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Siemens Building Technologies Basic Documentation LMV5... CC1P7550en
HVAC Products 5 Fuel / air ratio control (FARC) 13.08.2004
In Phase 36, all actuators are driven to their ignition positions. For that purpose - like in
prepurging - a maximum time is available within which the ignition position must be
reached → position check.
Ignition takes place only when the required position is reached. The ignition position
can be adjusted for all actuators, depending on the type of fuel.
Parameters: LMV51... LMV52...
IgnitionPosAir x x
IgnitionPosGas x x
IgnitionPosOil x x
IgnitionPosAux x x
Aux2 x
Aux3 x
VSD x
When ignition has taken place and the flame has stabilized, the actuators must be
brought into line. For that purpose, the control unit drives the actuators to their basic
part load position (low-fire) as defined by the curves.
The actuators which, for ignition, have assumed a special position, travel at individually
calculated speeds to ensure that all of them will reach the part load position at the
same time.
F
u
e
l
A
i
r
A
u
x
25 % 50 % 75 % 100 %
7550d03E/0202
0°
90°
Low fire Ignition positions
Position
Load
Traveling to the low-fire position after ignition
Note: The system also permits ignition positions that lie outside the range defined by
fuel / air ratio control, that is, not between high-fire and low-fire.
In the operating position, the dampers are adjusted according to demand. The ratio
curves are defined for gas and oil.
For modulating operation, the output can be adjusted in increments of 0.1°.
The actuators travel to the defined ratio curves.
In multistage operation, 2 or 3 load points can be approached.
For more detailed information, refer to section «Operating position».
After there is no more demand from the controller, the fuel / air ratio control system first
changes to low-fire (Phase 62) before the fuel valve close. For that purpose, a maxi-
mum time is available which can be parameterized → part load shutdown.
Ignition
Traveling to the
operating position
Operation
End of operating
position
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