REFERENCES
•All
Aboul
Boilers,·
Marine Engineering/Log, February
1974, pp.
~53.
Bender,
Rene
J.
(ed), ·Steam Generation,· Power,
Special Report,
June
1964, 48 pages.
Burkhardt, Charles H., Domestic
and
CommerciaJ Oil
Burners, 'Third Edition,
New
York et ai, McGraw-Hili Book
CompanV. 1969,
•Electrode Boilers Make sense.· Enert:t Marketing
cover slory, Electrical World, 8ep1801ber " 1971. pp.
70-72.
Faust,
Frank
H.
and Kaufman,
G.
lheOOore, (ed.),
Handbook

of
Oil
Burning,
Oil-Heat
lnslilule
of
America,
Inc., 1951.
Griswold, John, Fuels. Combustion
and
FurnactJ$.
Arst
EdItion, ThIrd Impression, New York
and
l.onQ::ln,
McGraw-HIli Book· Company, Inc., 1946.
Guide
for
the
Selection, Installation and Operation
01
Oil
Burning Units, Newark, New Jersey, American Boiler
Manufacturers Association, 1971.
LeJdcon,
Steam Generating Equipment,
Third
Edition,
Artingta'l. Virginia, Arrllilrlcan Boiler
Manufacturers

Ass0-
cIatiOn. 1974.
North American Combustion Handbook, Firsl Edilion,
Third Prlnling, Cleveland, Ohio,
The
North American
Manufacturing
Co., 1965.
• Power From
Coal"
- Parts
I,
II,
and
Ill, Power, Special
Repor1
t;7;
the
edllorsi, February, March,
and
April, 1974,
64
pages.
Schaphorst, W., "ThouQhts About Fir&-
Tube
vs.
Water-TUbe BoIiEll'S," Power,
september,
1972,
p.

167.
SImpson., James
H.,
-Conversion
of
Boilers
to
Dual·
Fuel Systems." ASHRAE Journal. May 1973,
pp. 46-54.
Steiner, Kalman,
Oil
Burners,
Third
Edition,
New
York,
Fueloil &
011
Heat, 1960.
Trinks, W.,
and
Mawhinney, M.H., Industrial Furnactls,
Volume
II, Fourth Edition,
New
York,
London, Sydney,
John
Wiley & Sons, Inc., 1967.

70
•
.~
PART
I-TYPES
OF
FLAME
DETECTION
SYSTEMS
The
purpose
of
a flame detection system Is
10
delect
the presence or absence
01
a safe flame so lhal bJrner
0p-
eration
may
be
conllnuedU
condil1ons are safe.
and
Inler-
fl.4'led
if/hey
are ~t
FLAME

CHARACTERISTICS USED BY FLAME
DETECTION SYSTEMS
All
flames
have certain characteristics In
CCM1VT1OI'l
in-
ch.Jding
Ihe
following:
ProducUO'1
of
heal.
Expansion
01
gases.
Prod.!cllon'
of
by-products
Emission
of
Ughl
Onfrared
10
ullraviolet).
Ionization
of
the atmosphere
in
and

around the flame.
Flame detection systems have been developed
using
several
of
these characteristics with Ihe flame detect-
ing
ponlon
01
Ihe
system emitting a signal
or
originaJing
soma physical action
In
Iha presence
01
Ihe detected
characteristic.
Many flame detection systems designed for
use
on
cb-
mastic
healing
systems
use
the thermal effect
of/he
flame

as
the
method
of
detection. The detecting eiement must
be
healed
by
Ihe flame for operation
01
the system to con-
tinue.
This
,Is
true
whelher
Ihe heat is converted
10
a physi-
cal force, as in a bimetal
or
hydraulic pilot
SElnsor,
or
to an
electrical signal
as
in
a Ihermocouple. Considerable lime
)s

required
for
the
SElnsor
to heal, and a similar time
pericx:1
Is required
for
It
to
cool
on
toss
or
flame.
Larger systems (commerCial
and industriaQ require
faster
flame
proving
leChnlQJ8S. Fast responding systems
have been
devel~
that
use
Ih!I
Ught
emitted
by
the

flame
On1rared,
Visible,
or
unraviolet) and the ionization
characteristics
of
the flame.
FLAME
ROD VS THERMAL SENSORS
Flame
rod
systems
dppend
on
the
abllily
of
the
flame
to
conduct a CUrretlt
when
a potenltal Is
awlied
across
il
(flame lonizalion).
The
flame rod

must
be
used
wllh a suitable electronic
flame safeo;uard control
to
al11=l1l1'1
the sig'\3l
frcm
lhe
flame rod. The flame rod usually is used to detect a
gas
flame.
011
flames
are
not
generally suitable
for
the
awli-
calion
of
a flame
rcd
because
of
their higher cperating
temperatures.
Flame rod

defection
systems have 4 ifTlXlrtant advan-
tages
over
thermal type
pilot
sensors:
, . .o.u !.CKAESPONSE
TO
FLAME
FAILURE-The
bi-
metal
pilOI
and
the thermocQt.4lJe
pilot
have a response
lime
of
up
to
3 minutes. Rarely
t:bes
this type
or
pilot
r&-
spend
In less than 1 minute.

On
domesllc Installations,
wtlere
these flame
detection
devices are normally
em-
ploved,
low
fuel consufT1)tion makes response time less
71
critical. Hence the maxil'l"lUTl
r8SjX)1"1S8
timings
for
(his
type
at
equipment have
been
eslabllshed at 3 miAJtes.
Thermocouple
systems are often
used
on
larger installa·
lions
for
gas
pilot

supervislO1 only, as an auxiliary
10
hl\1l
speed
rectifying flame
rod
systems.
On
larger installations, this
slow
response to flame fall·
ure
would
be dangerous. For exarrple,
on
a typical larger
Installation
burning
600 cLblc feet
at
gas an hour,
wring
the minute
or
so
It
takes the flame sensing device to reccg-
nlze (hal the
flame
has

been /ost,
at
least 10 cLblc teet
01
gas can be Introduced Info the
conbJslion
ct\atrtle(.
kr
suming
that natural gas
is
used.
it
will take an ad::filional
100
cubic
feel
of
air
for
Pfoper
corrbustlon.
ThiS
amounts
10
a
tolal
ot
,
10

cLblc feet
at
cornbuslj~
mixture intra-
wced
into
the combustion Chamber,
10000Ing
for
a
means
10
be ignited. If delayed ignition takes place,
lhal
voll.lTle
of
fuel·air mixture
COUld
caUSEI
a
SElrious
elCplosion. For
thIS
reason, larger jobs
need
electronic flame safE9J3rd sys-
tems that have a response
timing
of
2 to 4 SElcords.

2. PRQVES FLAME AT
IGNmON
POINT With the bi-
melal
pilot
and
Ihe thermocouPle pilaf, the pilot is essen-
tially proved
at
the source.
BecauSEI
of
lhe
flexibility
of
poslllonlng
a flame rod, a
pilot flame can
be
proved
aJ
the
point
of
interseclion with
the main flame.
3. PROTECTS ITSELF AGAINST FAILuRE OF ITS
CQM.!'ONENT PARTS A
bimetal
pilot

or
lherrTlOCOl.ple
pilot Installed
on
a large
burner
Is
5/.bjec1
to
the intense
heat
of
the corTt:Iustion c/1aIrt:ler and reflected h&aI
frcm
radiant brickwork:.
This
heal can cause
melal
f~,
lead-
ing
10
Sluggish operation, nuisance
shuldJwns,
or
eYElrt
failure
or
the
sansing

element. In some cases, the bimetal
pilot
has
actually failed In the
-on-
posllion. This,
Of
courSEl,
causes a hazardouS condition by allowing
lhe
main gas valve
to
remain
open
or
be
opened
with no real
proof
that a pilot flame
is
present
Wflh
eleclronic flame safeg.Jllfd systems, a checking
circuit
can
be
built
into
the

syslem. If abnOrmal cordlJons
occur
In the flame delee/or
circuit-SUCh
as c:pen circuits,
shOrt circuits.
or
leakage resistance
to
grOU'"d-they
simulate absence.
not
presence,
at
flame and cause the
system
to
fail safe.
4.
LONG
WFE
Of
CQNSISTE!'lT
OPERATION-As
pointed
out abOve, the intense heat encot.rIlered on larger
installations causes metal fatig.Je in thermocouple pilots
and
bimetal pilots.
With

electronic flame safE9J3rd syslen'lS, hoW8\'8r, a
flame rod
or
photocell is the flame sensing device TIle
flame rod normally
has
a temperature raUng In excess
or
2,000 degrees,
so
it
can withsland
the
hi\1l
1Iame
lempel'alures.
71-97558-1
FLAME CONDUCTIVITY VS
FLAME
RECTIFICATION SYSTEMS
There are 2 basic
principles
In flame rod
delecllon
sys-
tems-flame
conductivity
and
flame rectification. Conduc-
tivity

systm
are,
for
the
mOSI
part, no longer used.
Eilher
lype
of
system depends
on
the ab.lllty
at
the
flame
10
conduct current
when
a voltage Is applied across
The ac
VOltage
~Iied
10
the
electrodes looks like this:
In a 60
Hzsyslem,
II changes its direction /polarity} 120
times a second.
At

one
instant, one
of
the electrodes is
positive,
and
1/120
01
a
second
later it is negaliva.
/J.s
the
voltage Changes polarity, the flame current (ion flow) will
Change direction.
For a CondJClivity system, the areas
01
the 2 electrodes
(called flame
and
ground
electrooes) are equal and the
flame current between them is the same In both directions.
This
is
the principle
01
a
conduclivity
system, When an ac

voltage is applied across the flame electrode and the
ground
electrode,
alternating
currenl proportional to the
awtled
voltage flows
through
the flame.
Because the flame current
in
a conductivity system
Is
ac, this system
cannot
differentiate between a leakage
current
and
an actual flame current. It
i!$
possible
for
the.
system
to
falsely indicate the presence
01
a flame (with
possibly dangerous results)
if

the flame electrode is
shQrted to grcx.nd
through
a leakage circuit with about the
same resistance as the
impedance
of
a flame. A
carton
depOSit on the base
of
the
flame
electrode could form a
very effective leakage
path
and
cause a false flame indica-
lion. (A direct short
of
low
impedance
would,
01
course,
make the system Inoperative.)
lhe
flame rectification system
also
uses 2 electrooes,

bul
with 1
irfllortant
difference-lhe
grOUnd eleclrode is
+
~
y
>
6
-
,
L.c
.
~UU£NT
Feow
_£M
,

2 eleclrlXies in the flame. Heat frem the flame causes
!!lQIawJ~
be~weE!ln
the
electrOCies
10
colli.de
wllh
each
other
so

forcibly as
to
knock;
some
electrons out
of
the ai-
oms,
proC:liClng
ions. ThiSts called flame Ionization.
Posi-
tively Charged·,1ons flow
to
the negatively charged
electrocJe; negatively
charged
electrons flow
to
the posi-
tively charged eleclrode.
always
designed
to
be
much
larger than the flame elec·
trode
(flame
r~.
FOI"

effective operation,
the
area
of
the
ground
electrode must
be
atleasl4
limes
thai
01
the flame
rod. Usually, the
ground
electrode will
be
the
burner
head.
Because
of
the
difference In electrode size, more cur-
rent flows In
one
direction than In the other. When the
flame
rocl
is positive,

more
current flows.
: f ' '~
When the flame rod is negative. less current flows.
6
•
~
•

~
~I

~_"~O·

,,
'pO
".
With the current In one
direction
so
much
larger than
the current In the other direction, the resultant currenl is,
effectively, a
pulsating
dIrect current which operates the
electronic netWork.
The
flame relay
pulls

in, indicating the
presence
of
a flame and
allowing
the bUrner sequence
to
continue.
The
larger the ratio
of
ground
area to flame elec·
trode area, the greater the
flow
of
current
in
the proper di-
rection-in
other
words, a reclified current.
Only the ionized path
through
a flame
and
the different
sized electrodes can provide the rectified current required
for
the operation

of
the electronic
network
in
a rectification
system.
Should
a
high
resislance leakage
to
ground
occur
in the flame circuit, it
senc:ls
an ac signal Into the network,
and
lhe
system
shuts
down
safely.
The
rectification sys-
tem
does
re'Cognize the difference
between
a high resis·
tance leakage

to
ground
and
the presence
of
a flame.
72
-
-
PART
II-REQUIREMENTS
FOR
FLAME
ROD
RECTIFICATION
SYSTEMS
The 'requirements
thai
must
be
satisfied when
applying
a recUfying
flame
rod
are:
1.
Stable
flame
- The name

10
be
proved
must
be
sta-
ble-continuously
in contact with Ihe flame grounding
area.
We
are
primarily concerned with
pUOI
flames
since
1beS8
are the most common
and
the
most
difficult
awllcalions.
2. Adequate ground area.
3 Flame rod prq)9rly located in the flame
envel~.
4.
A
clrcuillo
carry the flame signal
10

the amplifier in
the primary control.
These 4 requirements will
be
covered In detail in the
sections thai follow.
REQUIREMENT
l-STABLE
(PILOT) FLAME
The pilot to use
if
the pilot
is
10
be proved by a flame rod
should
have the
following
characteristics.
1.
11
shoold
be
a
premixed
pilot
2.
tt
should
be

a strong pilot.
3.
II
should
be poSitioned where it will smoothly ignite
the main burner.

