253/327
Building Technologies
Basic Documentation LMV5...
CC1P7550en
19 O2 trim control with LMV52 and PLL52
22.05.2018
19.2.2 Definition of O2 setpoint
Using the ratio control curve as a basis, the O2 setpoint is adjusted by manually
lowering the air rate.
⇑
The system stores the O2 ratio value, the O2 setpoint, and the relative air rate
reduction (standardized value required to attain the O2 setpoint).
Example:
With a relative air rate reduction of 10%, the air rate must be lowered by
6 percentage points from 60% to 54%.
By measuring both O2 values and by having the relative air rate reduction required for
the readjustment, the system identifies the burner’s behavior. Effects, such as the fan
pressure’s impact on the amount of gas, are taken into consideration.
19.2.3 Lambda factor
The system calculates the lambda factor from the O2 ratio value, the O2 setpoint, and
the required air rate reduction (standardized value to attain the O2 setpoint). The
lambda factor reflects the ratio of the actual lambda change and the theoretical lambda
change, in relation to a change of air rate.
With an ideal burner, a relative air rate reduction of 10% produces a
lambda change of
κ
Theory =
κ
new = 0.9
κ
old
corresponding to a lambda factor of 1.
Example:
If the amount of gas is influenced by the fan pressure, a reduction of the air volume can
simultaneously lead to an increase in the amount of gas. In practice, this results in a
more pronounced change of the lambda value. If the change of lambda value is twice
the theoretical value, an air rate change of 10% produces
a value of
κ
Practice =
κ
new = 0.8
κ
old
Corresponding to a lambda factor of 2.
From the lambda values of the ratio control curve, the setpoint curve, and the
standardized value (required air ratio reduction), the lambda factor is calculated as
follows:
Lambda factor =
κ
setpoint -
κ
ratio
● 100
κ
ratio ● (- standardized value)
The system should be adjusted such that the lambda factor across the load range will
be as flat as possible. This can be checked with the ACS450 PC software. When no
tool via available, the lambda factors can be calculated according to the above formula
to be entered in a graph.
