IEC 61779-4:1998

INTERNATIONAL
IEC
STANDARD
61779-4
First edition
1998-04
Electrical apparatus for the detection
and measurement of flammable gases –
Part 4:
Performance requirements for group II apparatus
indicating a volume fraction up to 100 %
lower explosive limit
Appareils électriques de détection et de mesure
des gaz combustibles –
Partie 4:
Règles de performance des appareils du groupe II pouvant indiquer
une fraction volumique jusqu'à 100 % de la limite inférieure
d’explosivité
Reference number
Numbering
As from 1 January 1997 all IEC publications are issued with a designation in the

60000 series.
Consolidated publications
Consolidated versions of some IEC publications including amendments are
available. For example, edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the

base publication, the base publication incorporating amendment 1 and the base

publication incorporating amendments 1 and 2.

Validity of this publication
The technical content of IEC publications is kept under constant review by the IEC,
thus ensuring that the content reflects current technology.
Information relating to the date of the reconfirmation of the publication is available
in the IEC catalogue.
Information on the subjects under consideration and work in progress undertaken by
the technical committee which has prepared this publication, as well as the list of
publications issued, is to be found at the following IEC sources:
• IEC web site*
• Catalogue of IEC publications
Published yearly with regular updates
(On-line catalogue)*
• IEC Bulletin
Available both at the IEC web site* and as a printed periodical
Terminology, graphical and letter
symbols
For general terminology, readers are referred to IEC 60050: International
Electrotechnical Vocabulary
(IEV).
For graphical symbols, and letter symbols and signs approved by the IEC for
general use, readers are referred to publications IEC 60027: Letter symbols to be
used in electrical technology Graphical symbols for use on equipment.
, IEC 60417:
Index, survey and compilation of the single sheets and IEC 60617: Graphical symbols
for diagrams.
* See web site address on title page.

INTERNATIONAL
IEC
STANDARD
61779-4
First edition
1998-04
Electrical apparatus for the detection
and measurement of flammable gases –
Part 4:
Performance requirements for group II apparatus
indicating a volume fraction up to 100 %
lower explosive limit
Appareils électriques de détection et de mesure
des gaz combustibles –
Partie 4:
Règles de performance des appareils du groupe II pouvant indiquer
une fraction volumique jusqu'à 100 % de la limite inférieure
d’explosivité
 IEC 1998 Droits de reproduction réservés  Copyright - all rights reserved
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Pour prix, voir catalogue en vigueur
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– 2 – 61779-4 © IEC:1998(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION

___________
ELECTRICAL APPARATUS FOR THE DETECTION

AND MEASUREMENT OF FLAMMABLE GASES –

Part 4: Performance requirements for group II apparatus

indicating a volume fraction up to 100 % lower explosive limit

FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61779-4 has been prepared by subcommittee 31L: Electrical
apparatus for the detection of flammable gases, of IEC technical committee 31: Electrical
apparatus for explosive atmospheres.
This standard should be read in conjunction with IEC 61779-1.
The text of this standard is based on the following documents:

FDIS Report on voting
31L/50/FDIS 31L/55/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.
A bilingual version of this standard may be issued at a later date.

61779-4 © IEC:1998(E) – 3 –
ELECTRICAL APPARATUS FOR THE DETECTION

AND MEASUREMENT OF FLAMMABLE GASES –

Part 4: Performance requirements for group II apparatus

indicating a volume fraction up to 100 % lower explosive limit

1 Scope
1.1 This part of IEC 61779 specifies requirements for group II (as defined in part 1) portable,
transportable and fixed apparatus for the detection and measurement of combustible gas or
vapour concentrations with air. The apparatus, or parts thereof, may be installed or used in
potentially explosive atmospheres, other than mines susceptible to firedamp (i.e. group I). The
requirements and test methods applicable to the apparatus covered by this standard are
specified in part 1.
1.2 This standard is restricted to apparatus intended for the detection and measurement of
combustible gas or vapour concentrations with air up to 100 % lower explosive limit (LEL).
2 Definitions
For the purpose of this part of IEC 61779, the definitions given in part 1 apply.
3 General requirements
The apparatus shall comply with the general requirements specified in part 1 and with the
performance requirements specified in clause 4 of this standard.
Compliance shall be determined in accordance with the appropriate test requirements and
methods, including initial calibration, specified in part 1.
It shall be verified that the contents of the manufacturer's instruction manual are in accordance
with the requirements specified in part 1.
4 Performance requirements
4.1 General
The normal conditions for tests are specified in 4.3 of part 1. Compliance shall be determined
in accordance with the test methods specified in 4.4 of part 1.
4.2 Unpowered storage
After being submitted to the conditions specified in 4.4.2 of part 1, the apparatus shall meet the
requirements specified in 4.3 to clause 5 of this standard.
4.3 Calibration curve (not applicable to alarm-only apparatus)
4.3.1 Calibration curve
After initial adjustment with the standard test gas, each individual indication in the three sets of
indications (after correction using the manufacturer's calibration curve, if necessary) obtained
for each of the four gas volume ratios distributed over the measuring range, shall not differ

