IEC PAS 63312:2021

IEC PAS 63312 ®
Edition 1.0 2021-01
PUBLICLY AVAILABLE
SPECIFICATION
PRE-STANDARD
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inside
Technical specification for flame detector system of boiler

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IEC PAS 63312 ®
Edition 1.0 2021-01
PUBLICLY AVAILABLE
SPECIFICATION
PRE-STANDARD
colour
inside
Technical specification for flame detector system of boiler

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.060 ISBN 978-2-8322-9241-9

– 2 – IEC PAS 63312:2021  IEC 2021
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 General . 12
4.1 General requirements . 12
4.2 Power supply . 12
4.3 Functions and performance of flame detector . 12
4.4 Signal output. 13
4.5 Interchangeability . 13
4.6 Installation . 13
4.7 Commissioning . 13
4.8 Inspection and maintenance . 13
4.9 Tests . 14
5 Classification and requirements (design) . 14
5.1 Classification of flame detectors . 14
5.1.1 Classification principle . 14
5.1.2 Classification according to detection principle . 14
5.1.3 Classification according to the structure of flame detector . 15
5.1.4 Classification according to installation method . 15
5.1.5 Classification according to safety level . 15
5.2 Technical requirements of flame detectors . 15
5.2.1 Basic functional requirements . 15
5.2.2 Basic performance requirements . 17
5.2.3 Reliability requirements . 18
5.3 Technical requirements of cooling system (optional, depending upon the
actual requirements of flame detectors) . 20
5.3.1 Functional requirements of cooling air system . 20
5.3.2 Performance requirements of cooling air system . 21
6 Installation and commissioning requirements . 22
6.1 System installation requirements . 22
6.1.1 Installation preparations . 22
6.1.2 Installation of flame detectors . 23
6.1.3 Acceptance of installation . 26
6.2 Commissioning requirements after installation . 27
6.2.1 Static commissioning . 27
6.2.2 Dynamic commissioning . 29
6.2.3 Contents of system dynamic commissioning . 29
6.2.4 Acceptance of system commissioning . 31
7 Requirements on inspection, operation and maintenance . 32
7.1 System inspection and maintenance requirements . 32
7.1.1 Preparations . 32
7.1.2 Power supply inspection . 33
7.1.3 Installation inspection of flame detectors . 33
7.1.4 Dismantlement and inspection of optical fibers . 33

7.1.5 Inspection and maintenance of analysis and processing unit . 34
7.1.6 Inspection and maintenance of cables . 35
7.1.7 Inspection and maintenance of cooling air system . 35
7.2 System test requirements . 36
7.2.1 Power system test . 36
7.2.2 Inspection on the analysis and processing unit . 36
7.2.3 Inspection and tests on flame detector probes . 36
7.2.4 Basic functional tests . 37
7.2.5 Parameter adjustment test . 37
7.2.6 Check of parameter settings . 37
7.2.7 Tests on cooling fans . 37
7.3 System operation . 38
7.3.1 Restart . 38
7.3.2 Maintenance during operation . 38
7.3.3 Inspections before boiler shutdown . 39
7.4 System maintenance requirements . 39
7.4.1 Routine maintenance . 39
7.4.2 Regular maintenance . 39
7.5 Archives . 40
8 Test methods and requirements . 41
8.1 Test methods . 41
8.1.1 General . 41
8.1.2 Test reference conditions . 41
8.1.3 Test instruments and equipment . 41
8.1.4 Test items and methods . 42
8.2 Equipment factory acceptance test. 44
8.2.1 Test items . 44
8.2.2 Judgment of eligibility . 44
8.3 Type test . 44
8.3.1 General . 44
8.3.2 Situations requiring type test . 44
8.3.3 Sampling principles . 44
8.3.4 Judgment of eligibility in type test . 45
Annex A (informative) Composition of flame detector system . 46
A.1 General . 46
A.2 Flame detector . 46
A.3 Signal transmission components and cables . 47
A.4 Analysis and engineering tools . 47
A.5 Power system . 47
A.6 Cooling air system (optical, depending on design requirements) . 47
Annex B (informative) Marking, packaging, transportation and storage of flame
detectors . 48
B.1 Marking . 48
B.2 Packaging . 48
B.3 Transportation . 48
B.4 Storage . 48

