Electronic Combustion Control Unit - Viessmann Vitodens 200-W Series Installation And Service Instructions Manual

Function description

Electronic combustion control unit

The electronic combustion controller utilises the physi-
cal correlation between the level of the ionisation cur-
rent and the air ratio . The maximum ionisation cur-
λ
rent is achieved at an air ratio of 1 for all gas qualities.
The ionisation signal is evaluated by the combustion
controller and the air ratio is adjusted to a value
between =1.24 and 1.44. This range provides for an
λ
optimum combustion quality. Thereafter, the electronic
gas valve regulates the required gas volume subject to
the prevailing gas quality.
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
For optimum combustion control, the system regularly
carries out an automatic self-calibration; also after a
power failure (shutdown). For this, the combustion is
briefly regulated to max. ionisation current (corre-
sponding to air ratio =1). Automatic calibration is car-
λ
ried out shortly after the burner start and lasts approx.
5 s. During calibration, higher than normal CO emis-
sions may occur briefly.
102
O content (%) CO content (%) for
2 2
natural gas E
3.8
4.4
4.9
5.3
5.7
6.1
6.5
6.9
7.3
To check the combustion quality, the CO
the O content of the flue gas is measured. The pre-
2
vailing air ratio is determined with the measured val-
ues. The relationship between the CO
and air ratio is illustrated in the following table.
λ
CO content (%) for
2
natural gas LL
9.6
9.2
9.0
8.7
8.5
8.3
8.1
7.8
7.6
content or
2
or O content
2 2
CO content (%) for
2
LPG P
9.2 11.3
9.1 10.9
8.9 10.6
8.6 10.3
8.4 10.0
8.2 9.8
8.0 9.6
7.7 9.3
7.5 9.0