Electrical apparatus for the detection and measurement of combustible gases, toxic gases or oxygen - Requirements and tests for apparatus using software and/or digital technologies

This European Standard specifies minimum requirements and tests for electrical apparatus for the detection and measurement of combustible gases, toxic gases or oxygen using software and/or digital technologies.
This European Standard is applicable to fixed, transportable and portable apparatus intended for use in domestic premises as well as commercial and industrial applications.
This European Standard does not apply to external sampling systems, or to apparatus of laboratory or scientific type, or to apparatus used only for process control purposes.
This European Standard supplements the requirements of the European Standards for the detection and measurement of flammable gases and vapours (e.g. EN 60079 29 1, EN 60079-29-4, EN 50194 1, EN 50194 2), toxic gases (e.g. EN 45544 series, EN 50291 1, EN 50291 2) or oxygen (e.g. EN 50104).
NOTE 1 These European Standards will be mentioned in this European Standard as "metrological standards".
NOTE 2 The examples above show the state of the standardisation for gas detection apparatus at the time of publishing this European Standard. There may be other metrological standards for which this European Standard is also applicable.
This European Standard is a product standard which is based on EN 61508 series. It covers part of the phase 10 "realisation" of the overall safety life cycle defined in EN 61508 1.
Additional requirements are specified if compliance with safety integrity level 1 (SIL 1) according to EN 61508 series is claimed for fixed or transportable apparatus for low demand mode of operation.
NOTE 3 Compliance with safety integrity level 1 (SIL 1) for portable apparatus is not considered because portable apparatus cannot make an automatic executive action.
It is recommended to apply this European Standard for apparatus used for safety applications with SIL-requirement 1 instead of EN 50402. However, the technical requirements of EN 50271 and EN 50402 are the same for SIL 1.
NOTE 4 For apparatus used for safety applications with SIL-requirements higher than 1 EN 50402 is applicable.

Elektrische Geräte für die Detektion und Messung von brennbaren Gasen, giftigen Gasen oder Sauerstoff - Anforderungen und Prüfungen für Warngeräte, die Software und/oder Digitaltechnik nutzen

Diese Europäische Norm legt Mindestanforderungen und Prüfungen für elektrische Geräte für die Detektion und Messung von brennbaren Gasen, toxischen Gasen oder Sauerstoff fest, die Software und/oder Digitaltechnik nutzen. Diese Europäische Norm ist anwendbar auf ortsfeste, transportable und tragbare Geräte, die für die Verwendung in Wohnhäusern oder in gewerblichen oder industriellen Anwendungen vorgesehen sind, sowie auf deren softwaregesteuertes sicherheitsrelevantes Zubehör. Diese Europäische Norm gilt nicht für externe Entnahmesysteme, die kein Zubehör sind, oder für Labor- oder wissenschaftliche Geräte sowie für Geräte, die nur zur Prozesssteuerung eingesetzt werden. Diese Europäische Norm ergänzt die Anforderungen der Europäischen Normen für die Detektion und Messung von brennbaren Gasen und Dämpfen (z. B. EN 60079 29 1, EN 60079 29 4, EN 50194 1, EN 50194 2), toxischen Gasen (z. B. Reihe EN 45544, EN 50291 1, EN 50291 2) 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 Gaswarngeräte zum Zeitpunkt der Veröffentlichung dieser Europäischen Norm dar. Es können weitere messtechnische Normen bestehen, auf die diese Europäische Norm ebenfalls anwendbar ist. Diese Europäische Norm stellt eine Produktnorm auf Grundlage der Reihe EN 61508 dar. Sie deckt Teile der Phase 10 "Realisierung" des in EN 61508 1 definierten Gesamt-Sicherheitslebenszyklus ab. Zusätzliche Anforderungen sind festgelegt, wenn eine Übereinstimmung mit dem Sicherheits-Integritätslevel 1 (SIL 1) nach der Reihe EN 61508 für ortsfeste oder transportable Geräte in der Betriebsart mit niedriger Anforderungsrate angegeben wird. Diese können ebenso auf tragbare Geräte angewendet werden, die eine automatische Schalthandlung ausführen können. Es wird empfohlen, diese Europäische Norm für Geräte zum Einsatz in sicherheitsgerichteten Anwendungen mit SIL-Anforderung 1 anstelle der EN 50402 anzuwenden. Die technischen Anforderungen der EN 50271 und der EN 50402 sind jedoch für SIL 1 gleich. ANMERKUNG 3 Für Geräte zum Einsatz in sicherheitsgerichteten Anwendungen mit SIL-Anforderungen größer als 1 ist die EN 50402 anwendbar.

