Note: Descriptions are shown in the official language in which they were submitted.
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DANl~SS A~S, Nor~borg (Donmar~:~
~ontrol ci~ouit for a f~nB~ inst~llatio~
!l~he inve~tion relates to a c02lt~1 clrcuit ~or a firing i~stallation
comprieing at lea~t one fuel relea~e eleme~t ewitahed on by a~rit¢~on
elemont, i~tlo~ mea219, a flamo mo~tor with a ~lame rola;y a~d an
~lectronio Ba~ty timer which9 in the cour~e of the pro~amme~ 9UoC889iVeLJr
operates in t~o seauencei3, dur~ng ~e f~ret ee,~oe at the Qnd of the
safety pariod actuates a preparato~y a3?p~ratus w~th tlle aid of whioh the
ao~atio~ o~ the f~al relea3e element i~ ~repared, comme~loee its æeoond
s~quenoe w~th ~witehln~ on o~ ~e ~Q~l releasa el~n~t and, with the ald
of E~rit~hing o~ apparatus9 effqet~ ~witching of~ OI tha ~uel releaso
el~erlt a~ e end of the ea~et~ pe~Gd lf t~e fl~ne rel~ has failed to
n3spond.
~ a 8afbty p~Od.a it i6 ~tanda~d to take thi3 loneest permissible
period i ~ g ~hich the i^ontrol clrcuit relea:3eæ the supply o~ fuel without
a flame being notified. I* therefore com~ences wlth relaa~e of the fuel
and must te~nlnate with the 6ignal for bloc~ing the ~upply of .~uel if no
fl~mo has been ~oxmed. Thesa~ety periods are fixad. ~hey deore3se wi~k
an increase in the burner lo~d and~ particul æly in the case of larg~
burners, only amount to a f~w seconds, ~or example two to three ~eoond~.
I~ ad~itiong th0re i~ the raquirement that there mw~t not be ~n exce~sive
departura from th~se values even ~ith ~n undervoltage of 15%, an o~ervoltaære
of 10% &;:ld a t~m~exature chan~e between ~ and ~0~. Suoh re~ulrements
O~lOt: be mst w;Lth ~,he~31 ~afety timexs, for exampla tho~e oporatlng ~r.Lth
bi~etal .
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' A contro] circuit of the aforementioned kind is known, see German Patent
SpeciEication 19 ~5 790 of 'Landis and Gyr A.G., publ;shed February 11, 1971,
wherein an electronic safety timer is used in which a condenser is charged by
way of a resistor and discharged by way of a unijunction transistor and an
actuating relay when the threshold value of this transistor has been reached.
During a first sequence, a period is determined which is used as pre-ignition
or preventilating period. The actuating relay thereupon transformingly delivers
a switching pulse to an electronic switching element which switches on a burner
rel'ay. ~t the'same time the armature of the actuating relay is brought to a
preparatory position so that it may open a switching element at the input of the
control circuit when the actuating relay receives a fur-ther pulse during the
second sequence. The input of the timer is connected by way of a first diode
to a point between the burner relay and the associated electronic switching
element and by way oE a second diode to a'point between the flame relay and a
transistor for switching this relay. ~ccordingly, the associated condenser is
charged as long'as the electronic switching element andlor the last-mentioned
transistor are in the blocked condition.
In this way,' one can check during the first sequence-whether tke electronic
timer is in order. However, one cannot be certain that the fuel releasing
element is actually switched off at the end of the safety period during the
second sequence if, for example, the charging path leading through the second
diode is interrupted or if the armature oE the actuating relay fails to attract.
In addition, the known circuit cannot be used for larger burners bècause in that
case the safety periods are considerably longer than the corresponding preventil-
ating periods.
