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Building Technologies Basic Documentation LMV5... CC1P7550en
19 O2 trim control with LMV52 and PLL52 22.05.2018
19.4.12 Limiting the O2 trim controller manipulated variable
with shutdown
A minimum and a maximum value can be set for the O2 trim controller manipulated
variable using the O2MinManVariable and O2MaxManVariable parameters.
The behavior if the value falls below or exceeds the related threshold of the O2 trim
control manipulated variable limitation depends on the O2 parameter OptgMode:
Parameterization
conAutoDeac
A low fire safety shutdown is initiated followed by repetition and
with automatic deactivated O2 trim controller. That means the
system works in operation along the ratio control curves.
O2 Control
A low fire safety shutdown is initiated followed by a lockout
The addition or removal of combustion air by the O2 trim controller can be limited in the
following situations:
∂ Insufficient flow through QGO20
∂ Blockage of reference air inlets for QGO20
∂ False air (ambient air) in the flue gas channel for QGO20
∂ Blockage in the combustion air inlet
Parameter Gas: O2MaxManVariable
Oil: O2MaxManVariable
Gas: O2MinManVariable
Oil: O2MinManVariable
The thresholds for the manipulated variable are determined based on the anticipated
changes to the supply air temperature and air pressure.
The manipulated variables resulting from changes to air pressure and air temperature
can be determined graphically.
Temperature and air pressure are to be regarded as deltas for the setting conditions.
Attention!
On the one hand, the values for limiting the manipulated variables must be set in
such a way that climatic fluctuations (and similar variations) that occur during
regular operation do not allow the limit values to be reached.
On the other hand, the manipulated variable limit values must be as small as
possible to ensure that any violations of these limit values are detected as early
as possible and the burner is shut down as soon as possible in the situations
described above.
Refer to the diagram and example below for how to determine to values.
The preset manipulated variable limit values must be individually adjusted for
each plant.
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