Forced Travel Fan; Speed Control - Siemens LMV37.4 Series Basic Documentation

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12.7.3 Forced travel fan

When a symmetrical speed signal is used, like with the actuators, a forced travel is also
carried out for the fan to detect an error in the speed feedback signal when a speed is
maintained for a long period of time. The activation of the forced movement is started if
the fan has not moved by more than the neutral zone of the speed supervision
(parameter 662) for longer than 50 minutes.
During the forced movement, the fan travels 1.8% towards the lower speed and back to
the original speed. If the start speed is lower than 11.8%, the fan speed is increased to
prevent a drop below the minimum speed specification. The entire forced travel lasts
approx. 1-2 seconds.
All relevant actuators are always moved during the forced travel, which means that,
when the forced travel is actuated due to insufficient change in speed, the active
actuators are also subjected to a forced travel or vice versa. This procedure reduces the
frequency of the forced travel of the LMV37.4, as all actuators are processed
synchronously.
No. Parameter
662 Neutral zone of the speed supervision

12.8 Speed control

The LMV37.4 controls the fan motor's speed to the setpoint. To ensure that the speed
can still be increased when the maximum speed is reached, the speed is standardized
when the motor is controlled at 95%. Hence, with a speed setpoint of 100 %, a speed
increase of 5 % is still possible.
The control range of the LMV37.4 is +15% / -10%. If this range is not sufficient, error 80
or 83 can occur.
Error Diagnostic code
code
80 1
2
Note
Internal control with a VSD or PWM fan motor must not be activated. Otherwise,
speed variations can occur, resulting from simultaneous control actions from both the
LMV37.4 and internal control.
The internal control of the LMV37.4 can be deactivated via parameters. On the one
hand, this takes place automatically if a pneumatic operating mode is selected (see
chapter Selection of operating mode). This is also necessary when a self-regulated
PWM fan is used in an electronic fuel-air ratio control system.
The speed control setting also has an impact on the determination of the standardized
speed (see chapter Speed standardization).
No. Parameter
LMV37.4 internal speed control
0 = deactivated (self-regulated PWM fan)
661
1 = activated (VSD)
Basic documentation LMV37.4...
12 Fan control
Meaning for the LMV37.4
Control range limitation at the bottom
Control range limitation at the top
CC1P7546en
17.12.2018