Siemens LMV51 Series Basic Documentation page 272

272/301
Siemens Building Technologies
HVAC Products
19.4.8 Control interventions by the O
To prevent the burner from getting insufficient amounts of air when the load changes,
the O trim controller has additional means for counteracting. These become active if
2
the O trim controller or precontrol is not optimally adjusted, or if the burner's behavior
2
cannot be adequately mapped by the measured values. The control interventions are
also active during the controller locking time.
If the O value drops below the setpoint in the direction of the O
2
nipulated variable will be abruptly increased if predefined thresholds are exceeded ⇒
more air supply:
Example:
Progression of O
Setpoint
+3 %
+5 %
Min. value
value exceeds ½ of the differential between setpoint and min. value → manipu-
a) O
2
lated variable is increased by 3 %
value exceeds ¾ of the differential between setpoint and min. value → manipu-
b) O
2
lated variable is increased by 5 %
For the control interventions – using a software timing element PT1 – the setpoints and
O min. values will be delayed by the time constant Tau acquired during adaption. This
2
allows the actual O value (corresponding to a combustion value from the past as a re-
2
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.
Basic Documentation LMV5...
19 Addendum 4: LMV52... with O2 trim control and O2 module
trim controller
2
value
2
1/2
3/4
7550d35e/0903
min. value, the ma-
2
CC1P7550en
13.08.2004