The invention is based on the problem of providing a control circuit
of the aforementioned kind in which it is ensured that the fuel
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releasing element is switched off if no flame occurs at
: the end of the safety periodO
The present invention relates to an electric control
circuit for a fuel-fired burner, the circuit comprising at
least one fuel release means, a swi-tch actuable to render
operative the fuel release means, a fuel ignition means,
a flame monitoring means and a safety timer, wherein, in use,
in the course oE a firing programme the safety timer is
operated twice-over and on the first operation, at the end
of the safety period defined by the safety timer, the safety
timer actuates a preparatory control means so to conaition
the circuit as to allow the switch to be effective for
renderlng the fuel release means opexative, and wherein ~he
second operation of the safety timer is initiated by closure
of the switch and at the end of the safety period during the
second operation of the safety timer, the safety ti.mer, if
the flamc relay has failed to indicate ignition, causes the
preparatory control means so to condition the circuit as to
disable the switch from being effective for rendering the
fuel release means operative.
In this circuit, it is not only the operability of
the timer .that is checked during the first operation.
Instead, one also ensures that th~ safety timer has voltage
applied to it whenever a voltage is applied to the fuel
release means. Should there be a fault in the supply to the
safety timer, this would also preve.nt response of the fuel
release means. By reason of the fact that one and the same
device serves for preparation during the first operation and
for switching off during the second operation, one ensures
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that at the end of -the safety period there is actual switching
off during the second operation because the switching function
during the first operation was checked and there would have
been no switching on of the fuel release means if there had
been a fault. One thereby obtains a safety timer which is
of extraordinary reliability.
Desirably, the safety timer comprises a relay which
responds with a delay and remains energised as long as there
is a voltage at the input. This not only defines the instant
of switching on but also the switching-off point of the
associated switching elements. This simplifies the construc-
tion of the combined preparatory and switching-off apparatus
in comparison with an actuating relay which responds only
during a momentary pulse.
! There are numerous possihilities for constructing
the circuit according to the invention. In a preferred
example, it is ensured that the fuel release element can have
voltage applied to it on the one hand by way of a first
switching element which is in series with the switching-on
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~l~mcnt and which, by me3n~ of the preparato~y ~nd s~itchln~ofr apparatu~3
i8 ~witched on at the ~d of each ~fety perlod durln~ the ~r~t ~eque~ca
and switched off dur~ the secona BeqUea~oe 2s~d on the other h~nd by way
of a seco:~a ~l~ritc~ elemcnt which iB i21 E~e:L:leE~ ~rith a f~r~ flame
:rolay switchin~ element in the operati~e po~ition thereof and ~ switched
on by ~e sa~ety timer at the end of the ~a~t3r pe~odO ~e f~rat s~t~}
~a~ elem~t which has alread~r been chec}ced durl~ tho first ~equ~nce
switche~ ba~:k during the second 6e~uence basically at the end of the
cafe~r period. Whether the op~ratio~a of ~a bu~er can be cont~ued ~
te~bed ~ith the sid of theæc~nd switohing elem~nt whlch takos over the
fim¢tion of the firat ~tchin~ eleme~t lf the f'l:r~t fl~me rela;r switchi2a,~
ele~e~t ha~ responded.
5he fir~t ~witohlng clement ma~r be a s~ltch-o~rer el~m~nt ~ wag of
which the input of the saf~t~ timer c~;n ha~e volta ~ applied to it in the
re~t position thereof. This provias~ a simple po~sib$1ity for lntroduol~
the fir~t ~equence of the ~aety timer indepena~ntly of the switchin~o~
el~;ment"
Fhrtherp lt i~ favourable ~f the ~eoond ~wit~hin~ e sm~nt i8 a
s~itch-orer element by way of which the ie~ition me~ns caa havc ~oltage
~ppl~ed to them i~ the re~t po~ition ther~of. Sinca th~ flame should have
exl~ted at the ~nd of the ~afety period du~in~ the second sequenco9 the
ienition can be switchad o~f by the ~econd switching element~
I~ a fk~her embodl~nt o~ tha invantion3 lt i9 en~ured that the
preparatory a~d ~itch1n6~of~ appar~tus compri~o~ ~ t~rd ~wltol~ng slement
aatuated by the ~a~oty tlmer at the ~nd of the ~fet~ p~riod and ar.
