standard was approved by CENELEC on 2005-07-01. 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, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and 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
© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 50402:2005 E
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SIST EN 50402:2005
EN 50402:2005 – 2 –
Foreword
This European Standard was prepared by SC 31-9, Electrical apparatus for the detection and measurement of
combustible gases to be used in industrial and commercial potentially explosive atmospheres, of Technical
Committee CENELEC TC 31, Electrical apparatus for explosive atmospheres and by the Technical Committee
CENELEC TC 216, Gas detectors.
The text of the draft was submitted to the formal vote and was approved by CENELEC as EN 50402 on
2005–07-01.
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) 2006-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-07-01
__________
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Contents
Clause Page
Introduction.5
1 Scope .6
2 Normative references .7
3 Definitions.8
4 General requirements.12
4.1 Introduction .12
4.2 Functional safety characteristics of modules.13
5 Modules and elements - Characterisation and requirements .15
5.1 General requirements.19
5.2 Gas sampling.21
5.3 Sensor.23
5.4 Signal-transmission .24
5.5 Input of control unit .27
5.6 Signal processing in the control unit .29
5.7 Output of the control unit .32
6 Characterisation of safety requirement .35
6.1 General .35
6.2 Characterisation of safety function .36
6.3 Characterisation of safety integrity.37
6.4 Determination of SIL-capabilities for a safety function.38
6.5 Determination of hardware failure rates for a safety function .41
6.6 Safety performance requirements .42
7 Information requirements .42
7.1 Information delivered by the manufacturer of the gas detection system .42
7.2 Information delivered by the user of the gas detection system.43
8 Validation.43
Annex A (informative) Gas detection systems as part of a safety-related system .44
Annex B (normative) Transformation of the SIL-capabilities of gas detection systems .49
Annex C (normative) Transformation from generic standard requirements to modules .50
Annex D (normative) Management of functional safety.53
Annex E (informative) Determination of SIL-capability of a safety function of the gas detection system.55
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EN 50402:2005 – 4 –
Table 1 - Fault tolerance for complex modules according EN 61511-1, Table 5 .14
Table 2 - Fault tolerance for complex modules according EN 61508-2, Table 3 .14
Table 3 - Minimum hardware fault tolerance for simple modules according EN 61511-1, Table 6.15
Table 4 - Fault tolerance for simple modules according EN 61508-2, Table 2.15
Table 5 - Diagnostic measures for program sequence monitoring from EN 61508-2 .19
Table 6 - Diagnostic measures for memory from EN 61508-2.20
Table 7 - Determination of SIL-capability for a parallel chain block.40
Table B.1 - Transformation SIL-capability of EN 50402 to SIL of EN 61508.49
Table B.2 - Transformation SIL-capability of EN 50402 to Categories of EN ISO 13849-1 .49
Table E.1 - Determination of SIL-capability for a parallel chain block .57
Figure 1 - Definitions of measuring point, measuring group and measuring location.10
Figure 2 - Overview of safety-related system .16
Figure 3 - Modules of a gas detection system .18
Figure 4 - Implementation of a gas detection system in the overall safety life cycle (EN 61508-1: 7.1).36
Figure 5 - Single and parallel chains.38
Figure 6 – Handling of complex modules in a redundant structure .41
Figure A.1 - Functional safety of modules and systems (Proof test interval and mean time to repair (MTTR)
are not shown in the figure although they have to be included into the considerations) .47
Figure E.1 - Step 1 - Linkage of modules .55
Figure E.2 - Step 2 - Identification of modules necessary for the safety function.55
Figure E.3 - Step 3 - Elimination of modules and linkages without influence on the safety function.56
st
Figure E.4 - Step 4 (1 loop) - Summarising of single chains .56
st
Figure E.5 - Step 5 (1 loop) - Summarising of parallel chains .56
st
Figure E.6 - Step 6 (1 loop) - Adaptation of block diagram structure.58
nd
Figure E.7 - Step 4 (2 loop) - Summarising of single chains.58
nd
Figure E.8 - Step 5 (2 loop) - Summarising of parallel chains.58
nd
Figure E.9 - Step 6 (2 loop) - Adaptation of block diagram structure – No action required .58
rd
Figure E.10 - Step 4 (3 loop) - Summarising of single chains .58
rd
Figure E.11 - Step 5 (3 loop) - Summarising of parallel chains .59
rd
Figure E.12 - Step 6 (3 loop) - Adaptation of block diagram structure – No action required.59
th
Figure E.13 - Step 4 (4 loop) - Summarising of single chains – End of procedure.59
Figure E.14 - Step 1 - Linkages between modules for the example.60
Figure E.15 - Step 2 - Identification of modules with influence on the safety function.60
Figure E.16 - Step 3 - Elimination of modules and linkages without influence on the safety function .60
Figure E.17 - Step 4 - Summarising of single chains .61