USE A PREMIXED PILOT
Prembred pllots are recommended
beCause
the
stronger
flame anel
greater
speecl
01
flame propagation
contribute
to
go::id
contact
with
the
ground
area
ana
to
sta-
bility
with

respeclto
the
flame
electrode.
Raw
gas
pilots
are
generally difficult
to
Slfl9rvise
elec-
tronically
because
of
the difficulty in securing a slable
flame
ground.
In ad:l'ilion,
lheflame
o1a raw
gas
pilot
may
fluctuate excessively
and
changeposilion
in response
to
minor

draft
variations, cOrTJlllcaling the
prd:llem
01
flame
rod
location. - .
Fig. 1
shows
the
2
types
of
pllots. Note, with the raw
gas
pilol,
how
the
Insulaling
layer
of
raw
gas
keeps the flame
from
contacting
the
groond
area
until

near the end.
With
the raw
gas
pilot
reaching
oul
for
the
air
necessary for
combusllon,
even
this
small
contact is uncertain.
Com-
pare
this
with the flame-l<>groond-area contact in Ihe
premiXed plio!.
USE A STRONG PILOT
Make the
pilot
flame
strong
enough
to
be reasonably
stable

under
the most adverse
conditions
of
draft
and
modulation.
If the
pilot
flame
leavElS
the flame electrode
for
a
period
longer
than
the
flame
relay
liming,
nuisance
shut-
downs
are sure
to
result. Increase the gas pressure
to
the
pilot,

or
enlarge the
pilot
orifice_if necessary
to
provide
a
stronger flame. Increasing the
gas
pressure tends to
harden
and
lengthen the pilot flame,
increasing
ils stability
under adverse conditions. This stability
is
especially nec-
essary when the
main
burner
fires
with
hl~
pressure gas.
Adjust the
air
mixer
10
reduce traces

01
yellow
in the pilot
to
a minimum.
POSITION THE PILOT WHERE IT
WILL
SMOOTHLY
IGNITE THE MAIN BURNER
Follow the
burner
manufacturer's
recommendations
on
pilotlocauon,
if
available;
if
not, Iry
to
find the location
most favorable
to
the
smooth
ignition
01
main
flame.
For example,

with
a mullJple-head
or
multiple-Jet burn-
er,the
ideal location
isat
U1epolnt
where
gas
first emerges
from
bJrner
ports,
aM
a
point
near
the LpSheam
ed;J:I
of
the
burner
(with respect
to
the
direction
of
the drafl). The
pilot

can normally
be
mountec;l yertically
between
bu'ner
heads as shawn in Fig. 2
wilh
the
pilol
flarne playing up-
ward across the junction
of
the
gas
slreams
coming from
al
I6ast 2 heads.
Fig. 3 shows a satisfaclory
pilot
installation
on
an in-
spirator
or
venturi type
burner.
The
pilot
is

firing in the gen-
eral direction
of
the
main
flame.
The
pilot
is strong enough
to
intersectlhe
main
flame
envelCf.lE!,
aM
the flame rod is
Iocatea where it
can
prove
both
the
pilol
and
main flames
simultaneouSly. Fig. 3 is a
QOOd
example
o1a
pilot
that is in

a p::lSition
10
smoothly
igdte
the
main
burner.
Fig.
4,
however, shows
an
exaggerated
pcx:lr
installa-
tion. Here the
pilot
has
been
located
so
that no part
of
II
comes
near
intersecting the
main
burner
envelCf.lE!,
and

the
Rame
rectifier
is
positioned
where
a lazy
pilol
flame
~jr
ing
at
low
gas pressure)
can
still
coolacl
it. Obvioosly this
installation can
only
result In delayed
ignition
and
ro Ql
starts.
On
radiant type burners,
t~
pilot
is

often
ITlOl.nted
alongside the
burner
or
fires
throogh
one
of
the b.Jrner
c:penings In the radiant
burner
block
as
shown
in
FlO.
5.
TOP
VIEW
IlISIJLn,~~
lAYU
~l'~f
CO~T'CT
~IT~
OI'R""'\
""(JJ~C
oRE_
SIDE
VIEW

AG.
1-
FLAME
CONTACT WITH GROUND
AREA-RAW
GAS
PILOT
VERSUS
PREMIXED PILOT.
73
71·97558-1
Here the pilot fires In
the
dlrec:lion
of
draft
and
provides a
flame which readily
Inl9rwcls
with
t!"le
main burner flame.
Fig!.
6, 7, 8,
and
9
smw
recomlTlElOdad
pilolloc:ations

on
other burner types.
PosmON
THE
PILOT
$0
rr FIRES
IN
THE
GENERAL
DIRECTION OF
THE
DRAFT
Fig.
315
an
8l1:C9l1enl
BlI:arrple
at
a piJOllhai
is
localed
10
1Ire
In the direction
at
t!"le
drall. Obviously,
drall
etfecl

would not pull.
th8 piiOI away
from
lhe
main
11am&.
In fact,
prevailing draft would
anecl
both
pilOl and
main
flames
in
FIG.
2-TYPICAL
MOUNTING
OF
FLAME
RECTIFIER' P·ILOT
ON
MUlTIPLE
HEAD
GAS
BURNER.
11=j):::1!yP'LOl
lkd=j
FIG.
3-RECOMMENDED
PILOT

INSTALLATiON
ON
AN
INSPIRATOR
OR
VENTURI
TYPE
BURNER.
the same manner.
Any
drilllrlQ
of
one flame
would
be ac-
companjedbya
almUaralfling
0'
l!"le
other. The result
will
be
smooth reliable Ignition.
Never
instalilhe
plio! burner so
thallhe
pilot
flame can
st1i1l

Joaposiflon
whete
il
will not positively
IglU8lhe
main
burner,
but can still make conlact
wilh
the
flame
electrode.
For ell:atJl)le,
i1
the
pliol
burner Is installed horizontally
or
inclined. the flame electrode must
NOT
fie
along the
lop
of
(he pilot burner assembly where a weak
or
~Iazy'
pilot
PILOl
FIG.

4-INSPIRATOR
OR
VENTURI
TYPE
BURNER
WITH
EXAGGERATED
POORLY
POSITIONED
PILOT
AND
FLAME
RECTIFIER.
TDP
VIEW
""
J
'
FIG.
5-TYPICAL
MOUNTING
OF
FLAME
RECTIFIER
PILOT
ON
RADIANT
INSHOT
TYPE BURNER.
74

flame, inadequate to liQht the main burner, can curl
up
around
lhe
shank
01
lhe 1lame eleclrode.
PROTECT THE PILOT FROM THE EXTREME HEAT
OF
THE COMBUSTION CHAMBER AND RAOIAnON
00
not
locale the pilot burner nozzle where the main
11ame
will impinge on
il
under any
f1rinQ
conditions.
tf
p0s-
sible, keep the pilot oorner below or behind the main burn-
er
,(as
in
F(Q.
3)
so Ihat the burner frame and refractory help
aiDE
VIEW

BV~~ER
""
""
FIG.
6-POSSIBLE
MOUNTING
OF
PILOT AND
FLAME
ELECTROOE
ON
RING TYPE
BURNER.
FLAIoIC
RECTIFlU
TOP
VIEW
FIG.
7-POSSIBLE
MOUNTING
OF
PILOT AND
FLAME
ELECTRODE
ON
TUNNEL
BURNER,
75
10
shield the pilot burner. Locating lhe pilot

In
the secon-
dary air stream will also provide a cooling effect.
KEEP THE PILOT VENTURI ACCESSIBLE AND AWAY
FROM HIGH TEMP1::'AATURE AREAS
The
pilot venturi
/TILlS!
be accessible
10
make air
adjust-
ments
10r
the proper amount
of
premi:Jclng.
Preferably, the
venturi
ml:lCer
should be localed outside the combustion
chamber
and usually outside
of
any
wind
boll;
area. Fig. 2
shows the venturi located where
il

is readily accessible.
Hi.;;tl-temperature locations should
be
avoided
be-
cause Changes in air temperature al the pilol
mi:lCer
may
pr~ce
undesira changesble In the pilot flame
characteristics.
POSlllVE
COMBUSTION CHAMBER PRESSURES
Positive combustion charrtler pressures are
caused
t¥
lhe
rapid expanSion
of
lhe
fuel mixture
in
the oorner.
One
result is pilot instability, causing erratic flama prO\ling. In
severe cases the pressure may
be
emugn
to
snuff

oullhe
pliol.
It
may
be
necessary to relocate the pHot venturi where
the pressure will
be
equaliZedbetween it
and
lhepilotnoz-
zle; e.g.,
below
lhe oorner
bed
on
an
~hol
burner.
SIDE VIEW
FIG.
8-TYPICAL
MOUNTING
OF
PILOT
ASSEMBLY
ON
MULTIPLE HEAD
INSHOT BURNER.
PILcr

TOP VIEW
FIG.
9-
TYPICAL MOlJNTING OF PILOT
ASSEMBLY
ON
SINGLE- PORT INSHOT
BURN.ER.
71-9755&-1
REQUIREMENT
2-ADEQUATE
GROUND
AREA
,,,.
•
Ensure that the ground area In contact with the flame
exceeds
the
area
of
the flame
rod
normally
In
COTllact
with
the
flame by a raUoOf
alleast
4

10
1.
This
ratio Is sufficienlly
large
10
prevern
grOUnd
area.
problems
regardless
Of
the
pas/lion
of
lh". rod in the flame.
WHAT
IS
GROUND
AREA?
Ground
area
is
any malerial In contact
wllh
(he flame
that will carry the flame currenl10 ground.
Grourd
area Is
dasignecHnto the

buTner
ItseH.
In ad::Iition, melal burner or
COrnbusl.ion
chamber pal1&, refractory,
and
other maleri·
als In contact
with
the
flame all act
as
pan
01
the
ground
area. (Refractory
does
conliJcl
once
It
Is
healed·
this Is
why the flame rod must
not
be
In contact with refractory.)
A typical method
of

pro

iding
ground
area
tor
a pilO!
flame
is
shown
in
Fig. 10.
Ground
area
is
provided
on
the
C7005 Rectifier Pilot by
"bomb
fin"
grOUrd
plales that
are
part of the
burner
noz-
·l.~(
~lECTIItlDE
x"

FIG.
10-C7005
FlAME RECTIFIER PILOT.
zle. This type
of
pilot will rarely present
ground
ralio
ptcblems.
It
is
not usually necessary to provide special
grounding
a.sserrtlIles
for
main burner
flames-the
flame
COntact
with the walls
of
the
cont:ustion
cham/::le(
and
wllh
burner
parts is generally sufficiant
10
provide'

an
acceptable
ground-lo-flame-rod ratio.
ADDING
GROUND
AREA
TO
EXISTING
BURNERS
PILOT BURNERS
If
the existing
pilot
bJrner
does
not
proviae sufficient
ground
area for the flame,
it
may be replaCed with a recti-
fier pilot like the
C7005 which
does
have sufficienl ground.
II may also
be
filted
wilh a special
ground

assembly,
if
available;
or
grOUnd area may
be
added
to the pilot USing
one
ot
the methods Sl'lJwn below.
•
FLAT PLATE
MULTIPLE
ROD
TIle flat
plale
asserrbly
is
similar to the type
at
ground
area used
on
the C7005. It may be construc.led simply by
welding together pieces
of
high-temperature steel. The as-
sembly is then welded
10

the burner head.
TIle multiple rod assembly is constructed
b\'
welding
plecesofflame
rod
loa
melal strap. The
slrap
is then
fitled
around
lhe
burner
head
and
welded In position. TIle rods
may
also be welded directly to the burrier head,
or
the
head may
be tapped and the rods
screwed
Into the tapped
holes.
MAIN BURNERS
If
gtwnd
area musl be

added
10
a main burner flame,
add
rods
or
pipe
grOUnded
10
the
boiler
or
furnace wall
and
projecting Inlo the flame
al
all times.
RODS VS FLAT PLATES FOR
GROUND
AREAS
A curious
phenornenal
will be
noted
when using flal
metal surfaces
as
a grounding medium in
lhe
flame enve-

lope.
Allhc>lJl;t1
the metal may
bEl
complelely Immersed In
the flame, effective
ground
area In contacl
with
the flame
wlllex:lsi
only
around
lhe
edgeS
of
the tlal metal surface. A
thin layer
of
unburned
gas
tends
10
insulate the center por-
tions
of
(he flal surface from the
burning
fuel
and