a~Y~lial~ relay ~hioh i~ a~uipped ~rlth sel~-hold~ng m~anst oont~ols a
s~itoh.~n~ 61e~nt ln t,h3 suppl~ to ~he ~u~l rel~sin~ el~ment~ attracts
d~lri.2l~ th~ first s~uenGe in re~uon~o to ac~lation Or the ~hird ~t~tching
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slem~nt and dro~ orf d~ g the ~soond ~eque~ce. !Ihe u~e o~ the
~uxiliary rela~ provide~ ~ ~imple me~ of e3~ployin~ the same ~wlt~ng
beh~our ~or the third ~witohing elom~t du~ng ths :9'i"81; ~equ~noe ~or
~witching on the first ~witohin~ elemant and ~ng the second ~equ~oe
or switohine o~ sald 8WitChisl~ 01em~1t-
More paxtiaularly, the ~xiliary relay ma~r have volta~e applied~ it on the one ha~d b~r waar of the l~leI~ie8 cirauit Or the op~rati~o
po~ition of the third switohing el6ment ~a the r~5t position of ~L second
flame rela~r switchin6 el~ t and o~ the o1;her hand by w~ of t~e serles
oir~uitof the re0t positio~ of the third sk~tchin~ elem~t; a~d ~e operati~e
poBition of a aelf-holdl~ witching element"
q~he allxilis~ rela~ m~r be part of a pre~e~tilatin~ tiner. ~ the
o~e hand, this provides a clear ~ ration betwe~ the ~a:eety period a~d
the preventilatin~ poriodO ~ the other hand, it i~ po~lble for the
~ll~r relay to be a con8trUot~o~ componont which is neoessa~y for
o~er reasotls, whlch simpli~e~ the ¢onstruotion of the oircuit.
~ a preferred emboa~ t, the sw~tchin~o~ elem~t i~ a fi3cst
p3~e switch elem~t of a pro~Tamme timer w~ch, a~er re~ponse of' the
au~cllia~r rola~, oan have voltage applied to it by way of ~he rest pos~tion
of a third flamB rel~ ~w~tohl2~ eleme~t- qhis ~rogramme timer ensures
that a de~ined time lnterval ~33d8tB betwe~n the ~d o~ tho firet sequ~oe
~nd the ~tart o~ the seoond sequen~e durlng whi~ the ~ety timer oan
~as~ume its inltial oondition.
F~ther, the pro~ramme timer m~r oomprise a seoond progra~e
~wi.,o~ing eleme~t whioh is dispo~ed at the in~ut to the oontrol oircuit
flnd oponuafter a pxe;~ete~mined delay period for the purpose of f.~ult out-off.
~f the third fl~la rela~r switohlng eleme~nt fails to re~pond, the f~alt
out-of~ then occur~ ~ter the dela;r per~od.
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~ rther, the pro~ranune tlmer ma;r GompXi~e a l~hird BW~hillg elament
wbich open~ before the first programzne ~witohin~ el3ment alo~es ~nd 1
dispo~ed in ~a supply to ~ ~econd fuel feed~ng el~Q~t. q~ ~econd
~edin~ element i~ t~erefore 0108ed during ignition- ~Iowo~er, if the
voltage ~upply is removed from t~e pro~¢amma t~aer by ~atuati~g the thlrd
e rela~r ~tch~ng elemsnt, tha thlrd pro~an~e ~witahin~ elcment Cfl~
sub~equ~tly ope:rate ~e second ~el ~eeding eleme~t~,
It i~ al~o ~a~ourable i~ the f Lame monitor oan be ~witohed to
~reater ~sitivity prior to ~witc~ing on of the ~uel relea~i~element
~a the pro~ramme -~mer can ~uri~g thLs t~me hav~ voltage app:Lled to it
b~ way of sn operati~e position of a fou~h ~lame r~lay swltohing el~m~t.
