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Siemens Building Technologies
Basic Documentation LMU54... / LMU64...
CC1P7494en
HVAC Products
3 Functions
07.11.2002
«NhzMax» can be readjusted during operation via the HMI. Using the controller stop
function, a setting range of 0...100 % is possible on the HMI, QAA73... or PC tool,
whereby the following assignment applies:
0 %
→
N_TL
100 %
→
N_VL
When setting the maximum heat output, the following must be observed:
Maximum output in DHW mode:
N_TL
≤
N_VL
Maximum output in heating mode:
N_TL
≤
NhzMax
≤
N_VL
Maximum output in heating mode
and RU connected:
N_TL
≤
NhzMaxAkt
≤
NhzMax
Speed limitation maintains the preselected speeds when the maximum or minimum heat
output is reached. Disturbance variables with regard to fan speed are voltage variations
and changes in flueway resistance (length of flueways).
In the case of crossings of the maximum or minimum speed thresholds, speed limitation
acts like a one-sided speed control loop.
Depending on the demand for heat, the heat output range is thus as follows:
•
With all types of heat demand:
N_TL
≤
Nist
≤
NhzMaxAkt
The associated PWM setting range is:
LmodTL...PhzMaxAkt
•
With DHW demand:
N_TL
≤
Nist
≤
N_VL
The associated PWM setting range is:
LmodTL...LmodVL
LmodTL:
Minimum modulation value at which the flame is not yet lost and
combustion performance is still satisfactory
LmodVL:
Maximum permissible PWM value (parameter)
Speed limitation has 2 parameters («KpBegr» and «KpUnbegr»), which make it possible
to set the dynamics of speed limitation.
The parameter value of 10 represents the default setting.
An additional limit is introduced for the ionization current (parameter «IonLimit»).
This limit is used to determine the minimum speed such that an ionization current fault
cannot cause the burner to shut down.
For that function, speed limitation must be active.
If parameter «IonLimit» is set to 0, the function is deactivated.
If the ionization current drops below «IonLimit», the minimum speed will be set to the
current speed.
When the function is activated, this speed will then define the lower limit for the speed
limitation. If the ionization current drops below that limit, the lower speed limit will be
raised by 100 min
-1
every 10 seconds .
Speed limitation thus raises the PWM signal and the modulation, which leads to a higher
ionization current.
When the lower speed limit reaches the maximum speed («NhzMax» or «N_VL»), the
integrator will be stopped.
If the ionization current exceeds the limit, the speed limit is reduced again by 100 min
-1
every 10 seconds until the speed limit has reached the minimum speed (N_TL).
Speed limitation
Note
Limitation of ionization
current