Appareils électriques de détection et de mesure des gaz combustibles, des gaz toxiques ou de l'oxygène - Exigences et essais pour les appareils utilisant un logiciel et/ou des technologies numériques

La présente Norme européenne spécifie les exigences minimales et les essais pour les appareils électriques de détection et de mesure de gaz combustibles, de gaz toxiques ou d'oxygène qui utilisent un logiciel et/ou des technologies numériques. La présente Norme européenne s’applique aux appareils fixes, transportables et portables destinés à être utilisés dans des locaux à usage domestique ainsi qu’à applications commerciales et industrielles et leurs accessoires contrôlés par des logiciels relatifs à la sécurité. La présente Norme européenne ne s’applique ni aux systèmes d’échantillonnage externe qui ne sont pas des accessoires, ni aux appareils de laboratoire ou à vocation scientifique, ni aux appareils utilisés uniquement à des fins de maîtrise des processus. La présente Norme européenne complète les exigences des Normes européennes pour la détection et le mesurage des vapeurs et des gaz inflammables (par exemple, l’EN 60079-29-1, l’EN 60079-29-4, l’EN 50194-1, l’EN 50194-2), des gaz toxiques (par exemple, la série EN 45544, l’EN 50291-1, l’EN 50291-2) ou de l’oxygène (par exemple, l’EN 50104). NOTE 1: Dans la présente Norme européenne, ces Normes européennes sont appelées « normes métrologiques ». NOTE 2: Les exemples susmentionnés présentent l'état de la normalisation pour les appareils de détection de gaz au moment de la publication de la présente Norme européenne. La présente Norme européenne peut également s’appliquer à d’autres normes métrologiques. La présente Norme européenne est une norme de produit fondée sur la série EN 61508. Elle traite en partie de la phase 10 « réalisation » du cycle de vie de sécurité globale définie dans l’EN 61508-1. Des exigences supplémentaires sont spécifiées si la conformité au niveau d'intégrité de sécurité 1 (SIL 1) conformément à la série EN 61508 est revendiquée pour un appareil fixe ou transportable pour un mode de fonctionnement à faible sollicitation. Elles s’appliquent également aux appareils portables pouvant exécuter une action automatique. Il est recommandé d’appliquer la présente Norme européenne plutôt que l’EN 50402 pour des appareils utilisés dans des applications de sécurité exigeant le niveau de sécurité 1 (SIL 1). Toutefois, les exigences techniques de l’EN 50271 et de l’EN 50402 sont identiques pour le niveau SIL 1. NOTE 3: Pour des appareils utilisés dans des applications de sécurité exigeant un SIL supérieur à 1, l’EN 50402 s’applique.

Električne naprave za odkrivanje in merjenje vnetljivih plinov, strupenih plinov ali kisika - Zahteve in preskusi za naprave s programsko opremo in/ali digitalno tehnologijo