~hould the flame monitor deteot extraneou~ ht, the pro~ramme timer i~
8e~; into operatio~ ~nd ~here will be fa~t ~off ~fter a cert ~ time.
In a f~ther ernbodim~t oit the l~lve~tion~ there i~ an opexa~ g
rela~ whioh i~ Qnerglaed depending on response o~ the ~uxiliary relay ana
oomprisea a ~elf-holdi~g ~witohin~ element ~d ~ oparating awitchi~lg
el~m~nt in serie~ with the switohing-on el~3me2~t iIl the ope~ative po~ition
thereofO ~th the aid of thi~ operat~ng relayl one en~ure8 that the
programmo timer can be operated for the pu~po~e of fa~lt cut~o ~ eve~
before the in~tant at whioh the fhel ~elease elem~nt i0 to be a~ltched
on, w~thout the ~e~ultant operation of ~he ~witchlng-o~ ele~ent thereby
glvln~ ri6e to the releas0 of fuel.
In partioular9 the operatin~ relay mRy ba ~on~eoted to the 6elf~
holdln~ input of th~ auxiliary relay by way of a delay elQ~ent. rne del~
0n~ure~ that the as~o~iated ope~ating ~witc~ g el~m~nt i~ ~wltchsd over
orly after the flr~t ~witohing element followln~ the ~wito~ine-o~ element
has esta~ hed ao~mNnication to th~ fuel relea~e el6m~nt.
~ ll o-
~ xther~ tha op~r~ting ~t~itc~ng el~ment ma;y bs a ~witc~over
~ement preced~ng the ~ir~t and fourth flame rel~;y switchin~ element in
tha re~t position thereof. ~i~ ~i~plifie~ the constxuction o~ the
oir~t.
It is al~o ~av~urabla if the self holding ~;t~it¢hing el~ment of
the operating rela~r ~llo~ the operative position o:f ~e opexatln~ .
~itchin~ el~ t and precedes th~ ~econd ~a tnird ~ rel~. qh~
du~l function of the self-holding ~ritabing el~ t like~rise ~i~plifle~
the circuit oonstruction. j'
Ihe ~Em~ applie~ to the c,a~e ~here the ~econd and third flame
rel~ Bwitohing elem~nts ar~ oombi~d to for~ a ~wltching~over elem~nt or
the fir~t ~nd ~ourth flame relag ~witohing elements axe combinecl to form
a ~witching~over oleme~t.
Ih8 lnvention will now be dcscribed i~ ~ora deta~l with refer~nee
to a preferred example illu~trated in the drawing, whereins
~ lg. 1 ~ a ci~cuit diagræm of a control oircuit accordln~ to the
in~ention, and
~ ig. 2 i~ a time diagram for the noxmal starting of tha control
Girc~lt illu6tr~ted in Flg. 1 i~ energis~d by one phase of an alte~aati~
voltage applied betwe~n the terminal~ 1 and 2. ~he terminal 1 oommNni-
oatea with c~n input line 3 and the tarminal 2 with a line 4 which is at
~arth pot~ntial. Th~ following component~ nre diagrammatically illustrated
n~xt to each oth~r in the lowermo~t row from left to ri~ht~ A lamp 5 ia
lit up in the ~ase of a f~t. A relay ~I aer~es to ~witch on a fan motor
and ha~ a ~lf-holding contact b~l. A prev~ntila~ion timer TG ¢om~ri6ea
arL aNxiliary relay ~ whioh xe~pond~ aPter a prev~ntilatin~ time Or for
~.ample 30~econds, a re~ponsa input a and ~ holding input b and contr
a ~el:~holdin,~ swltohlng elem~t tl a~ well aa a flxst ~ itc'r~n~ovex
'7~ 7~ :
-- 12 --
elem~t t2 w~ch ~a a~so~i&ted -~rith the ~uel release. An opers.till~ r01a;r
