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Parameters
4 .6 Air control
4 .6 .1 Valve control
Parameter 25
Determines whether an actuator connected to termi-
nals 29 to 32 is activated for valve control.
If valve control is deactivated, the BCU 370 can be used
to control single-stage-controlled burners.
Parameter 25 = 1: valve control is active. The BCU
activates the outputs on terminals 29, 30 and 31 to
move the actuator to the Open (pre-purge), Closed and
Ignition positions. When the appropriate position is
reached, this information is signalled back by the actu-
ator via the input on terminal 32. The BCU 370 waits for
the feedback signal from the actuator once the outputs
have been activated. The time required depends on the
actuator running time. If the position is not reached
within the timeout time of 250 seconds, the BCU dis-
plays the fault message "Position not reached".
Parameter 25 = 0: the BCU 370 runs through all pro-
gram steps without waiting for a feedback signal from
the butterfly valve. The outputs for valve control are not
activated.
BCU 370 · Edition 01.19
4 .6 .2 Pre-purge
Parameter 06
This parameter determines whether the BCU pre-purg-
es on the next start-up after a controlled shut-down.
Within the scope of the application standard EN 676
pre-purge can be dispensed with under certain condi-
tions. This prevents cold air from entering the combus-
tion chamber and accelerates burner start-up.
Parameter 06 = 1: pre-purge occurs on each start-up.
Parameter 06 = 0: pre-purge is omitted if the last shut-
down was a controlled shut-down and occurred within
the last 24 hours. After switching on the BCU, after a
safety shut-down or a fault lock-out or after a pause of
more than 24 hours, the BCU completes an entire pre-
purge cycle.
For burner capacities as from 70 kW, application stand-
ard EN 676 requires that a valve check be carried out if
pre-purge has been omitted.
For burner capacities as from 117 kW, application
standards NFPA 85 and NFPA 86 require a valve check
before pre-purge and a pre-purge before each system
start.
The valves can be checked using a tightness control.
See "Function – Tightness control". Please note appli-
cation standards.
56
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