Ta evropski standard določa minimalne zahteve in preskuse v zvezi z električnimi napravami za odkrivanje in merjenje vnetljivih plinov, strupenih plinov ali kisika z uporabo programske opreme in/ali digitalne tehnologije.
Ta evropski standard se uporablja za nepremične, premične in prenosne naprave, namenjene za uporabo v bivalnih prostorih ter za poslovne in industrijske namene.
Ta evropski standard se ne uporablja za zunanje sisteme vzorčenja, laboratorijske ali znanstvene naprave in naprave, ki se uporabljajo samo za namene nadziranja procesov.
Ta evropski standard dopolnjuje zahteve evropskih standardov za odkrivanje in merjenje vnetljivih plinov ter hlapov (npr. EN 60079 29 1, EN 60079-29-4, EN 50194 1, EN 50194 2), strupenih plinov (npr. skupina standardov EN 45544, EN 50291 1, EN 50291 2) ali kisika (npr. EN 50104).
OPOMBA 1: Ti evropski standardi bodo v tem evropskem standardu navedeni kot »meroslovni standardi«.
OPOMBA 2: Spodnji primeri prikazujejo stanje standardizacije naprav za odkrivanje plina v času objave tega evropskega standarda. Ta evropski standard se morda lahko uporablja tudi za druge meroslovne standarde.
Ta evropski standard je standard za proizvode, ki temelji na skupini standardov EN 61508. Obravnava del »realizacije« 10. faze celotnega varnostnega življenjskega cikla, opredeljenega v standardu EN 61508 1.
Dodatne zahteve so določene, če je za nepremične ali premične naprave, ki delujejo na način z nizkimi zahtevami, navedena skladnost s stopnjo varnostne celovitosti 1 (SIL 1) v skladu s skupino standardov EN 61508.
OPOMBA 3: Skladnost s stopnjo varnostne celovitosti 1 (SIL 1) za prenosne naprave ni obravnavana, ker prenosne naprave ne morejo samodejno izvajati dejanj.
Priporočljivo je, da se ta evropski standard uporablja za naprave, namenjene varnostni uporabi, z zahtevo SIL 1 namesto standarda EN 50402. Vendar tehnične zahteve iz standarda EN 50271 in EN 50402 veljajo tudi za SIL 1.
OPOMBA 4: Za naprave, namenjene varnostni uporabi, z zahtevami SIL, večjimi od 1, se uporablja standard EN 50402.

General Information

Status
Published
Publication Date
03-Sep-2018
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
16-Jul-2018
Due Date
20-Sep-2018
Completion Date
04-Sep-2018

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SLOVENSKI STANDARD
SIST EN 50271:2018
01-oktober-2018
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SIST EN 50271:2010

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Electrical apparatus for the detection and measurement of combustible gases, toxic

gases or oxygen - Requirements and tests for apparatus using software and/or digital

technologies
Elektrische Geräte für die Detektion und Messung von brennbaren Gasen, giftigen
Gasen oder Sauerstoff - Anforderungen und Prüfungen für Warngeräte, die Software
und/oder Digitaltechnik nutzen

Appareils électriques de détection et de mesure des gaz combustibles, des gaz toxiques

ou de l'oxygène - Exigences et essais pour les appareils utilisant un logiciel et/ou des

technologies numériques
Ta slovenski standard je istoveten z: EN 50271:2018
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
SIST EN 50271:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 50271:2018
---------------------- Page: 2 ----------------------
SIST EN 50271:2018
EUROPEAN STANDARD EN 50271
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2018
ICS 13.320 Supersedes EN 50271:2010
English Version
Electrical apparatus for the detection and measurement of
combustible gases, toxic gases or oxygen - Requirements and
tests for apparatus using software and/or digital technologies

Appareils électriques de détection et de mesure des gaz Elektrische Geräte für die Detektion und Messung von

combustibles, des gaz toxiques ou de l'oxygène - brennbaren Gasen, giftigen Gasen oder Sauerstoff -

Exigences et essais pour les appareils utilisant un logiciel Anforderungen und Prüfungen für Warngeräte, die Software

et/ou des technologies numériques und/oder Digitaltechnik nutzen

This European Standard was approved by CENELEC on 2017-11-06. 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, Serbia, 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: Rue de la Science 23, B-1040 Brussels

© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 50271:2018 E
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SIST EN 50271:2018
EN 50271:2018 (E)
Contents

European foreword ................................................................................................................................. 3

Introduction ............................................................................................................................................. 4

1 Scope ............................................................................................................................................... 5

2 Normative references ..................................................................................................................... 5

3 Terms and definitions .................................................................................................................... 6

4 Design principles ............................................................................................................................ 8

4.1 Basic requirements ................................................................................................................. 8

4.1.1 General ..................................................................................................................... 8

4.1.2 Analogue/digital interface ......................................................................................... 8

4.1.3 Numerical errors ....................................................................................................... 8

4.1.4 Measuring operation ................................................................................................. 8

4.1.5 Special state indication ............................................................................................. 8

4.2 Displays .................................................................................................................................. 9

4.2.1 General ..................................................................................................................... 9

4.2.2 Indication of messages ............................................................................................. 9

4.2.3 Indication of measured values ................................................................................ 10

4.3 Software................................................................................................................................10

4.3.1 General ................................................................................................................... 10