~I oompri~es a respon~e input o whioh i~ oo~eoted b~r w~r o~ a delag element
6 in the fo~m of ~L ~C resl~tor to tho holdi:~g i~put b of the pr~ntilation
tim~ G, and a holding ~:nput d ~;nd con'rols a s~rit~n~oYer elem~t ~1
and a sel~ ng ewitchi~e element m2S A pro~Fr~n0r P operate~ wit;h a
thermal time elernent~ closes a ~itching~on ele3nent pla~t~r a prede~ormined
time~ operates a ~witchin~ovar eleEQont p2 in the ~nput li~e 3 ~fter a
predete~mined dela;r period and open9 a third swit~i~¢ elem~t p3 shortly
before the ~witGhine element pl ie closed. A sa~ety t~mer SG ¢o~rise~ a
relay S w~ch~ with the aid o~ an electronic t~er operat~, al'ter a
t;;r p~riod whioh may bc short ~nd amou~t to o~ly~ ~2r. two ~econ
a 8witching~0~ter slement 81 ~3;nd a ~xther ~witchin~o~er elem~t 82
h r~maln ~witohed over ~or as long~ a~ the voltage 18 applied to the
sa~ety timer SG~ 1~ flame monitor FW 003~pris~s a flame rela~r F to whioh
a ~roltage ¢ar be ~ed by wa;y of a line 7 ~nd a signal for inorea0ing ~ha
~ensitiv~ty by ~ of a line 8 arld w}~oh, wherl a ~lzme se~or 9 detect~
?l~tl aotuates a switohing-over el6~t ~1 ~Lnd a ~her switehin~over
elem~t ~2. q~ ia followed by an 1~3nition tr~ ormer ~" a first
f'ael releaao element VI and a Eecond f`lael relea~e ale¢sQlt ~II~ 3~1nall~,
the ~irouit compri~e~ a te~peratur~deponde~tl~ co~trolled ~witch KT~
for e~ample a boiler thermostat. A switch 1 i~ aotuated ln dep#ndenco
on the flow of air from th~ f~.
Durin~ normal operationj the ~ollowing ~equ~nce Or funotions will
t~ke place a~ described with part~al reference to ~ig. 2.
~ hen heat ~nergy i~ required and ths ~witoh KT there~ore closes~
voltc~ge is a~pliad to the ~an motor relay ~ bg way of tha switchlng
el~t~ p3, ~ $nd l. ~he ~lf.~hol~ing ~itching ~lQmOEnt bml close~
~ad tha fan ~otor 1~9 U'~ to full 3~eed.
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A8 floon aB tho air flow from the ~an motor i~ deteGt~d; the
~witc~in~over element 1 operates 60 that the voltage i~ now ~1180 Appli0d
to the line 1~)., ~li8 ;~ ta~lt i8 des~gnated ta in the 3ia~am of Fi~. 2.
~he ~et~ timar S~ thereby xeoeive~ rolta~e by wa~r of the ~witohin~ovor
~l~me~t t2. At the ~nd o~ thQ sa~et~ psrioa" i~e. ~ the in~tarlt b~,
the rel~r S switche~ the two ~ritohing~o~er ~lement~ 81 ~d ~2 to thelr
op~ratire po~ltion.
qhe exo~ter input a of` the prsve3ltilation ~Lmer TG the~eb;r rsceive~
701tage by way of the 8witchlng el~e~t~ ml~ ~1 and B2 ~0 that, after a
pxedetermined ~ntilatlng period, i~a. ~t the in~ta~t tO1 the auxiliary
relay T attracts, the sel~holaing ~wi~ohin~ element tl olo~es and the
Bwltohin~orer element t2 mova~ ~o the operati~e po~ition. ~hi~ dls&onneota
the safety t.imer SG ~rom the ~oltage. Its two switch~ng eleme~ts sl a~d
~2 retlrn to thQ reBt poB~t~on~ ~he fir~t ~equ~ce SI o~ the ~aPe~y
t~mer ha~ been concluded. At the Bame time, switching over o~ t2
constitute~ a prspaxatory ~tep for effactin~ r~lea~e of the f~el th~oush
the line 11.