– 4 – IEC PAS 63312:2021  IEC 2021
Figure A.1 – Schematic diagram of a typical light signal-based flame probe . 46
Figure A.2 – Schematic diagram of an imaging-based flame detector probe . 46

Table 1 – Configuration of monitoring and interlocking instruments of flame detector
cooling air system . 20
Table 2 – Installation acceptance criteria of flame detector system . 26
Table 3 – Commissioning acceptance items of flame detector system . 32
Table 4 – Test instruments and equipment . 41
Table 5 – Requirements on insulation resistance tester . 42

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
TECHNICAL SPECIFICATION FOR FLAME DETECTOR SYSTEM OF BOILER

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
A PAS is an intermediate specification made available to the public and needing a lower level
of consensus than an International Standard to be approved by vote (simple majority).
IEC PAS 63312 has been processed by subcommittee 65B: Measurement and control devices,
of IEC technical committee 65: Industrial-process measurement, control and automation.
The text of this PAS is based on the This PAS was approved for
following document: publication by the P-members of the
committee concerned as indicated in
the following document
Draft PAS Report on voting
65B/1175/DPAS 65B/1180/RVDPAS
Following publication of this PAS, which is a pre-standard publication, the technical committee
or subcommittee concerned may transform it into an International Standard.

– 6 – IEC PAS 63312:2021  IEC 2021
This PAS shall remain valid for an initial maximum period of 2 years starting from the
publication date. The validity may be extended for a single period up to a maximum of 2 years,
at the end of which it shall be published as another type of normative document, or shall be
withdrawn.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
The flame detector is the key testing equipment for the boiler furnace safety protection and
burner interlock control. In the whole combustion process of the boiler (especially in the
variable operating condition), it detects the change of the combustion condition, and the
corresponding control measures are taken through the connected terminal devices; so its
reliability is related to the safety of the combustion system and the quality of the terminal
products. Due to the difference in combustion conditions in the furnace, the reliability of the
flame detector itself and the quality of the installation and maintenance, many problems are
exposed during the operation, such as peeping of fire detection signals, missed detection,
instability, false alarm information, fiber overheating loss, etc. All of these will bring safety
hazards to the industrial production.
The purpose of this PAS is to develop comprehensive technical specifications for the
functions and performance of industrial boiler flame detectors, as well as the technical
requirements related to design, manufacture, installation, testing, operation, maintenance,
etc., so as to provide the technical basis for flame detector system users.

– 8 – IEC PAS 63312:2021  IEC 2021
TECHNICAL SPECIFICATION FOR FLAME DETECTOR SYSTEM OF BOILER

1 Scope
This PAS deals with the general requirements, classification and technical requirements,
installation and commissioning requirements, inspection and maintenance requirements, test
methods and requirements of radiant energy sensing flame detectors (including IR, UV, visible
light, and imaging-based flame detectors).
This PAS is applicable to the type selection, design, installation, commissioning, inspection,
maintenance and acceptance of the radiant energy sensing flame detectors, which monitor
the flame status of burners.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60034-30-1, Rotating electrical machines – Part 30-1: Efficiency classes of line operated
AC motors (IE code)
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Test B: Dry heat
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady
state
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
IEC 60079-1, Explosive atmospheres – Part 1: Equipment protection by flameproof
enclosures "d"
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 61010-1, Safety requirements for electrical equipment for measurement, control, and
laboratory use – Part 1: General requirements
IEC 61326-1, Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 1: General requirements
IEC 61326-2-5, Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 2-5: Particular requirements – Test configurations, operational conditions
and performance criteria for field devices with field bus interfaces according to IEC 61784-1
NFPA 85, Boiler and Combustion Systems Hazards Code

