Siemens SINAMICS S120 Function Manual page 93

If the motor is rotating and the start value for the search is as of the setpoint (p1400.11 = 1),
the speed setpoint must be in the same direction as the actual speed before the pulses can
be enabled. A large discrepancy between the actual and setpoint speed can cause a
malfunction.
Once the pulses have been canceled, no information about the motor speed is available.
The computed actual speed value is then set to zero, which means that all actual speed
value messages and output signals are irrelevant.
Switchover between closed-loop/open-loop operation and operation with/without encoder
Operation without an encoder is activated via parameter setting p1300 = 20. If p1300 = 20 or
p1404 = 0, operation without an encoder is active across the entire speed range. If the
speed value is less than the changeover speed p1755, the motor is operated in accordance
with the current/frequency.
During operation with an encoder, a switchover can be made to operation without an
encoder when the speed threshold p1404 is exceeded. If p1404 > 0 and p1404 < p1755, a
switchover is not made to operation without an encoder until the speed exceeds p1755.
Operation without an encoder is displayed in parameter r1407.1.
Figure 3-17 Area switchover
Note
In closed-loop control operating mode "Speed controller without encoder", a rotor position
encoder is not required. Since a temperature monitor is not usually connected in this case
either, this must be parameterized via p0600 = 0 (no sensor).
Drive functions
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
WARNING
3.11 Sensorless operation (without an encoder)
Servo control
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