~ rom the i~tsnt to, bhe operating relay ~ ha~ al~o ~oltag~ ~ppliea
to it by way o~ the delay element 6. Thl~ therefore respond~ at the
i~sta~b td, whersby the switchln~ el~ment~ ml and ~2 ~re actuatedO Ihe
op~xa~ng relay M i8 llOW held by the ~el~-holaing ~witchin,~ element m2.
~ rom the in~tant td, th~ pro~ram~e timer P ~hexef~re receives
voltag~ by wag of the ~witchin~ elem~nts ml, m2 and f2c A~ter a ~ir~t
p~ .od, namely at te~ the ~witching elem~t p3 op~n~ and a ~hort tlm~
there~fterl nflmely at the in~tant t~, the ewitching~on eleme~t pl 0109as-
On the ene h~ndl the ~e~ult of this ls that the ~a~ety ~lmer SG ha~ a
Yoltage appl~ed to it and a seoond sa$uenca SII ~ ~tarted. At the ~me
tima, ~oltage is applied to the ~uel relea~ elQment ~I b~ wa~y of the
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~witc~n~ ele~ents ml~ pl, t2 and ~e line 11 ~d to ~ ltio
transformer by wag of the ~witc~ elem~nt ~lo
~ onsaque~tly, the flame ~8 igrlited shortl~ therea~ter, namely
at ~he ~Btant t~. ~he ~lame rela~ F respond~ and BWit;Ohe~l th0
t;wo BW~tChi,~ ~1~6nta fl a~d f2 to t;heir operative po~itSo~ a
result, the pro~ramme timer P i~ di~connected :E~om the ~rolt~ge so that,
a:~ter ~ome time, namely at thc inbtant l;i, ~he switohing-on el~ t pl
opan~ ~nd the ~wit~hing element p3 elo8e6~ whexeupon the seoand ~u~l
xelea~e el~me~t VII i8 8et in op~ration.
A~ter the safety perlod staxted at the in3tant t~ h3~ e~pir~d
~o~ th~ ~eGorLd time, namely at tha i~ tant ~19 tha rela;y S a~ Bwit¢he3
th~ switohin~ elem~nt~ ~1 and ~2 to thel~ operative po~itlon. ~8 a
rosNlt, ~he i~itlon tran~former ZT i~ swltohad off and the ~lel
xelea~e elem~nt VI ~and later the ~econd r~laa~e el~m~nt VII) rec~va
~oltaee by wa~ of the sw~tchlng ~lQme~ts ml, m~9 ~2 and ~2~ As a xesult
0~ ~he BWitChin~ o~er of B2~ the auxiliary relay ~ h had ~ecently
~ece~ved ~oltag~ by way of the ~witchin~ elemQ~t~ ~l and tl, ~ ~witch~d
of~ so that th~ switchinæ el~m~nt tl also retu~ns to ~h~ re~t po8i~io~
IhiB i~ i~si~ficant for the ~nerglsation of the ~uel r~lease elements
becxuse the line ~ upplied wi~h voltage ovex a differ~nt path,
S~Ll.taneously, tha safoty tlmer SG oontlnuea to rec0ive ~olta~e by way
of tlle ~witching elem~nt t2, ffven ~î tlle switohin~on el~ne~t pl op~
!lhe ~ntire i2~tallatlo~ i8 llOW ~ operation ~d retains itB
condition until the BWitO~ nent K!l! opens-
Er:ror~ wi~ regard to the sa~ety period are avolded beoallse allthe element~ neces~ r for the 8a:fety per~od dJlrl~r:Lg; the ~econd BeqU~L¢a
SII are çha¢~ea in coltne¢tion with tha f~rat seguence SI~ beca~e
~herQ is a pr~para~3~y ~d BWito~orf ~pp~ratu~ 1~ whio~ switches ~e
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auxlllaxy relay ~ and ~t~ s~itohing el~me~t t2 on durln~ ~he first
sequa~ce ~nd o~f ~uring ~he ~eoond seque~lce by ~multaneous aotuatlo~
oX tho awitchin~ el~ment 82 duling the first and ~econd sequ~oe.