ANSI/TIA/EIA-232-F, Interface between Data Terminal Equipment and Data Circuit-
Terminating Equipment Employing Serial Binary Data Interchange
ANSI/TIA/EIA-422-B, Electrical Characteristics of Balance Voltage Digital Interface Circuits
ANSI/TIA/EIA-644-A, Electrical Characteristics of Low Voltage Differential Signaling (LVDS)
Interface Circuits
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
flame detector
device in the furnace safety supervisory system that detects the combustion status in real
time according to the flame characteristics of the fuel, and which, when the flame status fails
to meet the preset conditions, considers the target flame abnormal or disappeared and sends
a signal in a certain manner to stop the corresponding fuel supply
3.2
infrared signal
radiant energy signals falling within the infrared spectrum, emitted from the flames of burning
fuel such as coal and oil
3.3
ultraviolet signal
radiant energy signals falling within the ultraviolet spectrum, emitted from the flames of
burning fuel such as natural gas and light oil
3.4
visible light signal
radiant energy signals falling within the visible light spectrum, emitted from the flames of
burning fuel such as lean coal and mixed fuels
3.5
flame on
presence of flame in the furnace, as computed by the flame detector system
3.6
flame off
absence of flame in the furnace, as computed by the flame detector system
3.7
target flame
predefined flame to be detected, rather than the extended background radiation or the
adjacent and opposing flames
3.8
flame intensity
value computed by flame detector according to the received radiant energy intensity of flame,
representing the radiant energy intensity of the flame

– 10 – IEC PAS 63312:2021  IEC 2021
3.9
flicker frequency
pulsation frequency of flame radiant energy, representing the change rate of the target flame's
radiant energy intensity
3.10
AC amplitude
pulsation amplitude of radiant energy from flame, representing the peak-to-peak value of the
radiant energy intensity pulsation of target flame
3.11
flame quality
extent away from the flame-off status, computed from the detected flame intensity and flicker
frequency, representing the degree of flame stability
3.12
flame threshold
minimum value set for the flame detector to determine the presence of flame (i.e. flame-on
threshold) or the maximum value to determine the absence of flame (i.e. flame-off threshold)
3.13
flame relay
on/off control switch that switches on when the flame logic judges that flame is present and
switches off when it judges that flame is absent
3.14
fault relay
on/off control switch that switches on when no fault is detected and switches off when any
fault is detected
3.15
flame detector probe
device installed locally, capable of flame information sensing, photoelectric conversion and
signal amplification
3.16
analysis and processing unit
device that receives the signals transmitted from one or more flame detector probes, and,
after analysing and processing by the corresponding processor, outputs the digital and analog
signals of each flame signal
Note 1 to entry: The relevant parameters of each flame can be set independently.
3.17
one-to-one detection
detection mode in which each target flame has a separate, fixed flame detector
3.18
flame detector peeping
situation that exists when the flame detector cannot distinguish between a target flame and a
non-target flame, and considers a non-target flame as the target flame
3.19
static commissioning
commissioning of flame detector system using simulative light sources before the boiler is
started up
3.20
dynamic commissioning
commissioning of flame detector system after the boiler is started up, during which the flame
detection data throughout the period from the startup to the full load operation of the boiler
under typical operating conditions is analyzed and compared and the parameters setting is
completed to meet the actual operating requirements of the boiler
3.21
light signal-based flame detector
flame detector that detects flames relying on the intensity, pulsation and other signals of the
radiant light emitted by target flame, including infrared, visible light, ultraviolet, dual-spectrum,
and full-spectrum types
3.22
imaging-based flame detector
flame detector that detects the flame by acquiring the real-time video images of the target
flame
3.23
Class A unit overhaul
thorough inspection and repair on the generator unit, intended to maintain, restore or improve
the performance of the unit equipment
Note 1 to entry: Class A is the highest level overhaul among regular unit overhauls.
3.24
Class B overhaul
inspection and repair on the faulty or defective equipment within the unit, which may include
some targeted Class A overhaul items or rotational maintenance items depending on the
evaluation outcome of the unit
3.25
Class C overhaul
targeted inspection, evaluation and repair carried out on the unit according to the wearing and
aging trends of equipment, which may include the replacement of a small number of parts, the
defect elimination, adjustment, preventive tests and other operations on the equipment, as
well as some Class A overhaul items or rotational maintenance items
3.26
troubleshooting
activities performed on faulty equipment for the purpose of restoring it to such a status that it
can execute its intended functions
Note 1 to entry: Troubleshooting includes diagnosis, repair, and replacement.
3.27
mean time between operating failures
MTBF
expectation of the duration of the operating time between failures
[SOURCE: IEC 60050-192:2015, 192-05-13]

