SenseTek Flame Detector User Manual

Fire & Security Solutions

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This document is FD User Manual/2003/Issue 1

Information in this guide is given in good faith, but the manufacturer cannot be held responsible
for any omissions or errors. The company reserves the right to change the specifications of
products at any time and without prior notice.

12

Flame Detector

User Manual

General

Description

The flame detector is designed for use where open flaming fires may be expected. It responds to the
light emitted from flames during combustion. The detector discriminates between flames and other
light sources by responding only to particular optical wavelengths and flame flicker frequencies. This
enables the detector to avoided false alarms due to such factors as flicking sunlight.

Electrical Considerations

The flame detector can be connected in many different electrical configurations depending on the
application. The detector requires a 24Vdc (14Vmin. to 30Vmax.) supply to operate. The detector can
be connected as a two-wire loop powered device increasing its supply current to signal that a flame
has been detected. See Fig 8. The supply connections to the detector are polarity sensitive.
Also available are volt free contacts from two internal relays RL1 (Fire) and RL2 (Fault or pre-alarm).
Using the relay contacts connected in a four-wire configuration the detector status can be signalled
back to control equipment. See Fig 9.
Removing the detector front cover provides accesses the detector terminals and configuration DIL
switch. See Fig.4.

Alarm Response Modes
The detector is normally configured to latch into an alarm state when a flame is detected. The supply
to the detector has to be broken in order to reset the detector.
The configuration DIL switch within the detector can be set to place the detector into a non-latching
mode. The detector can then also produce proportional analogue current alarm signals i.e. 8-28mA or
4-20mA. In non-latching mode the detector only produces an alarm signal when a flame is in view
resetting itself to normal when the flame has gone.

Application for Flame Detectors

Flame detectors are used when detection is required to be:

•

Unaffected by convection currents, draughts or wind

•

Tolerant of fumes, vapours, dust and mist

•

Responsive to a flame more than 25m away

•

Fast reacting

The detector is capable of detecting the optical radiation emitted by burning material even non­carbonaceous materials. e.g. Hy

drogen

Numerous other potential fire sources can be detected such as

Liquids Solids Gases

● Aviation Fuels (kerosene) ● Coal

● Ethanol

● Cotton ● Fluorine

● Methylated Spirits ● Grain & Feeds

● n-Heptane

● Paraffin

● Paper ● Natural Gas

● Refuse ● Off Gas

● Petrol (gasoline) ● Wood

● Butane

● Hydrogen

● Propane

Typical applications examples are:

● Agriculture

● Aircraft hangars ● Engine rooms

● Atria

● Automotive industry

● Coal handling plant ● Pharmaceutical

● Power plants

● Generator rooms ● Textiles

● Metal fabrication ● Transformer stations

- spray booths ● Paper manufacture ● Waste handling

- parts manufacture ● Petrochemical ● Woodw

orking

Applications and Locations to Avoid:

● ambient temperatures above 55°C ● large IR sources – heaters, burners, flares

● close proximity

to RF sources

● exposure to severe rain and ice ● sunlight falling directly

● obstructions to field of view

on the detector optics

● large amounts of flickering reflections ● spot lighting directly on the detector optics

Quantities Required and Positioning of Detectors

The number of detectors required and their position depends on:

The flame detector is designed to have a class 1 performance as defined in BS EN54-10:2002
on the high sensitivity
methylated spirit (clear) fire of 0.25m² at a distance of up to 25m within 30 seconds.
The detector can be set to have to a lower sensitivity
Class 3 performance is defined as detecting the same size fires as for class 1 but at a distance
of only

the anticipated size of the flame

•

the distance of the flame from the detector

•

the angle of view of the flame detector

•

setting. That is the ability

12m.

to detect an n-heptane (yellow) fire of 0.1m² or

setting equivalent to class 3 performance.

Functional Testing

When 24Vdc power is applied to the detector
the green

supply on indicator LED will
illuminate. The fault relay RL2, if selected
with the DIL switch, will energise and the
contact between terminals 7 and 8 will close.
If 24Vdc is applied to terminals 3 and 4 or
terminal 3 is linked to terminal
w

ill perform a self-test. It does this by

1 the detector

causing internal optical test sources to
simulate the behaviour of flames and the
detector will alarm.