IonIzed
gases adjacent
10
lhe
ftame.
This
condition
Is
present, but
to 8
much
lesser degree, when rod materials are used
for
flame grounding.
76
Rod
materials also
offer
a
much
more flexible means
of
accompliShIng grounding, as they may
be
mounted In any
number
and In any pattern necessary to Insure contact
wilh
the flame
under

all conditions
of
varyIng drafts. The
qusstlon
01
flash-over
does
not
enler the picture with rod
grounding
either, as
II
may
with f1afplate ftame groundlng.
Protel;tion from flame snuffing In strong drafts Is
perhapS
even
grealer
with rod grOLrlding than II Is with flat plate
groundino.
The
flame
will
liang
behinc:l a rod, whereas
lhe
plate
lends
tpblock
the

air
flow, Ihus wiping the flame from
Ihe
surface

,
EFFECT OF
SOOT
OR SCALE BUILDUP
Soot
or
scale
buildup
on
a flame rod
can
rasull in reduc-
tion
of
the
grOUnd-te>-flame-rod-area rallo to IBS5lhan the 4
to
1 rEQJired
for
prc:per rectiflcallon and'flame currenr. Un-
-
,,',.
der
-no flarne-, condltions,
sool

and' scale
are
nonconduc-
tors
of
eleClricity. However when flame is
awlied,
they
actually
become
condJclors.
The problem Is In the addi·
tlonal area
acX1ed
10
the
flame red
by
fhis bui~. Ad:fI-
tlonal surface area
provided
by
Ihe hills and valleys
of
lhe
buildup
material can easily
cb.bIe
or
triple the flame rod

area.
Too
much
buildup
can
decrease the flame currene
below
the value required to hold in
Ihe
flame relay, and
burner
shuldown
will
occur.
This
points
out
Ihe necessity
of
inspecting
and
Cleaning the flame red periedically.
PROVING ADEQUATE GROUND AREA (FLAME
SIGNAL MEASUREMENlJ
The
best inc:licator
or
adequate ground area is a flame
signal reading
of

prq:>er size and steadiness. The flame
signal is measured with a
dc
microammeter (Honeywell
W136A
or
equivalent) connected in series with the F lead.
Most
HoneY'N8l1
conlrols
have a meter
jaCk
which
aute>-
malically places
Ihe
meter
in
serles with the flame rod.
Refer to the inseructions paCked with the flame safe-
guard
control
for
Ihe
exact flame
slglal
measurement
procedure.
WlIh
most

Honeywell
conlrols, the flame siliT'i!l should
be
at least 2 microart'f.lElres and s1eadj. The reading 00-
'\ained
on
self-Checking systems will
be
much
higher-re-
ter to the
controllnsfrucfions.
If the flame signal reading
is
not
correct, the
ground
area shOuld
be
the firsl ilem
checked. If In doubt,
~
more ground area 19lTIpOfarily
and recheck the
flame
slglal.
tt
a satlsfacfory reading is
obtained,
adj

permanent
ground
area.
REQUIREMENT
3-PROPER
LOCATION OF
THE
FLAME
ROO
IN
THE
FLAME
ENVELOPE
,

The location
of
the flame
ro:::l
In the flame en'l9lc:pe
must
meel the
following
requirements.
,.
The location must
provide
the req.Jlred type
of
flame

s~rvrsion.
2. The
flame
rod
must
be
In conlact
at
all times with the
flame fo
be
proved.
3. The rod must b&
located
so
lhat
II c8/TlOt defect the
pllof flame
if
il
becomes
too
small to Ignite
the
main
bumer
flame (pilot
proving
aw1icatlons
only).

4. The locatron should
prevent
changes In the flame
ro:::l
posillon
or
al
leasl eliminate the
PJSSlblllty
of
any
change causing a dangerous situation.
TYFES
OF
FLAME
SUPERVISION
The flame rod
may
provide
any
Of
3 possible types
of
flame supervision:
Pilot
anc:l
maIn flame slmultaneoosly.
Pilot flame only.
Main flame only.
BOTH

PILOT
AND
MAIN
FLAME
SUPERVISED
If
at all possible, the flame rod
should
be
Iocaled af the
intersection
of
the
pilot
and main flames. This type
01
awlj-
cation proves
lhalthe
plloe
Is
adecp.Ja.le
for
main flame igni-
tion
anc:l
proves
lhe
main flame
COO!lI1l.OJSIy

dJring the
run cycle.
Figs.
3,
6,
7,
and
8
show
flame
rods
awlied
fa super-
vise the pitof flame at
the
poinl
of
intersection with Ihe
main flame.
PILOT FLAME
ONLY
SUPERVISED
On some installations it
may
be
Impossible to prO'fflthe
pilot and' main flames SimUltaneously because
of
vari·
ations in the main flame envelq:::.e al different tiring rates.

Where
II
is
not
possible to
prove
lxlth pilot
anc:l
main
flames,
proving
the
pilot
only
is
the
nexl
best q:ltion.
Fig.
11
shows a mechanical fan type
burner
where the
gas pressure rotates
Ihe
fan blades
10
provide torced draft
for the burner.
[n

this burner, the flame
position
varies with
the
firing
rate, making
illmpossible
to prOl/e lxlth
pilo!.
anc:l
main flames. Alsa, b&cause
Of
the design
of
the
cermus-
tion chamber, It Is Il'fl)OSSible fa check the
main
flame and
pilot flame without
sub~ !!.ng
the pilot asserriJlv
to
the In-
tanse combustion
chamber
temperature.
Proving the
pilol
only

is also
ckJne
on
con1:linatlon
IOJ2S"
oil burners, particularly on
the
horizontal (otary type wllh
the
gas
ring
added.
When
proving
a pilot closer
10
Its source than at the ignl.
tion point
for
the main flame,
we
can
sHI!
prove the pres-
ence
of
an
adequate
pilol
flame by supervising the pilot

gas prBS5ure.
Fig. 12
shows
a raverse acting gas pressure switch
used
to intern pt the circuli to the
main
gas valve when-
ever the pilot pressure
drops
below
the point
at
which rell·
able ignllion
would
occur.
MAIN FLAME
ONLY
SUPERVISED
When
only
the main
flame
is to
be
supervised, the
flame
ro:::l
must be located where It will remain in the flame

eovelq:::.e
during
atl variations In firing rates and draft
ad-
jusfments.
On
larger burners, special conslc:leratlon
mUSl
bEl
given
to
main
flame

welq:::.e changeS that occur
0'l9f
T7
71-97558-1
considerable distances
wllh
variations In firing rates.
cer-
tain ring
and
gun burners produce regular fluctuations in
flame
loCation, even
during
steady firing.
AWlicalions

or
this kind shouldJ)e carefully checl<ed
under
all possible
draft
cerdtions
and
LKlder all firing rates before the instal-
latioo is considered complete.
ENSURE THAT
THE
FLAME
ROO REMAINS IN CON·
TACT WITH'THE
FLAME
UNDER
ALL
CONDITIONS
,
aiDE
VIEW
FIG.
11-
MECHANICAL
FAN-TYPE
BURNER
IN
WHICH
PILOT
FLAME

ONLY
IS
P
VEN
~:::"T"'"
l~R
"CO
;-;OVALV
""
•
PilaT
~
W "
"
PILOT

8UllNER
llJ"I'LT
'"
~
-
L::
RfvfR5f:
ACTlt,»l
PRE
5SURE
,
•
L
MAIN

Cl)/HlQ

GAl
IlIlh~1
ClllCun
10
III
VALvE VALVf lENP1LOT G
PREl~RE
DROP.;
~.
GAl
I>
6::
]
.~,
FIG.
12-
METHOD
OF
PROVING
AN
ADEQUATE
PILOT.
Main flame posilion
and
Siability are important
on
lhose
appllcalions where

II
is necessary to supervise both pilot
and
main flame simultaneously
or
when
the main flame
only
Is supervi&ed.
If
both
pilol
and
main flame are
10
be
supervised, then the flame roo must
be
located
so
thai
It
remains in contact with lhe main flame
under
as wIde a
range
of
draft and burner
I'TlOdLIlation
conditions as possi-

ble.
If
the main
11ame
only Is to
be
supervised. then the
flame
roo must stay in the flame envelqJ6 under all
COl'ldi-
tions
of
draft
and
rnoclllation.
AVOID
LOCATION
THAT
ALLOWS
FLAME
ROO TO
BE
IN
PILOT
FLAME
WHEN
PILOT
CANDLES
Avoid locating
lhe

rod Immediately aoove the pilot
flame (see
Figs.
'3
and 14). If the plio! pressure Is rEdJC8d
for
any reason, the pilot
flame
would obViously decrease in
its
int9l"\!'lJty,
and
a candling effect
would
be
noliceable. If
the flame rod Is localeo: immediately above the pilot, this
candling could allow the flame rod to sense the pilot even
lhough
the pilot flame is in
no
posilior'lto smoothly
or
sa/ely
ignjte
the main burner. Bringing the roo In
from
the side
or
from

undemealh the
pilol
flame avoids the
POSSibility
that
lhe flame roo will cootac! the pilot
flame
under a low pres-
sure condition where the pilot is incapable
of
prO\lidlng
safe ignition.
LOCATE
THE
FLAME
ROD TO
PREVENT
DANGEROUS
CHANGES
IN
POSITION
Keep the flame roo short, avoiding
bends
i1
possible.
Fig. 15 is
an
e.:ceilent example
01
an

application that
meets this r9CIuirement. Nole
how the flame roo is brought
PILOT
8U~N,~
.RONG
PO~TIIl<
Of
~O~
FIG.
13-IMPROPERLY
POSITIONED
FLAME
ROD
MAY
PROVE
AN
INADEQUATE
PILOT
FLAME.
NOTE·
INE
fLANE
H!CTIlOOE
INOI.JLO
6E
LOCA
TED
ON
EIT~!~

~IO[O~
8ELOW
T~[
PI~OT
WRONG
FIG.
14-IMPROPER
POSITION
OF
FLAME
ELECTRODE ON C700S
FLAME
RECTIFIER
PILOT.
78
do

n vertically
Irom
the Iq')
of
the
burner
assembly. This
llame rod will not sag and
dTOCP
away
rrom
the
location

where
il
can properly supervise the
pilol
and
main flame.
Had the flaiile
fOCI
been broughl
In
from behind, it would
have required a longer flame
rod
with a bend. The longer,
bent flame ro:!
could
drocp out
01
p::sition and
no
longer
provide
proper
supervision
of
the
pilot
Other
argu~ls
in

favo~.at
a
ShOrt
flame rod without
bends
are:
(1)
a
shorterro:!lessens
the chance
of
excess
flame
rod
area distortinQ the rCJd.area-lo-grouroarea ratio
upon which uame rectiticatio:n
depends,
and
(2)
straight
flame rodS are easier
10
replace than rlXiS that musl be
bent to reach the flame-proving point.
LOCATE THE FLAME ROD
6aOW
OA BESIDE
THE
FLAME
IF

II
CANNOT
BE
APPUED VEATICALLY
It
the flame, rod cannot be positioned
SO
lhat
it comes
down from directly
above
the flame as in Fig. 15. locate it
below
or
bes~
the piiOI flame. FIg.13 Shows how a flame
rod
may
plCve
an
Inadequate pilot
if
it
is
lX'SifiOMd along
the
top
o1lhe pilot burner. In ad1ition, the ro:! must not be
located where
II

can
drocp
Into a position where it mighl be
able to prove
an
unsafe pilot.
If
the rod is
lOCated
beside
or
below the pilot, it will,
if
affecled by excessive heat condi·
lions, drcq::l
away
rrom
the
pilot flame
and
cause a sate
shutdown.
UNUSUAL APPLICATIONS
RUNNEA PILOT INSTALLATION
Fig. 16 shows a burner with mullip/e firing
ports
iglited
by a runner type
pilotlhat
is proven at the extreme

encI
at
-
o
o
o
FIG.
15-INSTALLAnON
WIlli
SHORT,
STRAIGHT
FLAME
ROO.
79
the runner. This application Is used
on
many cast Iron
sec-
lional bollars, and
is
ideal for
the
flame rectification sys.
tam, The sna.ll, constantly
burning
pilot
may be proved
by
a
thefmOcQ1 1)le

IypQ assambly,
The
constanlly burning pl.
lat ignites the runner pilot and that, In turn, fires each
oftha
burner ports. The
rUMer
pilol
is
checked at the1ar
end
of
the runner,
A runner piiOI or this
type
should
have
adeq.ele
grounding area (the small flame
al
each runner port
Is
grounded),
Ar'rof
recbJClion
in pressure would make ilself
lell
flrst
at
the

far
end
of
the runner. Therefore,
in
lhe event
of
pilot
r9liJclJon.
the
flame rod
would
no
longer
be
able
10
prove
Ihe
pilot
at
lhe end
afthe
runner
ar'd would not allow
the main burner valve
to
open.
MULTIPLE PILOT INSTALlATION
If the runner typepilot is nol salisfactory

lor
thepartieu-
Iar installation,
end it It is necessary to have more than 1
pilot assen'tlly within a
burner
for
safe
i~llIon.
!hen sach
pilol
should
be
SlCle/Vised
by
its
own
flame ro:!
an::!
flame
safeguard control. With the RA890 Primary Controls, this
individual supervision can be accompliShed wil.toJl aUlfjl-
iary equipment.
Fig.
17
ShOws
one RA890 and one flame rod asserrbly
for
sach
pilot being- proven. The Interconneclion

is
SirTlJfe
because
of
tne fleXibility
of
the RA890. The control circuit
can
be
isolaled from the electronic network. After the first
pilot
haS been
prOViEln,
terminal 5
of
the first relay provides
the power to the control circuit
at
the
relay checking !he
second
pilot.
It the second pilot
is
also proven,
power
Is made avail-
able to operate the main
burner
valve.

