PFU 780 · Edition 02.12l
13
Function
3 .2 PFU 780 program sequence
Normal start-up
If an “old” fault is still being sig-
nalled after switching on, it will be
necessary to reset this first.
The safety interlocks (terminal 26e)
must be closed and the burner con-
trol unit must be switched on.
The PFU 780 conducts a self-test
when in the start-up position (the
burner is switched off). If it does
not determine a malfunction of the
internal electronic circuitry or of the
flame sensors, the burner can be
started. The pilot burner start-up is
activated via the signal input “Start-
up signal
ϑ
1” (terminal 10e). Once
the start-up signal
ϑ
1 has been
applied, the PFU 780 opens valve
V1 and ignites the burner. The igni-
tion time t
Z
is constant. If a flame
is detected during the safety time
t
SA1
, the flame proving period t
FS1
starts after the safety time t
SA1
has
elapsed.
If the pilot burner has been started
successfully and its flame has
stabilised, the burner control unit
issues the Enable signal for main
burner operation. The operation sig-
nalling contact for the pilot burner
(terminals 2c/4c) closes.
01
02
03
04
08
00
00
08
05
06
07
Switch on
PFU 780
Pilot burner start-up
with
ϑ
1 signal
Safety interlocks (Limits)
In the event of fault signal:
Reset
If parameter P15 = 1:
flame simulation check
Wait until
waiting time t
W
has elapsed
If parameter P15 = 0:
Flame simulation check
If no flame detected:
next start-up attempt (P10)
or fault lock-out
Start-up position/standby
Safety time t
SA1
running (P22),
ignition in process,
V1 opens and min.
combustion time t
B
starts to elapse (P20)
In the event of flame failure:
restart or fault lock-out
Operating signal
Pilot burner closes
Flame proving period t
FS1
running (P23)
In the event of flame failure:
restart or fault lock-out
Main burner start-up
with
ϑ
2 signal
Wait until
min. burner pause time t
BP
has elapsed (P21)
If parameter P15 = 0:
Flame simulation check
If no flame detected:
next start-up attempt (P11)
or fault lock-out
Safety time t
SA2
running (P24),
V2 opens and
min. combustion time t
B
starts to elapse (P20)
Normal shut-down
via
ϑ
signal for
pilot and main burners
If min. combustion time t
B
has elapsed:
Operation signalling contact
opens,
V1 and V2 close,
min. burner pause time t
BP
starts to elapse (P21)
In the event of flame failure:
restart or fault lock-out
Operating signal
Main burner closes
Flame proving period
t
FS2
running (P25)
In the event of flame failure:
restart or fault lock-out
PFU 780
If the air valve control is used,
the unit offers the following
additional functions:
In start-up position, the air
valve can be opened for cool-
ing
A
(display
A0
).
Using parameter 31, it can be
determined whether the air
valve can be activated exter-
nally during start-up (display
A1
).
The air valve can be set to open
together with V1 (display
A2
)
via parameter 30.
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