6913

F1

6912

FLAME SENSOR TEST UNIT

F3

F2

2

1

ABC

5

4

GHI

JKL

7

PQRS8TUV

0

*

SUPPLY

SIGNAL

F4

3

DEF

6

MNO

9

WXYZ

#

Fig 12 Portable Flame Detector Test Unit

Service & Repairs

Servicing of the fire protection system should
be car

ried out by competent persons familiar
with this type of system, or as recommended
by the local regulations in force.

Alternatively a portable flame sensor test unit
is available to generate simulated
behaviour and test the detector a few
in front of the detector. See Fig 12.
Finally, provided it is safe to do so, carry out
a flame test using a flickering flame
such as a portable Bunsen burner.
See Fig 13.
A still non-flickering flame w
response

Fig 13 Portable Bunsen Burner

from the detector.

ill not produce a

Only the manufacturer or equivalent
authorised body

may

carry out repairs to the
flame detectors. In practical terms this
means that flame detector may be repaired
only at the manufacturers factory.

flame

metres

source,

2

11

R

t

Control Unit / Interface

(Supplied by others)

Flame Detector

Fire
Relay

Fault
Relay

1

+

2

-

5
6
7
8

Two pair cable, also see note 1

Refer to note 2

24Vdc Normal

(Break supply to rese

+

if detector set to latch)

-

+

Zone

-

Flame Detector

Fire
Relay

Fault
Relay

1

+

2

-

5
6
7
8

EOL

Refer to note 3

NOTE 2
R = To indicate fire to control unit or interface.
E.g.: - 470R

NOTE 3
EOL = End of line device required by some control
units. This is required to monitor the cable to the
detectors and prevent fault indications on the control
unit.

Fig 9 4 Wire Connection Diagram

The circuit shown above enables the flame detectors to interface with most type of fire alarm control
systems. The fire relay RL1 is used to switch the required alarm load ‘R’ to generate a fire alarm
signal. An end of line device ‘EOL’ mounted in the last detector provides the system with the ability
to monitor the detector fault relay RL2 and the integrity of the interconnecting cables.

Installation

It is important that the detectors are installed
in such a way that all terminals and
connections are protected to at least IP20
with the detector cover fitted. The earth
bonding terminals are provided for

convenience where continuity of a cable
sheath or similar if required.
Adjustable mounting brackets and weather
shields are available as shown below.

In fact, the flame detector will detect fires at distances of up to 40 metres, but the flame size at
such distances needs to be proportionally greater in order to be sure of reliable detection. Thus
the yellow flickering flame that can be detected at 25m, provided that its size is not less than

0.1m², will have to be 0.4m² in order to be detected at 40metres.
In a rectangular room the distance from the flame detector to the fire is calculated by the
formula:

Maximum distance = √ L² + W² + H²

In the example shown in fig 1 the room in which the flame detector is to be installed measures
20m x 10m x 5m; the maximum distance from the detector to the flame will therefore be;

Height

Width

Fig 1 Calculation of distance from detector to flame

Field of View

The flame detector has a field of view of approximately 90°, as shown in the diagram below.

Fig 2 Conical field of view of the flame detector

F
I
R
E

I
R

S
E
N

S
O
R

Maximum distance = √ 20² + 10² + 5² = 22.9m

Length

F

I
R
E

I
R

S
E
N

S
O

R

90° Cone

Fig 10 Stainless Steel Adjustable Mount Fig 11 Stainless Steel Weather Shield

10

3

0.4m² flame seen at 40m

0.1m² flame seen at 25m

-75°

-90°

Fig 3 Detector Field of View Plot

The flame detector should be positioned at the perimeter of the room, pointing directly at the
anticipated flame or at the centre of the area to be protected. If the detector cannot ‘see’ the whole
of the area to be protected, one or more additional detectors may be required.

The flame detector is not affected by normal light sources but should be positioned so that sunlight
does not fall directly onto the viewing window.

-45°

-60°

Centre line of detector

-15°

-30°

0°

15°

0 25m

Detector

30°

45°

60°

75°

90°

40m

Detector Window Contamination

It is important to keep the detector window clean and checks should be carried out at regular
intervals – determine locally according to the type and degree of contamination encountered – to
ensure optimal performance of the flame detector. Although the IR detectors can detect flames
when the window is contaminated, there may be a reduction of sensitivity as shown in Table 1.