– 12 – IEC PAS 63312:2021  IEC 2021
3.28
reliability
ability to perform as required, without failure, for a given time interval, under given conditions
Note 1 to entry: The time interval duration may be expressed in units appropriate to the item concerned,
e.g. calendar time, operating cycles, distance run, etc., and the units should always be clearly stated.
Note 2 to entry: Given conditions include aspects that affect reliability, such as: mode of operation, stress levels,
environmental conditions, and maintenance.
[SOURCE: IEC 60050-192:2015, 192-01-24]
4 General
4.1 General requirements
The flame detector system mainly consists of flame detectors, signal transmission
components and cables, junction boxes, flame detection cabinets, the analysis and
processing unit, engineer tools, power supplies, installation accessories and the cooling
system (if necessary). For the use purpose of each component, see Annex A.
The flame detectors should be marked with QR codes. The outer surfaces and nameplates
shall be smooth, intact, scratch-free, and contamination-free. The film over the surface shall
have no peeling and scratching. The characters in panels and nameplates shall be legible.
There shall be no loose connections or junctions.
4.2 Power supply
The flame detector cabinet shall be provided with duplicate power supplies, which back up
each other. It shall have a built-in power switching module, which balances the two power
supplies via the automatic power distribution circuit.
Any failure of either power supply shall be alarmed, without affecting the normal operation of
the equipment and missending signals. Switching between the two power supplies shall
generate no disturbance and shall not enable the flame detector to send the "flame off" signal.
Each power supply circuit of the flame detector amplifier/flame detector shall be provided with
a separate fuse or other separate protective measures.
The power supply to the fans in the flame detector cabinet shall be independent of the power
supply to the flame detector system, or appropriate isolation measures shall be taken between
them.
4.3 Functions and performance of flame detector
The functions and performance of flame detectors shall meet the requirements of NFPA 85
Boiler and Combustion Systems Hazards Code. Flame detectors shall be able to correctly
identify the flames of fuel (coal, oil and gas) for the corresponding burners. They shall be
continuously adjustable within the full frequency spectrum under monitoring (or the
corresponding frequency spectrum), so that the flames can be detected throughout the whole
range of working conditions.
The flame detectors should allow selection among multiple parameters, so that appropriate
parameter groups can be selected for the specific fuel and combustion condition, and that the
flame parameters can be switched according to the current background conditions.

