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Building Technologies Basic documentation LMV37.4... CC1P7546en
12 Fan control 17.12.2018
12.9 Speed supervision
The fan’s current speed is acquired by the LMV37.4 and assessed from a safety point of
view. If the fan does not operate at the speed setpoint, speed control makes a corrective
action, trying to reach the setpoint. If it is not reached within a certain period of time,
safety shutdown is initiated. To ensure a high level of availability and safety, a number
of monitoring bands with different response times are defined.
To adapt to the application, the tolerance bands and response or shutdown times can
be changed via the OEM level in defined limits:
Tolerance band Adjustable value range Adjustment of the
shutdown time
0…Neutral zone
Neutral zone (0.5...3.5%)
Neutral zone…Close
range
Close range (2...5.5%) <8...16 s
> close range <3...7 s
The combination of tolerance band and shutdown time must be chosen by the OEM so
that no hazard potential can occur within the application.
No. Parameter
662 Neutral zone of the speed supervision
663 Close range of the speed supervision
664 Speed supervision: Maximum time between the neutral zone and close range
665 Speed supervision: Maximum time outside close range
It is possible to switch off speed supervision at standstill (no-load speed 0%) in standby
mode. This may be necessary if the fan rotates too much in standby mode due to a
chimney draft or if an extended ramp time is active with a PWM fan during the transition
from the postpurge speed to standstill.
No. Parameter
653 VSD standstill supervision in standby mode
0 = deactivate
1 = active
The following tolerance bands and shutdown times apply in the default setting:
Speed deviation in % points Shutdown time
0…0.5% Speed reached no shutdown
0.6...2% <8 s
2.1...10% <3 s
>10% <1 s
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