Contamination

Water spray 75%

Steam 75%

Smoke 75%

Oil film 86%

Salt water film 86%

Dry salt deposits 86%

Table 1 IR Detector window contamination

UV/IR detectors are more susceptible to window contamination and must be kept clean.

Typical percentage of
normal response

Connection Information

Flame Detector

Fig 8 Basic 2 Wire Connection Diagram

The simplest method of connecting the flame detector is in a 2-wire configuration as shown above.
With a 24Vdc supply the current (i) drawn by a detector/detectors can be monitored to determine the
detector status. The DIL switches within the detector can be set to produce different current values
(i) to suit control systems.

Detector Supply Current

i @ 24Vdc

Normal

Quiescent

Current

3mA 9mA 0 0 0 0 Lowest power configuration, RL1 only

4mA 20mA 0 0 1 0 For 4-20mA systems, no relays

8mA 14mA 1 1 1 0 Lowest power configuration & relays

8mA 20mA 1 1 0 1 For 4-20mA systems & relays

8mA 28mA 1 1 1 1 Fire control panels

Table 4 Detector Supply & Alarm Currents

If the detector supply current falls below the normal quiescent current consumption then a fault is
present. This could be simply an open circuit cable fault or a fault within the detector possibly due to
the detector being taken over its rated temperature.
Detectors can be connected in parallel increasing the overall quiescent current required. The alarm
current signal will remain the same with the additional quiescent current drawn from other detectors.

1

+

2

-

Alarm

(Fire)

Current

Single pair cable, also see note 1

DIL Switch Setting

2

1

3

4

Control Unit

(Supplied by others)

i

NOTE 1
Screened cable should be used with one end
of the screen connected to earth. Also care
should be taken not to run the detector cable
next to power cables.

Comment

24Vdc Normal

+

(Break supply to reset

if detector set to latch)

-

4

9

p

p

Theory of Operation

The detector responds to low-frequency
(1 to 15 Hz.) flickering IR radiation emitted
from flames during combustion.
IR flame flicker techniques enable the
sensor to operate through a layer of oil,
dust, water vapour, or ice.
Most IR flame sensors respond to 4.3µm
light emitted by hydrocarbon flames. By
responding to 1.0 to 2.7µm light emitted
by every fire all flickering flames can be
detected. Gas fires not visible to the
naked eye e.g. hydrogen may also be
detected.

Signal Processing

The detector views the flame at particular
optical wavelengths. The more differing
optical wavelength signals available the
better the detector is at discriminating
between flames and false optical sources.
So although IR², IR³ and UV/IR² detectors
can detect similar sized flames at the
same distances, the UV/IR² detector will

Flame Optics

If the detector has interpreted the optical
signals as a fire then it produces the
required output responses. This will be in
the form of supply current changes and
the illumination of the red fire LED. The
fire relay will also change state if required.

Fig 7 Block Diagram of the Detector Signal Processing

The dual (IR²) and triple (IR³) IR
photoelectric detectors, responding to
neighbouring IR wavelengths, enable it to
discriminate between flames and spurious
sources of IR radiation.
The combination of filters and signal
processing allows the sensor to be used
with little risk of false alarms in difficult
situations characterised by factors such
as flickering sunlight.

give the greatest optical false signal
immunity as it has the most diverse
selection of optical wavelengths.
The detector processes the optical signal
information to determine if a flame is in
view. This is achieved by comparing the
signals with known flame characteristics
stored within the detector.

Flame Detector

Terminals

Signal

Processing

Input/Output

Interface

The detector is constantly checking itself
to ensure it is performing correctly. If a
fault occurs the detector supply current
will reduce, the fault relay will de-energise
and the green supply LED will no longer
illuminate constantly.

Detector Interior

FLAME DETECTOR

TO EN 54-10

6903

1 2 3 4 5 6 7 8

0

1

3

1

Fig 4 Detector with Front Cover removed

SENSITIVITY

LOW CLASS 3

HIGH CLASS 1

7 8

42

5 6

IR Optics - IR optical flame sensors

& filters

Supply ON (Green) - Steady if detector

functioning correctly

Fire (Red) - Indicates a FIRE detected

Test (Yellow) - Indicates detector in test

mode

UV Optics (Option) - UV optical flame sensor

if fitted

DIL Switch - Select detector functions

Connection Terminals

Electrical Connections

The flame detector has eight connection terminals as show in Fig 5. Removing the front cover of the
flame detector accesses the connections. The cable is passed through the gland holes in the base
of the detector.

