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Internal diagram
LGA52... / LGA63...
Legend
Siemens Building Technologies
HVAC Products
When the switch-on command is given, the auxiliary fan starts to run.
When the air pressure switch closes its contact, the heating coil of the bimetal sequenc-
ing device is energized and the bimetal pushes contact set «c, d, e» towards «f»
(thereby opening «f - g»).
On completion of the prepurge time, «e - f» is closed so that both gas valve «BV1» and
the ignition transformer receive voltage: The safety time starts.
On flame establishment, the flame relay latches mechanically «e - f», pushes «c» back
at the same time and opens «fr».
The ignition transformer is thus switched off and the heating coil deenergized, so that
«d» can revert to its starting position.
When tilting back, «g - f» closes so that the main gas valve «BV2» receives voltage.
If no flame signal is generated, the flame relay does not open «c - d», so that the bi-
metal will continue to be heated.
The bimetal thus continues to bend until – tilting – it actuates contact «tz2»: → Lockout
In the event of an erroneous premature flame signal, the flame relay – by means of its
latch – prevents «e - f» from making, which means no release of gas.
«TZ», however, still receives power so that the bimetal continues to bend until, eventu-
ally, lockout is initiated by «tz2».
L1
tz2
EK
X Y Z
1 2
10
8
SB
W
AL M
R
1)
Si
H
L
N
AL
Fault status signal
BV...
Fuel valve
EK
Lockout reset button
ION
Ionization probe
FR
Flame relay
L1
Built-in lockout warning lamp
LP
Air pressure switch
1)
Not monitored to EN 298
LGA52... / 63...
tz1
a b
f g
c d
e
FR
fr
TZ
7
11
9
6
4
LP
Z
BV1
H
M
R
SB
Si
TZ
W
Z
5
12
ION
BV2
7418i01/0304
Main switch
Auxiliary fan
Thermostat or pressurestat
Safety limit thermostat
External primary fuse
Electro-thermal timer
(bimetal system) with contacts «tz»
Limit thermostat
Ignition transformer
9/11
CC1N7418en
08.04.2004
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