With
this arrange-
menl,
it makes no difference wheth9r Ihe
p~ots
are
intermittent,
Igli!ad
for
eaCh
burner
operallon,
or
c0n-
stantly burning. In
any
case, they
would
haY8 to
be
pfO'f91
separately
or
the main
burner
vaNe
could
nol
be
ener-

gized.
If
either pilot fails, the bUrner Is
IrTlITtIilCiaIely
sh.rt
down.
-
-
0
I~
.c
WULTIPlE
Olltll~
~~
PIlRfll(rl(l<[lIPllOf>,
~I
r
[Ii N
III
ElOIIIl[1I
/'
flAW[
1100

I'll
BUIiHEIl
o~
~~AI"_M£1I
",JoHIFClLO
NOZZLES

FIG.
15-FLAME
ROD PROVING RUNNER TYPE
PILOT.
71-9755&-1
()<\
T
JoHT
PILor
-
REQUIREMENT
4-PROPER
FLAME
CIRCUIT
•

"
We have
disCussed
lhe
·relatiOnshlp
01
the flame,
flame
rod,
and
grCll.S1Cf-area.
When
the flame rod
and

the
ground
area arelmmel'SEld In the flame, and a vollage Is
appIJEld,
a
current
flows
In order to use
this
current
flow,
we must
prO"lIda a circuli
In
which
the current
now
Is
noll,Jl'"lCUly
af-
fected
~
cspac:itance, Interference
from
OIher
vollage
sources,
or
leakage resistances
to

ground. The spectfic
Slaps thpt are
rBCJ.lirfld
10
provide
this
type
of
circuli
are
coverEld in
lhe
following paragraphs.
PROTECT
AGAINST
LEAKAGE
RESISTANCES
AT
THE
FLAME
ROD
INSULA
TOR.
The flame rod insulator Is normally a
nonconcilctor
of
eleclrlClty. However,
when
lhe
te~rature

at
the insula-
tor
exceeds 500° F, the resislance of the ceramlc material
decreases
enough
so
that II will conduct current.
This
leakage current may
be
enough to decrease the flame cur·
rent
bEllow
the value requirEld to
hold
In the flame relay,
and
burner shutOOwn will occur.
Dirt,
soot,
and
moisture
on
the insulalOf
can
also cause leakage current
gr~f
enou~
to cause shuloown.

For proper
qJ9ration
of
the rectification system,
1\
is
necessary
to
mainlain
alleast
a 20 megohm insulating
ra-
siSiance in
lheftame
roo circuil. If the insulating resistance
drq?S
below 20 megohms, a prc:portionate
drop
In
flame
reclification current occurs, evenlually reachinQ a low
point where InsuffiCIent
output
shuts
down
the system.
Fig. 18
Sh::lws
BIl
instalialiOfl with flame

and
ignition elec·
trode leads properly protecIEld.
The temperature at
the
flame rod insulator must
be
ccnsiderEld when selecting a flame roo location,
and
Ihe
insulalor must
be
cleanEld periodically.
CON~ER
<1!
FLAllf
,
•
~~·"'.r
-®
RfOlflE~
PILOT
,
liln
T~Ol
~A"O
rl'
lCl<lTlON
,
•

~
•
U,
,
FLAllf PilOT
VA\.VE
•
0
lll~OT~
u _
,(;)
Q;~A"f
Rr
@
_ RECTlFI£R
PILOT

"AIN A
VE
,
I~
"
'"

VALV
."
•
1(5
,
"

FIG.
17-MULTIPLE
PILOT
INSTALLATION.
USE PROPER WIRE
AND
WIRING
TECHNIQUES
FQR THE
FLAME
LEAD
No. 14 wire lralEld for
90
C
or
hlg,er)
Is
recommended
for
the flame lead. Actual wire size Is
not
critical:
No.
141s
easy to handle and
to
PJII
throug,
conclJlt. The Increased
resistance

lhal
occurs
wllh
decreased wire
size
Is
not
Sltt
ntficant. (For example,
200
feet
of
No.
30
wire-were
II
practical to
use
such
small wire - nas a resistance
of
only
20
ohms.
Cc:rTl)ar8
Ihis
10
the
internalt~nce
of

1500
ClhrTlS
In the
meier
we
connect In series with
Ihe
flame rod
when reecllng the flame current.)
The
type
of
Insulation Leed
on
the flame lead Is
Irrpor-
Iant, because It must protect against leakage resistance
10
grCU1C1
When a suitable wire Is used, leakage will
not
oc-
cur
from the wire Itself.
Taped
TEFLON (Honeywell Part
No. R1298020)
is
recommendecl
for

high
lemjJElrature
installations.
The
maximum
length
oflhe
flame
lead
is
IImllecl
by
the
electrlc:al capaCitance between the F
lead
and
ground
(condJll); In
olherwords,
bytheamouni
of
currenllhat
can
flow from the lead
10
ground. tf the
capacitance
is perml!·
ted
(by

excesslve lead length)
10
exceed
0.02
microfareds,
the
ttame
SI\7ltt1
will
be
maskEld
and
relay operation wlll be-
come uncertain. In practice,
1he flame lead can
be
Lp
to
150 feet long,
provided
proper wire Is
used
and an accept-
able flame sl\7ltt1 Is measurEld
althe
primary
conlrol.
The flame
lead
may

be
run in conduit with other line
vollage wiring without
being
affectEld
by
slray
electromatt
netic current pickup.
lhe
flame lead
should
not
be
run in
the same conduit with
hi~
voltage Ignition transformer
wiring.
PROTECT
AGAINST
THE
POSSIBILITY
OF
IGNITION INTERFERENCE
IQl1ition inlerference is a false signal superimposed.on
the flame signal. II is caused
by
ignilion
current feeding

through the flame
10
the flame rod.
From
the flame rod it
feeds
Ihroug,
the F lead
10
the primary control
and
back to
ground. When
the
iQl1llion current is small it will
00
no
damage to the relay, but it will either increase
or
decrease
the flame current.
Whelher
the currenl increasElS (positive
FIG.
l8-INSTALLATION
WITH
FLAME
AND
IGNITION ELECTRODE
LEADS

PROTECTED FROM
EXTREME
HEAT.
80
lnlerlerence) or decreases (negallve inlerlerencel d&-
pends
on the phase relationship
of
the ac vollage in the F
lead and
In
the Ignition electrode. Subtractive differential
may
~.sutricienl
to
cause the relay to
dr(fl
out.
If the inler-
ference
/s
severe
enoug.,
the relay ilself will be
damaged.
When ignition Interference
damageS
a relay, the relav
must be replaced.
rgnillon Interlerence

Is
most easily detected
~
rGading
[he flame currenl with
U'"
ignilion l::olh
on
and oft. A differ-
ence greater than 1/2 microampere indicates the pres-
ence
at
ignition lnterlerence; rearrange the name
eleclrode. ignition electrode,
and ground. Check for cor·
rect spacing
of
the
ignilionel~troda.
1he
ad::Iillon
at
more
groUnd area In the form
of
a flat plate between the flame
rod and the Ignition electrode
10
give a beller
grOLl"ld

for
the ignition
and
10
recl.Jce
the current to lhe fleme rod may
be sufflclenl to cure the prcblem.
81
71-91558·1
PART
III
-
FLAME
RODS,
HOLDERS,
AND
RECTIFIER
PILOTS
The
flame
rod
is held
In
position
by
a flame
rod
holderor
rectifier pilot
8SSeirDty.

The
method
used
depenc:E
on
the
size. type,
and
physical requIrement
01
the burner.
FlaIM
roo
holders
provide
a
mount
tor
lhe
flame
roo,
insulation
10
prOlect against leakage resistance
10
ground
al the mounling point,
and
terminals for connecting the
flame roo

10
the el9clronlc
n~rk
in lhe primary control.
Holders are provided
wlltdJl
flame
rods
to
allow seleclion
of
the
prcper
type
and
length
of
rod
for
the particular
awJication.
In standard holders, rods are
held
in place by chuck
and
setscrew arrangement. In miniature -spark plug"
type assemblies,
the
rods
are

screwed
inlo
threaded
bases.
',_
Rectifier pilots
are
cCllTbinaUon
flame
rod
holders
aOO'
pilol burnaIS. The flame electrode
Is
sU!=p1ied
as
part attha
reclifier
and
is
permanWllly
held
in
position
for
proper
pilot
provIng. Honeywell rectifier pilots may beprovided with
19-
nllion

electrodes for automatic
Ignition
systems If desired.
TYPES OF FLAME RODS
Whenever the
flame
rod
extends into the
main
flame
envelope, the temperatures
encountered
may have some
effect
on
the type
of
rod selected.
Most Honeywell
flame
reds
are
made
of
a stainless
sleel alloy called Kanthal
A·1
which
has
a

maximum
oper-
ating temperatLJl'e rating
of
2462 F
11350
C).
Two
rcx:ls
are
made
of
a similar material called
Jellif
Allay
~
K
n
with
a
maximum temperature fating
of
2200
F
['200
C). These
raUngs are ac!lq.Jate
for
atmospheric burners and
for

most
low
pressure partial premix burners. However, as the de-
gree
01
premixIng Increases, the flame
lends
10
shorten,
becomes colorless,
and
burns
wilh
hiQher velocJUes
and
at
higher temperatures.
On
power
burners where extremes In temperatures
are
encountered, e'tUfl Kantha!
rOdS
may
deform
and
delerio-
reJa.
In
many

of
these cases It Is necessary
10
use a
ce-
ramic rod. Ttls ceramic malarial
recommended
is Globar,
which
ha6 a
maxImum
temperature
rating
of
approxi-
mately 2600 F [1425
C).
NOTE: It
lhe
rod
materials mentioned above are used
at
higher
temperatures than
those
Irdicated,
rod
deterio-
ratlon may require a planned replacement
program.

