Siemens LMV5 Series Basic Documentation page 253

Siemens Building Technologies
HVAC Products
18.4.5 Initialization of O2 trim controller
The system starts operating with the O
locking time will start as soon as the system operates at constant load. The locking time
is determined based on the boiler plant delay times acquired during adaption. On
completion of the locking time, the O
setpoint as quickly as possible, the theoretically required manipulated variable is
calculated from the currently measured O
the time of setting, the O
variable will be increased by 3.7 % so that the value will lie slightly above the O
setpoint. With this 3.7 % increase, the O
O setpoint. The PI controller will then ensure fine-tuning until the O
2
reached.
18.4.6 Behavior in the event of load changes
As soon as the load changes, the O
manipulated variable will be maintained. If the O
change took place, precontrol will calculate the air rate such that the O
also be reached with all other loads. If the system stays at a stationary load for a period
of time longer than the controller locking time, the controller will be released again.
18.4.7 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
manipulated 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 →
a) O
2
manipulated variable is increased by 3 %
value exceeds ¾ of the differential between setpoint and min. value →
b) O
2
manipulated 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
2
result of the boiler running time) to be compared with the associated setpoints and min.
values.
Also refer to subsection 18.5.1, Delayed O2 min. value.
Basic Documentation LMV51...
18 Addendum 4: LMV52... with O2 trim control and O2 module
trim controller locked (safe ratio curve). The
2
trim controller will be initialized. To reach the O
2
ratio value, the O
2
setpoint, and the standardized value. The manipulated
2
value reached will be about 0.7 % above the
2
trim controller will be locked, that is, the last
2
2
value
2
1/2
3/4
7550d35e/0903
ratio value determined at
2
setpoint is
2
setpoint was reached before the load
setpoint will
2
trim controller
2
min. value, the
2
2
2
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CC1P7550en
01.10.2003