Siemens LMU54 Series - Modulating Control, Conventional

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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
The boiler circuit is a single temperature control loop:
Boiler
setpoint
Tsoll
+
TIst
Pneum. / el.
ratio control
Burner and
heat exchanger
P
KK
Adaption of
manipulated
variable
PWM
PWM
7494b06e/0201
Preset setpoint Controller
TK
T∆
Strecke
Fühler Fühler
T
T
N
V P
K
Stell
K TStrecke
Sensor
Basic structure of boiler controller
In the boiler circuit, the boiler temperature is maintained at the predefined setpoint. The
controller can be used for the heating circuit or the DHW circuit.
The overriding 2-position controller releases the above mentioned control loop and
ensures that the predefined setpoint will be maintained.
The result of the temperature controller is matched to the PWM signal of the controlling
element. The output is adjusted via the fan and via pneumatic or electronic ratio control.
In all cases, the temperature limiter overrides the temperature control loop. This means
that the temperature limiter switches off the boiler when «TkMax» is reached (triggering
safety shutdown).
Based on the control differential (∆T = Tsoll - Tist) and the selected controller
parameterization, the PID control algorithm calculates the required manipulated
variable. Using the controller parameters, the relevant controller part can be activated /
hidden or adapted to the controlled system.
It is also possible to set the sampling time for the boiler circuit and the DHW circuit.
The heat output determined by the PID controller is limited to the permissible output
range.
Modulating control,
conventional