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Building Technologies Boiler sequence controller RMK770 CE1P3132en
HVAC Products 7 Boiler control 23.04.2009
When the demand for heat is small, the basic stage cycles. When the demand for heat
increases, the 3-position output or a DC 0…10 V output is used to control the combus-
tion air damper.
At the same time, the amount of fuel supplied is also increased, typically via an addi-
tional switch on the air damper, or by simultaneous control of the amount of fuel (gas /
fuel ratio).
2526z02
P M BV OH Q...
z
LK
SA
M
Basic design of a forced draft burner
BV Fuel valve(s)
ACC Combustion air damper, fixed or motorized
M Fan
OH Oil preheater; located between nozzle and adjustable head with small
light-oil burners, separate unit with large heavy-oil burners
P Oil pump, coupled to fan motor
Q… Flame detector
SA Air damper actuator for automatic control
Z Ignition transformer
The functioning with regard to activation and deactivation of the basic stage corre-
sponds to that of 2-stage burner operation. Release of modulation takes place analo-
gously to the release of stage 2.
The parameters used for the release and reset integral are the same as those used for
the 2-stage burner. Compared to the 2-stage burner, the release integral should be
selected smaller however (because in this case, it is not the entire capacity of stage 2
that is switched on, but only the modulating part that is released), and the reset integral
can be selected larger.
Release integral stage 2 or modulation: 10 K×m
Reset integral stage 2 or modulation: 20 K×m
Locking time burner stage 2 10 min
The locking time (stage 2 or modulation) must be matched to the type of burner.
This ensures that the burner always operates with the basic stage for a certain mini-
mum period of time.
On burner startup and release of the basic stage, the controller drives the damper
actuator toward the fully closed position for a certain period of time. This ensures that –
after the burner startup sequence (prepurging, ignition, stabilization of flame, etc.) – the
damper actuator is driven to the start position so that only the basic stage will be used
for heating.
Deactivation or locking of modulation occurs at the same moment in time as the change
from the basic stage to cycling operation. If not yet done, the controller again drives the
damper actuator to the fully closed position.
Recommended values for
modulating burners
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