Figure E.18 - Step 5 - Summarising of parallel chains – End of procedure.61
Figure E.19 - Step 2 - Identification of modules with influence on the safety function.61
Figure E.20 - Step 3 - Elimination of modules and linkages without influence on the safety function .62
st
Figure E.21 - Step 4 (1 loop) - Summarising of single chains .62
st
Figure E.22 - Step 5 (1 loop) - Summarising of parallel chains .62
st
Figure E.23 - Step 6 (1 loop) - Adaptation of block diagram structure – No action required .63
nd
Figure E.24 - Step 4 (2 loop) - Summarising of single chains – End of procedure .63
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Introduction
This European Standard specifies requirements for functional safety of gas detection systems and
encompasses criteria for reliability, avoidance of faults and fault tolerance. Functional safety is that part of the
overall safety related to the measures within the gas detection system to avoid or to handle failures in such a
manner that the safety function will be assured. This includes not only design requirements of the gas
detection system but also information requirements for planning, putting into operation, maintenance and
repair.
Gas detection systems will fail to function if dangerous failures occur in the equipment used. Failure to
function will also occur if such systems are not installed or maintained in an appropriate manner. In some
applications failures of this type will dominate the functional safety achieved. This European Standard is only
targeted at reducing equipment failures to levels appropriate to the application. Users of gas detection
systems will therefore need to ensure installation and maintenance of such systems is carried out according
to requirements. This European Standard does not specify the physical positioning of sensors.
Gas detection systems may differ strongly in structure, complexity and performance. They may not be
handled in a uniform manner like low complexity devices. A general specification of requirements is not
possible on that basis.
Gas detection systems therefore need to be divided into functional modules for validation to ensure that
systems which have different structures are handled by appropriate procedures. A gas detection system will
not normally include all modules covered by this European Standard. Requirements are specified for each of
these modules in terms of hierarchical levels which represent one of the constituents of functional safety
performance. The hierarchical levels are termed as SIL-capabilities, with SIL-capability 1 representing the
minimum and SIL-capability 4 the maximum levels of performance to comply with this standard. The SIL-
capability of a module is related to the maximum safety integrity level that can be claimed for a safety function
which uses modules of that specified SIL-capability. Modules will be characterised in terms of the SIL-
capability. Information is also required on failure rate characteristics of modules or related physical
components to enable the overall performance of a gas detection system to be determined. In this way both
random failures of hardware components and systematic failures in hardware and software are taken account
of. The standard also specifies the requirements that will enable determination of whether the gas detection
system have a low enough failure rate when used in conjunction with other equipment necessary for
functional safety.
This European Standard will enable the functional safety characteristics of the gas detection system to be
determined from the characteristics of its modules and components (see Annex C). This will enable a gas
detection system to be used as a part of an overall safety system.
The characterisation including the determination of a SIL-capability and failure rate data will only need to be
carried out once for a particular design.
After characterisation of each module and component the properties of the whole gas detection system will
be specified depending on the chosen safety function. The procedure for determining the SIL-capability of the
safety function of a gas detection system will only need to be repeated for each new combination of modules
and components. Different combination of equivalent modules may lead to gas detection systems which
reach different SIL-capabilities.
A flexible adoption of the gas detection system to different applications will be possible without repeating all
steps of the validation procedure for each new configuration.
This European Standard does not include requirements for availability which will need to be considered
separately.
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EN 50402:2005 – 6 –
1 Scope
This European Standard is applicable to fixed gas detection systems for the detection and measurement of
1)
flammable or toxic gases or vapours or oxygen.
This European Standard supplements the requirements of the European Standards for electrical apparatus
for the detection and measurement of flammable gases, vapours (e.g. EN 61779 or EN 50241), toxic gases
(e.g. EN 45544) or oxygen (e.g. EN 50104).
NOTE 1 These European Standards will be mentioned in the text as "metrological standards".
