BCU 480 · Edition 03.16l 53
Parameters
4.7. 8 Low fire over-run time t
KN
after a controlled
shut-down
88 00
A8
t
t
KN
5
1
7
4
A
18-19
23
26
28-29
12
9
V1
1
14
V2
24
2
21
16-17
1
2
ϑ
1
ϑ
2
VR..R
BCU 480..L
A
P
L1
1
2
SPS
PLC
CPE
VAS 1
VG..N
GIK..B
1
2
Parameter 36
Settings: 0; 5; 15 or 25 (low fire over-run time in sec-
onds)
This parameter is applicable to systems with a pneu-
matic
air/gas ratio control system and On/Off control.
Parameter 36 = 0 (low fire over-run time t
KN
= 0 s):
Without low fire over-run, the gas circuit is closed im-
mediately owing to the quick-closing gas valve in the
case of On/Off control. The air circuit closes more slow-
ly. The air flowing in during the closing time increases
the O
2
content in the combustion chamber.
Parameter 36 = 5; 15 or 25 (low fire over-run time
t
KN
= 5, 15 or 25 s):
The air valve closes slowly after the activation signal has
been switched off. The gas valve remains open for t
KN
.
This means that the burner, after deactivation of the
start-up signal (ϑ), is initially adjusted down to low fire
and then switched off completely.
Using the low fire over-run function reduces the O
2
content in the furnace atmosphere.
Flame control is still operational. Can be used only in
the case of a pneumatic air/gas ratio control system
and On/Off control. It must be ensured that no excess
gas occurs.
The low fire over-run time has an effect on the behav-
iour of the main burner only.
Background: the pilot burner is only used in single-
stage operation.
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