Viessmann VITOCROSSAL Service Instructions Manual page 92

Function description
Electronic combustion control unit
To check the combustion quality, the CO
the O content of the flue gas is measured. The pre-
2
vailing air ratio is determined using the actual values.
The correlation between CO
ratio is shown in the following table.
λ
Air ratio CO /O content
λ–
2 2
Air ratio
λ
1.20
1.24
1.27
1.30
1.34
1.37
1.40
1.44
1.48
To achieve optimum combustion control, the system
regularly carries out an automatic self-calibration; also
after power failures (shutdown). For this, the combus-
tion is briefly regulated to maximum ionisation current
(corresponding to air ratio
place shortly after the burner start and lasts for about
5 s. During calibration, higher than normal CO emis-
sions may occur briefly.
92
(cont.)
content or
2
or O content and air
2 2
O content (%)
2
=1). Self-calibration takes
λ
CO content (%) for nat-
2
ural gas E
3.8
4.4
4.9
5.3
5.7
6.1
6.5
6.9
7.3
CO content (%) for natu-
2
ral gas LL
9.6
9.2
9.0
8.7
8.5
8.3
8.1
7.8
7.6
9.2
9.1
8.9
8.6
8.4
8.2
8.0
7.7
7.5