~ilure duri~g the ~econd ~equ~lce i~ ~here~ore inconoeivable slnce
not only the fknotion of the eleotronic t~mex but al~o ~he fun~tion o~
~he as~o¢ia~ed relay S ~ith the ~unotionally followlng ~witchingelement~
h~d been cheoked durlng tha first ~equ~nce. shOula ~here be a ~ault,
(~terTuption, ~hort-cirouit) i~ the suppl~ to ~he sa~e~y timer ~hat i~
~eeponsible for ~he aafety period during ~he seoond 8e~uance, no ~u21
ca~ be delivered ~nd thera~ora no damage oan be done.
o flame i8 ~e~ted aur1ng the safety period In ~ ~eaond
sequ~e, the flame relay swit¢hing~over el~mffnt ~2 retai~ th~ lllustrated
po~ltion. ~t the end Or tho ~afet~ period~ the~tohlng el~ant t2 mo~e~
t~ lt~ illu~trated ra~t position. ~hi~ ~wit~hee the ~uel relea~e elQment
11I o~ and dama8~ is a~oided. At the s~ne t~me, howev~r, the progr~n~
timer P ¢ont~ue~ to be heat0d by ~Ja~ Or the ~t¢~ng elem~Q3bs ml, 1n2
~nd f2 ~o that, a~ter a predetermined dela~ period~ the switchirl,~ element
~.
p2 i~ ~t¢hed over ~rhereby the en~re inata:llation is 3witched off a~d
~he ~g~al lamp 5 ~ lit up.
Should the flame aisappear durin~ operation9 the flame rela~
ElWitChillg' ole,m~t f2 moYes to the illustrated rest po~ition ~Jhereby the
flual release qlementa are ~ witohed off ana ~rolbage i~supplied to
the prngrRmme timer P until the AQ~uatin~ ~witohin~ elem~nt p2 rsspond~0
If extraneous light i~ deteoted before rd~ponae o~ the oporating
relay M (beoau~e of phosphoreso~nt wall~ an op~ door, by rea~on o~ a
de~eotiYe flame ~en~or), thc ~lame mo~itor ~ xe6pona~ bco~u~o lt r6cel~es
~ign~l for i~cr~a~ing itB ~an~itlvity by way o~ ths l~ne ~, Iho flam8
~elay ~wltoh$n8~over ele~ant ~ ~wltoha~ over ~o that th~ proer~mme t~me~
~ ' .
- , ,
.
, ~ 1~
P recev~s ~rolt~e by wa;y Di' the ~ ching elements ml and fl until ~e
aotuati~ ~witching element p2 respona~. Since the e:~traneous li8ht
1~ ~enerally dateGted even ba~ore tho rel~r S oî t~e ~a~e~y timer ha8
ra~ponded, o~a ~180 avoids switchin~ on vf the pre~Qntilation timer ~&.
:lh~ lllu~trated ~ircu~t i8 desi~ned for a gaE ~er ~irin~S
~stallation wi~ alr blo7~r and ha~ring a capcLoi~r of over 350 kW.
hi8 ca~;e the saf9t;;~ perlod amount~ to 2 ~ a~d l~he preve~tilatlo~
~oriod i~ longer th~ 30 ~0 Su¢h ~ol~trol oir~uits c~, howe~er~ o
be u~ed for oil ~ners and for tho~e f'i~g in~tallations wh~ the
s~fet~r per~od i~ ~ome-~at longer. ~Lectro~neticall~ controlled ~ e~
are prima;~ily considered ~or ~:Læe a~ the ~ l release el~ts but it i~
al~o pogsible to employ a~ oll pu~pO
. - .... .