Closes if flames

Normally closed

(N/C) when

owered

+IN -IN

+24Vdc Supply

ut

In

+R -R

FLAME

(N/O)

Test Input

Fig 5 Electrical Connection Terminals

Relay RL1

FAULT

(N/C)

Relay RL2

8

5

Connection Terminal Descriptions

Terminal
No.

1 +IN Power Supply +V. +IN is the power supply input to the flame detector

2 -IN Power Supply 0V. –IN is the return path for the detector supply current.

3 +R Remote Detector Test Input +V. No connection to +R is necessary if

4 -R Remote Detector Test Input 0V. No connection to -R is necessary if the

5

6

7

8

Table 2 Connection Terminal Descriptions

Mnemonic Function

RL1

RL2

and is normally 24Vdc with respect to terminal 2. The current
consumption of detector can be monitored to determine the detector
status (Fault, Normal, Pre-alarm, Fire). If the detector is in latching
mode then this supply line must be broken in order to reset the
detector. A thermal fuse within the detector will blow and break the +IN
connection if the detector operating temperature is exceeded.

-IN is also internally connected to terminal 4.

the detector optical and circuit test feature is not required. If 24Vdc is
applied to terminals 3 and 4 the detector internal optical test sources
will activate to simulate a flame. The detector yellow test LED will
flicker to indicate an optical test is progress. The detector will then
alarm indicating that the test was successful.

detector optical and circuit test feature is not required.

-R is internally connected to terminal 2.

Flame Relay RL1. This volt free contact is normally open (N/O) and
only closes when a flame has been detected. If the detector is in
latching mode (see DIL switch settings) the contact will remain closed
once a flame has been detected. Only when the detector supply +IN is
broken will the detector reset and the contact open once again. The
contact can be changed to a normally closed (N/C) state by moving the
link on JP1 in the rear of the detector.
Maximum relay contact ratings: Power=3W, Current=0.25Amp,
Voltage=30Vdc. Resistive loads only.

Fault or Pre-alarm Relay RL2. This volt free contact is normally closed
(N/C) if the detector has no faults and the supply voltage between
terminals +IN and –IN is the correct value. If the detector mode is
changed (see DIL switch settings) this relay can be de-energised to
reduce the detector current consumption. Alternatively RL2 can be set
to provide a pre-alarm fire signal. The normal contact state can be
changed state by moving the link on JP2 in the rear of the detector.
Maximum relay contact ratings: Power=3W, Current=0.25Amp,
Voltage=30Vdc. Resistive loads only.

Selectable Detector Functions

(DIL Switch Settings)

Fig 6 DIL Switch with Detector Front Cover Removed (Normal factory settings shown)

Selectable Functions DIL Switch Settings

Relay RL2 Function: 1 2

RL2 off (No fault relay) – For lowest detector current consumption. 0 0

RL2 off, or UV pre-alarm, flame or electrical sparks detected. 1 0

RL2 detector fault relay (Energised if detector powered and no faults) 1 ~ 1

Detector Supply Current (Detector Status): [-/ = see Output Mode below] 3 4

Low current mode, 3mA / 9mA (RL1 Only), 8mA / 14mA (RL1 & RL2) 0 0

Two-wire current signalling only. No relays operating. 4-20mA, 4/20mA 1 0

Two-wire current signalling 8-20mA, 8/20mA and both relays operating. 0 1

Two-wire current signalling 8/28mA and both relays operating. 1 ~ 1

Output Mode: 5

(-) Proportional analogue supply current. Non-latching fire alarm signalling. (-) 0

(/) Step change, supply current. Latching fire alarm signalling. (/) ~ 1

Response Time: 6 7

Faster response times reduce the optical interference immunity. Very Fast ≈ 1s 1 1

Sensitivity: See EN 54-10 8

Factory settings ~

Table 3 DIL Switch Settings

DIL Switch

0
1

SENSITIVITY

Low Class 3
High Class 1

12345678

RL2 energised on IR pre-alarm 0 1

Slowest ≈ 8s 0 0
Medium ≈ 4s 1 ~ 0

Fast ≈ 2s 0 1

Low Class 3 0

High Class 1 ~ 1

6

7