NOTE 2 The examples above show the state of the standardisation for industrial applications at the time of publishing this European
Standard. There may be other metrological standards covering other application fields, for which this standard is also applicable.
NOTE 3 For fixed apparatus used for safety applications with a SIL requirement up to 1 and for portable apparatus the European
Standard EN 50271 may be applied instead of this European Standard.
Applying the above mentioned metrological standards will ensure the measuring performance is adequate in
normal operation of a gas detection system. Additionally the requirements of this European Standard address
the functional safety of gas detection systems and encompass criteria for reliability, fault tolerance and
avoidance of systematic faults.
This European Standard will lead to the characterisation of the gas detection system by a SIL-capability and
related hardware failure rate representing a hierarchical order of safety levels. This will allow the user to
incorporate the gas detection system into an overall safety system according to the safety integrity levels of
EN 61508 or the categories of EN ISO 13849-1 (see Annex B).
This European Standard is a product standard which is based on EN 61508 and includes additional
requirements of EN ISO 13849-1. It covers part of the phase 9 “realisation” of the overall safety lifecycle
defined in EN 61508-1.
This European Standard is applicable for gas detection systems, which may consist of the following functional
units:
− gas-sampling;
− sensor;
− signal transmission;
− input to control unit;
− signal processing in control unit;
− output from control unit.
This European Standard does not specify requirements for the installation and maintenance of gas detection
systems. It also does not specify the physical positioning of sensors.
This European Standard does not specify which SIL-capability is sufficient for which application.
NOTE 4 The SIL-capability required for an application will be specified by the user (see Annexes A and B).
1)
For the purpose of this standard the word ‘toxic’ covers ‘very toxic’, ‘toxic’, ‘harmful’, ‘corrosive‘, ‘irritating‘, ‘sensitising‘,
‘carcinogenic‘, ‘mutagenic‘ and ‘teratogenic‘.
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2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
2)
Safety of machinery – Safety related parts of control systems – Part 1: General
EN ISO 13849-1
principles of design (ISO 13849-1:1999)
EN 45544-1 1999 Workplace atmospheres - Electrical apparatus used for the direct detection and
direct concentration measurement of toxic gases and vapours
Part 1: General requirements and test methods
EN 45544-2 1999 Part 2: Performance requirements for apparatus used for measuring
concentrations in the region of limit values
EN 45544-3 1999 Part 3: Performance requirements for apparatus used for measuring
concentrations well above limit values
EN 45544-4 1999 Part 4: Guide for selection, installation, use and maintenance
EN 50073 1999 Guide for selection, installation, use and maintenance of apparatus for the
detection and measurement of combustible gases or oxygen
EN 50104 2002 Electrical apparatus for the detection and measurement of oxygen -
Performance requirements and test methods
EN 50241-1 1999 Specification for open path apparatus for the detection of combustible or toxic
gases and vapours
Part 1: General requirements and test methods
EN 50241-2 1999 Part 2: Performance requirements for apparatus for the detection of combustible
gases
EN 61508-1 2001 Functional safety of electrical / electronic / programmable electronic safety-
related systems
Part 1: General requirements (IEC 61508-1:1998)
EN 61508-2 2001 Part 2: Requirements for electrical/electronic/programmable electronic safety-
related systems (IEC 61508-2:2000)
EN 61508-3 2001 Part 3: Software requirements (IEC 61508-3:1998)
EN 61508-4 2001 Part 4: Definitions and abbreviations (IEC 61508-4:1998)
EN 61508-5 2001 Part 5: Examples of methods for the determination of safety integrity levels
(IEC 61508-5:1998)
EN 61508-6 2001 Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3
(IEC 61508-6:2000)
EN 61508-7 2001 Part 7: Overview of techniques and measures (IEC 61508-7:2000)
EN 61511-1 2004 Functional safety – Safety instrumented systems for the process industry sector
Part 1: Framework, definitions, system, hardware and software requirements
(IEC 61511-1:2003)
EN 61779-1 2000 Electrical apparatus for the detection and measurement of flammable gases
Part 1: General requirements and test methods (IEC 61779-1:1998, mod.)
EN 61779-2 2000 Part 2: Performance requirements for group I apparatus indicating a volume
fraction up to 5 % methane in air (IEC 61779-2:1998, mod.)
2)
At draft stage.