The flame detectors shall correctly reflect the various flame statuses (such as flame
frequency and intensity). They shall be able to mitigate the interference from the adjacent,
opposite, furnace-reflected non-target flames or the interference from the adjacent main flame
to the minimal level.
The flame detectors shall have the self-test function, which allows them, in a timely manner,
to reflect their own conditions, make self-diagnosis of faults, and give alarms at the specified
interval.
4.4 Signal output
The flame detector of each burner shall provide analog signal (4 mA to 20 mA or 0 to 10 V)
outputs or communication means to indicate the intensity of flame output signal.
The flame detector of each burner shall have at least two passive dry contacts to output flame
status signals (flame on/flame off) and flame detector fault signals.
For digital outputs of flame detector, single relay mode or double relay mode may be used.
a) Single relay mode: The deenergized/energized status of flame relay (contact open/closed)
is used to indicate the flame on/flame off status, and the deenergized/energized status of
fault relay (contact open/closed) is used to indicate the faulty/normal status.
b) Double relay mode: Two relays are used to indicate the flame on and flame off statuses
respectively. When the flame-on relay is closed and the flame-off relay is open, it indicates
the presence of flame. When the flame-on relay is open and the flame-off relay is closed,
it indicates the absence of flame. When both relays are closed/open, it indicates a faulty
status.
4.5 Interchangeability
Parts of the same type shall be interchangeable. The measurements of the same target flame
indicated by different flame detection devices shall be substantially consistent and meet the
overall accuracy and linearity requirements.
4.6 Installation
Flame detectors from different manufacturers may have different probe installation methods
and requirements. They shall be installed in accordance with 6.1 and the manufacturer's
instructions, so that the probe detection point aligns with the sensitive area for flame
detection.
4.7 Commissioning
The commissioning of flame detectors consists of two stages: the static commissioning before
startup of the boiler and the dynamic commissioning after startup of the boiler. The two-stage
commissioning shall be so conducted that the internal parameters of each flame detector are
optimized and the flame status in the boiler is correctly indicated throughout the period from
boiler startup to full load operation.
4.8 Inspection and maintenance
The probe of flame detector is usually exposed to a harsh working environment. So proper
inspection and maintenance is necessary for keeping stable and reliable operation of the
flame detector system. In addition to the inspection and maintenance of the flame detector
system during unit overhauls, the maintenance personnel shall also carry out routine
maintenance and regular maintenance to identify and eliminate problems in a timely manner
and improve the reliability of the flame detector system.

– 14 – IEC PAS 63312:2021  IEC 2021
4.9 Tests
The purpose of tests is to verify the performance of flame detectors and the effectiveness of
their maintenance activities. In order to ensure reliable operation of flame detectors, targeted
tests shall be carried out during manufacture, delivery and maintenance.
5 Classification and requirements (design)
5.1 Classification of flame detectors
5.1.1 Classification principle
Flame detectors can be classified according to the detection principle, device structure,
installation method, and safety level.
5.1.2 Classification according to detection principle
5.1.2.1 Overview
The flames of coal, oil or gas in the furnace of boiler are characterized by the continuous
infrared, visible light and ultraviolet spectrums of radiation and the flame pulsation or flicker
phenomenon. The intensity and spectrum distribution of flames vary with the type of fuel. And
the spectral frequency and intensity of flame radiation constantly change with the combustion
zone. Generally, the flame combustion zones can be divided into the initial combustion zone,
the high temperature zone and the burn-out zone. The flame in the initial combustion zone
features the most intensive flicker frequency. Appropriate flame detectors shall be used
according to the specific characteristics of the target flame. The flame detector converts light
signal to pulsation electrical signal (current or voltage signal) and distinguishes the target
flame from background flame by detecting the frequency ranges, realizing effective detection
of flame signals. According to the detection principle, flame detectors can also be classified
into the light signal-based flame detectors and imaging-based flame detectors.
5.1.2.2 Light signal-based flame detector
Light signal-based flame detectors include the infrared, visible light, ultraviolet, dual-spectrum,
and full-spectrum types. They detect the target flame by analysing and processing the
intensity and spectral characteristics of flame radiation light. Electrical signals are pre-
processed in a printed circuit board in the shell of flame detector probe. After logarithmic
amplification and being converted into current signals by voltage/current conversion, the
signals are transmitted through a shielded cable to the analysis and processing unit (flame
amplifier) in the remote signal processing cabinet for processing. After various processes
including frequency detection, intensity detection, and circuit detection, standard signals
including the quality conditions of flame detector (flame intensity analog signal) and the
presence/absence of flame (digital signals and flame detector fault signals) are output for
display, alarming and boiler trip logic judgment.
5.1.2.3 Imaging-based flame detector
Real-time video images of flames are collected and the target flames are detected by using
the image processing technology. The flame image contains the position, brightness, and
pulsation information of target flame and background flame. By properly determining the
position of detection area, the target flame can be distinguished from most background flames.
Reasonably setting the parameters for judging the target flame could further improve the
identification of background flame. Generally, the imaging-based flame detector collects the
real-time video images of the target flame via the camera in burner's secondary air duct, and
transmits signals to its signal processing unit via a video coaxial cable for processing. After
the video analog-to-digital conversion, the built-in image processing algorithm is used to
identify the target flame, and the signals such as flame intensity, flame status, and faults are
output for display, alarming, and logic judgment.

