Characteristics Pwm Fan - Siemens LMV37.4 Series Basic Documentation

Building Technologies
12.14.1

Characteristics PWM fan

The LMV37.4 works with a standardized speed signal, with linear interpolation between
standstill and the standardized speed (nominal speed). The requirement for this
assumption is a linear fan characteristic, which is achieved solely by self-regulated
PWM fans.
To prevent conflicts between self-regulated fans and the internal speed control of the
LMV37.4, it must be deactivated (parameter 661; see chapter Speed control). The
tolerance limits may also have to be adapted to the speed supervision (see chapter
Speed supervision).
In contrast to a VSD, the fan speed of a PWM fan is heavily dependent on the load (air
throughput) of the fan. This characteristic is partially balanced out by a self-regulated
PWM fan, but still leads to a big time difference in the comparison between acceleration
and deceleration. The extreme case here is a closed air damper, e.g. during the
transition from postpurging to standby.
Another disadvantage of the current PWM fan is the partially significantly reduced
braking performance (without the option of additional braking resistances, e.g. with a
VSD). This means that the different ramp time values for run-up / run-down (parameter
522 / 523) have to be set. This behavior must also be taken into account with the
modulating operating ramp (parameter 544).
The LMV37.4 also has the option of activating the actuators with a time delay
(parameter 529). In this case, the braking performance is improved by carrying out the
speed reduction with the air damper open. The air throughput increases the braking
performance of the fan, which reduces the speed faster. This process can be set during
the transition from prepurging to ignition (phase 35), when moving in postpurging (phase
71) and from postpurging to standby (phase 79). The air actuator is only moved to the
relevant damper position once the ignition speed or standby speed is achieved.
If value 2 is set, an additional tolerance increase of 50% on the neutral zone (parameter
662) and the close range (parameter 663) of the speed supervision is possible outside
of operation.
No. Parameter
Ramp up
522
Ramp down
523
Separate movement of the fan (ignition speed / postpurge speed)
529
0 = deactivated
1 = activated
2 = activated (50% tolerance increase outside operation)
Ramp modulating
544
LMV37.4 internal speed control
661
0 = deactivated (self-regulated PWM fan)
1 = activated (VSD)
Neutral zone of the speed supervision
662
Close range of the speed supervision
663
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CC1P7546en
17.12.2018