BCU 580 · Edition 11.15
79
10 .6 .4 Low fire over-run
Parameter 43
The low fire over-run (t
KN
) is applicable to systems with a pneu-
matic air/gas ratio control system and On/Off control. Using
the low fire over-run function reduces the O
2
content in the
furnace atmosphere.
00
A8
t
t
KN
2
10
A
88
ϑ
46
1
9
5
13
V1
14
V2
57
V4
11
L1
41
42
1
43
2
Parameter 43 = 0: Off. No low fire over-run is performed. The
gas circuit is closed immediately owing to a quick closing gas
valve in the case of On/Off control. The air circuit is closed
more slowly. The air flowing in during this time increases the
O
2
content in the combustion chamber.
Parameter 43 = 1 (only for BCU..F1/F2): up to minimum capacity.
The burner is not immediately switched off after the start-up
signal
ϑ
(terminal 1) has been removed. During low fire over-
run, the control element is moved to the position for minimum
capacity and the gas valves remain open until the flame fails
or the position for minimum capacity is reached. If the flame
is extinguished, this does not result in a fault.
Parameter 43 = 2, 3, 4, 5, 10, 20, 30 or 40 (only for BCU..F3):
time in seconds. During this time, the gas valve remains open.
The air valve is closed with deactivated start-up signal (
ϑ
).
BCU 580..F3
µC
VAS
VAS 1
VAG
TZI/TGI
VR..L
V1
V2
V4
10
9
13
14
57
8
5
This means that the burner is initially adjusted down to low
fire and then switched off completely. Flame control is still
operational. It must be ensured that no excess gas occurs.
10 .6 .5 Controller enable signal delay time t
RF
Parameter 44 (only on BCU..F1/F2)
The controller enable signal is delayed by 0, 10, 20 or 30 up
to 250 s using parameter 44.
If the BCU has successfully started the burner, after the elapse
of the safety time and the flame proving period, if parameter-
ized, the controller enable signal to the external temperature
controller is delayed. The BCU shows program status
H8
. After
the elapse of the delay time t
RF
, the burner operation signalling
contact (terminals 17, 18) is closed and the controller enable
output (terminal 56) activated. The display changes to
08
.
Parameters > Air control