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Siemens Building Technologies Basic Documentation LMV5... CC1P7550en
HVAC Products 19 Addendum 4: LMV52... with O2 trim control and O2 module 13.08.2004
19.4.8 Control interventions by the O2 trim controller
To prevent the burner from getting insufficient amounts of air when the load changes,
the O
2 trim controller has additional means for counteracting. These become active if
the O
2 trim controller or precontrol is not optimally adjusted, or if the burner’s behavior
cannot be adequately mapped by the measured values. The control interventions are
also active during the controller locking time.
If the O
2 value drops below the setpoint in the direction of the O2 min. value, the ma-
nipulated variable will be abruptly increased if predefined thresholds are exceeded ⇒
more air supply:
Example:
Setpoint
Min. value
1/2
3/4
Progression of O
2
value
+3 %
+5 %
7550d35e/0903
a) O
2 value exceeds ½ of the differential between setpoint and min. value → manipu-
lated variable is increased by 3 %
b) O
2 value exceeds ¾ of the differential between setpoint and min. value → manipu-
lated variable is increased by 5 %
For the control interventions – using a software timing element PT1 – the setpoints and
O
2 min. values will be delayed by the time constant Tau acquired during adaption. This
allows the actual O
2 value (corresponding to a combustion value from the past as a re-
sult of the boiler running time) to be compared with the associated setpoints and min.
values.
Also refer to section 19.5.1 Delayed O2.
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