5.1.3 Classification according to the structure of flame detector
5.1.3.1 Overview
According to detector structure, flame detectors can be classified into the integrated flame
detector and split flame detector.
5.1.3.2 Integrated flame detector
The integrated flame detector is usually composed of a probe assembly and a flame signal
analysis and processing unit, of which all the electronic devices are integrated and installed at
the same local detection position.
5.1.3.3 Split flame detector
The split flame detector is also composed of a probe assembly and a flame signal analysis
and processing unit, which, however, are independent of each other. The probe assembly is
installed at the local detection position, while the flame signal analysis and processing unit is
installed at another place in a favorable environment (such as an electronics room).
5.1.4 Classification according to installation method
5.1.4.1 Internally sighting flame detector
In the "internally sighting" installation mode of flame detector, the optical signals of flame
radiation are transmitted to the flame sensor outside the boiler via the optical fibers or light
guide tubes installed inside the boiler for flame detection.
5.1.4.2 Externally sighting flame detector
In the "externally sighting" installation mode of flame detector, the flame detector is installed
outside the boiler and directly receives the light signals of the target flame in boiler for flame
detection.
5.1.5 Classification according to safety level
5.1.5.1 Explosion-proof flame detector
The explosion-proof flame detectors, capable of explosion resistance, are used in explosive
environments. Generally, the flame detectors for gas-fired boilers or gas-reacting boilers are
exposed to an explosive environment. The common explosive installation environments for
flame detectors mainly include gas-fired boiler, coal-fired boiler cofiring combustible gases,
waste gas-fired boiler, gas synthesis boiler (such as HCL synthesis boiler), and gas-reacting
boiler.
5.1.5.2 Non-explosion-proof flame detector
The non-explosion-proof flame detectors, incapable of explosion resistance, are used in non-
explosive environments. The common non-explosive installation environments for flame
detectors mainly include oil-fired boiler and coal-fired boiler.
5.2 Technical requirements of flame detectors
5.2.1 Basic functional requirements
5.2.1.1 Self-test function
Flame detectors shall be able to reflect their working conditions in real time by conducting
continuous self-test and shall ensure the continuity of their self-test. Under the specified
working conditions and when the flame input signal is valid, if the flame detector detects a
fault, it shall automatically give an alarm signal via the relay or communication devices.

– 16 – IEC PAS 63312:2021  IEC 2021
5.2.1.2 Flame threshold setting function
Under the specified working conditions, the flame-on and flame-off thresholds shall be
adjustable. For the imaging-based flame detectors, both the position of each flame judgment
zone and the flame recognition threshold shall be adjustable.
5.2.1.3 Flame intensity display
Under the specified working conditions and when the flame input signal is valid, the flame
detector shall display the intensity of the flame input signal in real time. For the imaging-
based flame detector, the flame signal intensity at the flame zone corresponding to the real-
time image shall be provided in the control software.
5.2.1.4 Flame-on delay setting
Under the specified working conditions, the period from the time the flame input signal
changes from flame-off to flame-on to the time the flame detector outputs flame-on signal is
referred to as the flame-on delay. The delay shall allow appropriate presetting.
5.2.1.5 Flame-off delay setting
Under the specified working conditions, the period from the time the flame input signal
changes from flame-on to flame-off to the time the flame detector outputs flame-off signal is
referred to as the flame-off delay. The delay may be provided by the boiler manufacturer or
preset by professionals.
5.2.1.6 Analog output signal
The analog output signal of flame detector is used for remote monitoring and shall meet the
following conditions.
a) When the intensity of flame input signal is less than the lower limit of measuring range of
flame detector, the output is DC 4 mA.
b) When the intensity of flame input signal is within the measuring range of flame detector,
the output is DC (4 to 20) mA.
c) When the intensity of flame input signal is greater than the upper limit of measuring range
of flame detector (overflow), the output is DC 20 mA.
5.2.1.7 Remote communication fun
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