Viessmann B2HF, Инструкции по установке и обслуживанию для подрядчиков

Страница: 129 / 136

129
The electronic combustion controller utilises the physi-
cal correlation between the level of the ionisation cur-
rent and the air ratio
λ
. The maximum ionisation cur-
rent is achieved at an air ratio of 1 for all gas qualities.
The ionisation signal is evaluated by the combustion
controller. The air ratio is regulated to a value that is
between
λ
= 1.2 and 1.5. This range provides for an
optimum combustion quality. Thereafter, the electronic
gas train regulates the required gas volume subject to
the prevailing gas quality.
To check the combustion quality, the CO
2
content or
the O
2
content of the flue gas is measured. The pre-
vailing air ratio is determined using the actual values.
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
λ
=1). Self-calibration takes
place shortly after the burner starts. The process lasts
approx. 20 s during which higher than normal CO
emissions may occur briefly.
Specification
Electronic combustion control unit
5593201
Service