BCU 580 · Edition 11.15
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19 .6 Safety shut-down
The burner control unit performs a safety shut-down imme-
diately after receiving a signal from a safety device or after a
fault is detected (e.g. flame or air pressure failure). The safety
shut-down prevents operation of the burner by closing the fuel
shut-off valves and deactivating the ignition device.
For this, the BCU disconnects the gas valves and the ignition
transformer from the electrical power supply. The operation
signalling contact and the controller enable signal are deac-
tivated. The fault signalling contact remains open. The display
blinks and displays the current program step, see page 47
After a safety shut-down, the BCU can restart automatically.
19 .7 Fault lock-out
A fault lock-out is a safety shut-down with subsequent fault
lock-out. The system can only be restarted following manual
reset. The protective system cannot be reset by mains failure.
In the event of a fault lock-out of the BCU, the fault signalling
contact closes, the display blinks and shows the current pro-
gram step, see page 47 (Fault signalling). The gas valves
are disconnected from the electrical power supply. The fault
signalling contact opens if the mains voltage fails.
In order to restart, the BCU can only be reset manually using
the button on the front panel, the OCU or the remote reset
input (terminal 3).
19 .8 Warning signal
The BCU reacts to operating faults, e.g. in the case of perma-
nent remote resets, with a warning signal. The display blinks
and shows the corresponding warning message. The warning
signal ends once the cause has been eliminated.
The program sequence continues. No safety shut-down or
fault lock-out occurs.
19 .9 Timeout
For some process faults, a timeout phase elapses before the
BCU reacts to the fault. The phase starts as soon as the BCU
detects the process fault and ends after 0 to 255 s. A safety
shut-down or fault lock-out is then performed. If the process
fault ends during the timeout phase, the process continues
as before.
19 .10 Lifting
After positioning the actuator IC 20, the BCU checks by means
of brief lifting whether its feedback input (terminal 52) has been
activated by the correct output signal from the actuator. The
signal of the relevant control output (ignition, OPEN, CLOSE) is
switched off briefly for this purpose. While the signal is switched
off, the BCU may not detect a signal at the feedback input.
19 .11 Air valve
The air valve can be used
– for cooling,
– for purging,
– to control the burner capacity in ON/OFF mode and in
High/Low mode when using a pneumatic air/gas ratio
control system.
Glossary