Un-
~rted
horizontally molKlted electrodes
may
sag
al
somewhaJ \oW8t temperatures, varying with
rod
lenglh
and
diameter. (Standard diameters
of
electrodes available
are
3116
inch
for Kanthal,
and
3IB
inch
10r Globar.) Ability
oftl1e
rod
to
maintain
i\s
position when
mounted
horizon-
lally

shOuld
be
determined
by
testing If the temperature is
within 400 degrees
of
the rated
maximum.
FLAME
ROD
LENGTH
Honeywell Kanthal
A-l
rcx:ls
are available in several
lengths from 3-1/2
10
48 inches. These
rcx:ls
are
adaplable
10
the standard
flame
rod holders
or
to
the miniature
~spark

plug" type assemblies. Jellrl Alloy
"K-
rcx:ls
are
available in 20
and
26
inch
lengthS; they
are
for
use
with
the C7008A miniature assembly only. G\Qbar
rcx:ls
are
available only in
12
inch
lenglhs.
The
Glebar
rod
is
1TIOlJnted
in a holder that can
be
filled
with
a

chuck
assem-
bly
to
adapt the
holder
to
the larger
diameter
of
the
ce-
ramic rod. Chucks are available for the C7004B
and
tor
the
C7011A
The
flame
rod
used
should
be
as
short
as possible
for
the flame
to
be

proved. Most flame
rod
holders
may
be
fit-
led
wllh
a threaded pipe
to
add
~rt
to
the
long
flame
rod
rltesung
indicates
that
the
rod
musl
be
supported.
82
HONEYWELL
FLAME
ROD
HOLDERS

AND
RECTIFIER
PILOTS
C7005A.
B RECTIFIER
PILOT
ASSEMBLY
Pliol burner and flame delector electrode for Industrial or commercial
burners-Ignition
electrode
on
C70Q5B - Kanlhal rcxl Included.
Q179A, B RECTIFIER
PILOT
ASSEMBLY
Pilol burner and flame detector electrode lot commercial or industrial
burners-Ignition
eleclrcde on
0179A-Slainless
staal electrode(s)-Selsction
of
pilol flame patterns.
at79C,
0 MINIATURE RECTIFIER PILOT
ASSEMBLY
Gas pilot burner, flame detector electrode, and ignilion electrode for commercial or indJs·
trial
burnars-Q179D
has a thermocouple adapter
In

place
oflhe
ignition elecfrode-Kan-
thaI
electrodes mounted in ceramic
insulators-Stainless
S!eellargel
to stabilize
Il'1e
flame
and
provide correct flame ground
area-Selection
01
mounting
brackel:s and target
configurations.
~
==='=~-
IC7007A FLAME ROD HOLDER
I
.
~
Small holder mounts on 1/2
NPT
male or female pipe
fitting-Kanthal
A·,
rod {order
~=========

separately).
C700SA,
C7009A
FLAME
ROD ASSEMBLIES
Miniature.
~spark
plug~
twa
holders-Kanthal
A·1
or
Jelli1
Alloy
·K~
rOd
included.
1+
r-=
I
C7011A FLAME ROD HOLDER
Angle boc:Iy-Tapped for
Vl;ll'1lilation
- Kanthal
A·1
or
Globar
rOd
(order separately - adapter
required

fOf
Globar)-MOUr1tS on 1-1/4 Inch threaded pipe.
REFER
TO
THE
HONEYWEll.
FLAME SAFEGUARD CATALOG FOR DETAILS
OF
EACH
MODEL
B3
71-97558-1
CHECKLIST FOR FLAME
ROD
APPLICATIONS
o Flame rocl remains in
gcxx:l
contact with flame
under
all normal firing conditions.
o Flame
rod
iS~
as
short as possible
-preferably
applied from below
or
beside the flame proved.
o Ground area is

alleasl
4 limes the area
of
(he rod in the flame.
o Flame lead
has
Insulation
raledfor
90 C
or
higher-usually
No. 14 wire for normal installations, Honeywell
specification
R1298020
101
hig,
temperature installations.
o Flame lead Is
as
short
as
possible.
o Temperature at
the
flame rod insulator
cbes
not exceed 500°F.
o ,A,pplicalion protected against ignilion inlerterence.
. 0 Mounting pasHian permits service.
o FLAME CURRENT CHECK INDICATES STEADY FLAME SIGNAL

OF
AT
LEAST 2 MICROAMPERES
(8
microamperes for
saM'
checking systems using the R4Q75,R4138,
or
R4181 controls).
84
A tlame radiates energy in the form
of
waves which pro-
duce
heat
and
Ilgn1.
We
can see that portion
oflhe
radia-
tion
whose wavelengfh 1alls wilhin the range
of
visible
light. Most
of
the radlallKi energy in the flame,
tnwever,
falls within

Ihe
Infrared banct, ils waves are too long
10
be
seen
by
the humar'r
f!1oje.
A small portion
of
the radiated en·
ergy
also
falls Into the. ullravlolet range, consistiOQ
of
waves
100
shOrt to be seen
by
the human
f!1oje.
Oplical sen·
sors are
divided
Into 3 groups, depending
on
which range
of
the total radiation
band

they are designed
10
delect:
- visible lignt sensors.
- Infrared sensors.
- ultraviolet sensors.
Fig. 1
shows
radiation inlensity
at
gas flames, oil
flames,
and
hot
refractory with respect
to
wavelength. II
also
shows
the response ranges
at
ultraviolet
(UV)
delec·
tors, Infrared (lead SUlfide) detectors,
and
rectifying photo-
cells. Each
of
these types

of
deteclors will be considered
in delalL
RECTIFYING
PHOTOCELL
FLAME
DETECTORS
In a rectifying flame detection system, alternating volt· negatively charged electrons are attracted to the
pos.i-
age
is
applied to the flame
(FJ
and
ground
(G)
terminals
of
livety charged anode,
and
at this
moment
current will
naw.
Ihe
primary
contrOl, but the operalion
at
the electronic net·
The magnitude

at
the current
depends
on
the lnlensi!¥
of
work
depends
on
direct
currenl. It is the
jcb
of
the flame
the light reaching the
cathode-Which
in turn determines
•
I
','
detector to
permit
the
flow
of
current,
and
10
convert alter·
the amount

at
electrons
which
are emilled
by
the actIve
nating
current to
direct
current, when II senses the pres-
coaling
of
the cathode. A fraction
of
a secord rater, when
enC'El
of
a flame.
the allernating CUrrent flow-isrev-ersed, the anode is
nega-
tive
and
the cathode
p:::ISilive.
The
anode, which
is
not
PHOTOCEll
OPERATION

coaled with active malerlal, cannot
give
off
electrons;
tal-
The rectifying photocell is a high vacuum type photo-
sequenlly, ciJring this
part
at
the'Cycle,
no
current wilt !low.
•
j ~ 11
i~::~EE:t~
i
~o ~O')
I
~:
"

""A
FIG.
1-
RESPONSE
RANGES
OF OPTICAL
FLAME
DETECTORS.
cell which is pracllcally a perlect rectifier.

+
A~ooe
CATttOOE_HAS
ElECTRO~S
•
LIGHT·SE!'lSITIYE
COUIHG

FIG.
2-
CONSTRUCTION OF THE RECTJFYING
PHOTOCELL.
WHEN ANODE IS
POSITIVE
ANO
CATHOOE NEGATIVE,
CURRENT
FLOWS.
In this way, the photocell acts
as
a true rectifier, changing
ac
to
de
when
flame it; presenl, and
permitting
no current
at all to
flow

when
lhe
flame Is
not
present.
The rectifying photocell
has
one very Important
advan-
tage
O'>'er
Ihe
cadmium sulfide and Infrared (lead sulfide)
type detectors, which are nonrectifying, in thai it is pro-
tected against a false flame signal ciJe
to
Ihe
presence
at
a
hir/1 resistance shOrt.
If
a high resistance short Is
p1acad
across Ihe photocell, It would
provide
an alternate current
path
and
only allernaling current

would
flaw in the circuit.
Consequenlly, the relay
would
drop
oul
and the
bumef
would
shuf down because dc
only
must
be
present lOoper·
ate/he
electronic network
of
the
relay.
The flame rectification clrcuil will distinguish between
The
cathode
of
the reclifler tube is coated with caesium
the presence
ot
an
oil flame
and
a

high
resistance short to
oxide
or
some
other
active material which
has
lhe
property
grOUnd.
This
characteristic
of
flame rectification systems
of
emilling
electrons whenever light strikes il. Thus, in the
makes the use
of
~cial
shielded
cables unnecessary.
presence
at
an
oit flame, light striking
the
cathode causes
No. 14 wire (rated for 90 C

or
higher) Is recommend9d
for"
electrons
to
be emitted.
Consider what happens
when
alternating vollage is ap-
normal temperature installations. 0100se insulation
plied
to lhe cell. AI the
instanlthe
anode
~rale)
at
the ph0-
which allows no
¥preclable
leakage resistance from wire
tocell
is
p:::ISitively charged with respect to the cathode, the
10
wire
or
from wire
to
ground.
85

71·97558-1
RECTIFYING PHOTOCELL APPLICATION
PhotOC8lIs
are
generally applied to commercial
and
in-
d.tstnal
011
burners,
where
the
aO::led
safety
of
shorted
lead protection
[os
r9qJlred.
Photocells
are
nol
used
10
d&-
teet
gas flames
bec:au6e
a well·adjusted
gas

flame emits
Insufficient
visib6e
light. There
are
4 basic
ree:,Jiremenls
for
a g::od
phoCoceIl
awllcalioo.
1. Photocell must have a
gqod
view
of
the
flame.
2. PholocelLmuSt
be
prot.ected from the light
emilledtlt
hol1'9fractory. . -
3. Terrpera'ure
al
the
cell must
be
under 155
F.
4.

Proper wire
must
be
used
for
the flame lead.
Each
of
these 4 basic requiremenls
will
be
covered
briefly In the following sections.
1.
PHOTOClU
MUST
HAVE
A GOOD
VIE:W
OF
T1iE
FLAME.
The reclifying J:holocell muSI
be
located where
it
wlll
continuously
siltll
a

stable
portion
of
the
flame
being de-
tected. PhOtocells
may
view
lhe
burner
name through a
hole In
the
cornbusllon
cha~r
wall, Irom inside the blast
h tle
of
a gun type burner,
or
from some other location
within
the
burner itself
which
is
determined
by
lhe

oorner
manufacturer
10
provide
adEq.Jate sighting. Cell
housings
are desiQ'l9Cllo adapt the plug-in type
pholoceilio
any
of
these
awlications.
2.
PHOTOCELL
MUST
BE PROTECTED
FROM
THE
LIGHT
EMITTED
BY
HOT
REFRACTORY.
Glowing refractory surtaces
emil
ligh! in
the
visible
range. If
the

photocell is Sighted
so
It
resp:lllds
to
Ihis
light,
the
flame relay will
be
held
in
atlhe
end
of
the
firing
cycle,
and
the burner cannot
be
restarted Lmtil the flame relay
drops
00.
care
should
be
taken in a.w1ying
the
photocell

to
aim it
at
aport
ion
of
the refractory which will remain rela-
ti""'ly cool.
An
Olitice
or
filter
may
also
be
used
with most
cell mounts to restrict
the
viewing
field
of
the cell
Of
to cut
cbwn the lotal li\11t reaChing the celi faCe so that hot re-
fractory will not
be
detected.
3. TEMPERATURE

AT
THE
PHOTOCELL
MUST
REMA.lN UNDER
165
F.
R9Clification .lype
phOIOCeJlS
must
be
protected from
arrbient
lerrperatures
above
165 F. The coating
on
the
cathode
of
the cell will
break
cb'M'l
al
higher
temperalUres.
A photocell damaged
by
excessive
heat

can
be recog-
nized
by
the
cracked
bluish
appearance
of
the face
of
the
cathode.
4.
PROPER WIRE
MUST
BE
USED FOR
THE
flAME
LEAD.
Use
of
Ihe
wrong
wire
lor
the
flarT'lB
delector

lead can
cause signall0S5
due
fa
moisture
in
the
insulation, actual
insulation damage
due
10
high
lemperatures,
or
capaci·
tance affects between
the
flame
(ead
and
ground. For rec-
tifying photocell
awlicalions
where
the
f1ama
lead is
nol
Slbiecfed
to

terrperatures in excess
of
125 F, No.
14
wire
(rated
for
90 C or higher) is
recommended
for
lhe
flame
sig1a1
leadwir8!i.
For
high
temperature installations, spe-
cial wire
(sUCh
as
Honeywell
Specification
No. A1298020,
rated
J.4)
10
400 F contir.u::tJS
ckJty,
or
9CJ,JIvalent)

must
be
used
for
the
flame signal leads.
MOUNTING THE
PHOTOCEll
ON THE BURNER
On
gun
type oil burners,
the
photocell
is oRen
mounted
in the blast tube itself
behind
Ihe all nozzle and Ignllion
eleclrcx:le.
In
this position, the
csl1
is
cooled
by
the
airstream
in
the blast tube. Different

mounts
are
used
for
standard
and
shell-head type burners.
If excessive heat
is reaching the Cell, a
filler
may
be
adjed
10
cut
down
the heat
on
lhe
cell face. A filter may
also
be
adjed
to
restrict the visible light
of
a
hot
refractory
which strikes

Ihe
ceU
face. If
lhe
photocell
signal
Is
weak, a
magnifying lens
may
be
actled
10
gel
a
beller
view
of
lhe
Ilame.
Burner
mounted
photocells
will
generally
have
been
lested
by
the

burner manulactuter
for
proper
line
at
sIght
and
proleclion
trom
excessive heal.
If
a
burner
mounted
photocell falls
or
is
damaged,
il
is
best
to
replace II
with
a
similar cell
mounted
in the same location as
the
old

one.
CU!'IOOE
PHOTOCELL

oUl·n
FIG.
3-
BLAST
TUBE MOUNTING OF
PHOTOCELL
(C7013A).
P!'IOTOCEll
"OU~T
1\
.0
FIG.
4-
SHELL-HEAD
MOUNTING
OF
PHOTOCELL
(C7014A}.
B6
I
FIG,S
- ADDING A FILTER
OR
MAGNIFYING
LENS
TO

A C7013A PHOTOCELL MOUNT.
MOUNTING THE PHOTOCELL
ON
A SIGHTING
PIPE
The photocell, in an
appr~riate
holder, may be
mounted on a sighting pipe
10
view the
all
'flame from a lo-
cation remote from the burner itself. A typical applit.alion
on a horizontal rotary burner is Shown.
Cl'lIlIlJl
PHQTOCfLL
1 tNC"
~IJl"fHR
>IOU

,
PIPE
UW.
LfI.c;rli
)I

c n
,
".