– 4 – 61779-4 © IEC:1998(E)
from these volume ratios by more than ±5 % of the measuring range or ±10 % of the indication,

whichever is the greater.
4.3.2 Response to gases other than the test gas

The apparatus indication (after correction using the manufacturer's calibration curves, if

necessary) obtained for each of the three gas volume ratios of each gas tested shall not differ

from these volume ratios by more than ±7 % of the measuring range or ±15 % of the indication,

whichever is the greater.
4.4 Stability (continuous duty apparatus)

Continuous duty apparatus shall comply with the following requirements.
a) short-term stability
The short-term variation shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
b) long-term stability (fixed and transportable apparatus)
The long-term variation shall not exceed ±10 % of the measuring range or ±30 % of the
indication, whichever is the greater.
c) long-term stability (portable apparatus)
The long-term variation shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.5 Stability (spot-reading apparatus)
The variation of the indication shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.6 Alarm
The alarm(s) shall operate during every cycle of the test. If a latching alarm is provided, the
manual reset action shall be checked.
4.7 Temperature
The variation of the indication from that at 20 °C, over the specified temperature ranges, shall
not exceed the following:
a) for portable or transportable apparatus where the control unit and the sensor are used in
the same general environment, the variation over the temperature range –10 °C to +40 °C

shall not exceed ±5 % of the measuring range or ±10 % of the indication, whichever is the
greater. Tests shall be carried out at temperatures of –10 °C, 20 °C and 40 °C;
b) for fixed apparatus with remote sensors, where the control unit and sensor are not used in
the same general environment, the following temperatures shall be applied:
1) Sensors
With the control unit under normal ambient test conditions, the sensor shall be tested in
air and in the standard test gas at –25 °C and +55 °C. The variation shall not exceed
±10 % of the measuring range or ±20 % of the indication, whichever is the greater.
2) Control units
With the sensor under normal ambient test conditions, the variation at +5 °C and +55 °C
shall not exceed ±5 % of the measuring range or ±10 % of the indication, whichever is
the greater;
61779-4 © IEC:1998(E) – 5 –
c) for fixed apparatus with sensors and control units in the same general environment, the

variation at –10 °C and +55 °C shall not exceed ±5 % of the measuring range or ±15 % of

the indication, whichever is the greater.

4.8 Pressure
The variation of the indications at 80 kPa and 110 kPa from the indication at 100 kPa shall not

exceed ±5 % of the measuring range or ±30 % of the indication, whichever is the greater.

4.9 Humidity
The variation of the indications at 20 % RH and 90 % RH from the indication at 50 % RH, at
+40 °C, shall not exceed ±7 % of the measuring range or ±15 % of the indication, whichever is
the greater.
4.10 Air velocity
The variation of the indication shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.11 Flow rate
The variation of the indication shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.12 Orientation
The variation of the indication shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.13 Vibration
During the vibration test, the apparatus shall not suffer any loss of function and shall not give a
false alarm or fault signal. The apparatus shall not suffer damage resulting in a hazard or loss
of function.
At the conclusion of the vibration test and after the apparatus sensor has been exposed to
clean air followed by the standard test gas mixture, the deviation of the indication from that
determined prior to the test shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.14 Drop test (applicable to portable apparatus and remote sensors)

The apparatus shall not suffer damage resulting in a hazard or loss of function.
The variation of the indication shall not exceed ±5 % of the measuring range or ±10 % of the
indication, whichever is the greater.
4.15 Warm-up time (not applicable to spot-reading apparatus)
4.15.1 Fixed and transportable apparatus
The apparatus shall warm up in clean air to indicate zero to within ±5 % of the measuring range
in a time specified by the manufacturer, and no false alarms shall be generated.

– 6 – 61779-4 © IEC:1998(E)
4.15.2 Continuous duty portable apparatus

The apparatus shall warm up in clean air to indicate zero to within ±5 % of the measuring range

in a time not exceeding 2 min, and no false alarms shall be generated.

4.16 Time of response (not applicable to spot-reading apparatus)

The time of response t(50) in either direction shall be not greater than 20 s, and t(90) in either
direction shall be not greater than 60 s.

4.17 Minimum time to operate (spot-reading apparatus)

For apparatus without a probe or sample line, the indication shall reach 90 % of the final value
in a time not exceeding 15 s.
For aspirated apparatus using a sample line or probe, an additional 3 s per metre is permitted.
4.18 High gas concentration above the measuring range
4.18.1 Non-ambiguity test
When tested in accordance with 4.4.18.1 of part 1, all gas
...