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Building Technologies
Basic Documentation LMV5...
CC1P7550en
19 O2 trim control with LMV52 and PLL52
22.05.2018
19.3 Precontrol
As a result of the
measurements
made when
setting the O2 setpoint,
the properties
and the
behavior of the burner are learned
.
Based on the type of fuel, the O2 ratio value, the O2 setpoint, and the standardized
value, precontrol calculates the air rate reduction such that changes in burner load
do not require the O2 trim controller to interfere.
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%.
To enable precontrol to function correctly, the outputs for the curvepoints must be
parameterized so that they concord with the actual burner output.
Example: 2'000 kW burner:
∂
100% point: 2'000 kW ≈ 200 m³/h natural gas
∂
75% point: 1'500 kW ≈ 150 m³/h natural gas
∂
50% point: 1'000 kW ≈ 100 m³/h natural gas
This can be achieved, for example, by measuring the amount of fuel with a fuel meter
when making the setting.
19.3.1 Calculation of precontrol
Based on the settings for O2 trim control, the system becomes familiar with the
characteristics and behavior of the burner. The lambda factor, which is taken into
consideration when calculating the air rate reduction, reflects these learned behavior.
Precontrol can be calculated in 3 different ways:
like P air
The learned 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 learned lambda factor is not considered when air density
(temperature / pressure) changes. Air pressure and air density have
no impact on the fuel throughput.
LambdaFact1
The system anticipates a lambda factor of 1. The learned value is
irrelevant.
This parameter setting is only intended for use with burners that have
a lambda factor of 1.
Recommendation:
When firing on gas:
like P air
When firing on oil:
like theory
For burners where the air pressure does not have any impact on the gas pressure (e.g.
burner head with metal mesh for Super-Low-NOx applications) :
LambdaFact1
Parameter
Type Air Change (like P air, like theory LambdaFact1)