FIG.
6-
TYPICAL MOUNTING WITH ROTARY OIL
BURNER.
This type
01
mounllng
Is
used,
of
course.
wher1
the
burner
is
not a type
easl1y
adapted
10
an internal celiloca-
lion.
Ills
also used, however,
wMre
it is dimcult
toproteci
the cell from high temperatures
atlheburner,
or
when

ills
necessary to select a particular locallon to avoid hot re-
fraclory sensing. The sightrng pipe musl
be
localed so that
the flame is sighted under all firing conditions. The cell
should generally
be
as close
to
the flame as
possible-
consistent with lemperalure restrictions.
The viewing angle
of
the photocell plane retall'ffl
to
the
burner plane should
be
as small
as
possible. This will di-
minish
as much
as
possible
lhe
effect
of

changes in the
flame size
on
the slghllng ability
of
the cell. In general, it
Is
best
to
aim the cell al a !XIlnl abOut
10
10
25
Inches ahead
of
the
nozz~
or
spinner cLP.
For steam
or
air atomizing burners, 1 or 2 additional de-
tectors ShOllld be connected in parallel to
Ql'lSure
sl~lIng
of
the flame at all firing rates.
If
possible, the slghtlng pipe should
be

slanted d0wn-
ward to prevent soot or all vapor
trom
accumulating
In
the
pipe. Viewing
wind::>Ws,
lenses, and filters must be clean
at all times.
IIlhe
sighting pipe slants t.pward, cleaning will
have
to
be done more IrequenUy.
If
the pipe
muSI
slanl
up-
ward, forced ventilation would
be
beneficial.
Two
types
of
cell holders are available for
sl~Ung
pipe
mounting-C7003

and C7010.
The
C7003 cell holder has a finned conslructlcn which
protects lhe ceU1rom excessive heat. EIther type
of
holder
permits removal
of
the cell for Cleaning or replacemenl,
and
haS provision for
adc:Iing
orifices
Q(
fillers.
For
~Ijcallons
where very extreme
healls
a problem,
a lappifIQ provided in the cell holder body may
be usecllo
provide forced venlllatron. Forced ventilation may also be
used
10
keep
lhe
sighting pipe face free of
all
base

vapor
which
ml~t
block Ihe ceU's view
of
Ihe flame.
LfflllT LENGT

OF
fllQUNTI/OG
PII'E
TO
1 IIiCIiES_2 IN. PIPE
FQII
C1OO3.
I_I/~
,,,.
PIPE
FOil C7010.
FORIoI
COHICAL
HOLE
lJI
R[FRACTORY(EKLA~E
CIAIllETERlIK. FOR
EACH
J
INCKES
OF
REFRACTORY)

,

FIG.
7-
MOUNTING TO OBTAIN MAXIMUM FIELD
OF
VIEW.
USING ORIFICES
TO
RESTRICT PHOTOCELL VIEW
Orifice slideS,
or
iris slides,
may
be
used
to
pr9Ye'1l
hal.
refractory from beifIQ
delecled
bv
the pholocell. To
check
for hoi refraclory hold-in, opera,te Ihe burner until refrac-
lory reaches Ifs maximum
f~rafure.
Shut
down
the

burner and lime
lhe
flame relay
dropoullflhe
flame relay
holds in for
5 10
10
seconds or longer after actual disap-
pearance
of
the flame, a slide with a smaller ortflce
8hould
be
Inserted In fronl
of
the
cell
When a slide
Is
changed,
flame current should
be
checked wllh a microarml8ler
to
'7
71-97558·1
~-~ ~~~~-

be certain that a flame CtJrrent

of
at least 2
mlcroarrps
Is
ctltainad. Recheck for
hot
refractory hold-In
at
the
end
of
the run cycle.
If
hot refractory hold-In
cannot
bEl
prevenled
thrClU(j1ll'!e
use
of
orifice
slIdes,
the
j:hotocell will
have
fa
be
slg.led
at
a cooler

refractory
background.
Orifice slidBs
mi~
be
used
in
one
other
situation.
With
the
photocell
pr~
installed,
flame
current
should
be
at
least 2 microamps. Readings as
hlg.
as
4to
7
mlcroan-ps
might
be
obtaIned
If the

pholocell
Is
reasonably
close
to
lhe
flame
(2~
feaI). FOl
maximum
j:holocellllfe.
a lens or
smaller
orifice
shcL1ld
bEi
used
10
limll
the
flame
current
10 5
microamperes.
INFRARED
(IR)
FLAME
DETECTORS
OPERATIDN
OF

INFRARED DETECTORS
Infrared'08I9Clors;
unlike
rectifying
j:holocells,
may
be
used 'If!lh either
oil
01 gas flames.
Since
more
than
90
per-
cent
of
the flame's
lolal
radiation
is
infrared,
these
delee-
lors
receive aJl1)Ie
radialloo
of
QUite
hi~

intensity, and
so
will C(l9rale
w~-very
weak flames as well as
with
very
hot
ones.
-i',
The Infrared
dBleclQ(
can
responc:110
infrared rays emit·
ted
by
a
hoi
refractory,
even
when
the
refractory has
vis-
Ibly Ceasad
to
rjow.
Infrared radiation
from

a
hot
refractory
is steady,
Whereas
radiallon
from
a
flame
has
a
flickering
characteristic. The Infrared d:!lection system responds
only
10
a tliCkering
infrared
radiation;
j(
can rejecl a steady
511;11al
trom
hoi.
refractory.
The
refractory's slaarjy sIgnal
can
be made
10
fluctuate

If It
Is reflected, benl, or blocked
by
smoke or fuel miSi within the combustion chamber.
Care must be taken when
applying
an
infrared system
to
ensu:e
Its
response
to
1lame
only.
CELL
CONSTRUCTION
The
sensitive
I\'at~rial
uSl1ld,in
-the
infrared
detector
is
lead sulfide.
The
electrical resistance
o'f
lead sulfide

drops
when
ex~
to
infrared
radiation. If a voltage is
applied
across lhe lead SUlfide irI
Ihe
cell,
currenl
will
flow
when
the
cell is exposed
10
infrared
radiation.
The
construction
at
the
cell
may
be
altered
to
vary
Us

sensitivity.
The
C7015A Infrared (Lead Sulfide)
Flame
D&
lector
providBs a
sel~!ion
of
4 plug-in cells.
FIG.
8-
LEAD
SULFIOE DETECTOR.
The
mounting
collar
faslens
the
ce/i
holder
10
a
314
inch
sighting
pipe. The
bushing
also
Includes a

viewing
wind::Jw
which
proteclS the cell. A replacement
bushing
is avail-
able
which
haS
a
magnifying
lens
In place
of
the
viewing
window
to
concentrate
available
radiation
on
lhe
cell face.
The d9!ectOl' typically
mounts
on
a
3/4
Inch

black
iron
pipe.
If
refractory mUSl
be
removed, II
should
bEl
t~_r~
sllghlly
away
from
the
ends
of
the
sighting
pipe
10
avoid
blockIng
the cell's view.
The
siglling
pipe
should
nol
bEl
88

extended
all
the way thrClU(j1lhe
refractory
to
avoid
can-
ductlng
excessive
heal
back
10
lhe
cell.
ACC8SSOlies-heat block, seal-ofl adapter,
pipe
nipple,
and
orifice-may
be
added
if
roquired,
as
shown
In
Fig.
9. -
_NAIN
- -

FLANE
-~
$EAL oFF
AOAPTEII-
>,.'"

~
EFII-ACTORY
_


=-
aUII-NEII-
FACE
PLAn
FIG.
9-
MOUNTING THE
C70j,SA
INFRARED
FLAME
OETECTOR.
INFRARED DETECTOR APPLICATION
Special applicalion r8QJirements
for
infrared
delectors
may
bEl
summarized under 4 gBrIerat

headings:
1.
The cell
musl
have a
goo:l
view
of
the
flame.
2.
The
cell
must
be
protected
from
excessive
hoI refrac-
tory radiation.
3.
The cell must
bEl
protecled
from
temperatures In 8)(-
cassof
125
F.
4. Correc!

wiring
procedures
must
bEl
usoo
for
lhe
flame detector leads.
Each
of
these eppIicalion
requirements
will
bEl
dis-
cussed In
the
following
sections.
1.
THE
CELL
MUST
HAVE
A GOOD
VIEW
OF THE
FLAME.
The
infrared

sensor
musf
continually
sl~l
a
stable
p:>r·
lion
of
lhe
flame
being
dBtected.
The
sensor
is
commonly
appliedlo
detect
bolh
gas
pilot
andmain
flame.
or
gas
pilot
and
main
oil

flame.
In
this case,
Ihe
&ansor
musl
be
care-
fully
aimed
at
lhe
inlersecUon
of
pllOI
and
main
flames,
A lead sutflde cell, like
other
j:hotocellS,
views
an
area
as
~
to
a point.
It
is

unable
10
pinpolnf
pilot
flame
location
as
easJJy
as a
flame
rod. tt
the
delector
is
to
prove
the
pilot flame
only
al
the
ignilion
p:>lnt. the
area
viewed
by
the
cell
must
bEl

only
thai
area
Where!he
pilot
can success-
fully
lightlhe
main
flame.
The
Viewing
area
must
not
be
SO
largelhat
weak
and
wavering
pilots
can
9f1ergize
lhe
cell
and
cause
lhe
flame relay

to
pull
in.
FIG.
10-
METHOgS
OF RESTRICTING THE
DETECTOR'S VIEW.
The area viewed by the cell
dePends an 3 things:
1.
The diameter
of
the opening in front
of
the cell.
,
'
2. The distance from the cell
to
the opening.
3. The distance from the opening
to
the area interk:led
to
be
vlewecl.
Fig.
10
shows

3 ways
of
redJcing the field
01
view, as·
suming that the distance from
tM

iewing opening to the
flame
or
refractory cannol
be
changed.
These
are
(1)
lengthening the sighting pipe,
(2)
redJCing the diameter
of
the sighting pipe, and
(3)
Installing an ormce ahead
of
the
cell. CorTtlinations
01
these methods may
be

used.
CHANGING
PIf'E
L£NGTH
OR
SIZE (OIAMETER)
The effect of Changing the length
of
the SiCflllng pipe
Is
shown
In
Table
r.
Olanging
the diameter
of
lhe sighting pipe
Is
not
as
sllTl'le as changing the length, since the
Cell
mountllsel1
and cell mounting accessories are all sized
lCIr
314
inch
pipe.
If

the sighting pipe diameter is redJced, the effect
Is
the same as
ad:::ling
an orifice to the
pipe
as discussed in
the following section.
ORIFICING
Three orifice sizes are available
for
the C7015 Infrared
(Lead SUlfide) Flame Detector-O.OS, 0.125, 0.250
inches. Any
of
these can
be
mounted ahead
01
the cell as·
sermly
In
lhe seal-off adapter
or
in a standard
314
Inch
CO"4lling.
(Refer to Fig.
1S.)

The size
01
the siCflted area at various distances may
be determined from Table II. For instance, if the distance
from the cell
to
a 0.250 In. diameter orifice is 4 inches, and
from the orifice
to
the flame junction (or refractory)
is
36
inches,
the
diameter
of
the sighted area is 3.5 Inches.
Fig.
11
shows
how
a typical orifice restricts the view
01
a
small area around the flame Junction.
2. THE CELL
MUST
8E
PROTECTED FROM
EXCESSIVE HOT REFRACTORY RADIATION.