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EN 50402:2005 – 8 –
EN 61779-4 2000 Part 4: Performance requirements for group II apparatus indicating a volume
fraction up to 100 % lower explosive limit (IEC 61779-4:1998, mod.)
EN 61779-5 2000 Part 5: Performance requirement for group II apparatus indicating a volume
fraction up to 100 % gas (IEC 61779-5:1998, mod.)
3 Definitions
For the purpose of this document the definitions given in EN 61779 and EN 61508-4 apply. Some definitions
are repeated for convenience. Some definitions from EN 61508-4 are adapted to gas detection.
3.1
functional safety (EN 61508-4: 3.1.9)
part of the overall safety relating to the equipment under control (EUC) and the EUC control system which
depends on the correct functioning of the electrical/electronic/programmable electronic safety-related
systems (E/E/PES), other technology safety-related systems and external risk reduction facilities
NOTE 1 The EUC is the equipment under control or the process that the gas detection system is assuring the safety of (EN 61508-4:
3.2.3).
NOTE 2 The EUC control system responds to input signals from the process and generates output signals causing the EUC to
operate in the desired manner (EN 61508-4: 3.3.4).
NOTE 3 The gas detection system is part of the E/E/PES.
3.2
safety function of a gas detection system
function (inclusive from gas sampling to output of the gas detection system) implemented by the gas
detection system to enable the safety-related system to achieve a safe state of the EUC
3.3
safety related part
any part, e. g. module or element, which is necessary to implement the required safety function of a gas
detection system
3.4
fault (EN 61508-4: 3.6.1)
abnormal condition that may cause a reduction in, or loss of, the capability of a functional unit to perform a
required function
3.5
fault tolerance (EN 61508-4: 3.6.3)
ability of a functional unit to continue to perform a required function in the presence of faults or errors
3.6
SIL-capability
the SIL-capability is determined by the measures and techniques for avoidance and control of faults in both,
hardware and software. The SIL-capability number is a property of an element, a module, a combination of
modules or of one or several safety function(s) of a gas detection system. There are four different SIL-
capability numbers existing from 1 to 4, with SIL-capability 4 representing the highest level of safety
performance
3.7
module
modules form the functional units of a gas detection system. A module executes a defined part of the
functionality within the gas detection system. It consists of one or more elements
NOTE Modules may be simple or complex (see 4.2).
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3.8
element
functional sub-unit of a module
NOTE The software or a part of it may be considered as an element.
3.9
component
the hardware of a gas detection system consists of components which are physically separable
subassemblies
NOTE Depending of the specific realisation an element of a functional module may belong to different hardware components.
3.10
periphery
components of the total system which do not belong to the gas detection system but are related with it
NOTE 1 See Figure 2.
NOTE 2 Periphery is not covered by this European Standard.
3.11
measuring point
location of a single sensor aspirated by diffusion or by a probe
NOTE See Figure 1.
3.12
measuring group
redundant combination of two measuring points belonging to one measuring location
NOTE See Figure 1.
3.13
measuring location
area containing one or more measuring points in which similar gas concentrations are expected
NOTE 1 See Figure 1.
NOTE 2 According to the definitions 3.11 to 3.13 it is possible that one sensor serves as a redundant partner for several other
sensors.
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SIST EN 50402:2005
EN 50402:2005 – 10 –
Location
Group
A
Point 1 Point 2
Group B Group C
Point 3
Figure 1 - Definitions of measuring point, measuring group and measuring location
3.14
measured signal
sensor signal in analogue or digital representation which may or may not be pre-amplified
3.15
measured value
processed measured signal including physical unit (e. g. % LEL). A measured value may be formed from a
single signal or a combination of several measurement signals. The combined measured signals may
represent different physical units, e. g. gas concentration and temperature
3.16
status signal
electrical signal which indicates operational states, switching status of devices, adherence of general
conditions (e. g. allowed temperature range or gas flow) within a module or to another module of the gas
detection system
3.17
alarm signal
electrical signal which indicates the alarm state of one or more measurement points. The alarm signal will be
processed either in the gas detection system (e. g. release of switching) or transmitted to the periphery
NOTE Alarm signals are handled separately from other signals because they are generally handled with higher priority.
3.18
special state
every state of a measurement point, module, control unit or the total gas detection system in which the
monitoring of gas concentration does not take place, e. g. put into operation, calibration mode or fault
condition
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