O2 Alarm; Delayed O2 Limit Value - Siemens LMV50 Series Manual

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Building Technologies

19.5 O2 alarm

The O2 alarm can be used with or without O2 trim control. When O2 trim control is
activated, the O2 alarm becomes automatically active.
There is one alarm for the O2 minimum value and one for the O2 maximum value.
For the O2 minimum value alarm, the thresholds are defined by the O2 minimum value
curve (refer to chapter Setting the O2 alarm, Direct entry of O2 min. values and
Measuring the O2 min. values by lowering the air rate).
For the O2 maximum value alarm, the user can select the O2 MaxValue parameter (all
LMV52) or the O2 ratio control curve values (only LMV52.4).
This is defined using the Type O2 MaxValue parameter:
∂
O2 MaxValue
The O2 MaxValue parameter is used
∂
O2MaxCurve
The O2 values at the ratio control curve that were measured when setting the O2
trim controller are used as O2 maximum alarm values.
Parameter Gas: Type O2 MaxValue (O2 MaxValue, O2MaxCurve)
Oil: Type O2 MaxValue (O2 MaxValue, O2MaxCurve)
Gas: O2 MaxValue
Oil: O2 MaxValue

19.5.1 Delayed O2 limit value

Due to the long time it takes for the flue gases to pass through the boiler's flueways, the
O2 value currently acquired is delayed compared to the residual O2 content occurring
the same moment in the combustion chamber.
To prevent O2 minimum and maximum values from being compared with O2 values
from an old load, these limit values are delayed accordingly. The delay is derived from
the acquired Tau value and simulates the boiler delay.
Basic Documentation LMV5...
19 O2 trim control with LMV52 and PLL52
CC1P7550en
22.05.2018