Although the lead sulfide cell will not respond
to
steady
radiation, such as that prodJced
by
hoi
refractory, care
must be exercised in protecting the cell 1rom hot refractory
radiation because
01
2 possible
conditions-"Shimmer·
and "radiation saluration."
a.
Shimmer-Turbulent
hot air, steam,
SlT'()ke.
or fuel
spray
In
the combustion ctlamber can reflect, bend,
or block the steady infrared radiation being emilled
by a hot refractory.
These
conditions can c.hang9
the steacly radiation from a hot refractory into a fluc-
tuating radiation. If these fluctuations occur
at
the
same frequency as that

of
a flickering flame, they
will simulate flame and will
hold
In the flame I'8lay
after the actual burner flame
has
been
extin-
guished.
b. Radiation
Saturation-Steady
hot refractory radia-
tion may become strong enough to mask the ftuctu-
TABLE
I-DIAMETER
OF AREA SIGHTED THROUGH VARIOUS
lENGTHS·OF
314-INCH PIPE
WITHOUT ORIFICE
IN
INCHES
DISTANCE FROM END OF PIPE TO SIGHTED AREA
INCHES
LENGTH OF
PIPE (INCHES)
12
30 36
42 48
'4

60 I 66
72
1
6 18 24
0",,40
11.9 28.4
6.3
17.6 23.2
34.'
2
11.9 14.8 17.6 20.4
3.5 6.3 9.1
23.2 26.0 26.9 31.7
34.'
3
10.1
11.9 12.9 15.7 17.6 19.5
2.6 4.4 6.3 8.2 21.3 23.2
4
9.
,
11.9 13.4 14.8 17.6
2.1 3.5 4.9 6.3 7.8
10.6 16.2
4.1 6.3 8.6 9.7
10.7 11.9
13.1
14.2
5 1.8 2.9 5.2
7.'

6 1.6 4.4 6.3 7.3 8.2 9.1 10.1 11.0 11.9
7
2.8
3.'
'.4
3.1
4.7 5.5 6.3
7.1
8.7 9.8
10.4
1.5 2.3 3.9 8.0
2.1
4.2 4.9 5.6 7.7 8.5
9.1
8 1.4 2.8 3.5 6.3 7.1
89
71·97558-1

TABLE
II-DIAMETER
OF
AI1EA
SIGI-fTED THI10UGH ORIFICE. IN INCHES
ORIFICE DIAMETER
INCHES
,
•.
'
CELl-TO-_
0.050

0.125
0.250
ORIFICE
DISTANCE
DISTANCE FROM ORIFICE TO SIGHTED
AREA
INCHES
ONeHES)
12
24
48
80
72
12
J6
24
36
48
60
I
72
12
24
36
48
60
72
6.8
Over
10

Over
10
Over 10
1
2.3
4.6
66
3.2
6.1
8.8
4.8
9.5
2 1.2 2.3
3.4
4.6
5.6
6.8 1.6
3.2
8.1
7.6
4.8
8.8
2.5
4.8 7.0
9.5
Over
'0
tess
3.0
3.8

2.3 4.8
1.1
2.1
3.2
4.2
5.2
1.75
3.2
3 8.1
4.8
8.2
7.8 9.5
""'n
1
.
1.5
Less
- 1.2 1.7 1.8
2.4
3.2
3.9
4.6
4 2.3
2.'
3.5
1.4 2.5
3.5
4.8
5.8
7.0

than 1
Less
2.3
1.3
1.1
- 2.8 1.9 2.5
3.2
3.'
2.1
2.9
4.6
5.6
than 1
1.'
-
1.4
3.'
5
1.5 1.9 2.3 1.1 2
.•
1.7
3.2
6 1.2 1.6
2.1
3.2
1.0
2.5
4.0
4.'
WITH ORIFICE

IIOT
RH~"'CTORY

"'IN
FL"''''f
,.
I
;'1
I
I I I
y-
I
1/.

___
J

/1"
1-"-
/)/

\

- :::,-
~
:::-
'~f
~
-r


-¥-~-
I I V
I'
",1'
.;.V
1
1
r
C
I
'1
I
I
''''
FIG. 11 - ORIFICE
MAY.
BE USED TO RESTRICT
Cell
FIELD
OF
VIEW TO
PILOT/MAIN
flAME
INTERSECTION,
WITHOUT ORIFICE
IIOT
RffIU.CTORY
PILOT _
,"AlII
n",,"(

PILOT
;,;'"
I
,;;
.
';h";;';;'
I,;
i:·;l
·1;·;
J
"l
":

1
I·
"K ";
,:~{
,-
;-c
I
I
/"""
-
,.
.V
I·
I
-
-
~

-
-
I-t
Iv'
-
-
l
-
V
-
~=~ ~
.
:\:: '- -
rr

-
_ -
/

-

I
'v'
\
fi'
-
-:::-
-
~
'

I.~
r-

:S::::
V
'V':

!'-
I
V
I
./1»:
1""'t:l';.I'·!
~
'"
r
;'1
.'
1:"",1
i:";:'
uii<,,',
. I
>1
I
I
.".
OR
TO
LIMIT
HOT

REFRACTORY
SENSING.
ating radiation
of
lhe
flame.
llis
is similar 10 Ihe
effect
of
holding a candle up
In
front
oflhe
sun-lhe
Jig1t
ot
the
sun
Is
so strong thai the candle
1i11l1
can-
nol
be
seen.
If
radialion saturation is extreme, the
flame relay will
drop out, and the system will shut

cbwn as lhough a flame failure has occurred.
Both of these
problems
will
be
minimized by aiming lhe
ceU
at a ponion
of
the refractory that
is-
- As
cool
as p:lSSlble.
- As far from the cell as possible.
- As small as possible.
Refractory letTlpElratures in the combustion chamber
will vary with combustion chamber
design-bul
generally
lhe
end
wall
of
the chamber will
be
(he hotlest p:lint. It will
normally
be
best

10
aim
the cell at the side wall
of
the re-
fractory-or
possibly
al
8 point above the refraclory. The
floor of the cDmbustion chamber will also
be
relatively
90
Cool;
but it the cell is being sighled af the piloVmain flame
junction.
it
may
be
difficult fo sight downward without
sighting oYer Ihe pilot flame.
In
sighling the cell, lhen, the 2 important 1actors to con-
sider are proper sighting
of
the flame being detecled (nor-
mally the pllot!main flame Junction),
and
avoidance
of

hot
refractory sighting.
A typical sighting arrangement is shown in
FIQ.
12. The
ceU
is
aimed at the intersection
01
the
piat
and main
flames, and a relatively cool side of the combustion cham·
ber_
The cell In this case would
be
located as close to the
burner as p:lSSible to Sight the maximum
deplh
of
the
flame.
"This
reduces
lhe
effects
of
variations in the main
flame patlem.
The cell may also

be
sighted from a point bellow and
close to the burner with the line
at
sIght abOve the
refraclory.
1
I
/,,1
_
//:

:

///
-'
I
( I
I
cTeu
I
SJG"TIN~
I
,
I
I
TO
WALL J
INTER3ECTION
OF

,.AI

I
ANO
PILOT
FL

U
I{
I ,
+-
'-'-""""'Et'

\ I
I
, ,
REFR

CTORT
.Ul
"REA
YIE"EO
IH
I
lURNfR
F.o.CE
C101J

: /,-
I 1 _

I
PLA
TEl
1

:
,;,
I
"

I
I _
:
;."

'-L-_
FIG.
12-
TYPICAL INFRARED DETECTOR
INSTALLATION
SHOWING LINE-OF·
SIGHT
TOWARD COMBUSTION
CHAMBER WALL.
CELL
VIEWS
JlRf

ABOYE
THE

RffR"CHll'lT
~-
~:W\H(;E/"""/
I

/ I


/ I
/ I
( / \ I
I
(\
I I
+ ,~L

I \ I
I
\~)
I
tliT~SECTJON
OF
fIlLOT
I
AIIO
II

FLAMfS
I
~.I.,lll;l

I
I _
,-
I
,
T-
I
"I



',I
"
_
FIG.
13-
TYPICAL INFRARED DETECTOR
INSTALLATION SHOWING
LlNE-OF-SIGHT ABOVE REFRACTORY.
The
third
method
is
10
aim the detector from above the
burner, sighting a portion
of
the refractory floor. This type
ot
aw1ication

requires thai (he pllol flame
be
carefully
sighted
from
Ihe
side. The cell stlould not be sighred
~over·lhe-shoulder·
of
the pilot because
the
chances
of
sighling
a
pilot
100
small
tosalls1actority
llgllthe
main
flame are Increased.
The
actual area of
hOI.
refractory
si~ed
should be as
small
as possible consistent With proper slg'lting

of
the
flame. Refer to Fig. 10 for methcxfs of redJclng the area
of
hot refraclory sighted.
"



_-

FIG.
14-
TYPICAL
INFRARED
DETECTOR
INSTALLATION
SHOWING
L1NE~OF
SIGHT
TOWARD
COMBUSTION
CHAMBER
FlOOR.
3. CELL
MUST
BE PROTECTED FROM
TEMPERATURES IN EXCESS
OF
125

F.
The sensitivity
of
the lead 5Utfida decreases as its tem-
peralure increases. Up to
125
F,
the loss In sansllivity is
neQ'lIglble, but temperalures abOve this point
must
be
avoidecl. The QJlckest check
for
excessive lemperabJre is
SirTllly
10
grasp
[he
detector-
il
shouJd not
be
too hot to
hold
comfortably in lhe bare hand.
A nurrbElr of methods are available
tor
coollng!hIJ lead
sulfide cell.
a.

O1eck for Pfope1
applicallon
of
the
de!ec1of".
The
sighting'
pipe
should
not
elltend
rn:;)(e
than haltway
Into
the
refractory (see Fig. 9).
b. A
314
Inch
pipe
nipple, 8
10
II Inches long, may
be
used
between the
CelllTVJUnl
and
the
sfglung

pipe
Uselt. Note
lhallhe
usa
of
a
longersiQhling~wlll
also r9liJce
Ihe
viewing area
of
the
delector.
c.
A heat block
may
be
aO:ied between the
del:ector
and
the
si~ting
pipe.
This
aevice
is
constructed of
non-heal-<:cnd.Jctlve synthel/c
IOOing,
ard

pte-
venls heat
from
lhe
sig,IIng
pipe
from being
c0n-
ducted to the delector. The heat
block
Itself
~
able
to
withstard
temperatures
~
to
250
F.
d. A seal-ofl adapler
may
also
be
ad::jed
belween lhe
detector and
sig,ting
pipe.
The

adapler contains a
glass wincbw
which
prevenls
hOt
gases from reach-
ing Ihe cell
base.
The
pholograph
below shows lhe
detector Installed
on
a burner with heal block
ard
seal-ofl adapter in place.
e.
Forced air cooling
may
be
addeId
If necessary
bV
connecting a
pipe
lee
between
the
slgltlng
pipe

anddetBClor.
A
pipe
ni~le
Is
usecl
toadapf
the
de-
leetor to
the
tee.
91
71-91556-1
&
PdT
NO.
lO_U,
n"'NO"'~1l
B~~'1ING
II"T'I
"I~WII'IG
WINDO
•.
P

ij1
>lC.
1106).1, BLI.lHING
.ITH

",

G'lIFYING
L!'l$.
& 2·s,,1
WITH
Jl

ND

ijO
IU$HIHG,
2.J
• WITIl
","'C'llfYI'lG
LENS.
"0'"
FIG.
15-
EXPLODED
VIEW
OF
THE
C7015A
ANO
ACCESSORIES.
FIG.
16-A
C7015A
FLAME

DETECTOR
INSTALLATION
ON A DUAL-FUEL
BURNER.
THE
CELL VIEWS THE GAS
PILOT
AND
MAIN
FLAME
AND
THE
MAIN
OiL
FLAME.
FIG.
17-
FORCED
VENTILATION
MAY
BE USED
TO COOL
THE
SENSOR.
4. CORRECT WIRING PROCEDURES
MUST
BE
USED
FOR
THE

FLAME
OETECTOR LEADS.
A
hll1l
resistance shan
in
lhe
detector circuit will
nor·
mally resull in a
drqxlUl
of
the flame relay
and
burner
shutdown, since
lhe
shOrt permits a Sleac!y signal
10
reach
the amplifier. while the amplifier requires
an
intermittent
Sigl'lal. capacitance effects between the
11ame
lead itself
and
the ground wire or conduit (or other wires) may also
cause signal
deterior~Jj.OI]

and
shutdown.
The possibUlty
of
an
inconvenient
and
costly shutdown
is
cause
In Ilsetf to exercise caution In wiring the flame
c:let-
leclor
leads. In applying Infrared ooleclors, however,
prcper
awIicatlon
Is
espeCially critical since a remole pos-
sibility also exists
of
a false flame indication. This
might
ra-
su1l1rom 2 possible conditions:
a.
An
intermittent short
of
the
proper

