46 Overview
define monitoring limits for the safety functions. Otherwise it is possible that
unnecessary monitoring limit hits occur. Using encoder for only control purposes
decreases the ripple in the safe speed estimate signal.
It is highly recommended to perform the best possible identification run that can be
performed in the typical motor operating conditions (for example, shafts connected to
motors, nominal temperature). This makes it possible to create the most accurate
motor model for the speed estimation. If the Normal ID run is not possible, do the
Reduced or Standstill identification run. For more information, see ACS880 primary
control program firmware manual (3AUA0000085967 [English]).
The safe speed estimation can only be calculated when the drive is modulating.
When the drive stops the modulation, the safe speed estimation shows 0 rpm.
Because of this main principle, it is a must that the motor speed starts to slow down
by coasting when the power is switched off. If the motor is not decelerating fast
enough by coasting, the rotation must be stopped with external device, for example
with a safe brake.
It is not allowed to use the safe speed estimation with an external active load that can
accelerate the motor shaft. For example, in a hoist drive, the hanging load would
potentially cause an accelerating motion because of the gravity, thus the safe speed
estimate cannot be used for these types of applications.
WARNING! Applications with external active load must use a safety encoder
and FSO-21 and FSE-31 modules.
WARNING! In an encoder fault situation, with an external active load, the FSO
module is not permitted to switch the feedback from encoder to safe speed
estimate (see parameter S_ENCGEN.11).
The diagram below shows an example of the SLS function, and the behavior of the
safe speed estimation with an induction motor and its slip. It also illustrates the
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