Siemens LMS14 User Manual page 553

The band of the 3 filter time constants Pt1 from a higher to a lower level can be
selected with 2 threshold parameters for the fan speed.
These fan speed threshold parameters are valid only when changing from a higher to a
lower level.
The setting is made via Pt1 upper spd falling [3698.1] and Pt1 lower spd falling
[3699.1].
For modulating to a higher level, all phases have no speed thresholds that could be
used to subdivide modulation into different ranges.
The subdivision of ramp slope is only possible in the operating phases when
modulating to a lower level. In that case, Diff setpoint filter [5285.1] must be set to Yes.
Modulating to a lower level upon shutdown when Diff setpoint filter [5285.1] is set
to Yes.
In the event of shutdown at the end of postpurging and a fan speed setpoint of 0 rpm,
the speed controller is switched off.
This means that the fan's PWM is switched off and the fan motor coasts – depending
on the fan's characteristic – until standstill is reached.
In this range, there is no control by the speed controller.
To enable the fan ramp to act when modulating to a lower level upon shutdown in
phases TNB, TLO and TNN, the fan controller is switched off in home run only when
the filtered fan speed setpoint drops below the speed threshold 2*NoGNull (Required
speed stop max (9551)).
Up to this threshold, the fan is controlled by the speed controller and modulates to a
lower level, depending on the preselected setpoint.
In that case, the setpoint filter must be set such that – under the most unfavorable
conditions – the current fan speed reaches speed threshold 2*NoGNull within 51
seconds.
If, within 51 seconds, the speed drops below the speed threshold, the burner control
goes to non-volatile lockout (Albatros code 160 Fan speed error).
If the burner control goes to lockout, the speed controller for the fan is still switched off.
This means that when going to lockout, time constants (Pt1 time const 4 drop [5283.1]
and Pt1 time const 1 incr [5284.1]) have no impact.
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Building Technologies Division User Manual LMS14... CC1U7471en
6 The settings in detail 28.01.2015