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Building Technologies Division User Manual LMS14… CC1U7471en
6 The settings in detail 28.01.2015
6.36 PWM limitation
The control range of the fan speed controller can be adjusted via Fan PWM-Min
[3997.1] and Fan PWM-Max [3998.1] (refer to chapter Setpoint filter for fan speed
control).
6.36.1 Supervising air supply by monitoring current fan speed
Basically, acquisition of the fan speed is not failsafe. Without extra measures,
monitoring the current fan speed is not sufficient to ensure air supply to the burner.
Errors in the acquisition of the fan speed or fan can be compensated by an appropriate
PWM level. Then, the acquired fan speed lies again within the valid range. To enable
fan speed monitoring to detect such errors, the PWM range of fan speed control must
be limited. For the relevant speed ranges used for prepurging, ignition and operation,
suitable parameters for PWM limitation are available.
PWM limits Fan speed limits
Min. Max. Min Max
Prepurging MinPwmPrepurge - 9505 –
N_Vor_Delta
N_Vor_Max
Ignition - MaxPwmIgnition 9513 –
N_ZL_Delta
9513 +
N_ZL_Delta
Operation MinPwmLowLoad MaxPwmHighLoad 9525 –
N_TL_Delta
9530 +
N_VL_Delta
The PWM limits must be defined for the most unfavorable conditions. With the minimum
limits, the ambient conditions must be selected such that the fan reaches the minimum
speed with the given PWM. If the PWM value is still reached with the minimum speed, it
is used as the minimum PWM value. The procedure is the same with the maximum
limits, only in the reverse sense.
Note!
Whether or not monitoring of the current fan speed is enough for supervision of the
air supply must be clarified with the approval authorities and the fan manufacturer.
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