4.3.2 Re-used or commercial operating systems ............................................................ 11

4.3.3 Software requirements ............................................................................................ 11

4.3.4 Requirements for software documentation ............................................................. 12

4.3.5 Requirements for the software development process ............................................ 12

4.4 Hardware ..............................................................................................................................20

4.5 Digital data transmission between components of apparatus ..............................................20

4.6 Test routines .........................................................................................................................20

4.7 Instruction manual ................................................................................................................22

4.8 Additional requirements for compliance with SIL 1 ..............................................................23

5 Test of the digital unit ..................................................................................................................24

5.1 General .................................................................................................................................24

5.2 Verification of functional concept ..........................................................................................25

5.3 Performance test ..................................................................................................................25

Annex A (normative) Hardware-software integration test ...............................................................27

A.1 Functional testing/Black-box testing ..........................................................................................27

A.2 Equivalence class test with boundary value analysis ..............................................................27

Annex ZY (normative) Significant changes between this European Standard and

EN 50271:2010 ...............................................................................................................................29

Annex ZZ (informative) Relationship between this European standard and the essential

requirements of Directive 2014/34/EU aimed to be covered ....................................................31

Bibliography ..........................................................................................................................................32

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SIST EN 50271:2018
EN 50271:2018 (E)
European foreword

This document (EN 50271:2018) has been prepared by CLC/SC 31-9, “Electrical apparatus for the

detection and measurement of combustible gases to be used in industrial and commercial potentially

explosive atmospheres”, of CLC/TC 31, “Electrical apparatus for potentially explosive atmospheres”,

and by CLC/TC 216 “Gas detectors”.
The following dates are fixed:
• latest date by which this document has to be (dop) 2018-12-15
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) 2021-06-15
conflicting with this document have to
be withdrawn
This document supersedes EN 50271:2010.

The State of the Art is included in Annex ZY “Significant changes between this European Standard

and EN 50271:2010” which lists all changes to EN 50271:2010.

This document has been prepared under a mandate given to CENELEC by the European Commission

and the European Free Trade Association and covers essential requirements of EU Directive

2014/34/EU.

For the relationship with EU Directive see informative Annex ZZ, which is an integral part of this

document.
---------------------- Page: 5 ----------------------
SIST EN 50271:2018
EN 50271:2018 (E)
Introduction

This European Standard specifies minimum requirements for functional safety of gas detection

apparatus using software and/or digital technologies and defines criteria for reliability and avoidance of

faults. Functional safety is that part of the overall safety which is related to the measures within the

gas detection apparatus to avoid or to handle failures in such a manner that the safety function will be

ensured.

Gas detection apparatus will fail to function if dangerous failures occur. The aim of this European

Standard is to reduce the risk of dangerous equipment failures to levels appropriate to typical

applications of such apparatus.

Failure to function will also occur if such apparatus are not selected, installed or maintained in an

appropriate manner. In some applications failures of this type will dominate the functional safety

achieved. Users of gas detection apparatus will therefore need to ensure that selection, installation

and maintenance of such apparatus are carried out appropriately. Guidance for the selection,

installation, use and maintenance of gas detection apparatus are set out in EN 60079-29-2 and

EN 45544-4, respectively.

This European Standard does not include requirements for operational availability which will need to

be considered separately.

Regarding the requirements for the software development process, this European Standard specifies

a practical approach to comply with the requirements of EN 61508-3 for SIL 1 without using this

generic standard.

This European standard also specifies additional optional requirements for compliance with SIL 1 in

low demand mode operation. The following apparatus or gas detection systems are not fully covered

by this standard:

– apparatus at SIL 1 when the apparatus or gas detection system contains functionality not covered

by EN 50271
– apparatus at SIL 1 high demand mode operation
– apparatus at SIL 2 and SIL 3;

For such apparatus or gas detection systems the European standard EN 50402 should be used

instead of EN 50271. EN 50402 includes all requirements of EN 50271.
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SIST EN 50271:2018
EN 50271:2018 (E)
1 Scope

This European Standard specifies minimum requirements and tests for electrical apparatus for the

detection and measurement of combustible gases, toxic gases or oxygen using software and/or digital

technologies.

This European Standard is applicable to fixed, transportable and portable apparatus intended for use

in domestic premises as well as commercial and industrial applications and their software-controlled

safety related accessories.

