Siemens LMU54 Series Basic Documentation page 23

Siemens Building Technologies
HVAC Products
• Safety time (TSA): As described above, the behavior of the burner control in the 2
different modes can be parameterized: Abortion of the safety time with flame
detection, and evaluation of the flame at the end of the safety time.
It must be noted that in the case of single-electrode operation, it is always «Evaluation of
the flame at the end of the safety time» that must be parameterized.
• Postpurging: Can be parameterized in 2 different ways, namely as postpurging on
the prepurging level, or as postpurging with the control used last. The duration of
postpurging is adjusted via «tn» (also see above)
• Start prevention: Certain internal or external events can trigger start prevention. In
that case, the burner control changes to the «PH_STARTVER» phase. The reason for
start prevention is given via the diagnostic code
The reason can be one of the following (examples):
−
Open-circuit or short-circuit of flame detector
−
No «GP» signal (depending on the parameterization)
−
Open «LP» input (depending on the parameterization)
−
Temperature limiter has cut out
Some of the functions that give rise to start prevention can be deactivated via
parameterization.
• Ramps: Fan control can be limited by a ramp. To do this, a number of
parameterization choices are available.
The rate of signal change towards a higher or lower speed is limited via parameter
(VmLauf, VmLaufBetr, VmLab, VmLabBetr).
In all phases - with the exception of «PH_MODULATION» - parameters «VmLauf»
and «VmLab» apply to the rate of change of fan control up or down.
PWM
100 %
Threshold
value
1 SW run
Control value following the setpoint while considering the threshold value and the ramps
In the «PH_MODULATION» phase, the increase of fan control is limited by the smaller
of the 2 parameters «VmLaufBetr» and «VmLauf».
The decrease is limited by the smaller of the 2 parameters «VmLab» and «VmLabBetr».
Also, when controlling the fan, a threshold value is to be considered. It is predefined by
the «LmodStart» parameter.
As long as the setpoint is lower than the threshold value, the fan will not be controlled. It is
controlled only - using the threshold value - when the setpoint is at least equal to the
threshold value.
Basic Documentation LMU54... / LMU64...
3 Functions
Setpoint
7494d21E
23/171
CC1P7494en
07.11.2002