Fuel / Air Ratio Control (Farc); General; Siemens Building Technologies; Basic Documentation Lmv5 - Siemens LMV51 Series Basic Documentation

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Fuel / air ratio control (FARC)

5.1 General

The electronic fuel / air ratio control system LMV51... can control up to 4 actuators, the
LMV52... up to 6 actuators. The functions of the dampers are ready assigned to the ad-
dresses and are defined as follows:
LMV51...
1 Air damper
2 Fuel 1 (gas)
3 Fuel 2 (oil)
Auxiliary actuator 1 (mixing device) ¹)
4
5
6
7
¹)
VSD (LMV51.2...)
²)
Actuators used in connection with air control (can be parameterized)
Actuators 1...6 are controlled with a resolution of 0.1°. They can be adjusted between
0° and 90°. The VSD is controlled with a resolution of 0.1 %. It can be adjusted be-
tween 0 % (off, prepurge / postpurge fan speed) or 10 % (ignition and operating
speeds) and 100 %.

5.1.1 Program sequence

The program phases are controlled by the burner control. They advance in tune with
the fuel / air ratio control system.
In standby, the actuators are driven to their home positions. A deviation from the re-
quired position does not lead to lockout, but only to start prevention. The home position
is defined for all actuators and can be adjusted differently for oil and gas.
Parameters:
HomePosAir
HomePosGas
HomePosOil
HomePosAux
Aux2
Aux3
VSD
In Phase 24, the actuators used for the control of air (air actuator and auxiliary actuator)
are driven to their postpurge positions. If the actuator does not reach the required posi-
tion within the maximum time, safety shutdown will take place → position check. The
prepurge time starts only when the actuators have reached their prepurge positions.
The prepurge position is only defined for the actuators used for the control of air and
can be parameterized depending on the type of fuel. The fuel actuators maintain their
home positions.
Parameters:
PrepurgePosAir
PrepurgePosAux
Aux2
Aux3
VSD

Basic Documentation LMV5...

5 Fuel / air ratio control (FARC)
LMV52...
Air damper ²)
Fuel 1 (gas)
Fuel 2 (oil)
Auxiliary actuator 1 (mixing device) ²)
Auxiliary actuator 2 ²)
Auxiliary actuator 3 (FGR) ²)
VSD ²)
LMV51... LMV52...
x x
x x
x x
x x
x
x
x
LMV51... LMV52...
x x
x x
x
x
x
CC1P7550en
13.08.2004