This European Standard does not apply to external sampling systems which are not accessories, or to

apparatus of laboratory or scientific type, or to apparatus used only for process control purposes.

This European Standard supplements the requirements of the European Standards for the detection

and measurement of flammable gases and vapours (e.g. EN 60079-29-1, EN 60079-29-4, EN 50194-

1, EN 50194-2), toxic gases (e.g. EN 45544 series, EN 50291-1, EN 50291-2) or oxygen (e.g.

EN 50104).

NOTE 1 These European Standards will be mentioned in this European Standard as “metrological standards”.

NOTE 2 The examples above show the state of the standardization for gas detection apparatus at the time of

publishing this European Standard. There may be other metrological standards for which this European Standard

is also applicable.

This European Standard is a product standard which is based on the EN 61508 series. It covers part

of the phase 10 “realisation” of the overall safety life cycle defined in EN 61508-1.

Additional requirements are specified if compliance with safety integrity level 1 (SIL 1) according to the

EN 61508 series is claimed for fixed or transportable apparatus for low demand mode of operation.

They can also be applied to portable apparatus which are able to perform an automatic executive

action.

It is recommended to apply this European Standard for apparatus used for safety applications with

SIL-requirement 1 instead of EN 50402. However, the technical requirements of EN 50271 and

EN 50402 are the same for SIL 1.

NOTE 3 For apparatus used for safety applications with SIL-requirements higher than 1 EN 50402 is applicable.

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.

EN 50402:2017, Electrical apparatus for the detection and measurement of combustible or toxic gases

or vapours or of oxygen - Requirements on the functional safety of gas detection systems

EN 60079-29-1:2016, Explosive atmospheres - Part 29-1: Gas detectors - Performance requirements

of detectors for flammable gases

EN 61508-1:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 1: General requirements

EN 61508-2:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 2: Requirements for electrical/electronic/programmable electronic safety-related

systems

EN 61508-3:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 3: Software requirements

EN 61508-4:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 4: Definitions and abbreviations
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SIST EN 50271:2018
EN 50271:2018 (E)

EN 61508-5:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 5: Examples of methods for the determination of safety integrity levels

EN 61508-6:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 6: Guidelines on the application of IEC 61508-2 and IEC 61508-3

EN 61508-7:2010, Functional safety of electrical/electronic/programmable electronic safety-related

systems - Part 7: Overview of techniques and measures
3 Terms and definitions

For the purposes of this document, the terms and definitions given in EN 60079-29-1:2016 and the

following apply.
3.1
digital unit

part of an electrical apparatus in which data is processed digitally. Analogue-digital(A/D)-converters

and digital-analogue(D/A)-converters as interfaces to analogue units of the apparatus belong to the

digital unit
3.2
special state

all states of the apparatus other than those in which monitoring of gas concentration and/or alarming is

intended, for example the special states of warm-up, calibration mode or fault condition

[SOURCE: EN 60079-29-1:2016, 3.5.4]
3.3
software

intellectual creation comprising the programs, procedures, rules and associated documentation

pertaining to the operation of the digital unit
3.4
failure

termination of the ability of a functional unit to provide a required function or operation of a functional

unit in any way other than as required
[SOURCE: EN 61508-4:2010, 3.6.4, mod.]
3.5
parameters

settings by the manufacturer or user which affect the operation of the apparatus, e.g. changing of the

alarm set points or measuring ranges. Parameter options are included in the hardware and/or software

during design of the apparatus. Changes of parameter settings are not modifications of the software.

In the software several different levels of permission to read or to change parameters may exist

3.6
specified range of input values

range of analogue input values corresponding to the digital output range of an A/D-converter or range

of digital input values corresponding to the analogue output range of a D/A-converter. The minimum

and maximum digital values of the converter are not to be considered to be within the specified range

because minima and maxima correspond to stuck-at faults which have to be detected by the

apparatus (see 4.1.4)
3.7
defined range of input values

range of input values defined by the manufacturer of the apparatus to be valid; the defined range is a

sub-range of the specified range of input values
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SIST EN 50271:2018
EN 50271:2018 (E)
3.8
output data

result of the digital data processing, which is used for driving the output interfaces

