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Building Technologies Boiler Sequence Controller RMK770 CE1P3132en
HVAC Products 7 Boiler control 23.04.2009
TBoSp
TBoSp-½ SDBo
TBoSp+SDBo
TBo
t
1 K
1 K
St
Basic
St
Modulat.
a
b
a
c ddd
TBoSp+½ SDBo
3131D01
Release integral for modulation
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 switching differential
St Basic Burner’s basic stage
St Modul. Burner’s modulating stage
t Time
TboSetp Boiler temperature setpoint
The controller uses 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 more than 4
seconds, no more positioning pulses are delivered.
If the boiler temperature does not stay within the neutral zone or outside for a sufficient
period of time, positioning pulses drive the actuator toward the fully open or fully closed
position.
Maximum limitation of the boiler temperature and minimum burner running time are
handled analogous to 2-stage burner operation.
Air damper control 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 quickly in-
creases heat production in a way that the boiler temperature will only slightly deviate
from its setpoint, and for short periods of time only.
The controller has the following positions:
• Actuator running time
• Proportional band (Xp)
• Integral action time (Tn)
• Derivative action time (Tv)
To ensure burner control, the damper actuator’s running time must be set. It must be
observed that the running time to be set only relates to the modulating range.
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
Neutral zone
Settings
Actuator running time
Example
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