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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
19.3 Precontrol
As a result of the measurements made when setting the O
2
setpoint, the properties and
the behavior of the burner will be acquired. Based on the type of fuel, the O
2
ratio, the
O
2
setpoint and the standardized value, precontrol calculates the air rate in a way that
the O
2
setpoint will be reached as long as the environmental conditions do not change,
irrespective of burner output.
Calculation of the air rate from the manipulated variable is made such that a manipulated
variable of +10 % will offset an air density change of –10 %.
19.3.1
Calculation of precontrol
Based on the settings for O
2
trim control, the system becomes familiar with the charac-
teristics and behavior of the burner. The lambda factor, which is taken into considera-
tion when calculating the air rate reduction, reflects these values which are gained from
practical experience.
Precontrol can be calculated in 2 different ways:
Parameter:
Type Air Change (like P air, like theory)
like P air
The measured lambda factor is also considered when air density
(temperature pressure) changes. Air pressure and air density have an
impact on the fuel throughput.
like theory
The measured lambda factor is not considered when air density
(temperature pressure) changes. Air pressure and air density have no
impact on the fuel throughput.
Recommendation:
With gas:
like P air
With oil:
like theory