Siemens LMV50 Series Manual

Also see for LMV50 series: Manual Operating instruction

253/327Building Technologies Basic Documentation LMV5... CC1P7550en19 O2 trim control with LMV52 and PLL52 22.05.201819.2.2 Definition of O2 setpointUsing the ratio control curve as a basis, the O2 setpoint is adjusted by manuallylowering the air rate.⇑ The system stores the O2 ratio value, the O2 setpoint, and the relative air ratereduction (standardized value required to attain the O2 setpoint).Example:With a relative air rate reduction of 10%, the air rate must be lowered by6 percentage points from 60% to 54%.By measuring both O2 values and by having the relative air rate reduction required forthe readjustment, the system identifies the burner’s behavior. Effects, such as the fanpressure’s impact on the amount of gas, are taken into consideration.19.2.3 Lambda factorThe system calculates the lambda factor from the O2 ratio value, the O2 setpoint, andthe required air rate reduction (standardized value to attain the O2 setpoint). Thelambda factor reflects the ratio of the actual lambda change and the theoretical lambdachange, in relation to a change of air rate.With an ideal burner, a relative air rate reduction of 10% produces alambda change of κTheory = κnew = 0.9κoldcorresponding to a lambda factor of 1.Example:If the amount of gas is influenced by the fan pressure, a reduction of the air volume cansimultaneously lead to an increase in the amount of gas. In practice, this results in amore pronounced change of the lambda value. If the change of lambda value is twicethe theoretical value, an air rate change of 10% producesa value of κPractice = κnew = 0.8κoldCorresponding to a lambda factor of 2.From the lambda values of the ratio control curve, the setpoint curve, and thestandardized value (required air ratio reduction), the lambda factor is calculated asfollows:Lambda factor = κsetpoint - κratio ● 100κratio ● (- standardized value)The system should be adjusted such that the lambda factor across the load range willbe as flat as possible. This can be checked with the ACS450 PC software. When notool via available, the lambda factors can be calculated according to the above formulato be entered in a graph.