Basic Documentation
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Siemens Modular Heating Controller RMH760B CE1P3133en
Building Technologies 6 Boiler temperature control 2017-09-29
TBoSetpt
TBoSetpt -
½ SDBo
TBoSetpt + SDBo
TBo
t
1 K
1 K
St
Basic
St
Modulat.
a
b
a
c
d dd
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
temperature 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°)
= 10 s
90°
The proportional band has an impact on the controller’s P-characteristic.
With a setpoint / actual value deviation of 20 K, a setting of Xp = 20 K produces a
manipulated variable corresponding to the damper actuator’s running time.
The integral action time has an impact on the controller’s I-characteristic.
Release integral
modulation
Neutral zone
Settings
Actuator running time
Example
Proportional band (Xp)
Integral action time (Tn)