1requency, sw:h
as
might
be
caused
by
vibration.
b. An intermillenl capacitance effect,
which
is
caused
by
leadwire vibration.
Figs.
18
and
19 Illustrate the
wiring
necessary
10r
an ac·
ceptable Installation.
To
minimize the possibility
01
either a
shutdown
or
a false flame Signal. lhese Importanf instruc·
tions

must
be
followed.
a.
Detector
wiring
mUS!
be
as
short
8S
possible
-maxj·
mum recommended length from detector to wiring
subbase is
50 feet. If greater distance is required,
clXlSultlhe nearest Honeywell
branch
office10r rec·
cmrnenda!ions.
b. Theflexible cable
must
be
grounded,.at the end with
the exposed wires, to the
wiring
su~
(Fig.
I;'
18-

remove
condJil
fitting and
attach
grounding

strap), Of to the junction
bOx
(Fig. 19
~
conduit fitting
is
SlWlIed).
c. The junciioo
bOx
(Fig. 19) must
be
grounded.
d.
Wiring must
be
ex.
shielded cable,
or
twisted pair.
e.
Wiringmust
be
run alone in conduit, all the way
'rom

inside the
junction
box
to
the wiring subbase.
UN-
DERWRITERS' LABORATORIES,
INC.
RE-
QUIRES THAT THE JUNCTION BOX BE
MARKED
C}o~

AS$EIlBLY
fL~XIBU
DIlLE
If

HEII
SfCUREL
Y
TO
",''''MIU
MOVENE'lTI
.1'lOc;R

ER
"""l'''C
sun


s.
F
OIl
TER

' L
ill
STRI'
,
&.
,
IRO_"IRE
"010' "Olin
""Jilt
fROM
Till
n~'~";CO'lHICT
TO
"""IHG
SUI

St'COlORHO'T
'

~OflT

HT.
(tl'
EXPO$tO
""

IIU
N;
SHORT ,
POSSIILf "'ND TWIST THEM
!:lJ.
FLVlIlLE
e

BU

lIST
IE
RUH
TO
"'OIil'l"'

ER
""RI"C
SUIIN;E

HD
CItOUHOEO RICHT
",'lE~ THllX,(l!IE~
""RU
5'

BEG'H.
FIG.
18-
TYPICAL

WIRING OF THE
C7015A
TO A
NEARBY
WIRING
SUBBASE.
92
TO INDICATE THAT
NO
OTHER WIRING CON-
NECTIONS MAY BE ROUTED THROUGH
IT.
AP-
PLY
CAUTION STICKER (FURNISHED) TO THE
JUNCTION
BOX.


1.
Use
rlfid
cond.Jll.
If
fl8lll1ble
conduilis
usec:I,
laslen It
securely to minimize vibration.
g.

The
conduit
must
be grounded
at
the wiring sub-
""50.
h. Keep exposed wires at end
of
tl8lllible cable
and
cond.Jlt
as
sharf as
fXJssibJa
•
twist
them as much as
lXlSSible
before
mak·u'lg
connections.
Shielded, moiswreproot, 2-wire, rubber·covered ml-
c~
cable
Is
recommended for most Installations,
This is available
from
Honeywell uneilr SpeCification No.

R1V8011.
It other wire is
usec:I,
make sure thai il is mols-
lureproof
and
shielded; otherwise nuisance S/lUloowns
can occur due
10 darrp wiring or false sIgnals caused
by
induced currents.
FQ(
hi~
lemperature awlications,
heat
and
moisture resistanl wiring
Is
available under
HOI'"I8't'Wen
SpeCification No. R1298020 (No. 20 Tefion-fiberQlass
In-
sulated leadwire, rated
~
to
400
F conlinuOlJs duly). This
wire
is unsllielded and should be tWisted and run in
c0n-

duit as speCified.
ULTRAVIOLET
(UV)
FLAME
DETECTORS
C7015,1,
,I,UEIolUf
CO~OUI~
fllTIHG
JUHCT,OH
BOl
&
& SR;""'

""'R~
AHO I

un
WIRE
fROIoI
nlE
C7D15A;
CO

EC,.
IH~OE
JUI'OCTIOiol
so:o;,
COLOR
NOT'IoOO'ORTAHT;

LEADS fROM
JUHCTlo.o<
8()l(
HEEO
HOT
IEPHItoSlO OR
I'(Il.ARIZlO.
& "'PPLY C UTIOH STICKIR.
fOR

><D
__
'OSUPPLIEO
'OjITH
C70lSA.
TO
~HIS
WNCTIOH
80l.
8()x

UST
BE
GROUHOED-
& COHoUIT
"'<JH
8E
R'-JH
TO
PAooA,I,_E'"

'OjIRIHGSUn
n
0
CiRO'-JIolOEO
THERl.
KEep
U.OUo
'OjiRES
""'
$>lOAT
""'
I'(IU'BLE
AND
JYjlST
THE

FIG.
19-
TYPICAL WIRING OF THE C7015A TO
A
DISTANT
WIRING SUBBASE.
OPERATION
Ullraviolelllame detection systems
depend
on
the abil·
ity
ot
the sensing

Itbe
fo
respond 10 ullraviolet radiation
and remain
in~i~ye
10
radialion in the infrared
and
vis-
ible light ranges.
The UV
sensi~
flbe
consists.ot 2 electrodes sealed In
a gas-filled quartz
Qlass
enveiope. (Normal
Qlass
blocks
UV
radiation, so
Ihetlbe
musl be constructed
01
a special
quartz
type
glass.)
Fig.
20 shOws a drawing

01
the anode
and
cathcde ar·
rangement
of
the sensing
tlbe
in the Minipeeper Ultravio-
leI Flame Detectors
{ClOVA, C7ll35A,
and
Cl044Al.
The
sensinQ tube
in
lhe Adjuslable Sensllivily Ultraviolet
Flame Detector (C7076A and
OJ
and
PurpJe
Peeper Ultra-
violet Flame Delectors lC7012A,C.C and -
FJ
-
is
con-
structed differently, but its operating principle is Similar.
GAS
FILLEO

TVBE
FIG.
20-UL
TRAVIOLET SENSING TUBE.
The
fiQure shown is simply a schematic representation
01
tlbe
conslruction.
The
actual power
Itbe
sensor
has
4 pin construction
10
provide increased resistance
10
Vibration.
When a
hi~
enough vollage is
awlied
across lhe elec·
trodes, and the
llbe
is exposed to a UV source,
the
cath-
ode

emils eleclrons. which ionize the gas
In
the
tlbe.
When the gas fill is ionizect, the
Ilbe
beCCmElS
cond.Jclive
and
current tlows thrCll Q'llhe
tlbe.
We
say that lhe ftbe
-fires" -
sinCe
the
flbe
glows
vIsibly while conducting.
The
~rance
01
the
tlbe
when it fires is a function
olthe
gas fill used. Honeywell sensors flre with a reddish glow.
Soma
tlbes
constructed

by
other manufacturers have a
blue
QIOW
which
is
nol
as apparent.
When
lhellbe
cond.Jcts,
or
Ilres, the vollage potenllal
between the electrodes
dr~ sharply. When it
has
drc::p;l9d
sufficienlly,
It
Is
no longer high enough to cause
electroos
10 be amlfled from the
catho:::te.
The
tlbe
r9-
stores itsel110 the
~i.onized
slale. During this phase

we
say
that the
llbe
is "quenched."
We
can
summarizelh6
operation
01
lhe UV tLbe as
follows:

Arry
time
lhallhe
UV tUbe is exposed to sufficient ul-
traviolet radiation
(or
other radiation
0'
higher energy
which
IS
capable
01
penelraling the
!tbe
envelope-see
Fig.

211.
and sufflcienl voltage potential
Is
awlied
across
the
eleclrodes at
the
ltbe
(1'rom
a properly desiglEld elec-
tronic
nelwof1o;),
the
ttbe
inlermlUantly fires (becomes
con-
93
71-9755&-1
DETECTOR
REwooos
NO
RESPQl~KS-
t :.:\
I
IHIGIi
EMERGYIlAOIHIOll
l.\SSIIlDCK
HO
ItESI'aol

PENHIt.uES
GlASS
r·OI.lIDllI
ENVELCPEI
r\
I
1
~
I
C~IC
I
I!
I
I
I
I
0
._.
I
I:
I
.
I
I
I
~·It.y
I
I I
I
I

I
I
.
-,-
I
I"'
VISIBlE
I
I
,
,
:,
I
:W
I
1:,
I
INFR.I!ED
I'
I
I
I
I
,
•
~
• •
!
"
•

• •
DETEC1D11
R£lPONOS
,.
"
.'
10'
.'
.'
,,'
10'
10'
FIG.
21-SUMMARY
OF
UV DETECTOR RESPONSE TO RADIATION
ductive\ and is
QJElnched
(restores itself
to
the ready
condition). "
These lubes
d;:J
fire
rand;:Jmly
even when not intention-
ally exposed to a
UV radiation. The firing rale under these
conditions is referred

to
as "backgrOl.Jl'ld count.· This ran-
dom firing
may
be
005eNed by looking al the
1ace
of
the
tube
when'ltls
powered;
it
is
nbrtT'l8f,
and
will not activate
the
nal1"le
detector relay under usual circumstances.
. .,'
SENSING TUBE TYPES
Honeywell ultravlolel
11ame
detectors use 2
~
of
sensing tubes which. although their principle
of
q:lEIration

is lhe same, are
not
Interchangeable.
The sensing
tlba
in.the
Minipeeper flame delectors
(C7027A, C703SA, arid C7044A) is called a UV
PJWElr
tube. When salurated with ultraviolet radiation, this tube
delivers
aoout
-;/10
Wau
to
the flame signal amplifier. The
flame relay requIres aoout
314
wall to pull
in,
so
mUe
power
~lification
is required.
The sensing tube in lhe
a~justable
se.nsitivity (C7076s)
and Purple Peeper flame detectors
(C7012s)

is called an
Aquadag tube. When saturaled with ullraviolet radiation,
(his tube delivers less than 1 microwaU to the flame Sig"lal
amplifier. II is not capable
of
delivering the amOunl
01
power required in UV power
Ilba
circuits without damage;
therefore, it should not be Interchanged with
UV PJwer
tubes.
For both detector
types, an electronic amplifier in the
flame safeguard control counts the firing rale
of
the sens-
ing tube. When the rate reaches a level indicating the
presence
of
a flame, the amplifier switches
PJW8r
to the
flame relay in the control. The flame relay pulls in and
stays in as long as the firing rate is high enough.
SPE~TML
RESPONSE
OF
THE UV OETECTOR

The UV deteclor will r&flOlld
to
any radiation which is
Capable
of
penetrating the glass envelq:lEl, and of causing
Ihe lube to become ionized. The tube is not sensitive
10
ra-
diation whose wavelength is longer than UV - visible and
infrared radiation. However,
if
we could disregard the
glass
8I1velq:lEl
itself, the lube Would:respbn'd"i'o"OVraaia-
tion and all radiation having a wavelength shorter than that
of
UV - X-rays, gamma
rays,
and cosmic rays.
The special glass envelq:lEl of the tube ooes, however,
limit the radiation which
passes Ihrough
n,
blocking out the
shorter
UV wavelengths and much
of
the X-ray radiation.

ThIs is shown in Fig.
21.
The band
of
radiation blocked is determined by care-
fully selecting the malerial
used
tor the tube
envelq:lE1.
Or-
dinary wind;)w glass blocks oul
UV radiation and
is
lherefore unsatisfactory for viewing
wind;:Jws,
lenses and
tube envelopes. Either
QUartz
or
special UV transmilling
glass must be used for these functions.
In
effect, the response
rarJQ8
of
the detector
is
limited
on both
ends

01
its wor\l:ing raflQEl-it is not sensitive to
longer wavelengths, and shorter wavelengths are blocked
by the gtass
envelq:lEl.
The glass envelope, however,
blocks out only a band
01
radiation. so the detector
re-
mains sensitive to cosmic, gamma, and some X-ray
radiation.
SOURCES OF UV RADIATION OTHER THAN
FLAME
WHICH
MAY
AFFECT
UV
SENSORS-
It is
awarent1rom
Fig.
21
lhat [he UV tube is sensitive
to some cosmic,
~ma,
and X·ray radiation,
as
well as
UV radiation. Examplss or radiation sources other than

flame which might actuate
(he
detector system are:
94