Speed Readjustment - Siemens LMU54 Series Basic Documentation

Speed readjustment

Description
Learning function
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HVAC Products
Speed readjustment is active during startup and shutdown (not during controller
operation where speed limitation can be activated).
The basic task of speed readjustment is to act on the fan control in such a way that the
resultant speed (after a certain settling time) will lie within an accepted speed band.
Hence, external effects (over- or undervoltage, minimum or maximum flueway, etc.) can
largely be offset.
The following parameters must be considered:
• N_NachstellKon1 (in «FaEinstellFlags2»)
This parameter is used to activate or deactivate the function during startup.
• N_NachstellKon2 (in «FaEinstellFlags2»)
This parameter is used to activate or deactivate the function during shutdown.
• N_Nachstell_lern (in «FaEinstellFlags2»)
This parameter is used to activate or deactivate the learning function of fan control.
• N_Nachstell_Delta
This parameter predefines the band (+/-) to which the speed will be readjusted (neutral
band).
• Nachstell_Zaehler
This parameter is used to define the time when ignition shall be started (depending on
the fan speed settling time à more or less overshoot on ignition permitted).
If the function is activated (N_NachstellKon1 + N_NachstellKon2), the fan output signal
will be readjusted in order to get the speed back into the predefined band (e.g. N_ZL +/-
N_Nachstell_Delta).
If speed readjustment is used, the actual speed will be readjusted to nearly the required
speed until ignition takes place.
Since with this readjustment, the fan speed requires a certain settling time, it is very
advisable to parameterize prepurging and ignition at the same level, so that the
prepurging time can be used for settling process.
If, for example, prepurging > ignition, a second settling process will take place, that is,
the deviation at the time of ignition will be greater.
In that case, the prepurging time should be changed and the level of prepurging and
ignition should be the same.
During startup, the fan output will be changed in order to readjust the resulting actual
speed.
To ensure that this practically fixed offset does not need to be readjusted on each
startup, the fan output signal will be acquired at the end of startup, and the value
learned will be used next time the burner is started up.
This means that the settling process will be accelerated.
The learning function can be deactivated with flag «N_Nachstell_lern» (in
«FaEinstellFlags2»).
Basic Documentation LMU54... / LMU64...
3 Functions
CC1P7494en
07.11.2002