Note 1 to entry: Output interfaces may be analogue or digital displays, analogue or digital outputs and/or alarm

indicators or relays.
3.9
output signal
analogue or digital signal which is available at an output interface
3.10
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 measured signals. The combined measured signals

may represent different physical units, e.g. gas concentration and temperature
3.11
smallest deviation of indication

value which is determined by the applicable metrological standards. In metrological standards the

allowed tolerances for deviation of indication during type testing are given. If there are different

requirements for the tolerances in different applicable metrological standards the smallest tolerance is

the “smallest deviation of indication”

Note 1 to entry: The smallest deviation of indication is basis for the required resolution of measured signals

which use digital transmission and data processing to meet the requirements of the metrological standards when

using digital technologies
[SOURCE: EN 50402:2017, 3.22]
3.12
message

indication on a display which gives an information about the status of the apparatus (e.g. alarm,

special state, warning)
3.13
software component

part of the program that consists of one or several software modules and that can also interact with

other such constructs
3.14
software module

construct that consists of subroutines and/or data declarations and that can also interact with other

such constructs
3.15
safety function of a gas detection apparatus

any function (inclusive from gas sampling to output of the gas detection apparatus) implemented by

the gas detection apparatus which is related to safety as defined by the manufacturer

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SIST EN 50271:2018
EN 50271:2018 (E)
4 Design principles
4.1 Basic requirements
4.1.1 General

The metrological standards define performance requirements for gas detection apparatus which have

direct implications on the digital units and software which may be used in such apparatus. This

subclause specifies basic requirements to digital units and software to fulfil the metrological standards.

4.1.2 Analogue/digital interface

The relationship between corresponding analogue and digital values shall be unambiguous. The

output range shall be capable of coping with the defined range of input values. Input values outside

the specified range of the converter shall not result in a valid measured value. A/D- and D/A-converter

quantisation steps shall be chosen so that the requirements in 4.1.3 for the accuracy of data

representation will be fulfilled. The design shall take into account the maximum possible A/D- and D/A-

converter errors.

NOTE This assessment need not include environmental interferences to the A/D- or D/A-converters, e.g.

temperature variation, since environmental testing is covered by the metrological standards.

Outputs at the limits of the specified range of D/A-converters shall result in output signals which are

described as fault signal by the manufacturer.
4.1.3 Numerical errors

Deviations of measured values arising from quantisation, rounding and calculation errors shall be

estimated assuming worst case conditions.

These worst case conditions shall be evaluated in detail. For example, nonlinear behaviour of the

sensor signal with gas concentration, ageing of sensors, varying sensitivities for different gases and

signal variation with temperature, pressure or humidity shall be taken into consideration.

The estimated deviation of measured values shall not be greater than 50 % of the smallest deviation

of indication.

NOTE The deviation of measured values arising from the digital unit will be typically much lower than 50 % of

the smallest deviation of indication. Deviations arising from other sources (e.g. sensor) are expected to be

dominant.
4.1.4 Measuring operation

During data processing the digital unit shall automatically control the specified input data range and

handle range violations. The minimum and maximum digital values of the converter shall not be

considered to be within the specified range in order to detect stuck-at faults.

The software design and verification shall guarantee that range violations for internal and output data

do not occur. Otherwise the digital unit shall automatically control the allowed data ranges and handle

range violations.

During measuring operation, the maximum overall time of four successive updates of the measured

value and all safety relevant output signals shall not exceed the response time t90 of the apparatus or,

for alarm only apparatus, the minimum time to alarm.

NOTE This timing requirement may not be applied to output signals which are explicitly claimed by the

manufacturer to be not safety-relevant.
4.1.5 Special state indication
4.1.5.1 General

It shall not be possible for any interface to an external device to adversely affect a safety function of

the apparatus without the apparatus entering a special state.
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EN 50271:2018 (E)
NOTE This includes both hardware and software interfaces.
4.1.5.2 Fixed and transportable apparatus
a) Control units

While a special state is present within the entire gas detection apparatus (i.e. control unit and

external sensors or transmitters) this shall be continuously indicated by a signal. This signal shall

be transmittable except when the apparatus is intended to be used in domestic premises only.

