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Building Technologies Modular Heating Controller RMH760B CE1P3133en
HVAC Products 6 Boiler temperature control 05.02.2007
damper actuator will be 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 will again drive
the damper actuator to the fully closed position.
TBoSetpt
TBoSetpt -
½ SDBo
TBoSetpt + SDBo
TBo
t
1 K
1 K
St
Basic
St
Modulat.
a
b
a
c ddd
TBoSetpt + ½ SDBo
3131D01
a
Release integral modulation (release integral stage 2 with 2-stage burner)
b
Reset integral modulation (reset integral stage 2 with 2-stage burner)
c Neutral zone
d On / off pulses
SDBo
Boiler’s switching differential
St Basic Burner’s basic stage
St Modul.
Burner’s modulation stage
TBoSetpt Boiler temperature setpoint
The controller has a neutral zone with a band of ±1 K about the current boiler tempera-
ture setpoint. If the boiler temperature stays within the neutral zone for a period of time
beyond the adjusted integral action time, no more positioning pulses will be delivered.
If the boiler temperature does not stay long enough in the neutral zone, or outside of it,
positioning pulses will drive the actuator toward the fully open or fully closed position.
Maximum limitation of the boiler temperature and minimum burner running time are
handled analogously to 2-stage burner operation.
Control of the air damper must be matched to the plant’s behavior (controlled system)
to ensure that if the load changes (e.g. increase of heat demand), the plant will quickly
increase heat production in a way that the boiler temperature will only slightly deviate
from its setpoint, and for short periods of time only.
The following settings can be made on the controller:
• Air damper running time
• Proportional band (Xp)
• Integral action time (Tn)
• Derivative action time (Tv)
To ensure correct control of the burner, the effective air damper running time must be
set. The modulation range is decisive for the actuator’s running time.
Running time of damper actuator (90°) = 15 seconds, minimum position of damper
actuator = 20°.
Maximum position of damper actuator = 80°.
Hence, the damper actuator running time effective for the control is as follows:
15 s * (80° – 20°)
90°
= 10 s
Release integral
modulation
Neutral zone
Settings
Actuator running time
Example