Signals provided for indicating that the entire gas detection apparatus is in the special state “fault”

shall be such that they de-energize when the special state occurs and also on power loss. In the

case of deactivation of alarm devices, e.g. for calibration purposes, it is not required to indicate a

special state by a transmittable signal if the alarm devices are automatically re-enabled within

15 min.
b) Gas detection transmitters intended to be used with control units

The special state “calibration” shall be transmitted to the control unit continuously or the

measured value shall be transmitted during calibration. All other special states shall be

transmitted to the control unit continuously. The test routine according to 4.6 c) is excluded.

c) All other apparatus

A special state shall be continuously indicated by a signal. This signal shall be transmittable

except when the apparatus is intended to be used in domestic premises only. Signals provided for

indicating that the apparatus is in the special state “fault” shall be such that they de-energize

when the special state occurs and also on power loss. In the case of deactivation of alarm

devices, e.g. for calibration purposes, it is not required to indicate a special state by a

transmittable signal if the alarm devices are automatically re-enabled within 15 min.

In the case of digital data transmission, the term “continuously” is used with the meaning: continually,

at the rate at which the output signal is updated (see 4.1.4).
4.1.5.3 Portable apparatus

The special state “fault” shall be continuously indicated by an optical and audible signal. It is permitted

that the audible signal can be silenced.

If it is not possible to show an indication in all possible fault situations the normal operation of the

apparatus shall be confirmed by a periodic optical and audible output signal (commonly called alive

signal or confidence signal). The time interval between two signals shall not exceed 60 s.

EXAMPLE: A sudden breakdown of battery voltage cannot be indicated without implementing a second

independent power supply.

The special state “warm-up” shall be indicated by an optical and/or audible signal.

The special states “calibration mode” and “parameterization mode” shall be indicated by an optical

signal.
4.2 Displays
4.2.1 General
If a display is provided the requirements of 4.2.2 and 4.2.3 apply.
4.2.2 Indication of messages
If it is intended to indicate messages on a display:
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SIST EN 50271:2018
EN 50271:2018 (E)

a) it shall be possible to display all active messages simultaneously or a consolidated signal shall be

generated (e.g. indicating lights for alarms or fault) and a consolidated message shall be

displayed. It shall be possible to interrogate all active messages;
b) a unique message shall be provided for each individual gas alarm;

c) if no special state is activated, it shall be possible to interrogate the measured values of all gas

sensors.

If a message includes another subsidiary message (e.g. exceeding the 2nd alarm threshold includes

exceeding the 1st alarm threshold) it is sufficient to show the message of higher priority. After

cancelling the higher order message the subsidiary message shall remain if the reason for its

activation still exists.

It is recommended that the manufacturer defines an appropriate set of messages in order to enable

the user an easy identification of alarms, special states, etc.
4.2.3 Indication of measured values

For measured values the displayed unit of measurement and any related sign shall be unambiguous.

Any under-range or over-range measurements shall be clearly indicated according to the requirements

of the metrological standards.
4.3 Software
4.3.1 General

This clause specifies minimum requirements for the software development process which are based

on EN 61508-3. Alternative procedures are permitted provided that the applicable requirements of

EN 61508-3 are fulfilled. Compliance through “proven in use” (Route 2s of EN 61508-3) shall not be

used.

NOTE This standard specifies minimum requirements and does not give additional recommendations (in the

tables of EN 61508-3 and in EN 50402:2017 marked as “R”).

In general, software will consist of device software and, if applicable, an operating system and libraries

(e.g. mathematical functions).

The requirements of this clause shall be applied to the entire software. A distinction between safety-

related and non safety-related software is not made.

New operating systems shall be developed according to 4.3.3 to 4.3.5. Re-used or commercial

operating systems shall comply with 4.3.2.

New device software and libraries shall be developed according to 4.3.3 to 4.3.5.

Bought or re-used software modules which were previously developed according to 4.3.3 to 4.3.5 or

commercial libraries which are only available as object code shall be qualified (see 4.3.5.3.2).

Bought or re-used software modules which are relevant for the basic gas detection functionality (signal

chain from sensor to safety relevant output(s)) or the effectiveness of the test routines (according to

4.6) which were not developed according to 4.3.3 to 4.3.5 shall be treated as new code (Route 3s

according to EN 61508-3, 7.4.2.13). All other bought or re-used software modules shall be qualified

(see 4.3.5.3.2).

Only the requirements of 4.3.3, 4.3.4 a)-e), g), h) and 4.7 shall be applied to so

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